Santander UK (STNDF) 20-F 24 Mar 20 2019 FY Annual report (foreign) Financial data

Cover Page

Cover Page	12 Months Ended
	Dec. 31, 2019shares
Document Information [Line Items]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY
Entity Registrant Name	Santander UK plc
Entity Central Index Key	0001087711
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding	31,051,768,866
Document Annual Report	true
Document Transition Report	false
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Entity Address, Country	GB
Document Shell Company Report	false
Document Registration Statement	false
Document Accounting Standard	International Financial Reporting Standards
2.375% Notes due March 16, 2020, issued by Abbey National Treasury Services plc [member]
Document Information [Line Items]
Trading Symbol	SAN/20A
Title of 12(b) Security	2.375% Notes due March 16, 2020, issued by Abbey National Treasury Services plc
Security Exchange Name	NYSE
2.125% Notes due November 3, 2020, issued by Santander UK plc [member]
Document Information [Line Items]
Trading Symbol	SAN/20C
Title of 12(b) Security	2.125% Notes due November 3, 2020, issued by Santander UK plc
Security Exchange Name	NYSE
Floating Rate Notes due November 3, 2020, issued by Santander UK plc [member]
Document Information [Line Items]
Trading Symbol	SAN/20D
Title of 12(b) Security	Floating Rate Notes due November 3, 2020, issued by Santander UK plc
Security Exchange Name	NYSE
2.500% Notes due January 5, 2021, issued by Santander UK plc [member]
Document Information [Line Items]
Trading Symbol	SAN/21B
Title of 12(b) Security	2.500% Notes due January 5, 2021, issued by Santander UK plc
Security Exchange Name	NYSE
3.400% Notes due June 1, 2021, issued by Santander UK plc [member]
Document Information [Line Items]
Trading Symbol	SAN/21C
Title of 12(b) Security	3.400% Notes due June 1, 2021, issued by Santander UK plc
Security Exchange Name	NYSE
Floating Rate Notes due June 1, 2021, issued by Santander UK plc [member]
Document Information [Line Items]
Trading Symbol	SAN/21D
Title of 12(b) Security	Floating Rate Notes due June 1, 2021, issued by Santander UK plc
Security Exchange Name	NYSE
3.750% Notes due 2021 due November 15, 2021, issued by Santander UK plc [member]
Document Information [Line Items]
Trading Symbol	SAN/21F
Title of 12(b) Security	3.750% Notes due 2021 due November 15, 2021, issued by Santander UK plc
Security Exchange Name	NYSE
Floating Rate Notes due November 15, 2021, issued by Santander UK plc [member]
Document Information [Line Items]
Trading Symbol	SAN/21G
Title of 12(b) Security	Floating Rate Notes due November 15, 2021, issued by Santander UK plc
Security Exchange Name	NYSE
4.000% Notes due March 13, 2024, issued by Abbey National Treasury Services plc [member]
Document Information [Line Items]
Trading Symbol	SAN/24
Title of 12(b) Security	4.000% Notes due March 13, 2024, issued by Abbey National Treasury Services plc
Security Exchange Name	NYSE
2.875% Notes due June 18, 2024, issued by Santander UK plc [member]
Document Information [Line Items]
Trading Symbol	SAN/24D
Title of 12(b) Security	2.875% Notes due June 18, 2024, issued by Santander UK plc
Security Exchange Name	NYSE
2.100% Notes due January 13, 2023, issued by Santander UK plc [member]
Document Information [Line Items]
Trading Symbol	SAN/23B
Title of 12(b) Security	2.100% Notes due January 13, 2023, issued by Santander UK plc
Security Exchange Name	NYSE

Consolidated Income Statement

Consolidated Income Statement - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	[1]	Dec. 31, 2017	[1]
Profit (loss) [abstract]
Interest and similar income	£ 5,917	£ 6,066		£ 5,905
Interest expense and similar charges	(2,625)	(2,463)		(2,102)
Net interest income	3,292	3,603		3,803
Fee and commission income	1,112	1,170		1,222
Fee and commission expense	(426)	(421)		(415)
Net fee and commission income	686	749		807
Net trading and other income	195	182		302
Total operating income	4,173	4,534		4,912
Operating expenses before credit impairment losses, provisions and charges	(2,499)	(2,579)		(2,499)
Credit impairment losses	(221)	(153)		(203)
Provisions for other liabilities and charges	(441)	(257)		(393)
Total operating credit impairment losses, provisions and charges	(662)	(410)		(596)
Profit before tax	1,012	1,545		1,817
Tax on profit	(279)	(399)		(515)
Profit after tax	733	1,146		1,302
Attributable to:
Equity holders of the parent	714	1,124		1,281
Non-controlling interests	19	22		21
Profit after tax	£ 733	£ 1,146		£ 1,302
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income - GBP (£) £ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	[1]	Dec. 31, 2017	[1]
Statement of comprehensive income [abstract]
Profit after tax		£ 733	£ 1,146		£ 1,302
Available-for-sale securities:
- Change in fair value	[2]				80
- Income statement transfers	[2]				(54)
- Taxation	[2]				(6)
Other comprehensive income available-for-sale securities, total	[2]				20
Movement in fair value reserve (debt instruments):
- Change in fair value	[2]	147	(74)
- Income statement transfers	[2]	(147)	21
- Taxation	[2]	0	13
Other comprehensive income fair value reserve (debt instruments)	[2]	0	(40)
Cash flow hedges:
- Effective portion of changes in fair value		(857)	793		(238)
- Income statement transfers		1,013	(752)		(94)
- Taxation		(41)	(13)		89
Other comprehensive income cash flow hedges, total		115	28		(243)
Currency translation on foreign operations		(4)
Net other comprehensive income/(expense) that may be reclassified to profit or loss subsequently		111	(12)		(223)
Pension remeasurement:
- Change in fair value		(522)	470		(103)
- Taxation		131	(118)		26
Pension remeasurement, total		(391)	352		(77)
Own credit adjustment:
- Change in fair value		(77)	84		(29)
- Taxation		19	(21)		7
Own credit adjustment, total		(58)	63		(22)
Net other comprehensive (expense)/income that will not be reclassified to profit or loss subsequently		(449)	415		(99)
Total other comprehensive (expense)/income net of tax		(338)	403		(322)
Total comprehensive income		395	1,549		980
Attributable to:
Equity holders of the parent		374	1,528		959
Non-controlling interests		21	21		21
Total comprehensive income		£ 395	£ 1,549		£ 980
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.
[2]	Following the adoption of IFRS 9, a fair value reserve was introduced to replace the available-for-sale reserve.

Consolidated Balance Sheet

Consolidated Balance Sheet - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets
Cash and balances at central banks	£ 21,180	£ 19,747	[1]
Financial assets at fair value through profit or loss:
- Derivative financial instruments	3,316	5,259
- Other financial assets at fair value through profit or loss	386	5,617
Financial assets at amortised cost:
- Loans and advances to customers	207,287	201,289
- Loans and advances to banks	1,855	2,799
- Reverse repurchase agreements – non trading	23,636	21,127
- Other financial assets at amortised cost	7,056	7,229
Financial assets at fair value through other comprehensive income	9,747	13,302
Interests in other entities	117	88
Intangible assets	1,766	1,808
Property, plant and equipment	1,967	1,832
Current tax assets	200	153
Retirement benefit assets	669	842
Other assets	2,520	2,280
Total assets	281,702	283,372
Financial liabilities at fair value through profit or loss:
- Derivative financial instruments	1,448	1,369
- Other financial liabilities at fair value through profit or loss	1,713	6,286
Financial liabilities at amortised cost:
- Deposits by customers	181,883	178,090
- Deposits by banks	14,353	17,221
- Repurchase agreements – non trading	18,286	10,910
- Debt securities in issue	41,129	46,692
- Subordinated liabilities	3,528	3,601
Other liabilities	2,344	2,448
Provisions	572	509
Deferred tax liabilities	149	223
Retirement benefit obligations	280	114
Total liabilities	265,685	267,463
Equity
Share capital	3,105	3,119
Share premium	5,620	5,620
Other equity instruments	2,191	1,991
Retained earnings	4,546	4,744
Other reserves	395	284
Total shareholders' equity	15,857	15,758
Non-controlling interests	160	151
Total equity	16,017	15,909
Total liabilities and equity	£ 281,702	£ 283,372
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Consolidated Cash Flow Statemen

Consolidated Cash Flow Statement - GBP (£) £ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Cash flows from operating activities
Profit after tax		£ 733	£ 1,146	[1]	£ 1,302	[1]
Non-cash items included in profit:
- Depreciation and amortisation		543	375	[1]	354	[1]
- Provisions for other liabilities and charges		441	257	[1]	393	[1]
- Impairment losses		239	189	[1]	257	[1]
- Corporation tax charge		279	399	[1]	515	[1]
- Other non-cash items		(439)	238	[1]	(208)	[1]
- Pension charge for defined benefit pension schemes		35	79	[1]	32	[1]
Adjustments to reconcile profit (loss)		1,098	1,537	[1]	1,343	[1]
Net change in operating assets and liabilities:
- Cash and balances at central banks		(71)	(255)	[1]	(25)	[1]
- Trading assets		0	24,528	[1]	(941)	[1]
- Derivative assets		1,943	14,683	[1]	5,529	[1]
- Other financial assets at fair value through profit or loss		1,664	(3,635)	[1]	25	[1]
- Loans and advances to banks and customers		170	(9,129)	[1]	(1,832)	[1]
- Other assets		247	(246)	[1]	(246)	[1]
- Deposits by banks and customers		641	926	[1]	10,900	[1]
- Derivative liabilities		79	(16,244)	[1]	(5,490)	[1]
- Trading liabilities		0	(31,101)	[1]	15,017	[1]
- Other financial liabilities at fair value through profit or loss		(959)	4,106	[1]	717	[1]
- Debt securities in issue		(529)	(2,524)	[1]	132	[1]
- Other liabilities		(568)	(556)	[1]	(1,397)	[1]
Net change in operating assets and liabilities		2,617	(19,447)	[1]	22,389	[1]
Corporation taxes paid		(292)	(391)	[1]	(484)	[1]
Effects of exchange rate differences		(1,079)	1,750	[1]	(574)	[1]
Net cash flows from operating activities		3,077	(15,405)	[1]	23,976	[1]
Cash flows from investing activities
Investments in other entities		0	(66)	[1]
Proceeds from disposal of subsidiaries	[2]	0	348	[1]
Purchase of property, plant and equipment and intangible assets		(505)	(696)	[1]	(542)	[1]
Proceeds from sale of property, plant and equipment and intangible assets		108	26	[1]	52	[1]
Purchase of financial assets at amortised cost and financial assets at fair value through other comprehensive income	[3]	(5,013)	(7,002)	[1]	(726)	[1]
Proceeds from sale and redemption of financial assets at amortised cost and financial assets at fair value through other comprehensive income	[3]	8,300	3,708	[1]	2,032	[1]
Net cash flows from investing activities		2,890	(3,682)	[1]	816	[1]
Cash flows from financing activities
Issue of other equity instruments		500			500	[1]
Issuance costs of other equity instruments		0			(4)	[1]
Issue of debt securities and subordinated notes		4,145	10,642	[1]	6,645	[1]
Issuance costs of debt securities and subordinated notes		(15)	(23)	[1]	(15)	[1]
Repayment of debt securities and subordinated notes		(7,969)	(6,281)	[1]	(13,763)	[1]
Repurchase of preference shares and other equity instruments		(318)	(290)	[1]
Dividends paid on ordinary shares		(315)	(1,139)	[1]	(829)	[1]
Dividends paid on preference shares and other equity instruments		(142)	(157)	[1]	(152)	[1]
Dividends paid on non-controlling interests		(12)	(22)	[1]	(19)	[1]
Net cash flows from financing activities		(4,126)	2,730	[1]	(7,637)	[1]
Change in cash and cash equivalents		1,841	(16,357)	[1]	17,155	[1]
Cash and cash equivalents at beginning of the year	[1]	26,029	42,226		25,705
Effects of exchange rate changes on cash and cash equivalents		(53)	160	[1]	(634)	[1]
Cash and cash equivalents at the end of the year		27,817	26,029	[1]	42,226	[1]
Cash and cash equivalents consist of:
Cash and balances at central banks		21,180	19,747	[1]	32,771	[1]
Less: regulatory minimum cash balances		(707)	(636)	[1]	(395)	[1]
Cash and bank balances at central banks less regulatory minimum cash balances		20,473	19,111	[1]	32,376	[1]
Net trading other cash equivalents		0			5,953	[1]
Net non-trading other cash equivalents		7,344	6,918	[1]	3,897	[1]
Cash and cash equivalents at the end of the year		£ 27,817	£ 26,029	[1]	£ 42,226	[1]
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.
[2]	In 2018, the Santander UK group sold a number of subsidiaries for a cash consideration of £348m, which equalled the carrying amount of the net assets disposed of.
[3]	Amounts in 2017, prior to the adoption of IFRS 9, are in respect of financial investments.

Consolidated Cash Flow Statem_2

Consolidated Cash Flow Statement (Parenthetical) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Statement of cash flows [abstract]
Cash consideration received on sale of subsidiaries	£ 348	[1],[2]
Carrying value of assets and liabilities	£ 348
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.
[2]	In 2018, the Santander UK group sold a number of subsidiaries for a cash consideration of £348m, which equalled the carrying amount of the net assets disposed of.

Consolidated Statement of Chang

Consolidated Statement of Changes in Equity - GBP (£) £ in Millions		Total		Share Capital [member]	Share premium [member]	Other Equity Instruments [member]	Other Reserves Available-For-Sale [member]		Other Reserves Fair Value Reserves [member]		Other Reserves Cash Flow Hedging [member]	Other Reserves Currency Translation [member]	Retained Earnings [member]		Total [member]	Non-Controlling Interests [member]
Beginning balance at Dec. 31, 2016		£ 15,453		£ 3,119	£ 5,620	£ 1,785	£ 48	[1]			£ 471	£ 5	£ 4,255	[2]	£ 15,303	£ 150
- Profit after tax		1,302	[2]										1,281	[2]	1,281	21
Other comprehensive income, net of tax:
- Available-for-sale securities		20	[1],[2]				20	[1]							20
- Fair value reserve (debt instruments)	[1],[2]
- Cash flow hedges		(243)	[2]								(243)				(243)
- Pension remeasurement		(77)	[2]										(77)	[2]	(77)
- Own credit adjustment		(22)	[2]										(22)	[2]	(22)
Total comprehensive income		980	[2]				20	[1]			(243)		1,182	[2]	959	21
Issue of other equity instruments		496				496									496
Dividends on ordinary shares		(553)											(553)	[2]	(553)
Dividends on preference shares and other equity instruments		(152)											(152)	[2]	(152)
Dividends on non-controlling interests		(19)														(19)
Ending balance at Dec. 31, 2017		16,205		3,119	5,620	2,281	68	[1]			228	5	4,732	[2]	16,053	152
Adoption of IFRS 9	[3]	(192)					(68)		£ 63				(187)		(192)
Ending balance at Jan. 01, 2018		16,013		3,119	5,620	2,281			63	[1]	228	5	4,545	[2]	15,861	152
Beginning balance at Dec. 31, 2017		16,205		3,119	5,620	2,281	£ 68	[1]			228	5	4,732	[2]	16,053	152
- Profit after tax		1,146	[2]										1,124	[2]	1,124	22
Other comprehensive income, net of tax:
- Available-for-sale securities	[1],[2]
- Fair value reserve (debt instruments)		(40)	[1],[2]						(40)	[1]					(40)
- Cash flow hedges		28	[2]								28				28
- Pension remeasurement		352	[2]										353	[2]	353	(1)
- Own credit adjustment		63	[2]										63	[2]	63
Total comprehensive income		1,549	[2]						(40)	[1]	28		1,540	[2]	1,528	21
Other		(45)											(45)	[2]	(45)
Repurchase of other equity instruments		(290)				(290)									(290)
Dividends on ordinary shares		(1,139)											(1,139)	[2]	(1,139)
Dividends on preference shares and other equity instruments		(157)											(157)	[2]	(157)
Dividends on non-controlling interests		(22)														(22)
Ending balance at Dec. 31, 2018		15,909		3,119	5,620	1,991			23	[1]	256	5	4,744	[2]	15,758	151
- Profit after tax		733		0	0	0			0	[1]	0	0	714	[2]	714	19
Other comprehensive income, net of tax:
- Available-for-sale securities	[1]
- Fair value reserve (debt instruments)	[1]	0
- Cash flow hedges		115		0	0	0			0	[1]	115	0	0	[2]	115	0
- Pension remeasurement		(391)		0	0	0			0	[1]	0	0	(393)	[2]	(393)	2
- Own credit adjustment		(58)		0	0	0			0	[1]	0	0	(58)	[2]	(58)	0
- Currency translation on foreign operations		(4)		0	0	0			0	[1]	0	(4)	0	[2]	(4)	0
Total comprehensive income		395		0	0	0			0	[1]	115	(4)	263	[2]	374	21
Issue of other equity instruments		500		0	0	500			0	[1]	0	0	0	[2]	500	0
Repurchase of other equity instruments		(318)		(14)	0	(300)			0	[1]	0	0	(4)	[2]	(318)	0
Dividends on ordinary shares		(315)		0	0	0			0	[1]	0	0	(315)	[2]	(315)	0
Dividends on preference shares and other equity instruments		(142)		0	0	0			0	[1]	0	0	(142)	[2]	(142)	0
Dividends on non-controlling interests		(12)		0	0	0			0	[1]	0	0	0	[2]	0	(12)
Ending balance at Dec. 31, 2019		£ 16,017		£ 3,105	£ 5,620	£ 2,191			£ 23	[1]	£ 371	£ 1	£ 4,546	[2]	£ 15,857	£ 160
[1]	Following the adoption of IFRS 9, a fair value reserve was introduced to replace the available-for-sale reserve.
[2]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.
[3]	The adoption of IFRS 9 decreased shareholders’ equity at 1 January 2018 by £192m (net of tax), comprised of a £49m decrease arising from the application of the new classification and measurement requirements for financial assets, and a £211m decrease arising from the application of the new ECL impairment methodology, these amounts being partially offset by the recognition of a deferred tax asset of £68m.

Consolidated Statement of Cha_2

Consolidated Statement of Changes in Equity (Parenthetical) £ in Millions	Jan. 01, 2018GBP (£)
Disclosure of changes in Equity
Adjustment for Adoption of IFRS 9	£ 192	[1]
Change in Financial Assets from application of IFRS 9	(49)
Change in Financial Assets from application of ECL impairment methodology	(211)
Recognition of deferred tax asset from application of ifrs9	£ 68
[1]	The adoption of IFRS 9 decreased shareholders’ equity at 1 January 2018 by £192m (net of tax), comprised of a £49m decrease arising from the application of the new classification and measurement requirements for financial assets, and a £211m decrease arising from the application of the new ECL impairment methodology, these amounts being partially offset by the recognition of a deferred tax asset of £68m.

Risk Framework

Risk Framework	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Risk Framework	Our risk governance structure We are committed to the highest standards of corporate governance in every part of our business. This includes risk management. For details of our governance, including the Board and its Committees, see the ‘Governance’ section of this Annual Report. The Board delegates certain responsibilities to Board Level Committees as needed and where appropriate. Our risk governance structure strengthens our ability to identify, assess, manage and report risks, as follows: • Committees: • Key senior management roles: • Risk organisational structure: Committees The Board Level Committee responsibilities for risk are: Board Level Committee Main risk responsibilities The Board •  Has overall responsibility for business execution and for managing risk •  Reviews and approves the Risk Framework and Risk Appetite. Board Risk Committee •  Assesses the Risk Framework and recommends it to the Board for approval •  Advises the Board on our overall Risk Appetite, tolerance and strategy •  Oversees our exposure to risk and our strategy and advises the Board on both •  Reviews the effectiveness of our risk management systems and internal controls. Board Responsible Banking Committee •  Responsible for culture and operational risk from conduct, compliance, competition, financial crime & legal matters •  Reviews reports from the CLRO on the adequacy and effectiveness of the compliance function •  Ensures that adequate and effective control processes are in place to identify and manage reputational risks •  Oversees our Corporate Social Responsibility programme and how it impacts on employees, communities, the environment including sustainability and climate change, reputation, brand and market positioning. Board Audit Committee •  Monitors and reviews the financial statements integrity, and any formal announcements on financial performance •  Reviews the adequacy and effectiveness of the internal financial controls and whistleblowing arrangements •  Monitors and reviews the effectiveness of the internal audit function. Board Remuneration Committee •  Oversees implementation of remuneration policies, ensuring they promote sound, effective risk management. The Executive Level Committee responsibilities for risk are: Executive Level Committee Main risk responsibilities Executive Committee •  Reviews business plans in line with our Risk Framework and Risk Appetite before they are recommended to the Board to approve. •  Receives updates on key risk issues managed by CEO-level Senior Management Committee •  Focuses on the responsibilities of the Executive Committee Senior Management Function holders and how they are discharged •  Reviews updates on key risk issues, customer, reputational and conduct matters. Executive Risk Control Committee (ERCC) •  Reviews Risk Appetite proposals before they are sent to the Board Risk Committee and the Board to approve •  Ensures that we comply with our Risk Framework, Risk Appetite and risk policies •  Reviews and monitors our risk exposures and approves any corrective steps we need to take. Asset and Liability Committee (ALCO) •  Reviews liquidity risk appetite (LRA) proposals •  Ensures we measure and control structural balance sheet risks, including capital, funding and liquidity, in line with the policies, strategies and plans set by the Board •  Reviews and monitors our key asset and liability management activities to ensure we keep our exposure in line with our Risk Appetite. Pensions Committee •  Reviews pension risk appetite proposals •  Approves actuarial valuations and reviews the impact they may have on our contributions, capital and funding •  Consults with the pension scheme trustees on the scheme’s investment strategy. Capital Committee •  Puts in place reporting systems and risk control processes to make sure capital risks are managed within our Risk Framework •  Reviews capital adequacy and capital plans, including the ICAAP, before they are sent to the Board to approve. Incident Accountability Committee •  Considers, calibrates, challenges and agrees any appropriate individual remuneration adjustments •  Presents recommendations to the Board Remuneration Committee. Credit Approval Committee •  Approves corporate and wholesale credit transactions which exceed levels delegated to lower level approval forums or individuals. Investment Approval Committee •  Approves equity type investment transactions which exceed levels delegated to lower level approval forums or individuals. Key senior management roles Senior roles with specific responsibilities for risk management are: Role Main risk responsibilities Chief Executive Officer The Board delegates responsibility for our business activities and managing risk on a day-to-day Chief Risk Officer (CRO) As the Risk Division leader, oversees and challenges risk activities, and ensures new lending decisions are made within our Risk Appetite. Accountable for the control and oversight of credit, market, liquidity, capital, pension, strategic and business, operational and model risks. Chief Legal and Regulatory Officer (CLRO) Accountable for the control and oversight of legal, conduct and regulatory, reputational and financial crime risk, and is responsible for reporting on these risks to the CRO to provide them with a holistic enterprise wide view of all risks. Chief Financial Officer Responsible for developing strategy, leadership and management of the CFO and Financial Accounting & Control Divisions. In supporting our corporate goals within our risk appetite, the CFO is responsible for managing interest rate, liquidity, pension and capital risks. Chief Internal Auditor (CIA) Designs and uses an audit system that identifies key risks and evaluates controls. The CIA also develops an audit plan to assess existing risks that involve producing audit, assurance and monitoring reports. Money Laundering Reporting Officer (MLRO) Responsible to the CLRO for control and oversight of financial crime risk but has regulatory responsibility to report on this risk type to Executive and Board Committees and the FCA.

Credit risk

Credit risk	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Credit risk	Credit risk Overview (unaudited) Key metrics (unaudited) Credit risk is the risk of loss due to the default or credit quality deterioration of a customer or counterparty to which we provided credit, or for which we assumed a financial obligation. Santander UK group level We start by discussing credit risk at a Santander UK group level. We set out how our exposures arise, our types of customer and how we manage them, and our approach to credit risk across the credit risk lifecycle. We provide an introduction into how climate change could impact credit risk. We also discuss our ECL approach and the key inputs to our ECL model. We then analyse our key metrics, credit performance and forbearance. Stage 3 ratio improved to 1.15% (2018: 1.29%). Loss allowances increased to £863m (2018: £807m). Average LTV of 65% (2018: 63%) on new mortgage lending. Business segments Then we cover Retail Banking separately from our other business segments – Corporate & Commercial Banking, Corporate & Investment Banking and Corporate Centre – in more detail. Credit risk – Santander UK group level SANTANDER UK GROUP LEVEL – CREDIT RISK MANAGEMENT Exposures Exposures to credit risk arise in our business segments from: Retail Banking Corporate & Commercial Banking Corporate & Investment Banking Corporate Centre •  Residential mortgages, business banking, consumer (auto) finance and other unsecured lending (credit cards, personal loans and overdrafts). •  Loans, bank accounts, treasury services, invoice discounting, cash transmission, trade finance and asset finance. •  Loans, bank accounts, treasury services, treasury markets activities, trade finance, receivables discounting and cash transmission. •  Asset and liability management of our balance sheet, as well as our non-core •  We provide these to individuals and small businesses. •  We provide these to SMEs and mid corporates, Commercial Real Estate and Social Housing associations. •  We provide these to large corporates and financial institutions. •  Exposures include sovereign and other international organisation assets that we hold for liquidity. The segmental basis of presentation in this Annual Report has been changed, and the prior periods restated, to report our short term markets business in Corporate Centre rather than in Corporate & Investment Banking. See Note 2 for more information. Our types of customers and how we manage them We manage credit risk across all our business segments in line with the credit risk lifecycle that we show in the next section. We tailor the way we manage risk to the type of customer. We classify our customers as standardised or non-standardised: Standardised Non-standardised •  Mainly individuals and small businesses. Their transactions are for relatively small amounts of money and share similar credit characteristics. •  Mainly medium and large corporate customers. Their transactions are for larger values and have more diverse credit characteristics. •  In Retail Banking, Corporate & Commercial Banking (for some small, non-complex non-core •  In Retail Banking (for some business banking transactions), Corporate & Commercial Banking, Corporate & Investment Banking and Corporate Centre. •  We manage risk using automated decision-making tools. These are backed by teams of expert analysts. •  We manage risk through expert analysis. We support this with decision-making tools based on internal risk assessment models. LOGO In 2019, we developed a high-level analysis of our credit portfolios based on various climate scenarios: a business-as low-carbon The aim of the Climate Portfolio Screen was to identify sectors and segments of the Santander UK lending book where there could be greater potential opportunities and risks associated with both the transition to a lower carbon economy and changes in physical climatic conditions. According to this analysis, the sectors of most concern based on exposure and or potential risks are mortgages, real estate, consumer finance and automotives. For the mortgage portfolio, we are working on a project that will help us understand the physical and transition risks in our mortgage book under different climate scenarios. Our approach to credit risk LOGO We manage our portfolios across the credit risk lifecycle (above), from drawing up our risk strategy, plans, budgets and limits to making sure the actual risk profile of our exposures stays in line with our business plans and within our Risk Appetite. We further tailor the way we manage risk across the lifecycle to the type of product. We say more on this in the Credit risk – Retail Banking and the Credit risk – Other business segments sections. 1. Risk strategy and planning All relevant areas of the business work together to create our business plans. We aim to balance our strategy, goals, and financial and technical resources with our Risk Appetite. To do this, we focus on economic and market conditions and forecasts, regulations, conduct matters, profitability, returns and market share. The result is an agreed set of targets and limits that help us direct our business. 2. Assessment and origination Managing credit risk begins with lending responsibly. That means only lending to customers who can afford to pay us back, even if things get tighter for them, and are committed to paying us back. We perform a thorough risk assessment to make sure customers can meet their obligations before we approve a credit application. We make these decisions with authority from the Board and we consider: • The credit quality of the customer • The underlying risk – and how we can mitigate it, such as through netting or collateral • Our risk policy, limits and appetite • Whether we can balance the amount of risk we face with the returns we expect, and • Assessment of customer affordability. We also use stress testing, for example to estimate how a customer might be able to cope if interest rates rise. 3. Monitoring We measure and monitor changes in our credit risk profile on a regular and systematic basis against our budgets, limits and benchmarks. We monitor credit performance by portfolio, segment, customer or transaction. If our portfolios do not perform as we expect, we investigate to understand the reasons. Then we take action to mitigate it as far as possible and bring performance back on track. We monitor and review our risk profile through formal governance forums and committees across our business. These agree and track any steps we need to take to manage our portfolios, to make sure the impact is prompt and effective. This structure is a vital feedback tool to coordinate issues, trends and developments across each part of the credit risk lifecycle. Credit concentrations A core part of our monitoring and management is a focus on credit concentrations, such as the proportion of our lending that goes to specific borrowers, groups or industries. We set concentration limits in line with our Risk Appetite and review them on a regular basis. We track how concentrated our portfolios are using a range of criteria. These include geographies, economic sectors, products and groups of customers. Geographical concentrations We set exposure limits to countries and geographies, with reference to the country limits set by Banco Santander. These are determined according to how the country is classified (whether it is a developed OECD country or not), its credit rating, its gross domestic product, and the products and services we or Banco Santander want to offer in that country. For more geographical information, see ‘Country risk exposures’. Industry concentrations We also set exposure limits by industry sector. We set these limits based on the industry outlook, our strategic aims and desired level of concentration, and relevant limits set by Banco Santander. We analyse committed exposures in the ‘Credit risk review’. 4. Arrears management Sometimes our customers face financial difficulty and may fall into payment arrears or breach the conditions of their credit facility. If this happens, we work with them to get their account back on track. We aim to support our customers and keep our relationship with them. To do this, we: • Find affordable and sustainable ways of repaying to fit their circumstances • Monitor their finances and use models to predict how they will cope. This helps us put in place the right strategy to manage their debt • Work with them to get their account back on track as soon as possible in a way that works for them and us • Monitor agreements we make to manage their debt, so we know they are working. For more, see the Forbearance section on the next page. 5. Debt recovery Sometimes, even when we have taken all reasonable and responsible steps we can to manage arrears, they are not effective. If this happens, we have to end our agreement with the customer and try to recover the whole debt, or as much of it as we can. Loan modifications We sometimes change the terms of a loan when a customer gets into financial difficulty (this is known as forbearance), or for other commercial reasons. Forbearance When a customer gets into financial difficulties, we can change the terms of their loan, either temporarily or permanently. We do this to help customers through temporary periods of difficulty so they can get back on to sustainable terms and fully pay off the loan over its lifetime, with support if needed. We try to do this before the customer defaults. Whatever we offer, we assess it to make sure the customer can afford the repayments. Forbearance improves our customer relationships and our credit risk profile. We review our approach regularly to make sure it is still effective. In a few cases, we can help a customer in this way more than once. This can happen if the plan to repay their debt doesn’t work and we have to draw up another one. When this happens more than once in a year, or more than three times in five years, we call it multiple forbearance. We only use foreclosure or repossession as a last resort. When we agree to forbearance, we consider that the account has suffered a Significant Increase in Credit Risk (SICR), as we explain later on. We review our loss allowance for it and report the account as forborne. For retail accounts, if an account is in Stage 1 (a 12-month 12-month Exit from forbearance or cure For a loan to exit forbearance, all the following conditions must be met: • The loan has been forborne for at least two years or, if forbearance was temporary, must have returned to performing under normal terms for at least two years • The loan has been performing under the forborne terms for at least two years • The account is no longer in arrears, and the customer has no other material debts with us which are more than 30 days in arrears. Other modifications When a customer is not showing any signs of financial difficulties, we can also change the terms of their loan. We do this to keep a good relationship with them. Risk measurement and control We measure and control credit risk at all stages across the credit risk lifecycle. We have a range of tools, processes and approaches, but we rely mainly on: • Credit control: • Models: • Review: Key metrics We use a number of key metrics to measure and control credit risk, as follows: Metric Description Expected Credit Loss (ECL) ECL tells us what credit risk is likely to cost us either over the next 12 months on qualifying exposures, or defaults over the lifetime of the exposure where there is evidence of a SICR since origination. We explain how we calculate ECL below. Stages 1, 2 and 3 We assess each facility’s credit risk profile to determine which stage to allocate them to, and we monitor where there is a SICR and transfers between the Stages including monitoring of coverage ratios for each stage. We explain how we allocate a facility to Stage 1, 2 or 3 below. Stage 3 ratio The Stage 3 ratio is total Stage 3 exposure as a percentage of customer loans plus undrawn Stage 3 exposures. We changed our definition of the Stage 3 ratio in 2019 and restated 2018 for consistency. The Stage 3 ratio was previously calculated as Stage 3 exposures as a percentage of customer loans. The Stage 3 ratio at 31 December 2018 using the new definition was 1.29%, compared to 1.20% using the previous definition. Following the introduction of IFRS 9 in 2018, the Stage 3 ratio became the main indicator of credit quality performance and replaces the NPL ratio which is no longer reported. Expected Loss (EL) EL is based on the regulatory capital rules of CRD IV and gives us another view of credit risk. It is the product of the probability of default, exposure at default and loss given default. We calculate each factor in accordance with CRD IV and include direct and indirect costs. We base them on our risk models and our assessment of each customer’s credit quality. There are differences between regulatory EL and IFRS 9 ECL, which we set out below. For the rest of our Risk review, impairments, losses and loss allowances refer to calculations in accordance with IFRS, unless we specifically say they relate to CRD IV. For our IFRS accounting policy on impairment, see Note 1 to the Consolidated Financial Statements. We also assess risks from other perspectives, such as geography, business area, product and process to identify areas we need to focus on. We also use stress testing to establish vulnerabilities to economic deterioration. Our business segments tailor their approach to credit risk to their own customers, as we explain later on. Key differences between regulatory EL and IFRS 9 ECL models (unaudited) There are differences between the regulatory EL and the IFRS 9 ECL approaches. Although our IFRS 9 models use the existing Basel advanced IRB risk components, we need to make several adjustments to ensure the outcome is in line with the IFRS 9 requirements, as follows. Basel advanced IRB EL IFRS 9 ECL Rating philosophy Mix of point-in-time, through-the-cycle Point-in-time, Parameters calibration Contains regulatory floors and downturn calibration Unbiased estimate, based on conditions known at the balance sheet date Calculation timing Considers aggregation of possible default events in the next 12 months Considers monthly calculation of parameters, for all possible future default dates. First 12 months are used for Stage 1, full lifetime for Stages 2 and 3. Probability of Default (PD) PD in the next 12 months Includes forward-looking economic data and removes conservatism and bias. Adjusted to convert from 12 months to lifetime for Stages 2 and 3 Loss Given Default (LGD) Lifetime LGD for defaults in the next 12 months Modelled without regulatory floors and exclusion of indirect costs Exposure at Default (EAD) Exposure at the point of default if the customer defaults in the next 12 months Floored at amount owed, except on some revolving facilities. Recognises ability for exposure to reduce from the balance sheet date to default date SICR Does not include SICR concept Includes SICR concept Discounting applied At the weighted average cost of capital to the default date At the effective interest rate (EIR) to the balance sheet date Recognising ECL The ECL approach estimates the credit losses arising from defaults in the next 12 months on qualifying exposures, or defaults over the lifetime of the exposure where there is evidence of a SICR since the origination date. The ECL approach takes into account forward-looking data, including a range of possible outcomes, which should be unbiased and probability-weighted in order to reflect the risk of a loss being incurred even when it is considered unlikely. Multiple economic scenarios and probability weights For all our portfolios, except CIB (which we cover in more depth below), we use five forward-looking economic scenarios. They consist of a central base case, two upside scenarios and two downside scenarios. We use five scenarios to reflect a wide range of possible outcomes in the performance of the UK economy. Base case Our base case assumes that the UK will negotiate a trade deal with the EU and that there will be an orderly exit. Base case key macroeconomic assumptions for 2019 • House price growth: 1 2 • GDP: • Unemployment rate: 4 • Bank of England Base Rate (Base Rate): 75 In the medium-term, the projections assume that current demographic and productivity trends will continue, causing a reduction in the UK’s growth potential. This is reflected in an average growth expectation of less than 1.6% pa, the OBR’s latest estimate of the UK’s long run average growth rate. We expect the low value of sterling to continue into 2020. However, we would expect some improvement if the economic data continues to recover and there is constructive dialogue between the UK and the EU on agreeing the terms of a future trade deal. Even though the continuing Brexit negotiations on a future trade deal are likely to result in some increased trade costs between the EU and UK, these are not expected to significantly impact the downwards trend in the share of UK exports going to the EU. CPI inflation is forecast to remain around the 2% target rate and nominal earnings growth of approximately 3% is expected to continue over the forecast horizon. This implies positive real earnings growth, which in turn will support household spending power. However, the effect of limited business investment on growth will continue until the final outcome of Brexit is known. Furthermore, with the household savings ratio stabilising and consumer credit growth slowing, consumer demand will be driven increasingly by the fundamentals of household income growth. In summary, the base case assumes that activity will continue to run at a relatively slow pace as we move through 2020 but will pick up further in subsequent years. Key changes to our base case in 2019 The key changes to our base case assumptions in 2019 were that we lowered our GDP forecasts for 2019, 2020 and 2021 to reflect the slower growth we have been seeing given the continuing Brexit uncertainty and the decline in global growth. We also reduced house price growth slightly for 2020 and 2021 and the unsecured lending path was amended to reflect Bank of England revisions to historic estimates. (i) For all our portfolios, except CIB Our forecasting approach We derive our scenarios in part by using a set of parameters in GDP fan charts published by the Office for Budget Responsibility (OBR) twice a year. To avoid major changes to the scenarios due to changes in the OBR fan charts, we place more weight on what the long-run We use the 0.6 and 0.7 fan chart paths for our Upside scenarios, and the 0.3 path for Downside 1. However, for Downside 2 we use a blend of the Downside 1 scenario and the recession of the early 1980s. We believe that a recession of that order of magnitude is more likely than a repeat of the 2008/09 recession. This means that in the longer run the GDP levels in our Downside 1 and 2 scenarios converge. To ensure that Downside 2 is kept consistent with any changes to the OBR fan charts, we calculate the Downside 2 GDP by taking the percentage difference between Downside 2 and Downside 1 GDP in the original forecast and applying this difference to the new Downside 1. Our use of five scenarios is designed to reflect different possible outcomes to the base case forecast highlighting the upside and downside risks associated with the central scenario. The downside risks include unfavourable developments for Brexit, a further and sharper downturn in global growth, continuation of the very low productivity growth seen in the UK, and a move to a more protectionist agenda for trade. The upside risks are more muted at present and include the quick implementation of a new free trade agreement with the EU and an upturn in global growth, coupled with a move to more open trade. The two upside scenarios are based on a faster global recovery and the UK quickly concluding trade agreements with a number of countries after leaving the EU, along with minimum effective tariffs. It is also based on productivity growth recovering. If this is combined with a strong supply side response, interest rate normalisation can occur in a gradual and well managed fashion. The difference between the two scenarios is how quickly the recovery happens and the strength of global recovery. Regarding the two downside scenarios, Downside 1 reflects slower growth for longer, representing a period of continued uncertainty as the Brexit process continues to mute expectations. It also assumes ‘lower for longer’ global growth. With sterling under continuing pressure, this causes the Monetary Policy Committee (the MPC) to raise rates to quell further inflation even though a looser stance would be more beneficial to growth. Business and household confidence continue to be negative and business investment struggles. In terms of trade, the UK defaults to WTO rules with the EU but maintains an open trade policy pursuing bilateral trade agreements with countries rather than pure free trade agreements. Downside 2 assumes the UK economy goes into outright recession. Here global growth is undermined by further weakness among the advanced economies and the emerging markets slowing more markedly than expected. This scenario also assumes that the UK leaves the EU without a trade deal and that business investment contracts further given the continued uncertainty over future trading arrangements. There is also widespread and substantial capital flight as overseas investors sell UK assets, which in turn leads to a tightening in domestic financial conditions. As overseas investors’ appetite for UK assets diminishes, this causes a sell-off Given the above, our scenarios and weights reflect the range of possible outcomes that the UK may face in 2020 and beyond. Once we have established the GDP paths for each scenario, we run them through the Oxford Global Economic Model (OGEM) to derive the other macroeconomic variables, such as unemployment and house prices. These variables are the product of the GDP growth paths we have forecast and the output of the OGEM for these particular growth paths. We then impose a Bank Rate profile for each scenario using expert judgement. We determine the Bank Rate by using the base case Bank Rate profile and adjusting this for each of the four scenarios. To do this, we firstly consider what each of the scenarios is trying to achieve. For the upside scenarios which have a higher growth path and rising productivity growth, a strengthening of sterling keeps CPI inflation low and allows for a managed tightening of the monetary stance. In contrast, the downside scenarios show monetary policy forced into a reactive stance to contain CPI inflation at a time of weakening output growth, so we assume the Bank of England would raise rates in this scenario in order to bring the inflation rate back to its target rate. The rising Bank Rate profiles are based on forward guidance from the Bank of England where increases are assumed to be gradual and incremental. We update the baseline in our economic scenarios at least twice a year in line with our annual budgeting and three-year planning processes, or sooner if there is a material change in current or expected economic conditions. We refresh all our economic scenarios each quarter to reflect the latest data and OBR fan charts if these have changed, which are then reviewed and approved by ALCO. ALCO also assess the probability weights at least once a quarter. We avoid embedding new economic scenarios into our models on a quarter-end quarter-end We do not use consensus forecasts as inputs to our models, but we do compare the outputs of our models against consensus views for the base case, to make sure that we understand any significant differences and address them, where needed. In 2019, there were no significant differences between our base case forecasts and the consensus views. Key changes to our forecasting approach in 2019 In 2019, there were no significant changes in our forecasting approach, except that for the two upside scenarios we have changed the Bank Rate profiles. Initially, we had a falling Bank Rate profile for the upside scenarios to maintain symmetry with the downside scenarios, which showed a rising Bank Rate. However, it was later decided that symmetrical outcomes were no longer required for the upside and downside scenarios; rather it was more logical to have Bank Rate rising when the economy is growing strongly, and inflation is picking up. Scenario weights To determine our initial scenario weights, we give the highest weight to the base case, whilst the outer scenarios typically attract lower weights than the more moderate ones. We also consider how the GDP five-year average growth rates for each scenario fits with the average growth rates over the last 10 years in helping to determine the weights to apply. We use a 10-year As part of our review of the scenarios and weights that we use, we perform statistical analysis to assess whether their use ensures that we capture the non-linearity non-linear 1-2%; 0-1% In terms of applying scenario weights to this for, say, Downside 1 we consider how much weight should be attached to an outcome where GDP is between 0-1%. 0-1%, 20-40% The scenario weights we applied for 2019 and 2018 were: Scenario weights Upside 2 % Upside 1 % Base case % Downside 1 % Downside 2 % 2019 5 10 40 30 15 2018 5 15 40 30 10 Key changes to our scenario weights in 2019 The key changes to our scenario weights were made in Q3 2019 to reduce the Upside 1 weight by 5% to reflect the lower upside risk to the base case forecast from global economic conditions and increase the Downside 2 weight by 5% to reflect the higher downside risks relating to Brexit and the risk of global recession. Our macroeconomic assumptions and their evolution throughout the forecast period Our macroeconomic assumptions and their evolution throughout the forecast period for 2019 and 2018 were: 2019 Upside 2 Upside 1 Base case Downside 1 Downside 2 House price growth 5-year 4.90 3.70 1.60 (1.20 ) (9.30 ) Peak/(trough) (1) 8.10 5.80 2.00 (2.80 ) (13.50 ) GDP 5-year 2.40 2.00 1.60 0.70 0.20 Cumulative growth/(fall) to peak/(trough) (2) 1.50 1.00 0.70 (1.10 ) (5.60 ) Unemployment rate 5-year 1.90 2.70 4.00 5.60 7.40 Peak/(trough) at 1.88 2.73 4.10 5.64 7.84 Bank of England base rate 5-year 2.00 2.00 0.75 2.00 2.25 Peak/(trough) at 2.00 2.00 0.75 2.00 3.00 2018 House price growth 5-year 3.40 2.30 2.00 (2.00 ) (9.50 ) Peak/(trough) at 7.40 4.60 2.00 (5.80 ) (15.60 ) GDP 5-year 2.50 2.10 1.60 0.70 0.30 Cumulative growth/(fall) to peak/(trough) 1.60 1.10 0.60 (0.60 ) (6.10 ) Unemployment rate 5-year 2.80 3.80 4.30 6.90 8.60 Peak/(trough) at 2.58 3.71 4.39 7.30 8.65 Bank of England base rate 5-year 1.00 1.25 1.50 2.50 2.25 Peak/(trough) at 2.00 2.00 1.50 2.50 3.00 (1) Peak/(trough) refers to the peak that the variable will reach in the upside scenario and the trough that the variable will reach in the downside scenario. (2) Cumulative growth/(fall) refers to the cumulative change from the last historical data point for GDP growth to the peak (for Upside scenarios) or to the trough (for Downside scenarios). The historical and forecast growth rates for the GDP assumptions we use for scenario modelling The evolution of the historical and forecast growth rates for the GDP assumptions we used for scenario modelling at 31 December 2019 was: LOGO Our forecasting period for GDP is five years and then we revert to the average trend growth over three years based on the OBR’s long-run In the Upside 1 and Upside 2 scenarios, the economy is assumed to peak by the end of Q4 2022, after which GDP declines. In the Downside 1 the trough occurs in Q4 2020 and in Downside 2 a trough is assumed to occur in Q2 2020. In all scenarios, we assume that GDP will have reverted to the OBR’s long-run Key changes to our alternative scenarios in 2019 In terms of key changes to our alternative scenarios in 2019, these only related to changes to the base case, historic data for each variable, OBR fan charts and the OGEM. We did not make any methodological changes to the scenarios. The combination of these different inputs will mean differences across the variables for each of the alternative scenarios when we update them each quarter. As such it is not possible to pin-point (ii) For our CIB portfolios Our forecasting approach For our CIB portfolios, we adopted the approach developed centrally by Banco Santander to ensure consistent treatment of these large and/or international counterparties across the Banco Santander group. For CIB, we use three scenarios (Base case, Upside and Downside). Like the UK scenarios, the base case uses the base scenario that has been developed and is used in other work that Banco Santander performs for planning and stress testing purposes. To develop the Downside scenario, the path of GDP for each country is calculated using the distribution probability of GDP estimated using a Monte Carlo simulation. The path used is the one that falls into a percentile that sits halfway between the baseline and global stress we use for our ICAAP. For the Upside, the distribution probability of GDP is again used, for each country the GDP path is consistent with the symmetric percentile selected on the Downside. This means that the scenarios maintain the asymmetry that comes with the probabilities of distribution. Key changes to our forecasting approach in 2019 In 2019, there were no significant changes in our forecasting approach. Scenario weights For our CIB portfolios, to determine our initial scenario weights, we give the highest weight to the base case. As set out above, we base the GDP path associated with the Upside scenario on the distribution probability of GDP consistent with the symmetric percentile selected on the Downside. This allows us to maintain the asymmetry of the scenarios that has been introduced in the probabilities of distribution. It also enables us to assign centred weights. The scenario weights we applied to the scenarios for our CIB portfolio for 2019 and 2018 were: Upside Base case Downside Scenario weights % % % 2019 30 40 30 2018 20 60 20 Our macroeconomic assumptions and their evolution throughout the forecast period Our macroeconomic assumptions and their evolution throughout the forecast period for our CIB portfolio for 2019 and 2018 were: Upside Base case Downside GDP assumption % % % 2019 5 year average increase/decrease 3.7 3.5 3.0 Cumulative growth/(fall) to peak/(trough) (1) 0.3 0.5 (1.2 ) 2018 5 year average increase/decrease 4.2 3.6 2.7 Cumulative growth/(fall) to peak/(trough) 0.4 0.3 (0.8 ) (1) Cumulative growth/(fall) refers to the cumulative change from the last historical data point for GDP growth to the peak (for upside scenarios) or to the trough (for downside scenarios). Key changes to our alternative scenarios in 2019 There were no key changes to our alternative scenarios in 2019. Significant Increase in Credit Risk (SICR) Loans which have suffered a SICR since origination are subject to a lifetime ECL assessment which extends to a maximum of the contractual term of the loan, or the behavioural term for a revolving facility. Loans which have not experienced a SICR are subject to 12 month ECL. We assess the credit risk profile of each facility to determine which of three stages to allocate them to: • Stage 1: • Stage 2: • Stage 3: We use a range of quantitative, qualitative and backstop criteria to identify exposures that have experienced a SICR. The Credit Risk Provisions Forum (CRPF) reviews and approves our SICR thresholds periodically. The Board Audit Committee reviews and challenges the appropriateness of them each year, or more often if we change them. Quantitative criteria We use quantitative criteria to identify where an exposure has increased in credit risk. The criteria we apply are based on whether any increase in the lifetime PD since the recognition date exceeds a set threshold both in relative and absolute terms. We base the value anticipated from the initial recognition on a similar set of assumptions and data to the ones we used at the reporting date, adjusted to reflect the account surviving to that date. The comparison uses either an annualised lifetime PD, where the lifetime PD is divided by the forecast period, or the absolute change in lifetime PD since initial recognition. For each portfolio, the quantitative criteria we used for 2019 were: Retail Banking (1) Consumer (auto) Other unsecured Corporate & Corporate & Mortgages finance (2) Personal loans Credit cards Overdrafts Commercial Banking Investment Banking 30bps 300bps 30bps 340bps 260bps 30bp

Market risk

Market risk	12 Months Ended
	Dec. 31, 2019
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Market risk	Market risk Overview (unaudited) Market risk comprises banking market risk and trading market risk. Banking market risk is the risk of loss of income or economic value due to changes to interest rates in the banking book or to changes in exchange rates, where such changes would affect our net worth through an adjustment to revenues, assets, liabilities and off-balance Trading market risk is the risk of losses in trading positions, both on and off-balance In this section, we set out which of our assets and liabilities are exposed to banking and trading market risk. Then we explain how we manage these risks and discuss our key market risk metrics. We also provide some insight into the process of replacing LIBOR and other Interbank Offered Rates. Key metrics (unaudited) Net Interest Margin (NIM) sensitivity to +50bps was £99m and to -50bps was £56m (2018: £207m and £(23)m) Economic Value of Equity (EVE) sensitivity to +50bps was £10m and to -50bps was £(88)m (2018: £162m and £(124)m) BALANCE SHEET ALLOCATION BY MARKET RISK CLASSIFICATION We manage our assets and liabilities exposed to market risk as either banking or trading market risk. We classify all our assets and liabilities exposed to market risk as banking market risk, except for certain derivatives that we manage on a trading intent basis. For accounting purposes, we classify all derivatives as held for trading unless they are designated as being in a hedging relationship. The derivatives that we manage on a trading intent basis are a small proportion of the derivatives that we classify as held for trading for accounting purposes. For more, see Note 12 to the Consolidated Financial Statements. BANKING MARKET RISK OUR KEY BANKING MARKET RISKS (UNAUDITED) Banking market risk mainly comes from providing banking products and services to our customers, as well as our structural balance sheet exposures. It arises in all our business segments. In Retail Banking and Corporate & Commercial Banking, it is a by-product In Corporate & Investment Banking, it arises from short-term markets and lending to corporates, which we also transfer to Corporate Centre to manage. Corporate Centre also manages our structural balance sheet exposures, such as foreign exchange and Income Statement volatility risk. Our key banking market risks are: Key risks Description Interest rate risk Yield curve risk off-balance non-rate Basis risk Spread risks Spread risk arises when the value of assets or liabilities which are accounted for at fair value (either through Other Comprehensive Income or though Profit and Loss) are affected by changes in the spread. We measure these spreads as the difference between the discount rate we use to value the asset or liability, and an underlying interest rate curve. Spread risks can be split into Swap Spread (where the instrument has been issued by a Sovereign counterparty) and Credit Spread (where the instrument has been issued by for example a corporate or bank counterparty). It principally arises in the bond portfolios we hold for liquidity purposes. We measure spread risk with sensitivities, stress tests and VaR measures. Foreign exchange risk Our non-trading Income statement volatility risk We measure most of the assets and liabilities in our banking book balance sheet at amortised cost. We sometimes manage their risk profile by using derivatives. As all derivatives are accounted for at fair value, the mismatch in their accounting treatment can lead to volatility in our Income Statement. This happens even if the derivative is an economic hedge of the asset or liability. BANKING MARKET RISK MANAGEMENT Risk appetite Our framework for dealing with market risk is part of our overall Risk Framework. The banking market risk framework sets out our high-level arrangements and standards to manage, control and oversee banking market risk. Our Risk Appetite sets the controls, risk limits and key risk metrics for banking market risk. We articulate risk appetite by the income and value sensitivity limits we set in our Risk Appetite, at both Santander UK and Banco Santander group levels. Risk measurement For banking market risk, we mainly measure our exposures with NIM and EVE sensitivity analysis. We support this with VaR risk measures and stress testing. We also monitor our interest rate repricing gap. NIM and EVE sensitivities The calculations for NIM and EVE sensitivities involve many assumptions, including expected customer behaviour (such as early repayment of loans) and how interest rates may move. These assumptions are a key part of our overall control framework, so we update and review them regularly. Our NIM and EVE sensitivities include the interest rate risk from all our banking book positions. Our banking book positions generate almost all our reported net interest income. NIM sensitivity • NIM sensitivity is an income-based measure we use to forecast the changes to interest income and interest expense in different scenarios. It gives us a combined impact on net interest income over a given period – usually 12 or 36 months. • We calculate NIM sensitivity by simulating the NIM using two yield curves. The difference between the two NIM totals is the NIM sensitivity. • Our main model assumptions are that: • The balance sheet is dynamic. This means that it includes the run-off • We use a behavioural balance sheet rather than contractual one. This means that we adjust balances for behavioural or assumed profile. We do this with most retail products whose behavioural maturity is different to the contractual maturity. This is usually because customers are exercising the option to withdraw or prepay early, or there is no contractual maturity. EVE sensitivity • We calculate EVE as the change in the net present value of all the interest rate sensitive items in the banking book balance sheet for a defined set of instantaneous parallel and non-parallel • We use a static balance sheet. This means that all balance sheet items run-off run-off The limitations of sensitivities We use sensitivities to measure the impact of standard, instantaneous, parallel shifts in relevant yield curves. The advantage of using standard parallel shifts is they generally give us a constant measure of the size of our market risk exposure, with a simple and consistent stress. This compares to specific scenarios like ‘flat rates’. The magnitude of flat rates depends on the shape of the current curve and the shift required to reach the flat rate scenario. There is one exception to the relative simplicity of parallel shifts. In order to limit negative interest rates, the yield curve may be ‘floored’. Using material parallel shocks does not always seem realistic, or it might not necessarily test the scenarios that have the most impact on us. So we run non-parallel non-parallel VaR VaR • VaR indicates the losses that we might suffer because of unfavourable changes in the markets under normal (non-stressed) • We run a historical simulation using the past two years of daily price moves, at a 99% confidence level, to find how much we might lose – the Value at Risk. • For any given day’s position, we expect to suffer losses greater than the VaR estimate 1% of the time – once every 100 trading days, or two to three times a year. • This gives us a consistent way of assessing risk for all relevant market risk factors in our portfolios. The limitations of VaR Whilst VaR is a useful and important market standard measure of risk, it does have some limitations. These include: • VaR assumes what happened in the past is a reliable way to predict what will happen in the future. This may not always be the case • VaR is based on positions at the end of the business day so it doesn’t include intra-day • VaR does not predict how big the loss could be on the 1% of trading days that it is greater than the VaR • Using a time horizon of one day means VaR does not tell us everything about exposures that we cannot liquidate or hedge within a day, or products with infrequent pricing. Back-testing – comparing VaR estimates with reality To check that the way we estimate VaR is reasonable, we back-test our VaR by comparing it against both actual and hypothetical profits and losses, using a one-day Other ways of measuring risk As well as using sensitivities and stress tests, we can measure banking market risk using net notional positions. This can give us a simple expression of our exposure, although we generally need to combine it with other risk measures to cover all aspects of a risk profile, such as projected changes over time. Other metrics we can use include Earnings at Risk (EaR). Although VaR can be useful as it captures changes in economic values, as we describe above, VaR will not reflect the actual Income Statement impact of most of our banking book positions. This is because we account for them at amortised cost rather than fair value. EaR is like VaR but captures changes in income rather than value. We use this approach mainly to generate a one-year Stress testing Stress testing is an essential part of our risk management. It helps us to measure and evaluate the potential impact on portfolio values of more extreme, although plausible, events or market moves. We express limits as on how much we could lose in a stress event, and this restricts how much risk we take. Stress testing scenarios Simple stress tests (like parallel shifts in relevant curves) give us clear measures of risk control and a consistent starting point for setting limits. More complex, multi-factor and multi-time period stress tests can give us information about specific potential events. They can also test various outcomes that we might not capture through parallel stresses or VaR-type We can adapt our stress tests to reflect current concerns such as Brexit and other macroeconomic events or changing market conditions quicker than we can with other risk measures, like VaR. We can include both individual business area stresses and Santander UK-wide How we use stress testing We discuss stress testing results at senior management committees. They affect Corporate Centre’s decisions by highlighting possible risks in the banking book and the effectiveness of remedial actions we could take. We compare stress test results with stress limits and triggers set by our internal committees, or against metrics set by the PRA. If the results are over our limits or triggers, we take remedial actions and follow an escalation process. Risk mitigation We mitigate Income Statement volatility mainly through hedge accounting. We monitor any hedge accounting ineffectiveness that might lead to Income Statement volatility with a VaR measure and trigger, reported monthly. For our accounting policies for derivatives and hedge accounting, see Note 1 to the Consolidated Financial Statements. We typically hedge the interest rate risk of the securities we hold for liquidity and investment purposes with interest rate swaps, retaining spread exposures. These retained exposures are the key drivers of the VaR and stress tests we use to assess the risk of the portfolio. We hedge our foreign currency funding positions back to sterling, so our foreign exchange positions tend to be residual exposures that remain after hedging. These positions could be, for example, to ‘spot’ foreign exchange rates or to cross currency basis. We monitor foreign exchange risk against absolute net exposures and VaR-based For more on this, see ‘Funding strategy’ and ‘Term issuance’ in the ‘Liquidity risk’ section. Risk monitoring and reporting We monitor the banking market risks of the portfolios we hold for liquidity and investment purposes using sensitivities, VaR and stress tests. We report them against limits and triggers to senior management daily and to ALCO and ERCC each month. The VaR we report captures all key sources of volatility (including interest rate and spread risks) to fully reflect the potential volatility. BANKING MARKET RISK REVIEW Interest rate risk Yield curve risk The table below shows how our base case income and valuation would be affected by a 50 basis point parallel shift (both up and down) applied instantaneously to the yield curve at 31 December 2019 and 2018. Sensitivity to parallel shifts represents the amount of risk in a way that we think is both simple and scalable. 50 basis points is the stress we typically focus on for banking market risk controls, although we also monitor sensitivities to other parallel and non-parallel 2019 2018 +50bps -50bps +50bps -50bps NIM sensitivity 99 56 207 (23 ) EVE sensitivity (unaudited) 10 (88 ) 162 (124 ) Basis risk We report basis risk using the EaR approach. 2019 2018 £m £m Basis risk EaR 18 25 Interest rate repricing gap The table below shows the interest rate repricing gap of our balance sheet by repricing buckets. 3 months 1 year 3 years 5 years >5 years Not sensitive Total 2019 £m £m £m £m £m £m £m Assets 107,155 50,284 67,439 32,918 12,561 16,539 286,896 Liabilities 188,773 17,513 22,774 12,892 21,900 24,064 287,916 Off-balance 14,945 (18,495 ) 4,481 (1,516 ) 1,605 0 1,020 Net gap (66,673 ) 14,276 49,146 18,510 (7,734 ) (7,525 ) 0 2018 Assets 128,173 46,354 61,946 26,048 13,705 16,607 292,833 Liabilities 194,362 16,762 23,987 13,508 23,345 23,845 295,809 Off-balance 11,096 (12,204 ) (2,731 ) 6,870 (55 ) — 2,976 Net gap (55,093 ) 17,388 35,228 19,410 (9,695 ) (7,238 ) — Spread risks The table below shows the risk metrics covering the portfolios of securities we hold for liquidity and investment purposes. 2019 2018 £m £m VaR 3 4 Worst three month stressed loss 1 3 190 2019 compared to 2018 (unaudited) The reduction in NIM and EVE sensitivities in 2019 was largely driven by balance sheet management activities. These included leaving fixed rate assets unhedged, increasing the net structural position over the latter end of the year primarily to mitigate further margin compression risk as a result of lower levels of the yield curve. The movement in sensitivities over the year also reflected the separation of SFS exposures from the ring-fenced bank group sensitivities following the implementation of our ring-fencing plans. In 2019, the worst three month stressed loss decreased more compared to the decrease in VaR in the year due to the sale of £2bn of liquidity assets in Q4 2019. The assets that were sold had a greater impact on the stress results than the VaR. This was due to the conservative nature of the stress scenarios that we use. The basis risk EaR in 2019 decreased due to the natural evolution of the balance sheet leading to a reduced underlying net basis position, as well as methodology updates to ensure we fully capture LIBOR transition risks. We continue to periodically review our risk models and metrics including underlying modelling assumptions to ensure they continue to reflect the risks inherent in the current rate environment and incorporate regulatory expectations. In addition, as discussed earlier, climate-related risks could eventually manifest in risks for financial institutions. During 2020, we will review the appropriate parts of the Risk Framework, Risk Type Frameworks (in particular Credit and Operational risk, but also market risk) and the Risk Appetite Statement to explicitly include climate-related risks. TRADING MARKET RISK OUR KEY TRADING MARKET RISKS (UNAUDITED) Our main exposure to trading market risk is in Corporate & Investment Banking and it is an inherent part of providing financial services for our customers. Our exposures are mainly affected by market movements in interest rates, credit spreads, and foreign exchange. We have no exposures in Retail Banking, Corporate & Commercial Banking or Corporate Centre. Trading market risk can reduce our net income. Its effect can be seen in our Consolidated Income Statement, where it appears in the ‘Net trading and other income’ line, under ‘Net trading and funding of other items by the trading book’. Following the implementation of our ring-fencing plans in 2018, only a small amount of trading market risk from permitted products and permitted customers remains. This arises from hedging activity and back-to-back We have two trading desks. The Link Desk sells ring-fenced bank permissible products to clients. The Retail Structured Products desk (RSP) sells investments (Santander UK plc issued notes) to retail investors, through our UK branches and elsewhere. The Link Desk has risk exposure to the credit quality of our clients. The adjustment for this is known as the Credit Valuation Adjustment (CVA) and feeds our valuations and hence income and expense. The low level of direct market risk in our trading business means that this is the main driver of income statement movements, along with similar factors – principally Debt Valuation Adjustment (DVA) driven by our own credit, and Liquidity Valuation Adjustment (LVA) driven by the market price of liquidity. These valuation adjustments are collectively referred to as XVAs. Our reduced level of trading market risk after ring-fencing led us to decommission our Internal Model. As a result, from 1 January 2019, we calculate market risk capital using standardised rules. TRADING MARKET RISK MANAGEMENT Risk appetite Our framework for dealing with market risk is part of our overall Risk Framework. The market risk framework sets out our high-level arrangements and minimum standards for managing, controlling and overseeing trading market risk. Our Risk Appetite for trading market risk is low, so we only report a qualitative measure to the Board. We monitor trading market risk using stress measures which we report to the ERCC each month. Risk measurement For trading market risk, we have a range of ways of measuring trading market risk, including VaR (which we explain in the Banking market risk management section above) and detailed sensitivity measures. Stress testing Stress testing is an essential part of our risk management. It helps us to measure and evaluate the potential impact on portfolio values of more extreme, although plausible, events or market moves. We express limits to how much we could lose in a stress event, and this restricts how much risk we take. Stress testing scenarios We calculate the impact of over 100 scenarios on our trading books, each month. The scenarios we create may be inspired by past events, like the global financial crisis. They may also include plausible ways that unusual market conditions could occur in the future that impact interest rates, equity prices and exchange rates. Most are reported against limits, and so could lead to our front office being asked to reduce risk. Our scenarios are not all calibrated to the same severity – some may be for a much longer holding period or a completely artificial and unrealistic scenario. We therefore do not limit all of them in the same way. How we use stress testing We use limits to manage how much risk we take, expressed as how much we could lose in a stress event. We need to make sure the effects of possible events do not exceed the Risk Appetite set by the Board. We regularly inform senior managers, including ERCC and BRC, of the results. Risk mitigation We manage and control trading market risk within clear parameters. We measure and monitor our risk exposures against these limits. There are specific levels that trigger relevant teams to act or alert people in other functions. This means we can limit the impact of any negative market movements, while also improving our earnings. We keep the business units that originate trading market risk separate from the functions responsible for managing, controlling and overseeing risk. Risk monitoring and reporting We maintain a complete set of written policies, procedures and processes to help identify, assess, manage and report trading market risk. TRADING MARKET RISK REVIEW VaR This table and graph show our Internal VaR for exposure to each of the main classes of risk for 2019 and 2018. The VaR figures show how much the fair values of all our tradeable instruments could have changed. Since trading instruments are recorded at fair value, these are also the amounts by which they could have increased or reduced our net income. Year-end exposure Average exposure Highest exposure Lowest exposure 2019 2018 2019 2018 2019 2018 2019 2018 Trading instruments £m £m £m £m £m £m £m £m Interest rate risks 0.2 0.5 0.4 1.4 0.6 3.9 0.1 0.2 Equity risks 0.0 — 0.0 0.2 0.1 0.6 0.0 — Foreign exchange risks 0.4 0.1 0.2 0.3 0.4 0.9 0.1 — Diversification offsets (1) (0.3 ) (0.2 ) (0.3 ) (0.5 ) (0.5 ) — (0.0 ) — Total correlated one-day 0.3 0.4 0.3 1.4 0.6 3.8 0.2 0.3 (1) The highest and lowest exposures for each risk type did not necessarily happen on the same day as the highest and lowest total correlated one-day LOGO 2019 compared to 2018 (unaudited) In 2019, only a small amount of trading market risk from permitted products and permitted customers remained. There were no breaches of the total VaR limit in 2019. Following the completion of ring-fencing in 2018, we saw an increase in the number of back-testing exceptions. This was due to the profit and loss on the residual activity in the trading book being driven by non-market

Liquidity risk

Liquidity risk	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Liquidity risk	Liquidity risk Overview (unaudited) Key metrics (unaudited) Liquidity risk is the risk that, while still being solvent, we do not have the liquid financial resources to meet our obligations when they fall due, or we can only obtain them at high cost. In this section, we describe our sources and uses of liquidity and how we manage liquidity risk. We also analyse our key liquidity metrics, including our LCRs and our eligible liquidity pools. We then explain our funding strategy and structure and we analyse our wholesale funding. Finally, we analyse how we have encumbered some of our assets to support our funding activities. RFB DoLSub LCR of 142% (2018: DoLSub LCR of 164%) Wholesale funding and AT1 with maturity <1 year £22.5bn (2018: £16.5bn) RFB DoLSub LCR eligible liquidity pool of £42.0bn (2018: DoLSub £54.1bn) OUR KEY LIQUIDITY RISKS (UNAUDITED) Through our LRA framework, we manage our funding or structural contingent and market liquidity risks wherever they arise. This can be in retail and corporate deposit outflows, wholesale secured and unsecured liquidity outflows and off-balance intra-day Our main sources of liquidity Customer deposits finance most of our customer lending. Although these funds are mostly callable, in practice they give us a stable and predictable core of funding. This is due to the nature of retail accounts and the breadth of our retail customer relationships. We have a strong wholesale funding investor base, diversified across product types and geographies. Through the wholesale markets, we have active relationships in many sectors including banks, other financial institutions, corporates and investment funds. We access the wholesale funding markets through the issuance of capital, senior unsecured debt, covered bonds, structured notes and short-term funding. We also access these markets through securitisations of certain assets of Santander UK plc and our operating subsidiaries. For more on our programmes, see Notes 14, 21 and 25 in the Consolidated Financial Statements. We generate funding on the strength of our own balance sheet, our own profitability and our own network of investors. We comply with rules set by the PRA, other regulators, and Banco Santander standards. While we manage, consolidate and monitor liquidity risk centrally, we also manage and monitor it in the business area it comes from. For more on our structural relationship with Banco Santander and how that impacts our liquidity management, see the Directors’ report. In addition, we have access to UK Government funding schemes. Our main uses of liquidity Our main uses of liquidity are to fund our lending in Retail Banking and Corporate & Commercial Banking, to pay interest and dividends, and to repay debt. Our ability to pay dividends depends on various factors. These include our regulatory capital needs, the level of our distributable reserves, and our financial performance. We also use liquidity to pay for business combinations. LIQUIDITY RISK MANAGEMENT Introduction We manage liquidity risk on a consolidated basis in our CFO division, which is our centralised function for managing funding, liquidity and capital. We created our governance, oversight and control frameworks, and our LRA, on the same consolidated basis. From 1 January 2019, following the implementation of ring-fencing, we monitor and manage liquidity risk for the Santander UK plc group and SFS separately. Under this model, and the PRA’s liquidity rules, Santander UK plc and its subsidiary Cater Allen Limited form the RFB Domestic Liquidity Sub-group Prior to 1 January 2019, Santander UK plc, SFS and Cater Allen Limited formed the Domestic Liquidity Sub-group Stress testing We have a liquidity stress test framework in place which is central to our LRA measurement and monitoring. It includes three severe but plausible stress test scenarios. To fit with our risk appetite, the liquidity outflows that come from these stress tests must be fully covered with high-quality liquid assets, other liquid assets and management actions sanctioned at the right level of governance. Additionally, a funding plan disruption stress scenario forms part of our LRA monitoring. Our Risk division runs a range of stress tests. Our LRA stress test is a combination of three tests that cover idiosyncratic, market-wide and combined scenarios. Our other tests consider scenarios such as a global economic slowdown that results in reduced confidence in the banking industry, a slowdown in one of the major economies or a deterioration in the availability of liquidity. These are considered on both an acute and protracted basis. We also run severe combined stress tests which look at both a deep and prolonged UK recession that results in a reduction in wholesale funding availability and a simultaneous idiosyncratic shock that would lead to retail and commercial outflows. We also conduct sensitivity analysis and reverse stress testing for instant liquidity shocks by each key liquidity risk. We do this to understand the impacts they would have on our LRA and our regulatory liquidity metrics. We monitor our LCR to ensure we continue to meet the requirements. Although the Basel Committee published its final Net Stable Funding Ratio (NSFR) standards in October 2014, the NSFR has not yet been implemented within the EU (unlike the LCR). As such, there is no formal NSFR requirement applicable to UK or other EU banks until such time as the European Commission adopts appropriate regulatory and technical standards. Nonetheless, we monitor our NSFR on an ongoing basis and will be ready to comply with the standards once agreed. Risk mitigation The Board aims to make our balance sheet resilient at all times and for it to be perceived as such by stakeholders. This preserves our short and long-term viability. The Board recognises that as we are involved in maturity transformation, we cannot hold enough liquidity to cover all possible stress scenarios. The Board requires us to hold enough liquidity to make sure we will survive three plausible but severe stress scenarios (our LRA stress). We do this by maintaining a prudent balance sheet structure and approved liquid resources. Recovery framework In the event of a liquidity or capital stress, we have developed a series of actions outlined in our Recovery Plan. This enables us to respond to a wide variety of stresses, from mild to severe, in a coordinated and efficient manner. Our Recovery Plan addresses how we would manage a capital or liquidity stress. We would invoke it in response to triggers across a range of metrics falling outside threshold levels, or a qualitative assessment of potential serious risks to our financial position and balance sheet strength. All of these metrics are part of our existing risk management processes. The Recovery Plan would be invoked as early and proactively as possible in order to mitigate a stress with suitable actions. Our Recovery Plan is approved by the Board under advice from the Board Audit Committee and is subject to ongoing review and enhancement. The CFO division manages the recovery and resolution plans and the operational continuity process. Risk monitoring and reporting We monitor liquidity risk daily, weekly and monthly. We do this through different committees and levels of management, including ALCO and the Board Risk Committee. LIQUIDITY RISK REVIEW (UNAUDITED) Liquidity Coverage Ratio This table shows our LCR and LRA at 31 December 2019 and 2018. The LCR at 31 December 2019 reflects the RFB DoLSub, and at 31 December 2018 reflects the previous DoLSub. The LRA data reflect the stress testing methodology in place at that time. LCR RFB DoLSub (1) LRA RFB (2) 2019 2018 2019 2018 £bn £bn £bn £bn Eligible liquidity pool (liquidity value) 41.6 53.0 40.6 52.2 Net stress outflows (29.3 ) (32.4 ) (31.7 ) (32.1 ) Surplus 12.3 20.6 8.9 20.1 Eligible liquidity pool as a percentage of anticipated net cash flows 142 % 164 % 128 % 163 % (1) For 2019, in accordance with our ring-fence structure, data is for the RFB DoLSub. For 2018, i.e. before the implementation of ring-fencing, data is for the previous DoLSub. The RFB LCR was 146%. (2) The LRA is calculated for the Santander UK plc group (the RFB Group) and is a three-month Santander UK specific requirement. LCR eligible liquidity pool This table shows the carrying value and liquidity value of our eligible liquidity pool assets at 31 December 2019 for the RFB DoLSub and 31 December 2018 for the previous DoLSub. It also shows the weighted average carrying value in the year. RFB DoLSub Weighted average carrying Carrying value Liquidity value (1) value in the year 2019 2018 2019 2018 2019 2018 £bn £bn £bn £bn £bn £bn Cash and balances at central banks 19.3 22.4 19.3 22.4 19.1 24.4 Government bonds 17.9 26.1 17.7 25.7 20.8 16.8 Supranational bonds and multilateral development banks 2.9 1.1 2.9 1.1 2.9 1.1 Covered bonds 1.5 2.7 1.4 2.5 2.4 2.6 Asset-backed securities 0.4 1.7 0.3 1.3 1.4 1.4 Equities 0 0.1 0 — 0 2.1 42.0 54.1 41.6 53.0 46.6 48.4 (1) Liquidity value is the carrying value with the applicable LCR haircut applied. Currency analysis This table shows the carrying value of our eligible liquidity pool by major currencies at 31 December 2019 for the RFB DoLSub and 31 December 2018 for the previous DoLSub. The composition of the pool is consistent with the currency profile of our net liquidity outflows. RFB DoLSub US Dollar Euro Sterling Other Total £bn £bn £bn £bn £bn 2019 3.6 1.2 36.1 1.1 42.0 2018 5.3 3.9 42.2 2.7 54.1 Composition of the eligible liquidity pool This table shows the allocation of the carrying value of the assets in our eligible liquidity pool for LRA and LCR purposes at 31 December 2019 for the RFB DoLSub and 31 December 2018 for the previous DoLSub. RFB DoLSub 2019 2018 LCR eligible liquidity pool LCR eligible liquidity pool Level 1 Level 2A Level 2B Total Of which LRA eligible Level 1 Level 2A Level 2B Total Of which LRA eligible £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Cash and balances at central banks 19.3 0 0 19.3 19.3 22.4 — — 22.4 21.8 Government bonds: – AAA to AA- 16.7 0 0 16.7 16.7 23.6 — — 23.6 23.3 – A+ to A 0 1.2 0 1.2 1.2 — 2.5 — 2.5 2.5 Supranational bonds and multilateral development banks: – AAA to AA- 2.9 0 0 2.9 2.5 1.1 — — 1.1 1.1 Covered bonds: – AAA to AA- 1.4 0.1 0 1.5 1.5 1.6 1.1 — 2.7 2.7 Asset-backed securities: – AAA to AA- 0 0 0.4 0.4 0.4 — — 1.7 1.7 1.7 Equities 0 0 0 0 — — 0.1 0.1 0.1 40.3 1.3 0.4 42.0 41.6 48.7 3.6 1.8 54.1 53.2 2019 compared to 2018 While RFB DoLSub LCR remains high at 142%, it is lower than 2018 reflecting reduced uncertainty. The RFB DoLSub LCR and LCR eligible liquidity pool both decreased following the transfer of our Isle of Man and Jersey businesses (Crown Dependencies) into SFS in 2018 as part of ring-fencing implementation. FUNDING RISK MANAGEMENT Funding strategy Our funding strategy continues to be based on maintaining a conservatively structured balance sheet and diverse sources of funding to meet the needs of our business strategy and plans. The CFO Division maintains a funding plan and ensures it is compliant with the LRA and regulatory liquidity and capital requirements. Most of our funding comes from customer deposits. We source the rest from a mix of secured and unsecured funding in the wholesale markets. Overall, this means that we do not rely too heavily on wholesale funds. We manage funding requirements by targeting a specific Liquidity Coverage Ratio, we ensure maturities are prefunded and capital/TLAC requirements are prioritised. We also have checks and controls to limit our asset encumbrance from our secured funding operations. As part of maintaining a diverse funding base, we raise funding in a number of currencies, including euro and USD, and convert it into sterling through currency swaps to fund our commercial assets which are largely sterling denominated. Our base of stable retail and corporate deposits is a key funding source for us. We leverage our large and diverse customer base to offer products that give us a long-term sustainable source of funding. We do this by focusing on building long-term relationships. Over 85% of our total core retail customer liabilities are covered by the Financial Services Compensation Scheme (the FSCS). Behavioural maturities The contractual maturity of our balance sheet assets and liabilities highlights the maturity transformation that underpins the role of banks to lend long term, but to fund themselves mainly with shorter-term liabilities, like customer deposits. We do this by diversifying our funding operations across a wide customer base, both in numbers and by type of depositor. In practice, the behavioural profiles of many liabilities show more stability and longer maturity than their contractual maturity. This is especially true of many types of retail and corporate deposits that, while they may be repayable on demand or at short notice, have shown good stability even in times of stress. We model behaviour profiles using our experience of customer behaviour. We use this data to determine the funds transfer pricing interest rates at which we reward and charge our business units for sources and uses of funds. We apply this rate until a customer changes to a different product or service offered by us or by one of our competitors. We continue to improve the quality of our retail, commercial and wholesale deposits. We aim to deepen our customer relationships across all customer segments. We do this to lengthen the contractual and behavioural profile of our liability base. Deposit funding We mainly fund our Retail Banking and Corporate & Commercial Banking activities by customer deposits. We fund the rest through wholesale markets. Wholesale funding Wholesale funding and issuance model Banco Santander is a multiple point of entry resolution group. This means that should it fail; it would be split up into parts. Healthy parts might be sold or be kept as a residual group without their distressed sister companies. The resolution or recapitalisation of the distressed parts might be effected via ‘bail in’ of bonds that had been issued to the market by a regional intermediate holding company. Santander UK is a single point of entry resolution group. This means that resolution would work downwards from the group’s holding company (i.e. Santander UK Group Holdings plc). Losses in subsidiaries would first be transferred up to Santander UK Group Holdings plc. If the holding company is bankrupt as a result, the group is deemed to be failing or likely to fail, it will be put into resolution. The ‘bail in’ tool is applied to the holding company, with the equity being written off and bonds written off or converted into equity as needed to recapitalise the group. Those bondholders would become the new owners, and the group would stay together. Santander UK Group Holdings plc is the immediate holding company of Santander UK plc but does not guarantee its debts or other obligations. This structure is a Bank of England recommended configuration which aims to ensure the activities of the operating company are not disrupted as the group goes through resolution, thereby maintaining continuity of services for customers. Composition of wholesale funding We are active in the wholesale markets and we have direct access to both money market and long-term investors through our funding programmes. This makes our wholesale funding well diversified by product, maturity, geography and currency. This includes currencies available across a range of channels from money markets, repo markets, senior unsecured, secured, medium-term and capital. For details of our main programmes, see the Funding Information section of our website www.santander.co.uk/uk/about-santander-uk/investor-relations/funding-information. Following the implementation of our ring-fencing plan, Santander UK plc is now our main operating company issuer of senior unsecured debt, structured notes, short-term funding and covered bonds. Our immediate parent Santander UK Group Holdings plc is the issuer of capital and MREL/Total Loss Absorbing Capacity (TLAC) eligible senior unsecured debt. The Financial Stability Board established the TLAC standard in 2015 and it is applied from 1 January 2019. The standard is designed to enhance the resilience of the global financial system by ensuring that failing Global Systemically Important Banks (G-SIBs) G-SIBs, G-SIBs G-SIBs G-SIB We also access the wholesale markets through securitisations of certain assets of our operating subsidiaries. In addition, we have access to UK Government funding schemes. Eligible collateral for these schemes includes all collateral that is eligible in the Bank of England’s Discount Window Facility. We ensure that enough collateral is placed and available at the Discount Window. FUNDING RISK REVIEW 2019 compared to 2018 (unaudited) • Together with our immediate parent, Santander UK Group Holdings plc, our overall funding strategy remains to develop and sustain a diversified funding base. We also need to fulfil regulatory requirements as well as support our credit ratings. • 2019 had a much lower funding requirement than average. We pre-funded • In 2019, our total term funding was £4.5bn (2018: £17.1bn), of which £4.1bn (2018: £14.8bn) was medium-term issuance and none (2018: £2.3bn) was from the closed UK Government’s Term Funding Scheme (TFS). • The £4.1bn medium-term funding included £0.9bn of senior unsecured notes, £2.9bn of covered bonds and £0.1bn of securitisations. • Maturities in 2019 were £8.1bn (2018: £6.9bn). At 31 December 2019, 67% (2018: 77%) of wholesale funding had a maturity of greater than one year, with an overall residual duration of 33 months (2018: 37 months). The total drawdown outstanding from the TFS was unchanged at £10.8bn (2018: £10.8bn) and the total drawdowns of UK Treasury Bills under the FLS were £1.0bn (2018: £1.0bn). • In 2019, c£7bn of medium-term funding was left in US Dollars and a further £1bn in Euro. These balances were used to fund customer assets and our HQLA portfolio. • Our level of encumbrance from external and internal issuance of securitisations and covered bonds remained broadly static in 2019, as planned. Reconciliation of wholesale funding to the balance sheet This table reconciles our wholesale funding to our balance sheet at 31 December 2019 and 2018. Balance sheet line item Financial Repurchase liabilities Debt Funding Deposits Deposits agreements – designated securities Subordinated Other equity analysis by banks by customers (1) non trading at fair value in issue liabilities instruments (2) 2019 £bn £bn £bn £bn £bn £bn £bn £bn Deposits 0.3 0.3 0 0 0 0 0 0 Certificates of deposit and commercial paper 5.8 0 0 0 0 5.8 0 0 Senior unsecured – public benchmark 18.8 0 8.6 0 0 10.2 0 0 – privately placed 2.7 0 0.1 0 1.0 1.6 0 0 Covered bonds 18.2 0 0 0 0 18.2 0 0 Securitisation and structured issuance 5.6 0 0 1.4 0.5 3.7 0 0 Term Funding Scheme 10.8 10.8 0 0 0 0 0 0 Subordinated liabilities and equity 5.2 0 0 0 0 0 3.0 2.2 Total wholesale funding 67.4 11.1 8.7 1.4 1.5 39.5 3.0 2.2 Repos 16.9 0 0 16.9 0 0 0 0 Foreign exchange and hedge accounting 2.5 0 0.4 0 0 1.6 0.5 0 Other 3.5 3.3 (3) 0 0 0.2 0 0 0 Balance sheet total 90.3 14.4 9.1 18.3 1.7 41.1 3.5 2.2 2018 Deposits by banks 1.0 1.0 — — — — — — Certificates of deposit and commercial paper 6.4 — — — — 6.4 — — Senior unsecured – public benchmark 21.2 — 8.6 — — 12.6 — — – privately placed 4.0 — 0.1 — 1.0 2.9 — — Covered bonds 16.6 — — — — 16.6 — — Securitisation and structured issuance 7.8 — 0.5 2.2 — 5.1 — — Term Funding Scheme 10.8 10.8 — — — — — — Subordinated liabilities and equity 5.0 — — — — — 3.0 2.0 Total wholesale funding 72.8 11.8 9.2 2.2 1.0 43.6 3.0 2.0 Repos 10.8 — — 8.7 2.1 — — — Foreign exchange and hedge accounting 4.2 — 0.5 — — 3.1 0.6 — Other 8.6 5.4 (3) — — 3.2 — — — Balance sheet total 96.4 17.2 9.7 10.9 6.3 46.7 3.6 2.0 (1) This is included in our balance sheet total of £181,883 m (2018: £178,090 m). (2) Consists of £nil (2018: £14m) fixed/floating rate non-cumulative Step-up (3) Other consists of items in the course of transmission and other deposits, excluding the TFS. See Note 23 to the Consolidated Financial Statements. Maturity profile of wholesale funding This table shows our main sources of wholesale funding. It does not include securities finance agreements. The table is based on exchange rates at issue and scheduled repayments and call dates. It does not reflect the final contractual maturity of the funding. £ 1 >1 and £ 3 >3 and £ >6 and £ 9 >9 and £ 12 Sub-total >1 and >2 and month months 6 months months months £ 1 year £ 2 years £ 5 years >5 years Total 2019 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Downstreamed from Santander UK Group Holdings plc to Santander UK plc (1) Senior unsecured – public benchmark 0 0 0 0 0.8 0.8 1.8 4.2 1.7 8.5 – privately placed 0 0 0 0 0 0 0 0 0.1 0.1 Subordinated liabilities and equity (incl. AT1) 0 0 0 0 0 0 0 1.0 2.0 3.0 0 0 0 0 0.8 0.8 1.8 5.2 3.8 11.6 Other Santander UK plc Deposits by banks 0.1 0 0 0.2 0 0.3 0 0 0 0.3 Certificates of deposit and commercial paper 0.6 3.1 2.0 0.1 0 5.8 0 0 0 5.8 Senior unsecured – public benchmark 0.8 1.4 0 0.6 1.9 4.7 2.9 1.9 0.8 10.3 – privately placed 0 0.9 0 0.9 0 1.8 0.4 0.1 0.3 2.6 Covered bonds 0 0 1.8 0 1.0 2.8 5.6 6.2 3.6 18.2 Securitisation and structured (2) 0.2 0 0.8 0.2 0.2 1.4 1.3 1.3 0 4.0 Term Funding Scheme 0 0 0 0 4.5 4.5 4.0 2.3 0 10.8 Subordinated liabilities 0 0 0 0 0 0 0 0.9 1.3 2.2 1.7 5.4 4.6 2.0 7.6 21.3 14.2 12.7 6.0 54.2 Other group entities Securitisation & structured (3) 0 0.1 0.1 0.1 0.1 0.4 0.6 0.6 0 1.6 Total at 31 December 2019 1.7 5.5 4.7 2.1 8.5 22.5 16.6 18.5 9.8 67.4 Of which: – Secured 0.2 0.1 2.7 0.3 5.8 9.1 11.5 10.4 3.6 34.6 – Unsecured 1.5 5.4 2.0 1.8 2.7 13.4 5.1 8.1 6.2 32.8 1.7 5.5 4.7 2.1 8.5 22.5 16.6 18.5 9.8 67.4 2018 Total at 31 December 2018 3.1 6.8 3.0 2.7 0.9 16.5 15.9 30.1 10.3 72.8 Of which: – Secured 0.8 0.7 0.7 1.7 0.5 4.4 8.5 18.3 4.0 35.2 – Unsecured 2.3 6.1 2.3 1.0 0.4 12.1 7.4 11.8 6.3 37.6 (1) 94% of Senior Unsecured debt issued from Santander UK Group Holdings plc has been downstreamed to Santander UK plc as ‘secondary non-preferential (2) Includes funding from mortgage-backed securitisation vehicles where Santander UK plc is the asset originator. (3) Includes funding from asset-backed securitisation vehicles where entities other than Santander UK plc are the asset originator. Currency composition of wholesale funds This table shows our wholesale funding by major currency at 31 December 2019 and 2018. 2019 2018 Sterling US Dollar Euro Other Sterling US Dollar Euro Other % % % % % % % % Downstreamed from Santander UK Group Holdings plc to Santander UK plc Senior unsecured – public benchmark 11 65 22 2 11 65 22 2 – privately placed 0 0 0 100 — — — 100 Subordinated liabilities and equity (incl. AT1) 67 33 0 0 64 36 — — 25 56 16 3 23 57 17 3 Other Santander UK plc Deposits by banks 3 97 0 0 3 97 — — Certificates of deposit and commercial paper 45 54 1 0 48 52 — — Senior unsecured – public benchmark 14 54 32 0 11 56 33 — – privately placed 21 15 59 5 13 12 72 3 Covered bonds 54 0 45 1 50 — 49 1 Securitisation & structured issuance 72 28 0 0 61 35 4 — Term Funding Scheme 100 0 0 0 100 — — — Subordinated liabilities 49 51 0 0 49 51 — — 54 22 24 0 48 25 26 1 Other group entities Securitisation & structured issuance 95 5 0 0 89 11 — — Total 50 27 22 1 46 30 24 — Term issuance In 2019, our external term issuance (sterling equivalent) was: Sterling US Dollar Euro Other Total 2019 Total 2018 £bn £bn £bn £bn £bn £bn Downstreamed from Santander UK Group Holdings plc to Santander UK plc Senior unsecured – public benchmark 0 0 0 0 0 2.7 Subordinated debt and equity (inc. AT1) 0.5 0 0 0 0.5 0 0.5 0 0 0 0.5 2.7 Other Santander UK plc Securitisations and other secured funding 0 0 0 0 0 2.9 Covered bonds 2.0 0 0.9 0 2.9 4.3 Senior unsecured – public benchmark 0.1 0.8 0 0 0.9 2.9 – privately placed 0 0 0 0 0 1.6 Term Funding Scheme 0 0 0 0 0 2.3 2.1 0.8 0.9 0 3.8 14.0 Other group entities Securitisations 0.2 0 0 0 0.2 0.4 Total gross issuances 2.8 0.8 0.9 0 4.5 17.1 Encumbrance We have encumbered an asset if we have pledged or transferred it as collateral against an existing liability. This means it is no longer available to secure funding, meet our collateral needs or be sold to reduce future funding needs. Being able to pledge or transfer assets as collateral is an integral part of a financial institution’s operations. We do various things that lead to asset encumbrance. These include where we: • Enter into securitisation, covered bonds, and repurchase agreements (including central bank programmes) to access medium and long-term funding • Enter into short-term funding transactions. These include repurchase agreements and stock borrowing transactions as part of our operational liquidity management • Pledge collateral as part of participating in payment and settlement systems • Post collateral as part of derivatives activity. We monitor our mix of secured and unsecured funding sources in our funding plan. We aim to use our available collateral efficiently to raise secured funding and to meet our other collateralised obligations. Our biggest source of encumbrance is where we use our mortgage portfolio to raise funds through securitisation, covered bonds or other structured borrowing. We control our levels of encumbrance from these by setting a minimum level of unencumbered assets that must be available after we factor in our future funding plans, whether we can use our assets for our future collateral needs, the impact of a possible stress and our current level of encumbrance. Assets classified as readily available for encumbrance include cash and securities we hold in our eligible liquidity pool. They also include other unencumbered assets that give us a source of contingent liquidity. We do not rely on these extra unencumbered assets in our LRA, but we might use some of them in a time of stress. We can create liquidity by using them as collateral for secured funding or through outright sale. Loans and advances to customers are only classified as readily available for encumbrance if they are already in a form we can use to raise funding without any other actions on our part. This includes excess collateral that is already in a secured funding structure. It also includes collateral that is pre-positioned All other loans and advances are classified as not readily available for encumbrance, however, may still be suitable for use in secured funding structures. Encumbrance of customer loans and advances We have issued prime retail mortgage-backed and other asset-backed securitised products to a diverse investor base through our mortgage-backed and other asset-backed funding programmes. We have raised funding with mortgage-backed notes, both issued to third parties and retained – the latter being central bank eligible collateral for funding purposes in other Bank of England facilities. We also have a covered bond programme, under which we issue securities to investors secured by a pool of residential mortgages. For more on how we have issued notes from our secured programmes externally and also retained them, and what we have used them for, see Notes 14 and 25 to the Consolidated Financial Statements. On-balance Encumbered with counterparties other than Unencumbered assets not pre-positioned central banks with central banks Covered bonds Securitis- ations Other Total Assets positioned at central banks (3) Readily available Other available assets Cannot be encumbered Total Total assets 2019 £m £m £m £m £m £m £m £m £m £m Cash and balances at central banks (1)(2) 0 0 1,080 1,080 707 19,393 0 0 20,100 21,180 Financial assets at FVTPL: – Derivative financial instruments 0 0 0 0 0 0 0 3,316 3,316 3,316 – Other financial assets at FVTPL 0 0 0 0 0 0 0 386 386 386 Financial assets at amortised cost: – Loans and advances to customers 23,310 12,915 332 36,557 55,273 76,567 22,875 16,015 170,730 207,287 – Loans and advances to banks 0 0 403 403 0 0 0 1,452 1,452 1,855 – Repurchase agreements – non trading 0 0 0 0 0 0 0 23,636 23,636 23,636 – Other financial assets at amortised cost 0 0 3,026 3,026 0 4,030 0 0 4,030 7,056 Financial assets at FVOCI 0 0 6,009 6,009 0 3,738 0 0 3,738 9,747 Interests in other entities 0 0 0 0 0 0 0 117 117 117 Intangible assets 0 0 0 0 0 0 0 1,766 1,766 1,766 Property, plant and equipment 0 0 0 0 0 0 1,967 0 1,967 1,967 Current tax assets 0 0 0 0 0 0 0 200 200 200 Retirement benefit assets 0 0 0 0 0 0 0 669 669 669 Other assets 0 0 0 0 0 0 0 2,520 2,520 2,520 Total assets 23,310 12,915 10,850 47,075 55,980 103,728 24,842 50,077 234,627 281,702 2018 Cash and balances at central banks (1)(2) — — 1,080 1,080 636 18,031 — — 18,667 19,747 Financial assets at FVTPL: – Derivative financial instruments — — — — — — — 5,259 5,259 5,259 – Other financial assets at FVTPL — — — — — — — 5,617 5,617 5,617 Financial assets at amortised cost: – Loans and advances to customers 21,240 14,454 256 35,950 52,497 71,941 20,943 19,958 165,339 201,289 – Loans and advances to banks — — 218 218 — — — 2,581 2,581 2,799 – Repurchase agreements – non trading — — — — — — — 21,127 21,127 21,127 – Other financial assets at amortised cost — — 3,763 3,763 — 3,466 — — 3,466 7,229 Financial assets at FVOCI — — 5,825 5,825 — 7,477 — — 7,477 13,302 Interests in other entities — — — — — — — 88 88 88 Intangible assets — — — — — — — 1,808 1,808 1,808 Property, plant and equipment — — — — — — 1,832 — 1,832 1,832 Current tax assets — — — — — — — 153 153 153 Retirement benefit assets — — — — — — — 842 842 842 Other assets — — — — — — — 2,280 2,280 2,280 Total assets 21,240 14,454 11,142 46,836 53,133 100,915 22,775 59,713 236,536 283,372 (1) Encumbered cash and balances at central banks include minimum cash balances we have to hold at central banks for regulatory purposes. (2) Readily realisable cash and balances at central banks are amounts held at central banks as part of our liquidity management activities. (3) Comprises pre-positioned

Capital risk

Capital risk	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Capital risk	Capital risk Overview (unaudited) Capital risk is the risk that we do not have an adequate amount or quality of capital to meet our internal business needs, regulatory requirements and market expectations, including dividend and AT1 distributions. In this section, we set out how we are regulated. We explain how we manage capital on a standalone basis as a subsidiary in the Banco Santander group. We then analyse our capital resources and key capital ratios including our leverage and RWAs. Key metrics (unaudited) CET1 capital ratio of 14.3% (2018: 13.2%) Total qualifying regulatory capital decreased to £15.8bn (2018: £15.9 bn) THE SCOPE OF OUR CAPITAL ADEQUACY Regulatory supervision For capital purposes, we are subject to prudential supervision by the PRA, as a UK banking group, and by the European Central Bank (ECB) as part of the Banco Santander group. The ECB supervises Banco Santander as part of the Single Supervisory Mechanism (SSM). Although we are part of the Banco Santander group, we do not have a guarantee from our ultimate parent Banco Santander SA and we operate as a standalone subsidiary. As we are part of the UK sub-group Our basis of consolidation for our capital disclosures is substantially the same as for our Consolidated Financial Statements. Following the implementation of ring-fencing, with effect from 1 January 2019, Santander UK plc is now the head of the ring-fenced bank sub-group sub-group. CAPITAL RISK MANAGEMENT The Board is responsible for capital management strategy and policy and ensuring that we monitor and control our capital resources within regulatory and internal limits. We manage our funding and maintain capital adequacy on a standalone basis. We operate within the capital risk framework and appetite approved by our Board. This reflects the business environment we operate in, our strategy for each material risk and the potential impact of any adverse scenarios or stresses on our capital position. Management of capital requirements Our capital risk appetite aims to maintain capital levels appropriate to the level of stress applied, and the expected regulatory response. In: • An adverse economic stress, which we might expect to occur once in 20 years, the firm should remain profitable and exceed all regulatory capital minimums at all times. • A very severe economic stress, which we might expect to occur once in 100 years, and which has been designed to test any specific weaknesses of a firm’s business model, the firm should meet all regulatory capital minimums at all times. This is subject to the use of regulatory buffers designed to absorb losses in such a stress. Management of capital resources We use a mix of regulatory and EC ratios and limits, internal buffers and restrictions to manage our capital resources. We also take account of the costs of differing capital instruments and capital management techniques. We also use these to shape the best structure for our capital needs. We decide how to allocate our capital resources as part of our strategic planning process. We base this in part on the relative returns on capital using both EC and regulatory capital measures. We plan for severe stresses and we set out what action we would take if an extremely severe stress threatened our viability and solvency. This could include not paying dividends, selling assets, reducing our business and issuing more capital. Risk measurement We apply Banco Santander’s approach to capital measurement and risk management for CRD IV. Santander UK plc is classified as a significant subsidiary of Banco Santander SA. Key metrics The main metrics we use to measure capital risk are: Key risk metrics Description CET1 capital ratio CET1 capital divided by RWAs. Total capital ratio Total capital divided by RWAs. UK leverage ratio CRD IV end-point Stress testing Each year we create a capital plan, as part of our ICAAP. We share our ICAAP with the PRA. The PRA then tells us how much capital (Pillar 2A), and of what quality, it thinks we should hold on top of our Pillar 1 requirements. We also develop a series of economic scenarios to stress test our capital needs and confirm that we have enough regulatory capital to meet our projected and stressed capital needs and to meet our obligations as they fall due. We augment our regulatory minimum capital with internal buffers. We hold buffers to ensure we have enough time to take action against unexpected movements. Risk mitigation We have designed our capital risk framework, policies and procedures to ensure that we operate within our Risk Appetite. We manage capital transferability between our subsidiaries in line with our business strategy, our risk and capital management policies, and UK laws and regulations. There are no legal restrictions on us moving capital resources promptly, or repaying liabilities, between the Company and its subsidiaries except for distributions between Santander UK entities in the ring-fenced bank sub-group sub-group, From 1 January 2019, following the implementation of ring-fencing, Santander UK plc, Cater Allen Limited and certain other non-regulated Sub-Group Sub-Group non-regulated Prior to 1 January 2019, Santander UK plc, SFS and Cater Allen Limited, which are the PRA-regulated non-regulated Other than the change of the entities in scope, the purpose of the RFB Sub-Group Risk monitoring and reporting We monitor and report regularly against our capital plan. We do this to identify any change in our business performance that might affect our capital. Each month, we also review the economic assumptions we use to create and stress test our capital plan. We do this to identify any potential reduction in our capital. CAPITAL RISK REVIEW 2019 compared to 2018 (unaudited) Our CET1 capital ratio increased 110bps to 14.3% at 31 December 2019 (2018: 13.2%), through active RWA management. CET1 capital was stable at £10.4bn, with ongoing capital accretion through profits retained after dividend payment, offset by market-driven pension movements. Our total capital ratio increased to 21.7% at 31 December 2019 (2018: 20.3%). Impact of IFRS 9 on regulatory capital Although the adoption of IFRS 9 in 2018 did not have a material impact on our capital position, we expect our ECL-based pro-cyclicality ECL-based We reflect projections of ECL provisions in our capital position forecasting under base case and stress scenarios for ICAAP and capital management purposes. We also consider the dynamics of ECL in how we assess, monitor and manage capital risk. The greater volatility from IFRS 9 ECL could result in material favourable and unfavourable swings to our Income Statement. Whilst the initial impacts of IFRS 9 were based on estimates prepared in a supportive economic environment, a period of economic instability could significantly impact our results and our financial assets. It could also impact the amount of capital we have to hold. We take into account the volatility of ECL in our capital planning strategy. Meeting evolving capital requirements We target a CET1 management buffer of sufficient size to absorb volatility in CET1 deductions, capital supply and capital demand whilst remaining above the regulatory CET1 requirement. Distribution restrictions would be expected to be applied if we were unable to meet both our minimum requirement, which consists of the Pillar 1 minimum plus Pillar 2A, and the CRD IV buffers consisting of the Capital Conservation Buffer (CCB), and the Countercyclical Capital Buffer (CCyB) and the Systemic Risk Buffer (SRB). Distance of our CET1 capital ratio to our current MDA trigger level at 31 December 2019 (unaudited) At 31 December 2019, the distance of our CET1 capital ratio of 14.3% to our 7% AT1 permanent write down (PWD) securities trigger was 7.3% of total RWAs or £5.3bn (2018: 6.2% of total RWAs or £4.9bn). The distance of our CET1 capital ratio to our current maximum distributable amount (MDA) trigger level at 31 December 2019 was: Current MDA % Pillar 1 4.5 Pillar 2A (1) 3.2 CCB 2.5 CCyB (2) 1.0 SRB 1.0 Current MDA trigger 12.2 Distance to current MDA 2.1 Total CET1 capital ratio 14.3 (1) Santander UK’s (i.e. the Ring-Fenced Bank’s) Pillar 2 CET1 requirement was 3.24% at 31 December 2019. Pillar 2A guidance is a point in time assessment. (2) The current applicable UK CCyB rate is 1%. Santander UK’s (i.e. the Ring-Fenced Bank’s) current geographical allocation of the CCyB is 0.99%. At 1 January 2020, Santander UK plc’s total Pillar 2A requirements reduced to 4.8% and CET1 Pillar 2A requirements reduced to 2.7%. MREL recapitalisation We have made major progress to meet MREL requirements. To date, we have down streamed £7.4bn of senior unsecured bonds from Santander UK Group Holdings plc as Internal MREL compliant, secondary non-preferential Key capital ratios 2019 2018 CET1 capital ratio 14.3 13.2 AT1 2.7 2.2 Grandfathered Tier 1 0.7 0.8 Tier 2 4.0 4.1 Total capital ratio 21.7 20.3 The total subordination available to Santander UK plc bondholders was 21.7% (2018: 20.3%) of RWAs. Regulatory capital resources This table shows our qualifying regulatory capital. 2019 2018 CET1 capital 10,419 10,374 AT1 capital 2,443 2,349 Tier 1 capital 12,862 12,723 Tier 2 capital 2,925 3,223 Total regulatory capital (1) 15,787 15,946 (1) Capital resources include a transitional IFRS 9 benefit at 31 December 2019 of £16m (2018: £21m). AT1 capital These are preference shares and innovative/hybrid Tier 1 securities. None of the instruments we issued before 1 January 2014 fully meet the CRD IV AT1 capital rules, which apply from that date. These instruments will be phased out by CRD IV rules which restrict their recognition as capital. The £750m Fixed Rate Reset Perpetual AT1 Capital Securities (net of issuance costs), the £800m Perpetual Capital Securities and the £500m Perpetual Capital Securities we issued since then fully meet the CRD IV AT1 capital rules. In August 2019, as part of a capital management exercise, the Company purchased and redeemed the £300m Fixed Rate Reset Perpetual AT1 Capital Securities, and issued a further £500m Fixed Rate Reset Perpetual AT1 Capital Securities to Santander UK Group Holdings plc. Tier 2 capital These are fully CRD IV eligible Tier 2 instruments and grandfathered Tier 2 instruments whose recognition as capital is being phased out under CRD IV. Risk-weighted assets The tables below are consistent with our regulatory filings for 2019 and 2018. 2019 2018 Total RWAs 72.6 78.5

Accounting Policies

Accounting Policies	12 Months Ended
	Dec. 31, 2019
Statement [Line Items]
Accounting Policies	1. ACCOUNTING POLICIES These financial statements are prepared for Santander UK plc (the Company) and the Santander UK plc group (the Santander UK group) under the UK Companies Act 2006. The principal activity of the Santander UK group is the provision of a wide range of banking and financial services to personal, business and corporate customers. Santander UK plc is a public company, limited by shares and incorporated in England and Wales having a registered office at 2 Triton Square, Regent’s Place, London, NW1 3AN, phone number 0870-607-6000. It is an operating company undertaking banking and financial services transactions. Basis of preparation These financial statements incorporate the financial statements of the Company and entities controlled by the Company (its subsidiaries) made up to 31 December each year. The Consolidated Financial Statements have been prepared on the going concern basis using the historical cost convention, except for financial assets and liabilities that have been measured at fair value. An assessment of the appropriateness of the adoption of the going concern basis of accounting is disclosed in the statement of going concern in the Directors’ Report. Compliance with International Financial Reporting Standards The Santander UK group Consolidated Financial Statements have been prepared in accordance with IFRSs as issued by the IASB, including interpretations issued by the IFRS Interpretations Committee (IFRS IC) of the IASB (together IFRS). The Santander UK group has also complied with its legal obligation to comply with IFRSs as adopted by the European Union as there are no applicable differences between the two frameworks for the periods presented. Disclosures required by IFRS 7 ‘Financial Instruments: Disclosure’ relating to the nature and extent of risks arising from financial instruments, and IAS 1 ‘Presentation of Financial Statements’ relating to objectives, policies and processes for managing capital, can be found in the Risk review. Those disclosures form an integral part of these financial statements. Recent accounting developments IFRS 16 ‘Leases’ (IFRS 16) On 1 January 2019 the Santander UK group adopted IFRS 16 and the revised accounting policies as lessee which have been applied from 1 January 2019 are set out below. Comparatives have not been restated. The impact of applying IFRS 16 is disclosed in section (ii). As described below, IFRS 16 impacted property and equipment leases where the Santander UK group is the lessee. IFRS 16 had no impact for leases where the Santander UK group is the lessor. i) Accounting policy change The Santander UK group as lessee The Santander UK group assesses whether a contract is or contains a lease at the inception of the contract and recognises a right-of-use (ROU) asset representing its right to use the underlying leased asset and a lease liability representing its obligation to make lease payments for all leases, except for short-term leases, being those with a term of 12 months or less, or leases for which the underlying asset is of low value which are expensed in the income statement on a straight-line basis over the lease terms. Lease payments exclude irrecoverable VAT which is expensed in the income statement as lease payments are made. The lease liability, which is included within Other liabilities on the balance sheet, is initially measured at the present value of the lease payments that are not paid at the commencement date, discounted using the incremental borrowing rate appropriate to the lease term. The lease liability is subsequently measured at amortised cost using the effective interest rate method. Remeasurement of the lease liability occurs if there is a change in the lease payments (when a corresponding adjustment is made to the ROU asset), the lease term or in the assessment of an option to purchase the underlying asset. At inception, the ROU asset, which is included within Property, plant and equipment on the balance sheet, comprises the lease liability, initial direct costs and the obligations to restore the asset, less any incentives granted by the lessor. The ROU asset is depreciated over the shorter of the lease term or the useful life of the underlying asset and is reviewed for indications of impairment as for owned assets. The obligation to restore the asset is included within Provisions on the balance sheet. ii) Impact of adoption The Santander UK group elected to apply the modified retrospective approach whereby the ROU asset at the date of initial application was measured at an amount equal to the lease liability. The ROU asset was adjusted for any prepaid lease payments and incentives relating to the relevant leases that were recognised on the balance sheet at 31 December 2018 and included an estimate of the costs of restoring the underlying assets to the condition required by the terms of the lease. In addition, the following practical expedients permitted by the standard were applied: • a single discount rate being the incremental borrowing rate was applied to a portfolio of leases with reasonably similar characteristics; and • operating leases with a remaining lease term of less than 12 months as at 1 January 2019 were treated as short term leases. For the Santander UK group, the application of IFRS 16 at 1 January 2019 increased property, plant and equipment by £210m (being the net increase in ROU assets referred to above), reduced other assets by £12m and increased other liabilities by £181m from recognising lease liabilities. In addition, we also increased provisions by £17m (see Note 27). There was no impact on shareholders’ equity. The amount of the lease liabilities above differed from the amount of operating lease commitments at 31 December 2018 and is reconciled as follows: Group £m Rental commitments under non-cancellable 246 Recognition exemption for short-term leases (72 ) Effect from discounting at the incremental borrowing rate at 1 January 2019 7 Additional liabilities recognised based on the initial application of IFRS 16 at 1 January 2019 181 In addition to the choice of transition approach, the determination of the discount rate is the most significant area of judgement. The Santander UK group applies an incremental borrowing rate (based on 3-month GBP LIBOR plus a credit spread to reflect the cost of raising unsecured funding in the wholesale markets) appropriate to the relevant remaining lease term. IAS 12 The Santander UK group has also applied the amendment to IAS 12 ‘Income Taxes’ (part of ‘Annual Improvements to IFRS Standards 2015-2017 Cycle’) in these Condensed Consolidated Interim Financial Statements. The amendment clarifies that the income tax consequences of dividends on financial instruments classified as equity should be recognised according to where the past transactions or events that generated distributable profits were recognised. This means that, to the extent that profits from which dividends on equity instruments were recognised in the income statement, the income tax consequences would be similarly recognised in the same statement. The amendment, which has been applied retrospectively, reduces the effective tax rate where the tax relief on dividends in respect of other equity instruments is recognised in the income statement rather than as a separate line item within the statement of changes in equity. Overall, there was no impact on shareholders’ equity for the Santander UK group from applying the amendment to IAS 12 at 1 January 2019. For the Santander UK group, the impact of the amendment to IAS 12 on the income statement for the year ended 31 December 2019 was to reduce tax on profit by £39m (2018: £42m, 2017: £46m), increasing profit after tax by the same amount. London Inter-Bank Offered Rate (LIBOR) reform In September 2019, the IASB issued Interest Rate Benchmark Reform: Amendments to IFRS 9 ‘Financial Instruments’, IAS 39 ‘Financial Instruments: Recognition and Measurement’ and IFRS 7 ‘Financial Instruments: Disclosure’. Santander UK applies IAS 39 hedge accounting so the amendments to IFRS 9 do not apply. The IAS 39 amendments provide temporary exceptions from applying specific hedge accounting requirements to hedging relationships that are directly affected by the reform to LIBOR and other Interbank Offered Rates, hereinafter referred to as LIBOR reform. The exceptions have the effect that LIBOR reform should not generally cause hedge accounting to terminate, however any hedge ineffectiveness continues to be recognised in the income statement. The exceptions end at the earlier of: • when the uncertainty regarding the timing and the amount of interest rate benchmark based cash flows is no longer present, and • discontinuance of the hedge relationship (or reclassification of all amounts from the cash flow hedge reserve). The IAS 39 amendments apply to all hedging relationships directly affected by uncertainties related to LIBOR reform and must be applied for annual periods beginning on or after 1 January 2020. However, following their endorsement for use in the European Union, Santander UK has elected to apply the IAS 39 and IFRS 7 amendments in the preparation of the financial statements for the year ended 31 December 2019. The exceptions given by the IAS 39 amendments mean that LIBOR reform had no impact on hedge relationships for affected hedges at and for the year ended 31 December 2019. The main assumptions or judgements made by Santander UK in applying the IAS 39 amendments are outlined below. • For cash flow hedges affected by LIBOR reform, Santander UK management has assumed that the interest rate benchmark on which hedged cash flows are based is not altered as a result of LIBOR reform when assessing whether the future cash flows are highly probable. For discontinued hedging relationships, the same assumption has been applied for determining whether the hedged future cash flows are expected to occur. • In making its prospective hedge effectiveness assessments, Santander UK has assessed whether the economic relationship between the hedged item and the hedging instrument exists based on the assumption that the interest rate benchmark on which the hedged item and the hedging instrument are based is not altered as a result of LIBOR reform. • Santander UK will not discontinue hedge accounting during the period of LIBOR-related uncertainty solely because the retrospective effectiveness falls outside the required 80-125% range. • For hedges of a non-contractually specified benchmark portion of an interest rate, Santander UK only considers at inception of such a hedging relationship whether the separately identifiable requirement is met. Details of the significant interest rate benchmarks to which hedging relationships are exposed, the extent of risk exposure that is affected by LIBOR reform, and how Santander UK’s transition to alternative benchmark interest rates is being managed, are disclosed in the Banking market risk section of the Risk review. The nominal amount of the hedging instruments in hedging relationships directly affected by uncertainties related to LIBOR reform is disclosed in Note 11. Future accounting developments At 31 December 2019, for the Santander UK group, there were no significant new or revised standards and interpretations, and amendments thereto, which have been issued but which are not yet effective or which have otherwise not been early adopted where permitted. Comparative information As required by US public company reporting requirements, these financial statements include two years of comparative information for the consolidated income statement, consolidated statement of comprehensive income, consolidated statement of changes in equity, consolidated statement of cash flows and related Notes. Consolidation a) Subsidiaries The Consolidated Financial Statements incorporate the financial statements of the Company and entities (including structured entities) controlled by it and its subsidiaries. Control is achieved where the Company (i) has power over the investee; (ii) is exposed, or has rights, to variable returns from its involvement with the investee; and (iii) has the ability to use its power to affect its returns. The Company reassesses whether or not it controls an investee if facts and circumstances indicate that there are changes to one or more of the three elements of control listed above. When the Company has less than a majority of the voting rights of an investee, it has power over the investee when the voting rights are sufficient to give it the practical ability to direct the relevant activities of the investee unilaterally. The Company considers all relevant facts and circumstances in assessing whether or not the Company’s voting rights in an investee are sufficient to give it power, including: • The size of the Company’s holding of voting rights relative to the size and dispersion of holdings of the other vote holders • Potential voting rights held by the Company, other vote holders or other parties • Rights arising from other contractual arrangements • Any additional facts and circumstances that indicate that the Company has, or does not have, the current ability to direct the relevant activities at the time that decisions need to be made, including voting patterns at previous shareholders’ meetings. Consolidation of a subsidiary begins when the Company obtains control over the subsidiary and ceases when the Company loses control of the subsidiary. Specifically, the results of a subsidiary acquired or disposed of during the year are included in the consolidated income statement and the consolidated statement of comprehensive income from the date the Company gains control until the date when the Company ceases to control the subsidiary. Inter-company transactions, balances and unrealised gains on transactions between Santander UK group companies are eliminated; unrealised losses are also eliminated unless the cost cannot be recovered. The acquisition method of accounting is used to account for the acquisition of subsidiaries which meet the definition of a business. The cost of an acquisition is measured at the fair value of the assets given up, shares issued or liabilities undertaken at the date of acquisition. Acquisition-related costs are expensed as incurred. The excess of the cost of acquisition, as well as the fair value of any interest previously held, over the fair value of the Santander UK group’s share of the identifiable net assets of the subsidiary at the date of acquisition is recorded as goodwill. When the Santander UK group loses control of a subsidiary, the profit or loss on disposal is calculated as the difference between (i) the aggregate of the fair value of the consideration received and the fair value of any retained interest and (ii) the previous carrying amount of the assets (including goodwill), less liabilities of the subsidiary and any non-controlling interests. Amounts previously recognised in other comprehensive income in relation to the subsidiary are accounted for (i.e. reclassified to profit or loss or transferred directly to retained earnings) in the same manner as would be required if the relevant assets or liabilities are disposed of. The fair value of any investment retained in a former subsidiary at the date when control is lost is regarded as the fair value on initial recognition for subsequent accounting under IFRS 9 or, when applicable, the costs on initial recognition of an investment in an associate or joint venture. Business combinations between entities under common control (i.e. fellow subsidiaries of Banco Santander SA, the ultimate parent) are outside the scope of IFRS 3 – ‘Business Combinations’, and there is no other guidance for such transactions under IFRS. The Santander UK group elects to account for business combinations between entities under common control at their book values in the acquired entity by including the acquired entity’s results from the date of the business combination and not restating comparatives. Reorganisations of entities within the Santander UK group are also accounted for at their book values. Interests in subsidiaries are eliminated during the preparation of the Consolidated Financial Statements. b) Joint ventures Joint ventures are joint arrangements whereby the parties that have joint control of the arrangement have rights to its net assets. Joint control is the contractually agreed sharing of control of an arrangement, which exists only when decisions about the relevant activities require unanimous consent of the parties sharing control. Accounting policies of joint ventures have been aligned to the extent there are differences from the Santander UK group’s policies. Investments in joint ventures are accounted for by the equity method of accounting and are initially recorded at cost and adjusted each year to reflect the Santander UK group’s share of their post-acquisition results. When the Santander UK group’s share of losses of a joint venture exceed its interest in that joint venture, the Santander UK group discontinues recognising its share of further losses. Further losses are recognised only to the extent that the Santander UK group has incurred legal or constructive obligations or made payments on behalf of the joint venture. Foreign currency translation Items included in the financial statements of each entity in the Santander UK group are measured using the currency that best reflects the economic substance of the underlying events and circumstances relevant to that entity (the functional currency). The Consolidated Financial Statements are presented in sterling, which is the functional currency of the Company. Income statements and cash flows of foreign entities are translated into the Santander UK group’s presentation currency at average exchange rates for the year and their balance sheets are translated at the exchange rates ruling on 31 December. Exchange differences on the translation of the net investment in foreign entities are recognised in other comprehensive income. When a foreign entity is sold, such exchange differences are recognised in the income statement as part of the gain or loss on sale. Foreign currency transactions are translated into the functional currency of the entity involved at the exchange rates prevailing at the dates of the transactions. Foreign exchange gains and losses resulting from the settlement of such transactions and from the translation of monetary assets and liabilities denominated in foreign currencies are recognised in the income statement unless recognised in other comprehensive income in connection with a cash flow hedge. Non-monetary items denominated in a foreign currency measured at historical cost are not retranslated. Exchange rate differences arising on non-monetary items measured at fair value are recognised in the consolidated income statement except for differences arising on equity securities measured at fair value through other comprehensive income (FVOCI) (2017: available-for-sale asset measured at fair value), which are recognised in other comprehensive income. Revenue recognition a) Interest income and expense Interest and similar income comprises interest income on financial assets measured at amortised cost, investments in debt instruments measured at FVOCI (2017: available-for-sale measured at fair value) and interest income on hedging derivatives. Interest expense and similar charges comprises interest expense on financial liabilities measured at amortised cost, and interest expense on hedging derivatives. Interest income on financial assets measured at amortised cost, investments in debt instruments measured at FVOCI (2017: available-for-sale The effective interest rate is the rate that discounts the estimated future cash payments or receipts over the expected life of the instrument or, when appropriate, a shorter period, to the gross carrying amount of the financial asset (i.e. its amortised cost before any impairment allowance) or to the amortised cost of a financial liability. When calculating the effective interest rate, the future cash flows are estimated after considering all the contractual terms of the instrument excluding expected credit losses. The calculation includes all amounts paid or received by the Santander UK group that are an integral part of the overall return, direct incremental transaction costs related to the acquisition, issue or disposal of the financial instrument and all other premiums or discounts. Interest income is calculated by applying the effective interest rate to the gross carrying amount of financial assets, except for financial assets that have subsequently become credit-impaired (or ‘Stage 3’), for which interest revenue is calculated by applying the effective interest rate to their amortised cost (i.e. net of the ECL provision). For more information on stage allocations of credit risk exposures, see ‘Significant increase in credit risk’ in the ‘Santander UK group level – credit risk management’ section of the Risk Review. b) Fee and commission income and expense Fees and commissions that are not an integral part of the effective interest rate are recognised when the service is performed. Most fee and commission income is recognised at a point in time. Certain commitment, upfront and management fees are recognised over time but are not material. For retail and corporate products, fee and commission income consists principally of collection services fees, commission on foreign currencies, commission and other fees received from retailers for processing credit card transactions, fees received from other credit card issuers for providing cash advances for their customers through the Santander UK group’s branch and ATM networks, annual fees payable by credit card holders and fees for non-banking financial products. For insurance products, fee and commission income consists principally of commissions and profit share arising from the sale of building and contents insurance and life protection insurance. Commissions arising from the sale of buildings and contents insurance are recognised over the period of insurance cover, adjusted to take account of cancelled policies. Profit share income from the sale of buildings and contents insurance which is not subject to any adjustment is recognised when the profit share income is earned. Commissions and profit share arising from the sale of life protection insurance is subject to adjustment for cancellations of policies within 3 years from inception. Fee and commission income which forms an integral part of the effective interest rate of a financial instrument (for example certain loan commitment fees) is recognised as an adjustment to the effective interest rate and recorded in ‘Interest income’. c) Dividend income Except for equity securities classified as trading assets or financial assets held at fair value through profit or loss, described below, dividend income is recognised when the right to receive payment is established. This is the ex-dividend d) Net trading and other income Net trading and other income includes all gains and losses from changes in the fair value of financial assets and liabilities held at fair value through profit or loss (comprising financial assets and liabilities held for trading, trading derivatives and other financial assets and liabilities at fair value through profit or loss), together with related interest income, expense, dividends and changes in fair value of any derivatives managed in conjunction with these assets and liabilities. Changes in fair value of derivatives in a fair value hedging relationship are also recognised in net trading and other income. Net trading and other income also includes income from operating lease assets, and profits and losses arising on the sales of property, plant and equipment and subsidiary undertakings. Borrowing costs Borrowing costs directly attributable to the acquisition, construction or production of qualifying assets, including computer software, which are assets that necessarily take a substantial period of time to develop for their intended use, are added to the cost of those assets, until the assets are substantially ready for their intended use. All other borrowing costs are recognised in profit or loss in the period in which they occur. Pensions and other post-retirement benefits a) Defined benefit schemes A defined benefit scheme is a pension scheme that guarantees an amount of pension benefit to be provided, usually as a function of one or more factors such as age, years of service or compensation. Pension costs are charged to ‘Administration expenses’, within the line item ‘Operating expenses before impairment losses, provisions and charges’ with the net interest on the defined benefit asset or liability included within ‘Net interest income’ in the income statement. The asset or liability recognised in respect of defined benefit pension schemes is the present value of the defined benefit obligation at the balance sheet date, less the fair value of scheme assets. The defined benefit obligation is calculated annually by independent actuaries using the projected unit credit method. The assets of the schemes are measured at their fair values at the balance sheet date. The present value of the defined benefit obligation is estimated by projecting forward the growth in current accrued pension benefits to reflect inflation and salary growth to the date of pension payment, then discounted to present value using the yield applicable to high-quality AA rated corporate bonds of the same currency and which have terms to maturity closest to the terms of the scheme liabilities, adjusted where necessary to match those terms. In determining the value of scheme liabilities, demographic and financial assumptions are made by management about life expectancy, inflation, discount rates, pension increases and earnings growth, based on past experience and future expectations. Financial assumptions are based on market conditions at the balance sheet date and can generally be derived objectively. Demographic assumptions require a greater degree of estimation and judgement to be applied to externally derived data. Any surplus or deficit of scheme assets over liabilities is recognised in the balance sheet as an asset (surplus) or liability (deficit). An asset is only recognised to the extent that the surplus can be recovered through reduced contributions in the future or through refunds from the scheme. The income statement includes the net interest income/expense on the net defined benefit liability/asset, current service cost and any past service cost and gain or loss on settlement. Remeasurement of defined benefit pension schemes, including return on scheme assets (excludes amounts included in net interest), actuarial gains and losses (arising from changes in demographic assumptions, the impact of scheme experience and changes in financial assumptions) and the effect of the changes to the asset ceiling (if applicable), are recognised in other comprehensive income. Remeasurement recognised in other comprehensive income will not be reclassified to the income statement. Past-service costs are recognised as an expense in the income statement at the earlier of when the scheme amendment or curtailment occurs and when the related restructuring costs or termination benefits are recognised. Curtailments include the impact of significant reductions in the number of employees covered by a scheme, or amendments to the terms of the scheme so that a significant element of future service will no longer qualify for benefits or will qualify only for reduced benefits. Curtailment gains and losses on businesses that meet the definition of discontinued operations are included in profit or loss for the year from discontinued operations. Gains and losses on settlements are recognised when the settlement occurs. b) Defined contribution plans A defined contribution plan is a pension scheme under which the Santander UK group pays fixed contributions as they fall due into a separate entity (a fund). The pension paid to the member at retirement is based on the amount in the separate fund for each member. The Santander UK group has no legal or constructive obligations to pay further contributions into the fund to ‘top up’ benefits to a certain guaranteed level. The regular contributions constitute net periodic costs for the year in which they are due and are included in staff costs within Operating expenses in the income statement. c) Post-retirement medical benefit plans Post-retirement medical benefit liabilities are determined using the projected unit credit method, with actuarial valuations updated at each year-end. The expected benefit costs are accrued over the period of employment using an accounting methodology similar to that for the defined benefit pension scheme. Share-based payments The Santander UK group engages in cash-settled and equity-settled Options granted under the Employee Sharesave scheme are accounted for as cash-settled share-based payment transactions. Awards granted under the Long-Term Incentive Plan and Deferred Shares Bonus Plan are accounted for as equity-settled share-based The fair value of the services received is measured by reference to the fair value of the shares or share options initially on the date of the grant for both the cash and equity settled share-based payments and then subsequently at each reporting date for the cash-settled share-based payments. The cost of the employee services received in respect of the shares or share options granted is recognised in the income statement in administration expenses over the period that the services are received i.e. the vesting period. A liability equal to the portion of the services received is recognised at the fair value determined at each balance sheet date for cash-settled share-based The fair value of the options granted under the Employee Sharesave scheme is determined using an option pricing model, which takes into account the exercise price of the option, the current share price, the risk free interest rate, the expected volatility of the Banco Santander SA share price over the life of the option and the dividend growth rate. The fair value of the awards granted for the Long-Term Incentive Plan was determined at the grant date using an option pricing model, which takes into account the share price at grant date, the risk free interest rate, the expected volatility of the Banco Santander SA share price over the life of the award and the dividend growth rate. Vesting conditions included in the terms of the grant are not taken into account in estimating fair value, except for those that include terms related to market conditions. Non-market vesting conditions are taken into account by adjusting the number of shares or share options included in the measurement of the cost of employee service so that, ultimately, the amount recognised in the income statement reflects the number of vested shares or share options. Where vesting conditions are related to market conditions, the charges for the services received are recognised regardless of whether or not the market–related vesting conditions are met, provided that the non-market vesting conditions are met. Where an award has been modified, as a minimum, the expense of the original award continues to be recognised as if it had not been modified. Where the effect of a modification is to increase the fair value of an award or increase the number of equity instruments, the incremental fair value of the award or incremental fair value of the modification of the award is recognised in addition to the expense of the original grant, measured at the date of modification, over the modified vesting period. Cancellations in the vesting period are treated as an acceleration of vesting, and recognised immediately for the amount that would otherwise have been recognised for services over the vesting period. Goodwill and other intangible assets Goodwill represents the excess of the cost of an acquisition, as well as the fair value of any interest previously held, over the fair value of the share of the identifiable net assets of the acquired subsidiary, associate, or business at the date of acquisition. Goodwill on the acquisition of subsidiaries and businesses is included in intangible assets. Goodwill on acquisitions of associates is included as part of investment in associates. Goodwill is tested for impairment annually, or more frequently when events or changes in circumstances dictate, and carried at cost less accumulated impairment losses. Gains and l

Segments

Segments	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Segments	2. SEGMENTS Santander UK’s principal activity is financial services, mainly in the UK. The business is managed and reported on the basis of the following segments, which are strategic business units that offer different products and services, have different customers and require different technology and marketing strategies: • Retail Banking • Corporate & Commercial Banking • Corporate & Investment Banking value-added • Corporate Centre non-core The segmental data below is presented in a manner consistent with the internal reporting to the committee which is responsible for allocating resources and assessing performance of the segments and has been identified as the chief operating decision maker. The segmental data is prepared on a statutory basis of accounting, in line with the accounting policies set out in Note 1. Transactions between segments are on normal commercial terms and conditions. Internal charges and internal UK transfer pricing adjustments are reflected in the results of each segment. Revenue sharing agreements are used to allocate external customer revenues to a segment on a reasonable basis. Funds are ordinarily reallocated between segments, resulting in funding cost transfers disclosed in operating income. Interest charged for these funds is based on Santander UK’s cost of wholesale funding. Interest income and interest expense have not been reported separately. The majority of segment revenues are interest income in nature and net interest income is relied on primarily to assess segment performance and to make decisions on the allocation of segment resources. The segmental basis of presentation was changed, and the prior periods restated, to report our short term markets business in Corporate Centre rather than in Corporate & Investment Banking. This reflects the run down or transfer to Banco Santander London Branch of the prohibited part of the business in 2018, as part of the transition to our ring-fenced model, with the remaining permitted business forming part of our liquidity risk management function. Results by segment 2019 Retail Corporate & £m Corporate & £m Corporate Total £m Net interest income/(expense) 2,876 359 63 (6 ) 3,292 Non-interest 698 78 112 (7 ) 881 Total operating income/(expense) 3,574 437 175 (13 ) 4,173 Operating expenses before credit impairment losses, provisions and charges (1,994 ) (264 ) (171 ) (70 ) (2,499 ) Credit impairment losses (160 ) (37 ) (22 ) (2 ) (221 ) Provisions for other liabilities and charges (292 ) (20 ) (17 ) (112 ) (441 ) Total operating credit impairment losses, provisions and charges (1) (452 ) (57 ) (39 ) (114 ) (662 ) Profit/(loss) before tax 1,128 116 (35 ) (197 ) 1,012 Revenue from external customers 4,311 530 181 (849 ) 4,173 Inter-segment revenue (737 ) (93 ) (6 ) 836 0 Total operating income/(expense) 3,574 437 175 (13 ) 4,173 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) - Current account and debit card fees 702 27 29 0 758 - Insurance, protection and investments 76 0 0 1 77 - Credit cards 86 0 0 0 86 - Non-banking (3) 61 56 71 3 191 Total fee and commission income 925 83 100 4 1,112 Fee and commission expense (373 ) (23 ) (17 ) (13 ) (426 ) Net fee and commission income/(expense) 552 60 83 (9 ) 686 Customer loans 180,398 16,297 4,114 4,199 205,008 Total assets (4) 187,556 16,297 4,727 73,122 281,702 Customer deposits 145,050 18,234 6,101 2,331 171,716 Total liabilities 145,917 18,260 6,500 95,008 265,685 Average number of staff 20,832 1,796 901 41 23,570 (1) Credit impairment losses for 2018 and later are calculated on an IFRS 9 basis and for 2017 on an IAS 39 basis. (2) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (3) Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance. (4) Includes customer loans, net of credit impairment loss allowances. 2018 Retail Corporate & Corporate & (5) Corporate (5) Total Net interest income 3,126 403 69 5 3,603 Non-interest 638 82 183 28 931 Total operating income 3,764 485 252 33 4,534 Operating expenses before credit impairment losses, provisions and charges (1,929 ) (258 ) (250 ) (142 ) (2,579 ) Credit impairment (losses)/releases (124 ) (23 ) (14 ) 8 (153 ) Provisions for other liabilities and charges (230 ) (14 ) (8 ) (5 ) (257 ) Total operating credit impairment losses, provisions and (charges)/releases (1) (354 ) (37 ) (22 ) 3 (410 ) Profit/(loss) before tax 1,481 190 (20 ) (106 ) 1,545 Revenue from external customers 4,421 638 297 (822 ) 4,534 Inter-segment revenue (657 ) (153 ) (45 ) 855 — Total operating income 3,764 485 252 33 4,534 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) - Current account and debit card fees 697 27 29 — 753 - Insurance, protection and investments 105 — — — 105 - Credit cards 85 — — — 85 - Non-banking (3) 75 62 87 3 227 Total fee and commission income 962 89 116 3 1,170 Fee and commission expense (382 ) (25 ) (14 ) — (421 ) Net fee and commission income 580 64 102 3 749 Customer loans 172,747 17,702 4,613 4,524 199,586 Total assets (4) 179,572 17,702 8,607 77,491 283,372 Customer deposits 142,065 17,606 4,853 2,791 167,315 Total liabilities 142,839 17,634 8,885 98,105 267,463 Average number of staff 21,215 1,732 1,083 175 24,205 2017 Net interest income 3,270 391 67 75 3,803 Non-interest 615 74 261 159 1,109 Total operating income 3,885 465 328 234 4,912 Operating expenses before credit impairment losses, provisions and charges (1,856 ) (223 ) (292 ) (128 ) (2,499 ) Credit impairment (losses)/ releases (1) (36 ) (13 ) (174 ) 20 (203 ) Provisions for other liabilities and charges (342 ) (55 ) (11 ) 15 (393 ) Total operating credit impairment losses, provisions and (charges)/releases (378 ) (68 ) (185 ) 35 (596 ) Profit/(loss) before tax 1,651 174 (149 ) 141 1,817 Revenue from external customers 4,534 639 396 (657 ) 4,912 Inter-segment revenue (649 ) (174 ) (68 ) 891 — Total operating income 3,885 465 328 234 4,912 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) - Current account and debit card fees 737 27 27 — 791 - Insurance, protection and investments 100 — — — 100 - Credit cards 92 — — — 92 - Non-banking (3) 45 63 123 8 239 Total fee and commission income 974 90 150 8 1,222 Fee and commission expense (367 ) (31 ) (17 ) — (415 ) Net fee and commission income 607 59 133 8 807 Customer loans 168,729 19,391 6,037 6,167 200,324 Total assets (4) 174,524 19,391 25,368 95,482 314,765 Customer deposits 143,834 17,760 4,546 9,781 175,921 Total liabilities 150,847 18,697 24,388 104,628 298,560 Average number of staff 17,194 1,240 1,006 119 19,559 (1) Credit impairment losses for 2018 and later are calculated on an IFRS 9 basis and for 2017 on an IAS 39 basis. (2) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (3) Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance. (4) Includes customer loans, net of credit impairment loss allowances. (5) The re-segmentation of our short term markets business has resulted in profit before tax of £77m being re-presented in Corporate Centre rather than Corporate & Investment Banking in 2018 (2017: £98m).

Net Interest Income

Net Interest Income	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Net Interest Income	3. NET INTEREST INCOME Group 2019 2018 2017 Interest and similar income: Loans and advances to customers 5,230 5,458 5,494 Loans and advances to banks 137 202 164 Reverse repurchase agreements – non trading 244 124 20 Other 306 282 227 Total interest and similar income (1) 5,917 6,066 5,905 Interest expense and similar charges: Deposits by customers (1,540 ) (1,433 ) (1,330 ) Deposits by banks (134 ) (117 ) (35 ) Repurchase agreements – non trading (126 ) (42 ) (5 ) Debt securities in issue (678 ) (721 ) (590 ) Subordinated liabilities (137 ) (142 ) (134 ) Other (10 ) (8 ) (8 ) Total interest expense and similar charges (2) (2,625 ) (2,463 ) (2,102 ) Net interest income 3,292 3,603 3,803 (1) This includes £203m (2018: £209m) of interest income on financial assets at fair value through other comprehensive income. (2) This includes £310m (2018: £298m) of interest expense on financial assets at fair value through other comprehensive income.

Net Fee and Commission Income

Net Fee and Commission Income	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Net Fee and Commission Income	4. NET FEE AND COMMISSION INCOME Group 2019 2018 2017 Fee and commission income: Current account and debit card fees 758 753 791 Insurance, protection and investments 77 105 100 Credit cards 86 85 92 Non-banking (1) 191 227 239 Total fee and commission income 1,112 1,170 1,222 Total fee and commission expense (426 ) (421 ) (415 ) Net fee and commission income 686 749 807 (1) Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance.

Net Trading and Other Income

Net Trading and Other Income	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Net Trading and Other Income	5. NET TRADING AND OTHER INCOME Group 2019 2018 2017 Net trading and funding of other items by the trading book 6 245 205 Net gains/(losses) on other financial assets at fair value through profit or loss 19 (6 ) 80 Net losses on other financial liabilities at fair value through profit or loss (83 ) (44 ) (97 ) Net gains/(losses) on derivatives managed with assets/liabilities held at fair value through profit or loss 69 (128 ) (17 ) Hedge ineffectiveness 8 34 5 Net profit on sale of available-for-sale 54 Net profit on sale of financial assets at fair value through other comprehensive income 15 19 Income from operating lease assets 124 86 44 Other 37 (24 ) 28 195 182 302 Following the implementation of our ring-fencing plans in 2018, assets and liabilities held at fair value through profit or loss, including derivatives, are predominantly used to provide customers with risk management solutions, and to manage and hedge the Santander UK group’s own risks, and do not give rise to significant overall net gains/(losses) in the income statement. ‘Net trading and funding of other items by the trading book’ includes fair value losses of £42m (2018: gains of £22m, 2017: losses of £27m) on embedded derivatives bifurcated from certain equity index-linked deposits, as described in the derivatives accounting policy in Note 1. The embedded derivatives are economically hedged, the results of which are also included in this line item, and amounted to gains of £43m (2018: losses of £21m, 2017: gains of £28m). As a result, the net fair value movements recognised on the equity index-linked deposits and the related economic hedges were net gains of £1m (2018: £1m, 2017: £1m). In 2019, ‘net profit on sale of financial assets at fair value through other comprehensive income’ included additional consideration of £15m in connection with the 2017 Vocalink Holdings Limited shareholding sale. In 2017, ‘Net profit on sale of available-for-sale assets’ included a gain of £48m in respect of the sale of the Vocalink Holdings Limited shareholding. Exchange rate differences recognised in the Consolidated Income Statement on items not at fair value through profit or loss were £1,102m income (2018: £689m expense, 2017: £109m expense) and are presented in the line ‘Net trading and funding of other items by the trading book.’ These are principally offset by related releases from the cash flow hedge reserve of £1,013m expense (2018: £752m income, 2017: £94m income) as set out in the Consolidated Statement of Comprehensive Income, which are also presented in ‘Net trading and funding of other items by the trading book’. Exchange rate differences on items measured at fair value through profit or loss are included in the line items relating to changes in fair value. In 2019, our accounting treatment for residual value risk changed. This resulted in a £24m reversal of RV provisions recognised in other income (of which £22m relates to charges taken in prior periods) which was partially offset by £7.5m accelerated depreciation of the underlying asset (prior periods: £2.3m). The net adjustment is not considered material and therefore the 2018 accounts were not restated.

Operating Expenses Before Credi

Operating Expenses Before Credit Impairment Losses, Provisions and Charges	12 Months Ended
	Dec. 31, 2019
Statement [Line Items]
Operating Expenses Before Credit Impairment Losses, Provisions and Charges	6. OPERATING EXPENSES BEFORE CREDIT IMPAIRMENT LOSSES, PROVISIONS AND CHARGES Group 2019 2018 2017 Staff costs: Wages and salaries 852 898 743 Performance-related payments 159 159 157 Social security costs 111 111 93 Pensions costs – defined contribution plans 66 67 54 – defined benefit plans 35 79 32 Other share-based payments 0 3 10 Other personnel costs 40 52 45 1,263 1,369 1,134 Other administration expenses 693 835 1,011 Depreciation, amortisation and impairment 543 375 354 2,499 2,579 2,499 Staff costs ’Performance-related payments’ include bonuses paid in cash and share awards granted under the Long-Term share-based Costs recognised in 2019 Costs expected to be recognised in 2020 or later Arising from Arising from Total Arising from Arising from Total Cash 3 7 10 7 10 17 Shares 3 6 9 6 9 15 6 13 19 13 19 32 The following table shows the amount of bonus awarded to employees for the performance year 2019. In the case of deferred cash and share awards, the final amount paid to an employee is influenced by forfeiture provisions and any performance conditions to which these awards are subject. The deferred share award amount is based on the fair value of these awards at the date of grant. Expenses charged in the year Expenses deferred to future periods Total 2019 £m 2018 2019 £m 2018 2019 2018 Cash award – not deferred 130 123 0 — 130 123 – deferred 10 12 17 20 27 32 Shares award – not deferred 10 11 0 — 10 11 – deferred 9 13 15 17 24 30 Total discretionary bonus 159 159 32 37 191 196 On 26 October 2018, the High Court handed down a judgement concluding that defined benefit schemes should equalise pension benefits for men and women in relation to GMP and concluded on the methods that were appropriate. The estimated increase in liabilities at the date of the judgement was £40m and was based on a number of assumptions and the actual impact may be different. This was reflected in the income statement and in the closing net accounting surplus of the Scheme in 2018. The allowance included in the Scheme liabilities at 31 December 2019 increased by £5m to £45m (2018: £40m) to reflect the latest assumptions. This change was recognised in other comprehensive income. We continue to await implementation guidance on the judgement from the UK Government and HMRC. ‘Other share-based The average number of full-time equivalent staff was 23,570 (2018: 24,205, 2017: 19,559). The increase in staff numbers in 2018 reflected Santander UK plc’s acquisition of Santander UK Operations Ltd (formerly Geoban UK Ltd, a subsidiary of Geoban SA) and Santander UK Technology Ltd (formerly Isban UK Ltd, a subsidiary of Ingenieria de Software Bancario SL). Depreciation, amortisation and impairment In 2019, depreciation, amortisation and impairment was impacted by operating lease depreciation of £103m (2018: £63m) on operating lease assets (where the Santander UK group is the lessor) with a net book value of £574m at 31 December 2019 (2018: £470m). It was also impacted by depreciation of £60m on right-of-use assets with a net book value of £152m at 31 December 2019, following the adoption of IFRS 16 on 1 January 2019.

Audit and Other Services

Audit and Other Services	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Audit and Other Services	7. AUDIT AND OTHER SERVICES Group 2019 2018 2017 £m £m £m Audit fees: Fees payable to the Company’s auditor and its associates for the audit of the Santander UK group’s annual accounts 8.0 7.2 7.4 Fees payable to the Company’s auditor and its associates for other services to the Santander UK group: - Audit of the Santander UK group’s subsidiaries 1.3 1.1 1.4 Total audit fees (1) 9.3 8.3 8.8 Non-audit Audit-related assurance services (2) 0.8 0.7 0.7 Other assurance services 0.2 0.1 0.1 Other non-audit 0.2 1.0 0.4 Total non-audit 1.2 1.8 1.2 (1) 2019 audit fees included £0.1m (2018: £nil) which related to the prior year. (2) 2019 audit-related assurance services included £0.1m (2018: £0.1m) which related to the prior year. Audit-related assurance services mainly comprises services performed in connection with review of the interim financial information of the Company and reporting to the Company’s UK regulators. Of the total non-audit fees, £0.6m (2018: £0.1m, 2017: £0.1m) accords with the definition of “Audit Fees” per US Securities and Exchange Commission (SEC) guidance, £0.4m (2018: £0.6m, 2017: £0.6m) accords with the definition of “Audit related fees” per that guidance and £0.2m (2018: £1.1m, 2017: £0.5m) accords with the definition of “All other fees” per that guidance. In 2019, the Company’s auditors earned no fees (2018: £150,000, 2017: £45,000) payable by entities outside the Santander UK group for the review of the financial position of corporate and other borrowers.

Credit Impairment Losses and Pr

Credit Impairment Losses and Provisions	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Credit Impairment Losses and Provisions	8. CREDIT IMPAIRMENT LOSSES AND PROVISIONS Group 2019 2018 2017 £m £m £m Credit impairment losses: (1) Loans and advances to customers 239 189 257 Recoveries of loans and advances, net of collection costs (40 ) (42 ) (54 ) Off-balance 22 6 221 153 203 Provisions for other liabilities and charges (excluding off-balance 435 257 385 Provisions for RV and voluntary termination 6 — 8 441 257 393 662 410 596 (1) Credit impairment losses for 2018 and later are calculated on an IFRS 9 basis and for 2017 and earlier on an IAS 39 basis. In 2019 and 2018 there were no material credit impairment losses on loans and advances to banks, non-trading reverse repurchase agreements, other financial assets at amortised cost and financial assets at fair value through other comprehensive income.

Taxation

Taxation	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Taxation	9. TAXATION Group 2019 2018 (1) 2017 (1) £m £m £m Current tax: UK corporation tax on profit for the year 265 408 510 Adjustments in respect of prior years (25 ) (20 ) (27 ) Total current tax 240 388 483 Deferred tax: Charge for the year 46 16 23 Adjustments in respect of prior years (7 ) (5 ) 9 Total deferred tax 39 11 32 Tax on profit 279 399 515 (1) Adjusted to reflect the amendment to IAS 12, as described in Note 1. The standard rate of UK corporation tax was 27% for banking entities and 19% for non-banking entities (2018: 27% for banking entities and 19% for non-banking entities; 2017: 27.25% for banking entities and 19.25% for non-banking entities) following the introduction of an 8% surcharge to be applied to banking companies from 1 January 2016. Taxation for other jurisdictions is calculated at the rates prevailing in the relevant jurisdictions. Finance Act 2016 introduced a reduction in the standard rate of corporation tax rate to 17% from 2020. The effects of the changes in tax rates are included in the deferred tax balances at both 31 December 2019 and 2018. The Santander UK group’s effective tax rate for 2019, based on profit before tax, was 27.6% (2018: 25.8%, 2017: 28.3%). The tax on profit before tax differs from the theoretical amount that would arise using the basic corporation tax rate of the Company as follows: Group 2019 2018 (1) 2017 (1) £m £m £m Profit before tax 1,012 1,545 1,817 Tax calculated at a tax rate of 19% (2018: 19%, 2017: 19.25%) 192 294 350 Bank surcharge on profits 65 109 132 Non-deductible 8 8 9 Non-deductible 24 20 25 Non-deductible 44 6 35 Other non-deductible non-taxable 31 30 30 Effect of change in tax rate on deferred tax provision (14 ) (1 ) (2 ) Tax relief on dividends in respect of other equity instruments (39 ) (42 ) (46 ) Adjustment to prior year provisions (32 ) (25 ) (18 ) Tax charge 279 399 515 (1) Adjusted to reflect the amendment to IAS 12, as described in Note 1. The increase in effective tax rate from 2018 to 2019 was largely due to the increased impact of non-deductible conduct remediation, fines and penalties net of releases in accruals for prior periods. It is anticipated that the Santander UK group’s effective tax rate in future periods will continue to be impacted by the 8% surcharge, the level of any non-deductible conduct remediation, fines and penalties, changes to the cost of the Bank Levy and reductions in the statutory rate as noted above. The adjustment to prior year provisions in 2019 and 2018 principally related to the reassessment of prior year tax provision estimates following the filing of relevant tax returns and the resolution of certain legacy matters with tax authorities. Current tax assets and liabilities Movements in current tax assets and liabilities during the year were as follows: Group 2019 2018 (1) £m £m Assets 153 — Liabilities 0 (3 ) At 1 January 153 (3 ) Income statement charge (240 ) (388 ) Other comprehensive income (charge)/credit (4 ) 34 Corporate income tax paid 292 391 Other movements (1 ) 119 200 153 Assets 200 153 Liabilities 0 — At 31 December 200 153 (1) Adjusted to reflect the amendment to IAS 12, as described in Note 1. The amount of corporation income tax paid differs from the tax charge for the period as a result of the timing of payments due to the tax authorities together with the effects of movements in deferred tax, adjustments to prior period current tax provisions and current tax recognised directly in other comprehensive income. Other movements in 2018 primarily arose due to the transfer of subsidiaries to fellow subsidiaries of Banco Santander SA outside of the Santander UK group as part of our ring-fencing plans. Santander UK proactively engages with HM Revenue & Customs to resolve tax matters relating to prior years. The accounting policy for recognising provisions for such matters are described in Note 1. It is not expected that there will be any material movement in such provisions within the next 12 months. Santander UK adopted the Code of Practice on Taxation for Banks in 2010. Deferred tax The table below shows the deferred tax assets and liabilities including the movement in the deferred tax account during the year. Deferred tax balances are presented in the balance sheet after offsetting assets and liabilities where the Santander UK group has the legal right to offset and intends to settle on a net basis. Group Fair value of Pension Cash flow Available- for-sale Fair value Tax losses Accelerated tax Other Total At 1 January 2019 (51 ) (183 ) (43 ) (13 ) 20 (6 ) 53 (223 ) Income statement (charge)/credit (1 ) (44 ) 0 0 (7 ) 23 (10 ) (39 ) Transfers/reclassifications 0 0 22 5 0 0 (27 ) 0 Credited/(charged) to other comprehensive income 0 131 (37 ) 0 0 0 19 113 At 31 December 2019 (52 ) (96 ) (58 ) (8 ) 13 17 35 (149 ) At 31 December 2017 (41 ) (41 ) 3 (26 ) 25 (4 ) (4 ) (88 ) Adoption of IFRS 9 — — — 26 (26 ) — — 68 68 At 1 January 2018 (41 ) (41 ) 3 (26 ) 25 (4 ) 64 (20 ) Income statement (charge)/credit (10 ) (24 ) — — (5 ) — 28 (11 ) Transfers/reclassifications — — — — — (2 ) (18 ) (20 ) Credited/(charged) to other comprehensive income — (118 ) (46 ) 13 — — (21 ) (172 ) At 31 December 2018 (51 ) (183 ) (43 ) (13 ) 20 (6 ) 53 (223 ) The deferred tax assets and liabilities above have been recognised in the Santander UK group on the basis that sufficient future taxable profits are forecast within the foreseeable future, in excess of the profits arising from the reversal of existing taxable temporary differences, to allow for the utilisation of the assets as they reverse. Based on the conditions at the balance sheet date, management determined that a reasonably possible change in any of the key assumptions underlying the estimated future taxable profits in the Santander UK group’s five-year plan (described in Note 20) would not cause a reduction in the deferred tax assets recognised. At 31 December 2019, the Santander UK group had a recognised deferred tax asset in respect of UK capital losses carried forward of £11m (2018: £17m) included within tax losses carried forward. There are no unrecognised deferred tax assets on capital losses carried forward (2018: £nil). As part of the election campaign, the UK government indicated that it would look to reverse or defer the future tax rate reduction due to apply from 1 April 2020. The next UK Budget scheduled for 11 March 2020 is likely to clarify the position and give an indication of the possible impact on the deferred tax position. It is estimated that the effect could increase the Santander UK Group’s deferred tax liability by up to £12m.

Dividends on Ordinary Shares

Dividends on Ordinary Shares	12 Months Ended
	Dec. 31, 2019
Statement [Line items]
Dividends on Ordinary Shares	10. DIVIDENDS ON ORDINARY SHARES Dividends on ordinary shares declared and paid in the year were as follows: Group Group 2019 2018 2017 2019 2018 2017 In respect of current year - first interim 0.53 0.81 1.04 164 250 323 - second interim 0.49 2.15 0.74 151 668 230 - third interim 0 0.71 — 0 221 — 1.02 3.67 1.78 315 1,139 553 In 2018, in addition to the dividends of £250m and £221m that were made as part of our policy to pay 50% of recurring earnings, we also paid a dividend of £668m that related to the ring-fencing transfers to Banco Santander, London Branch.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Derivative Financial Instruments	11. DERIVATIVE FINANCIAL INSTRUMENTS a) Use of derivatives The Santander UK group undertakes derivative activities primarily to provide customers with risk management solutions and to manage and hedge the Santander UK group’s own risks. The Santander UK group’s derivative activities do not give rise to significant open positions in portfolios of derivatives. Any residual position is managed to ensure that it remains within acceptable risk levels, with matching transactions being used to achieve this where necessary. When entering into derivatives, the Santander UK group employs the same credit risk management procedures to assess and approve potential credit exposures that are used for traditional lending. For information on how the Santander UK group is managing the transition to alternative benchmark interest rates, see ‘Managing LIBOR transition’ in the Banking market risk section of the Risk review. b) Analysis of derivatives The table below includes the notional amounts of transactions outstanding at the balance sheet date; they do not represent actual exposures. Group 2019 2018 Fair value Fair value Notional Assets Liabilities Notional Assets Liabilities Derivatives held for trading: Exchange rate contracts 14,149 134 200 13,830 454 351 Interest rate contracts 46,564 718 315 79,038 1,421 1,105 Equity and credit contracts 2,474 283 160 2,762 251 168 Total derivatives held for trading 63,187 1,135 675 95,630 2,126 1,624 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 1,482 166 2 3,010 357 — Interest rate contracts 94,550 1,022 1,488 86,422 1,065 1,315 96,032 1,188 1,490 89,432 1,422 1,315 Designated as cash flow hedges: Exchange rate contracts 28,502 2,023 462 33,901 3,537 200 Interest rate contracts 17,451 184 35 18,808 46 102 Equity derivative contracts 0 0 0 — — — 45,953 2,207 497 52,709 3,583 302 Total derivatives held for hedging 141,985 3,395 1,987 142,141 5,005 1,617 Derivative netting (1) (1,214 ) (1,214 ) (1,872 ) (1,872 ) Total derivatives 205,172 3,316 1,448 237,771 5,259 1,369 (1) Derivative netting excludes the effect of cash collateral, which is offset against the gross derivative position. The amount of cash collateral received that had been offset against the gross derivative assets was £222m (2018: £9m) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was £629m (2018: £354m). For information about the impact of netting arrangements on derivative assets and liabilities in the table above, see Note 39. The reduction in the notional value of interest rate derivatives held for trading reflected the completion of a series of derivative trade compressions to reduce our gross LIBOR exposure. The table below analyses the notional and fair values of derivatives by trading and settlement method. Notional Traded over the counter Asset Liability Traded on recognised exchanges Settled by central counterparties Not settled by central counterparties Total Traded on recognised exchanges Traded over the counter Traded on recognised exchanges Traded over the counter 2019 £m £m £m £m £m £m £m £m Exchange rate contracts 0 0 44,133 44,133 0 2,324 0 663 Interest rate contracts 0 131,538 27,027 158,565 0 709 0 625 Equity and credit contracts 0 0 2,474 2,474 0 283 0 160 0 131,538 73,634 205,172 0 3,316 0 1,448 2018 Exchange rate contracts — — 50,741 50,741 — 4,349 — 551 Interest rate contracts — 154,106 30,162 184,268 — 659 — 650 Equity and credit contracts — — 2,762 2,762 — 251 — 168 — 154,106 83,665 237,771 — 5,259 — 1,369 c) Analysis of derivatives designated as hedges The Santander UK group applies hedge accounting on both a fair value and cash flow basis depending on the nature of the underlying exposure. We establish the hedge ratio by matching the notional of the derivative with the underlying position being hedged. Only the designated risk is hedged and therefore other risks, such as credit risk are managed but not hedged. For interest rate hedges, the designated hedged risk is determined with reference to the underlying benchmark rate. Fair value hedges Portfolio hedges of interest rate risk Santander UK holds various portfolios of fixed rate assets and liabilities which expose it to changes in fair value due to movements in market interest rates. We manage these exposures by entering into interest rate swaps. Each portfolio contains assets or liabilities that are similar in nature and share the risk exposure that is designated as being hedged. The interest rate risk component is the change in fair value of fixed rate instruments for changes in the designated benchmark rate. Such changes are usually the largest component of the overall change in fair value. Separate hedges are maintained for each underlying currency. Effectiveness is assessed by comparing changes in fair value of the hedged item attributable to changes in the designated benchmark interest rate, with changes in the fair value of the interest rate swaps. The Santander UK group is exposed to changes in fair value of financial assets and liabilities due to movements in market interest rates and / or FX rates. These exposures arise from holding either fixed rate assets and liabilities or non-GBP Micro hedges of interest rate risk and foreign currency risk Santander UK accesses international markets to obtain funding, issuing fixed rate debt in its functional currency and other currencies. We are therefore exposed to changes in fair value due to changes in market interest rates and/or foreign exchange rates, principally in USD and EUR, which we mitigate through the use of receive fixed/pay floating rate interest rate swaps and/or receive fixed/pay floating rate cross currency swaps. The interest rate risk component is the change in fair value of the fixed rate debt due to changes in the benchmark LIBOR rate. The foreign exchange component is the change in the fair value of the fixed rate debt issuance due to changes in foreign exchange rates prevailing from the time of execution. Effectiveness is assessed by using linear regression techniques to compare changes in the fair value of the debt caused by changes in the benchmark interest rate and foreign exchange rates, with changes in the fair value of the interest rate swaps and/or cross currency swaps. Cashflow hedges Hedges of interest rate risk Santander UK manages its exposure to the variability in cash flows of floating rate assets and liabilities attributable to movements in market interest rates by entering into interest rate swaps. The interest rate risk component is determined with reference to the underlying benchmark rate attributable to the floating rates asset or liability. Designated benchmark rates referenced are currently SONIA or LIBOR. Effectiveness is assessed by comparing changes in the fair value of the interest rate swap with changes in the fair value of the hedged item attributable to the hedged risk, applying a hypothetical derivative method using linear regression techniques. Hedges of foreign currency risk As Santander UK obtains funding in international markets, we assume significant foreign currency risk exposure, mainly in USD and EUR. In addition, the Santander UK group also holds debt securities for liquidity purposes which assumes foreign currency exposure, principally in JPY. Santander UK manages the exposures to the variability in cash flows of foreign currency denominated assets and liabilities to movements in foreign exchange rates by entering into either foreign exchange contracts (spot, forward and swaps) or cross currency swaps. These instruments are entered into to match the cash flow profile and maturity of the estimated interest and principal repayments of the hedged item. The foreign currency risk component is the change in cash flows of the foreign currency debt arising from changes in the relevant foreign currency forward exchange rate. Such changes constitute a significant component of the overall changes in cash flows of the instrument. Effectiveness is assessed by comparing changes in the fair value of the cross currency or foreign exchange swaps with changes in the fair value of the hedged debt attributable to the hedged risk applying a hypothetical derivative method using linear regression techniques. LIBOR Reform As described above, the Santander UK group designates both fair value and cash flow hedges with reference to the underlying benchmark rate. Where these benchmark rates are subject to uncertainty as a result of LIBOR reform (as explained in Note 1) we have early adopted the amendments to IAS 39 which provide temporary relief from applying specific hedge accounting requirements to those affected hedge relationships. Hedge relationships that are impacted comprise fair value hedges where fixed rate exposures are hedged to a benchmark rate subject to reform and cash flow hedges, where future hedged cash flows are benchmarked to interest rates impacted by the reform. It is assumed that the cash flows will remain highly probable and that the hedge relationship will remain highly effective. The table below shows the notional value of hedging instruments by benchmark interest rate impacted by the reform. Group GBP LIBOR £m USD LIBOR £m Other £m Total £m 2019 Total notional value of hedging instruments: - Cash flow hedges 23,396 8,001 0 31,397 - Fair value hedges 53,244 5,070 1,187 59,501 76,640 13,071 1,187 90,898 Maturing after 31 December 2021: - Cash flow hedges 11,773 2,644 0 14,417 - Fair value hedges 16,455 1,897 740 19,092 28,228 4,541 740 33,509 Hedge effectiveness measurement and possible sources of hedge ineffectiveness Hedge effectiveness is assessed by using either dollar offset or linear regression techniques to compare changes in the fair value of the hedged item attributable to changes in the designated hedged risk and the hedging instrument. For cash flow hedges, a hypothetical derivative method is used to model the cash flows of the hedged item. Possible sources of hedge ineffectiveness arise from differences in discounting and timing of cash flows between the hedged item and hedging instrument, basis risk, hedging derivatives with a non-zero fair value upon designation and counterparty credit risk. Maturity profile and average price/rate of hedging instruments The following table sets out the maturity profile and average price/rate of the hedging instruments used in the Santander UK group’s hedging strategies: Group 2019 Hedging Instruments £ >1 and £ >3 and £ >1 and £ >5 years Total Fair value hedges: Interest rate risk Interest rate contracts – Notional amount (£m) 4,354 5,804 27,405 43,652 13,099 94,314 Average fixed interest rate – GBP 0.77 % 0.90 % 0.88 % 1.33 % 3.00 % Average fixed interest rate – EUR (0.41 )% 0.29 % 2.21 % 1.36 % 2.36 % Average fixed interest rate – USD 0 1.54 % 1.99 % 2.69 % 4.56 % Interest rate/FX risk Exchange rate contracts – Notional amount (£m) 0 755 0 317 410 1,482 Interest rate contracts – Notional amount (£m) 0 0 0 18 218 236 Average GBP – EUR exchange rate 0 0 0 1.1781 1.1603 Average GBP – USD exchange rate 0 1.5110 0 0 0 Average fixed interest rate – EUR 0 0 0 3.52 % 2.12 % Average fixed interest rate – USD 0 2.38 % 0 0 0 Cash flow hedges: Interest rate risk Interest rate contracts – Notional amount (£m) 0 339 1,066 4,671 500 6,576 Average fixed interest rate – GBP 0 0.76 % 0.82 % 1.46 % 0.40 % FX risk Exchange rate contracts – Notional amount (£m) 1,187 2,119 3,758 5,217 0 12,281 Interest rate contracts – Notional amount (£m) 0 0 0 755 0 755 Average GBP – JPY exchange rate 0 145.9275 143.0857 140.8152 0 Average GBP – EUR exchange rate 0 1.1444 1.1167 1.1526 0 Average GBP – USD exchange rate 1.2856 1.2624 1.2925 1.2991 0 Interest rate/FX risk Exchange rate contracts – Notional amount (£m) 812 0 3,367 8,009 4,033 16,221 Interest rate contracts – Notional amount (£m) 0 0 3,121 4,829 2,170 10,120 Average GBP – EUR exchange rate 1.2742 0 1.1689 1.3114 1.2090 Average GBP – USD exchange rate 0 0 1.5357 1.5811 1.4499 Average fixed interest rate – GBP 2.49 % 0 2.16 % 2.87 % 2.96 % 2018 Fair value hedges: Interest rate risk Interest rate contracts – Notional amount (£m) 6,162 8,411 14,611 39,508 15,652 84,344 Average fixed interest rate – GBP 0.63 % 0.79 % 1.06 % 1.59 % 2.85 % Average fixed interest rate – EUR (0.22 )% 0.67 % 0.91 % 1.09 % 1.26 % Average fixed interest rate – USD 1.51 % 1.31 % 1.34 % 2.68 % 2.18 % Interest rate/FX risk Exchange rate contracts – Notional amount (£m) 392 1,295 — 1,101 222 3,010 Interest rate contracts – Notional amount (£m) 392 1,295 — 90 301 2,078 Average GBP – EUR exchange rate — — — 1.1827 1.1682 Average GBP – USD exchange rate 1.5800 1.3325 — 1.5110 — Average fixed interest rate – EUR — — — 3.89 % 3.92 % Average fixed interest rate – USD 3.62 % 2.50 % — 2.38 % 7.95 % Cash flow hedges: Interest rate risk Interest rate contracts – Notional amount (£m) — 1,715 1,991 3,100 — 6,806 Average fixed interest rate – GBP — 0.73 % 0.73 % 1.33 % — FX risk Exchange rate contracts – Notional amount (£m) 3,916 2,552 2,961 5,596 — 15,025 Interest rate contracts – Notional amount (£m) — — — 785 — 785 Average GBP – JPY exchange rate — 147.2149 146.3718 145.3191 — Average GBP – EUR exchange rate — — 1.2803 1.1349 — Average GBP – USD exchange rate 1.3035 1.3067 1.3099 1.3049 — Interest rate/FX risk Exchange rate contracts – Notional amount (£m) — — 1,773 11,481 5,622 18,876 Interest rate contracts – Notional amount (£m) — — 784 7,562 2,871 11,217 Average GBP – EUR exchange rate — — 1.2523 1.2707 1.2167 Average GBP – USD exchange rate — — 1.6333 1.5447 1.5109 Average fixed interest rate – GBP — — 2.34 % 2.66 % 2.90 % Net gains or losses arising from fair value and cash flow hedges included in net trading and other income Group 2019 2018 2017 Fair value hedging: (Losses)/gains on hedging instruments (360 ) 4 56 Gains/(losses) on hedged items attributable to hedged risks 414 75 (2 ) Fair value hedging ineffectiveness 54 79 54 Cash flow hedging ineffectiveness (46 ) (45 ) (49 ) 8 34 5 Hedge ineffectiveness can be analysed by risk category as follows: Group 2019 2018 Change in FV Change in FV Recognised Change in FV Change in FV Recognised Fair value hedges: Interest rate risk (264 ) 284 20 26 15 41 Interest rate/FX risk (96 ) 130 34 (22 ) 60 38 (360 ) 414 54 4 75 79 Group 2019 2018 Hedging Instruments Hedging Instruments Income statement line item Change Recognised Recognised Reclassified Change Recognised Recognised Reclassified Cash flow hedges: Interest rate risk Net interest income 34 (33 ) 1 13 20 (14 ) 6 26 FX risk Net interest income/net trading and other income (333 ) 329 (4 ) (316 ) 18 (20 ) (2 ) 9 Equity risk Operating expenses 0 0 0 0 (12 ) 12 — (9 ) Interest rate/FX risk Net interest income/net trading and other income (604 ) 561 (43 ) (709 ) 722 (771 ) (49 ) 726 (903 ) 857 (46 ) (1,012 ) 748 (793 ) (45 ) 752 In 2019, cash flow hedge accounting of £4m (2018: £12m) had to cease due to foreign currency denominated cash flows relating to IT project expenditure no longer being expected to occur. The following table provides a reconciliation by risk category of components of equity and analysis of OCI items (before tax) resulting from hedge accounting. Group 2019 2018 Balance at 1 January 326 285 Effective portion of changes in fair value: - Interest rate risk 33 14 - Foreign currency risk (329 ) 20 - Equity risk 0 (12 ) - Interest rate/foreign currency risk (561 ) 771 (857 ) 793 Income statement transfers: - Interest rate risk (13 ) (26 ) - Foreign currency risk 316 (9 ) - Equity risk 0 9 - Interest rate/foreign currency risk 709 (726 ) 1,012 (752 ) Balance at 31 December 481 326 Hedged exposures Santander UK hedges its exposures to various risks, including interest rate risk and foreign currency risk, as set out in the following table. Group 2019 2018 Carrying Accumulated amount of FV hedge Change in value to calculate hedge Carrying Accumulated amount of FV hedge Change in Hedged Portfolio rate risks Of which Hedged Portfolio Of which Fair value hedges Interest rate risk: Loans and advances to customers 43,098 0 870 630 258 42,075 — 638 729 (149 ) Other financial assets at amortised cost 6,627 0 142 121 83 6,640 — 59 — 59 Reverse repos – non trading 17,121 0 (2 ) 0 (2 ) 10,954 — — — — Other financial assets at FVOCI 5,944 102 0 82 125 7,429 10 — 123 (46 ) Deposits by customers (9,944 ) (85 ) 4 (11 ) (110 ) (702 ) — 1 — — Deposits by banks (517 ) (16 ) 0 (17 ) (1 ) (516 ) (15 ) — (23 ) 9 Debt securities in issue (8,099 ) (303 ) (166 ) (300 ) (50 ) (11,920 ) (199 ) (191 ) (369 ) 121 Subordinated liabilities (707 ) (181 ) (48 ) (204 ) (19 ) (694 ) (161 ) (52 ) (223 ) 21 Interest rate/FX risk: Other financial assets at FVOCI 241 3 0 0 (4 ) 18 — — — — Debt securities in issue (1,396 ) (135 ) 0 (122 ) 136 (3,192 ) (170 ) — (179 ) 37 Subordinated liabilities 7 7 0 7 (2 ) 9 9 — 9 23 52,375 (608 ) 800 186 414 50,101 (526 ) 455 67 75 Group 2019 2018 Hedged item balance sheet line item Change in value to Cash flow Balances on cash Change in value Cash flow Balances on cash Cash flow hedges: Interest rate risk: Loans and advances to customers (34 ) 21 (11 ) (19 ) (4 ) (2 ) Loans and advances to banks (2 ) 0 0 — (2 ) — Deposits by banks 3 (2 ) 0 6 (1 ) — Debt securities in issue 0 0 0 (1 ) — — FX risk: Other financial assets at FVOCI (122 ) 3 0 199 (1 ) — Not applicable – highly probable forecast transactions 267 2 0 (1 ) — — Deposits by customers 3 0 0 — — — Deposits by banks 4 0 0 — — — Debt securities in issue 177 (3 ) 0 (218 ) 22 3 Equity risk: Other liabilities 0 0 (1 ) 12 — — Interest rate/FX risk: Debt securities in issue/loans and advances to customers 630 280 20 (564 ) 233 50 Subordinated liabilities/loans and advances to customers (69 ) 180 0 (207 ) 79 — 857 481 8 (793 ) 326 51

Other Financial Assets At Fair

Other Financial Assets At Fair Value Through Profit Or Loss	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Other Financial Assets At Fair Value Through Profit Or Loss	12. OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS Group 2019 £m 2018 Loans and advances to customers: Loans to housing associations 12 13 Other loans 80 81 92 94 Debt securities 294 3,251 Equity securities 0 — Reverse repurchase agreements – non trading 0 2,272 386 5,617 For the Santander UK group, other financial assets at FVTPL comprised £12m (2018: £1,095m) of financial assets designated at FVTPL and £374m (2018: £4,522m) of financial assets mandatorily held at FVTPL. Loans and advances to customers principally represented other loans, being a portfolio of roll-up mortgages and deferred consideration following the partial sale of the portfolio. These are managed, and have their performance evaluated, on a fair value basis in accordance with a documented investment strategy, and information about them is provided on that basis to management. Since 2009, the Santander UK group’s policy has been not to designate similar new loans at fair value through profit or loss. The deferred consideration was transferred outside the Santander UK group as part of the sale of the share capital of SFS by Santander UK plc to Santander UK Group Holding plc in 2018. For more, see Note 19. In 2019 £2.1bn of senior tranches of credit linked notes related to an SRT securitisation, which were previously classified as debt securities in the table above, were presented on a net basis. This followed a deed of amendment, including a legal right of set-off between the principal amounts of the senior tranches of credit linked notes and the related cash deposits included as collateral in Note 21. At 31 December 2019 the amount of this netting was £1.5bn. The net (loss)/gain in the year attributable to changes in credit risk for loans and advances at fair value through profit or loss was £nil (2018: £(1)m, 2017: £49m). The cumulative net loss attributable to changes in credit risk for loans and advances at fair value through profit or loss at 31 December 2019 was £2m (2018: £2m).

Loans and Advances to Customers

Loans and Advances to Customers	12 Months Ended
	Dec. 31, 2019
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Loans and Advances to Customers	13. LOANS AND ADVANCES TO CUSTOMERS Group 2019 £m 2018 Loans secured on residential properties 165,356 157,957 Corporate loans 27,043 27,763 Finance leases 6,264 6,821 Secured advances 0 — Other unsecured loans 7,096 7,554 Amounts due from fellow Banco Santander subsidiaries and joint ventures 2,366 1,997 Amounts due from Santander UK Group Holdings plc 8 17 Amounts due from subsidiaries 0 — Loans and advances to customers 208,133 202,109 Credit impairment loss allowances on loans and advances to customers (785 ) (751 ) RV and voluntary termination provisions on finance leases (61 ) (69 ) Net loans and advances to customers 207,287 201,289 For movements in expected credit losses, see the Credit risk section of the Risk review. The contractual amount outstanding on financial assets that were written off in the year and are still subject to enforcement activity was £72m (2018: £76m). Finance lease and hire purchase contract receivables may be analysed as follows: Group 2019 2018 Gross investment £m Unearned finance income £m Net investment £m Gross Unearned Net No later than one year 2,650 (371 ) 2,279 3,730 (210 ) 3,520 Later than one year and not later than two years 1,829 (207 ) 1,622 1,839 (148 ) 1,691 Later than two years and not later than three years 1,047 (119 ) 928 1,056 (87 ) 969 Later than three years and not later than four years 473 (54 ) 419 488 (39 ) 449 Later than four years and not later than five years 41 (4 ) 37 32 (4 ) 28 Later than five years 1,116 (137 ) 979 210 (46 ) 164 7,156 (892 ) 6,264 7,355 (534 ) 6,821 The Santander UK group enters into finance leasing arrangements primarily for the financing of motor vehicles and a range of assets for its corporate customers. Included in the carrying value of net investment in finance leases and hire purchase contracts is £1,219m (2018: £1,034m) of unguaranteed RV at the end of the current lease terms, which is expected to be recovered through re-payment, re-financing or sale. Contingent rent income of £nil (2018: £nil, 2017: £5m) was earned during the year, which was classified in ‘Interest and similar income’. Finance income on the net investment in finance leases was £299m (2018: £346m, 2017: £201m). Finance lease receivable balances are secured over the asset leased. The Santander UK group is not permitted to sell or repledge the asset in the absence of default by the lessee. The Directors consider that the carrying amount of the finance lease receivables approximates to their fair value. Included within loans and advances to customers are advances assigned to bankruptcy remote structured entities and Abbey Covered Bonds LLP. These loans provide security to issues of covered bonds and mortgage-backed or other asset-backed securities issued by the Santander UK group. For more, see Note 14.

Securitisations and Covered Bon

Securitisations and Covered Bonds	12 Months Ended
	Dec. 31, 2019
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Securitisations and Covered Bonds	14. SECURITISATIONS AND COVERED BONDS The information in this Note relates to securitisations and covered bonds for consolidated structured entities, used to obtain funding or collateral. It excludes structured entities relating to credit protection vehicles that are described in more detail in Note 19. The Santander UK group uses structured entities to securitise some of the mortgage and other loans to customers that it originates. The Santander UK group also issues covered bonds, which are guaranteed by, and secured against, a pool of the Santander UK group’s mortgage loans transferred to Abbey Covered Bonds LLP. The Santander UK group issues mortgage-backed Loans and advances to customers include portfolios of residential mortgage loans, and receivables derived from credit agreements with retail customers for the purchases of financed vehicles, which are subject to non-recourse finance arrangements. These loans and receivables have been purchased by, or assigned to, structured entities or Abbey Covered Bonds LLP, and have been funded primarily through the issue of mortgage-backed a) Securitisations i) Master trust structures The Santander UK group makes use of master trust structures, whereby a pool of residential mortgage loans is assigned to a trust company by the asset originator. A funding entity acquires a beneficial interest in the pool of assets held by the trust company with funds borrowed from qualifying structured entities, which at the same time issue asset-backed securities to third-party investors or the Santander UK group. Santander UK plc and its subsidiaries receive payments from the securitisation companies in respect of fees for administering the loans, and payment of deferred consideration for the sale of the loans. Santander UK plc and its subsidiaries have no right or obligation to repurchase any securitised loan, except if certain representations and warranties given by Santander UK plc or its subsidiaries at the time of transfer are breached and, in certain cases, if there is a product switch or further advance, if a securitised loan is in arrears for over two months or if a securitised loan does not comply with regulatory requirements. ii) Other securitisation structures The Santander UK group issues notes through pass-through stand-alone vehicles for the securitisation of receivables derived from credit agreements with retail customers for the purchase of financed vehicles. Santander UK plc and its subsidiaries are under no obligation to support any losses that may be incurred by the master trust or other structures, securitisation companies or holders of the securities, and do not intend to provide such further support. b) Covered bonds Santander UK plc also issues covered bonds, which are its direct, unsecured and unconditional obligation. The covered bonds benefit from a guarantee from Abbey Covered Bonds LLP. Santander UK plc makes a term advance to Abbey Covered Bonds LLP equal to the sterling proceeds of each issue of covered bonds. Abbey Covered Bonds LLP uses the proceeds of the term advance to purchase portfolios of residential mortgage loans and their security from Santander UK plc. Under the terms of the guarantee, Abbey Covered Bonds LLP has agreed to pay an amount equal to the guaranteed amounts when the same shall become due for payment but which would otherwise be unpaid by Santander UK plc. c) Analysis of securitisations and covered bonds The Santander UK group’s principal securitisation programmes and covered bond programme, together with the balances of the advances subject to securitisation (or for the covered bond programme assigned) and the carrying value of the notes in issue at 31 December 2019 and 2018 are listed below. Gross assets External notes Notes issued to Santander UK 2019 2018 2019 2018 2019 2018 Mortgage-backed master trust structures: - Holmes 4,262 4,414 1,931 3,182 463 463 - Fosse 3,708 4,646 295 199 1,404 34 - Langton 3,076 3,034 0 — 2,354 2,354 11,046 12,094 2,226 3,381 4,221 2,851 Other asset-backed securitisation structures: - Motor 490 1,055 324 738 197 374 - Auto ABS UK Loans 1,532 1,468 1,229 1,212 368 316 2,022 2,523 1,553 1,950 565 690 Total securitisation programmes 13,068 14,617 3,779 5,331 4,786 3,541 Covered bond programmes: - Euro 35bn Global Covered Bond Programme 23,323 21,578 19,004 18,653 0 — Total securitisation and covered bond programmes 36,391 36,195 22,783 23,984 4,786 3,541 Less: held by Santander UK group: - Euro 35bn Global Covered Bond Programme 0 (539 ) Total securitisation and covered bond programmes (See Note 25) 22,783 23,445 The following table sets out the internal and external issuances and redemptions in 2019 and 2018 for each securitisation and covered bond programme. Internal issuances External issuances Internal redemptions External redemptions 2019 2018 2019 2018 2019 2018 2019 2018 Mortgage-backed master trust structures: - Holmes 0 0.1 0 1.8 0 — 1.1 0.1 - Fosse 1.4 — 0.1 — 0 — 0 0.4 Other asset-backed securitisation structures: - Motor 0 — 0 — 0.2 0.1 0.4 0.1 - Auto ABS UK Loans 0.1 — 0.2 0.4 0.1 — 0.2 0.4 Covered bond programme 0 — 2.9 4.3 0.5 0.5 1.5 1.9 1.5 0.1 3.2 6.5 0.8 0.6 3.2 2.9 Holmes Funding Ltd has a beneficial interest of £2.1bn (2018: £3.2bn) in the residential mortgage loans held by Holmes Trustees Ltd. The remaining share of the beneficial interest in residential mortgage loans held by Holmes Trustees Ltd belongs to Santander UK plc. Fosse Funding (No.1) Ltd has a beneficial interest of £1.7bn (2018: £0.2bn) in the residential mortgage loans held by Fosse Trustee (UK) Ltd. The remaining share of the beneficial interest in residential mortgage loans held by Fosse Trustee (UK) Ltd belongs to Santander UK plc. Langton Funding (No.1) Ltd has a beneficial interest of £2.4bn (2018: £2.3bn) in the residential mortgage loans held by Langton Mortgage Trustee (UK) Ltd. The remaining share of the beneficial interest in residential mortgage loans held by Langton Mortgage Trustee (UK) Ltd belongs to Santander UK plc. The Holmes securitisation companies have cash deposits of £283m (2018: £218m), which have been accumulated to finance the redemption of a number of securities issued by the Holmes securitisation companies. The share of Holmes Funding Ltd in the trust assets is therefore reduced by this amount. Fosse Master Issuer plc has cash deposits of £nil (2018: £nil), which have been accumulated to finance the redemption of a number of securities issued by Fosse Master Issuer plc. Fosse Funding (No.1) Ltd’s beneficial interest in the assets held by Fosse Trustee (UK) Ltd is therefore reduced by this amount.

Transfers of Financial Assets N

Transfers of Financial Assets Not Qualifying for Derecognition	12 Months Ended
	Dec. 31, 2019
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Transfers of Financial Assets Not Qualifying for Derecognition	15. TRANSFERS OF FINANCIAL ASSETS NOT QUALIFYING FOR DERECOGNITION The Santander UK group enters into transactions in the normal course of business by which it transfers recognised financial assets directly to third parties or to structured entities. These transfers may give rise to the full or partial derecognition of those financial assets. Transferred financial assets that do not qualify for derecognition consist of (i) securities held by counterparties as collateral under repurchase agreements, (ii) securities lent under securities lending agreements, and (iii) loans that have been securitised under arrangements by which the Santander UK group retains a continuing involvement in such transferred assets. As the substance of the sale and repurchase and securities lending transactions is secured borrowings, the asset collateral continues to be recognised in full and the related liability reflecting the Santander UK group’s obligation to repurchase the transferred assets for a fixed price at a future date is recognised in deposits from banks or customers, as appropriate. As a result of these transactions, the Santander UK group is unable to use, sell or pledge the transferred assets for the duration of the transaction. The Santander UK group remains exposed to interest rate risk and credit risk on these pledged instruments. The counterparty’s recourse is not limited to the transferred assets. The Santander UK group securitisation transfers do not qualify for derecognition. The Santander UK group remains exposed to credit risks arising from the mortgage loans or credit agreements and has retained control of the transferred assets. Circumstances in which the Santander UK group has continuing involvement in the transferred assets may include retention of servicing rights over the transferred assets, entering into a derivative transaction with the securitisation vehicle, retaining an interest in the securitisation vehicle or providing a cash reserve fund. Where the Santander UK group has continuing involvement it continues to recognise the transferred assets to the extent of its continuing involvement and recognises an associated liability. The net carrying amount of the transferred assets and associated liabilities reflects the rights and obligations that the Santander UK group has retained. The following table analyses the carrying amount of financial assets that did not qualify for derecognition and their associated financial liabilities: Group 2019 2018 Nature of transaction Assets Liabilities Assets Liabilities Sale and repurchase agreements 7,592 (6,739 ) 7,642 (7,188 ) Securities lending agreements 195 (143 ) 144 (120 ) Securitisations (See Notes 14 and 25) 9,992 (3,779 ) 11,583 (5,331 ) 17,779 (10,661 ) 19,369 (12,639 )

Reverse Repurchase Agreements -

Reverse Repurchase Agreements - Non Trading	12 Months Ended
	Dec. 31, 2019
Reverse repurchase agreements - non-trading [member]
Statement [Line Items]
Reverse Repurchase Agreements - Non Trading	16. REVERSE REPURCHASE AGREEMENTS – NON TRADING Group 2019 2018 Agreements with banks 2,161 3,254 Agreements with customers 21,475 17,873 23,636 21,127

Other Financial Assets At Amort

Other Financial Assets At Amortised Cost	12 Months Ended
	Dec. 31, 2019
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Other Financial Assets At Amortised Cost	17. OTHER FINANCIAL ASSETS AT AMORTISED COST Group 2019 2018 Asset backed securities 532 720 Debt securities 6,524 6,509 7,056 7,229 A significant portion of the debt securities are held in our eligible liquidity pool and consist mainly of government bonds and covered bonds. Detailed disclosures can be found in the ‘Liquidity risk’ section of the Risk review.

Financial Assets At Fair Value

Financial Assets At Fair Value Through Other Comprehensive Income	12 Months Ended
	Dec. 31, 2019
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Financial Assets At Fair Value Through Other Comprehensive Income	18. FINANCIAL ASSETS AT FAIR VALUE THROUGH OTHER COMPREHENSIVE INCOME Group 2019 2018 Debt securities 9,691 13,229 Loans and advances to customers 56 73 9,747 13,302 A significant portion of the debt securities are held in our eligible liquidity pool and consist mainly of government bonds and covered bonds. Detailed disclosures can be found in the ‘Liquidity risk’ section of the Risk review.

Interests in Other Entities

Interests in Other Entities	12 Months Ended
	Dec. 31, 2019
Investments accounted for using equity method [abstract]
Interests in Other Entities	19. INTERESTS IN OTHER ENTITIES Group 2019 2018 Subsidiaries 0 — Joint ventures 117 88 117 88 The Santander UK group consists of a parent company, Santander UK plc, incorporated and domiciled in the UK and a number of subsidiaries and joint ventures held directly and indirectly by the Company. The Company has no individually significant associates. Details of subsidiaries, joint ventures and associates are set out in the Shareholder Information section. a) Interests in subsidiaries The Company holds directly or indirectly 100% of the issued ordinary share capital of its principal subsidiaries. All companies operate principally in their country of incorporation or registration. Subsidiaries with significant non-controlling interests The only subsidiary with significant non-controlling interests is PSA Finance UK Limited, which operates in the UK. In 2019 and 2018, the proportion of ownership interests and voting rights held by non-controlling interests was 50%. 2019 2018 Profit attributable to non-controlling 19 22 Accumulated non-controlling 160 151 Dividends paid to non-controlling 12 22 Summarised financial information: - Total assets 3,228 3,289 - Total liabilities 2,905 2,987 - Profit for the year 40 43 - Total comprehensive income for the year 40 43 Interests in consolidated structured entities Structured entities are formed by Santander UK to accomplish specific and well-defined objectives. Santander UK consolidates these structured entities when the substance of the relationship indicates control, as described in Note 1. In addition to the structured entities disclosed in Note 14 which are used for securitisation and covered bond programmes, the only other structured entities consolidated by Santander UK are described below. All the external assets and liabilities in these entities are included in the financial statements and in relevant Notes. Other than as set out below, no significant judgements were required with respect to control or significant influence. i) Guaranteed Investment Products 1 PCC Limited (GIP) GIP is a Guernsey-incorporated, ii) Motor Securities 2018-1 Designated Activity Company (Motor 2018) Motor 2018 is a credit protection entity, and a Designated Activity Company limited by shares, incorporated in Ireland. It has issued a series of credit linked notes varying in seniority which reference portfolios of Santander UK group loans. Concurrently, these entities sell credit protection to Santander UK in respect of the referenced loans and, in return for a fee, are liable to make protection payments to Santander UK upon the occurrence of a credit event in relation to any of the referenced loans. The entity has been consolidated as Santander UK holds a variable interest by retaining the junior tranche of notes issued by the entity. b) Interests in joint ventures Santander UK does not have any individually material interests in joint ventures. As set out in the accounting policies in Note 1, interests in joint ventures are accounted for using the equity method. In 2019, Santander UK’s share in the profit after tax of its joint ventures was £30m (2018: £15m) before elimination of transactions between Santander UK and the joint ventures. At 31 December 2019, the carrying amount of Santander UK’s interest was £117m (2018: £88m). At 31 December 2019 and 2018, the joint ventures had no commitments and contingent liabilities. c) Interests in unconsolidated structured entities Structured entities sponsored by the Santander UK group Santander UK has interests in structured entities which it sponsors but does not control. Santander UK considers itself a sponsor of a structured entity when it facilitates the establishment of the structured entity. Other than as set out below, no significant judgements were required with respect to control or significant influence. The structured entities sponsored but not consolidated by Santander UK are as follows. i) Santander (UK) Common Investment Fund The Santander (UK) Common Investment Fund (the Fund) is a common investment fund that was established to hold the assets of the Santander (UK) Group Pension Scheme. The Fund is not consolidated by Santander UK, but its assets of £12,446m (2018: £11,433m) are accounted for as part of the defined benefit assets and obligations recognised on Santander UK’s balance sheet. For more on the Fund, see Note 28. As the Fund holds the assets of the pension scheme, it is outside the scope of IFRS 10. Santander UK’s maximum exposure to loss is the carrying amount of the assets held. ii) Credit protection entities Santander UK has established four (2018: three) unconsolidated credit protection entities, which are Designated Activity Companies limited by shares, incorporated in Ireland. Each entity has issued a series of credit linked notes varying in seniority which reference portfolios of Santander UK group loans. Concurrently, these entities sell credit protection to Santander UK in respect of the referenced loans and, in return for a fee, are liable to make protection payments to Santander UK upon the occurrence of a credit event in relation to any of the referenced loans. Senior credit linked notes, which amounted to £3,766m (2018: £3,053m), are issued to, and held by, Santander UK. Junior credit linked notes, which amounted to £825m (2018: £408m), are all held by third party investors and suffer the first losses incurred in the referenced portfolios. Funds raised by the sale of the credit linked notes are deposited with Santander UK as collateral for the credit protection. £110m (2018: £3,053m) of the senior credit linked notes are presented on a gross basis and included within ‘Other financial assets at fair value through profit or loss’ on the balance sheet (see Note 12). Deposits and associated guarantees relating to the senior notes are included within ‘Other financial liabilities at fair value through profit or loss’ (see Note 21). The remainder of the senior credit linked notes, along with the deposits and associated guarantees, are presented on a net basis, to reflect a legal right of set-off The entities are not consolidated by Santander UK because the third party investors have the exposure, or rights, to all of the variability of returns from the performance of the entities. No assets are transferred to, or income received from, these vehicles. Since the credit linked notes (including those held by Santander UK) are fully cash collateralised, Santander UK’s maximum exposure to loss is equal to any unamortised fees paid to the credit protection entities in connection with the credit protection outlined above. Structured entities not sponsored by the Santander UK group Santander UK also has interests in structured entities which it does not sponsor or control. These consist of holdings of mortgage and other asset backed securities issued by entities that were established and/or sponsored by other unrelated financial institutions. These securities comprise the asset backed securities included in Note 17. Management has concluded that the Santander UK group has no control or significant influence over these entities and that the carrying value of the interests held in these entities represents the maximum exposure to loss.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2019
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Intangible Assets	20. INTANGIBLE ASSETS a) Goodwill Group Cost Accumulated Net book At 31 December 2018, 1 January 2019 and 31 December 2019 1,269 (66 ) 1,203 Impairment of goodwill In 2019 and 2018, no impairment of goodwill was recognised. Impairment testing in respect of goodwill allocated to each cash-generating unit (CGU) is performed annually or more frequently if there are impairment indicators present. For the purpose of impairment testing, the CGUs are based on customer groups within the relevant business divisions. The cash flow projections for each CGU are based on the five-year plan prepared for regulatory purposes, based on Santander UK’s 3-Year 3-Year The rate used to discount the cash flows is based on a pre-tax Based on the conditions at the balance sheet date, management determined that a reasonably possible change in any of the key assumptions described above would not cause an impairment of goodwill to be recognised. The following CGUs include in their carrying values goodwill that comprises the goodwill reported by Santander UK. The CGUs do not carry on their balance sheets any other intangible assets with indefinite useful lives. The calculations have been based on value in use using cash flows based on the five-year plan. Goodwill Discount rate Growth rate (1) CGU 2019 2018 2019 2018 2019 2018 Personal financial services 1,169 1,169 9.8 10.5 3 2 Private banking 30 30 9.8 10.5 4 2 Other 4 4 9.8 10.5 3 2 1,203 1,203 (1) Average growth rate based on the five-year plan for the first five years and a growth rate of 1.6% (2018: 1.6%) applied thereafter. In 2019, the discount rate decreased by 0.7 percentage points to 9.8% (2018: 10.5%). The decrease reflected changes in current market and economic conditions. In 2019, the change in growth rates reflected Santander UK’s updated strategic priorities in the context of forecast economic conditions. b) Other intangibles Group Cost Accumulated Net book At January 2019 1,090 (485 ) 605 Additions 173 0 173 Disposals (14 ) 0 (14 ) Charge 0 (191 ) (191 ) Impairment 0 (10 ) (10 ) At 31 December 2019 1,249 (686 ) 563 At 1 January 2018 962 (423 ) 539 Additions 204 — 204 Write offs (76 ) 76 — Charge — (138 ) (138 ) Sales — — — At 31 December 2018 1,090 (485 ) 605 Other intangibles consist of computer software.

Other Financial Liabilities at

Other Financial Liabilities at Fair Value Through Profit or Loss	12 Months Ended
	Dec. 31, 2019
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Other Financial Liabilities at Fair Value Through Profit or Loss	21. OTHER FINANCIAL LIABILITIES AT FAIR VALUE THROUGH PROFIT OR LOSS Group 2019 £m 2018 US$30bn Euro Medium Term Note Programme 159 165 Structured Notes Programmes 809 696 Eurobonds 137 129 Structured deposits 435 133 Collateral and associated financial guarantees 173 3,053 Repurchase agreements – non trading 0 2,110 1,713 6,286 For the Santander UK group, all (2018: all) of the other financial liabilities at fair value through profit or loss were designated as such. Collateral and associated financial guarantees in the table above represent collateral received, together with associated credit protection guarantees, in respect of the proceeds of the retained senior tranches of credit linked notes described in Note 12. The financial guarantees are valued using the same parameters as the related credit linked notes, such that changes in the respective valuations are offset exactly, and there is no charge or credit to the income statement. In 2019 £2.1bn of cash deposits, which were previously included within collateral and associated financial guarantees in the table above, were presented on a net basis. This followed a deed of amendment, including a legal right of set-off Gains and losses arising from changes in the credit spread of securities issued by the Santander UK group reverse over the contractual life of the debt, provided that the debt is not repaid at a premium or a discount. The net loss during the year attributable to changes in the Santander UK group’s own credit risk on the above securities was £77m (2018: £84m gain, 2017: £29m loss). The cumulative net gain attributable to changes in the Santander UK group’s own credit risk on the above securities at 31 December 2019 was £nil (2018: £77m). At 31 December 2019, the amount that would be required to be contractually paid at maturity of the securities above was £4m lower (2018: £128m lower) than the carrying value.

Deposits by Customers

Deposits by Customers	12 Months Ended
	Dec. 31, 2019
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Deposits by Customers	22. DEPOSITS BY CUSTOMERS Group 2019 £m 2018 Current and demand accounts 89,221 86,207 Savings accounts (1) 65,835 66,039 Time deposits 16,680 15,485 Amounts due to other Santander UK Group Holdings plc subsidiaries 44 83 Amounts due to Santander UK Group Holdings plc (2) 8,869 9,206 Amounts due to fellow Banco Santander subsidiaries and joint ventures 1,234 1,070 181,883 178,090 (1) Includes equity index-linked deposits of £1,139m (2018: £1,176m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,139m and £18m (2018: £1,176m and £28m) respectively. (2) Includes downstreamed funding from our immediate parent company Santander UK Group Holdings plc.

Deposits by Banks

Deposits by Banks	12 Months Ended
	Dec. 31, 2019
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Deposits by Banks	23. DEPOSITS BY BANKS Group 2019 £m 2018 Items in the course of transmission 337 262 Deposits held as collateral 2,169 4,048 Other deposits (1) 11,847 12,891 Amounts due to Santander UK subsidiaries 0 20 14,353 17,221 (1) Includes drawdown from the TFS of £10.8bn (2018: £10.8bn).

Repurchase Agreements - Non Tra

Repurchase Agreements - Non Trading	12 Months Ended
	Dec. 31, 2019
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Repurchase Agreements - Non Trading	24. REPURCHASE AGREEMENTS – NON TRADING Group 2019 £m 2018 Agreements with banks 10,227 5,865 Agreements with customers 8,059 5,045 18,286 10,910

Debt Securities in Issue

Debt Securities in Issue	12 Months Ended
	Dec. 31, 2019
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Debt Securities in Issue	25. DEBT SECURITIES IN ISSUE Group 2019 £m 2018 Medium-term notes: - US$30bn Euro Medium Term Note Programme 4,679 7,229 - Euro 30bn Euro Medium Term Note Programme 1,896 1,975 - US SEC-registered 5,891 7,649 - US$20bn Commercial Paper Programmes 3,014 3,131 15,480 19,984 Euro 35bn Global Covered Bond Programme (See Note 14) 19,004 18,114 Certificates of deposit 2,806 3,221 Credit linked notes 60 42 Securitisation programmes (See Note 14) 3,779 5,331 41,129 46,692

Subordinated Liabilities

Subordinated Liabilities	12 Months Ended
	Dec. 31, 2019
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Subordinated Liabilities	26. SUBORDINATED LIABILITIES Group 2019 2018 £325m Sterling Preference Shares 344 344 Undated subordinated liabilities 581 574 Dated subordinated liabilities 2,603 2,683 3,528 3,601 The above securities will, in the event of the winding up of the issuer, be subordinated to the claims of depositors and all other creditors of the issuer, other than creditors whose claims rank equally with, or are junior to, the claims of the holders of the subordinated liabilities. The subordination amongst each of the subordinated liabilities upon a winding up of the issuer is specified in their respective terms and conditions. In 2019 and 2018, the Santander UK group had no defaults of principal, interest or other breaches with respect to its subordinated liabilities. No repayment or purchase by the issuer of the subordinated liabilities may be made prior to their stated maturity without the consent of the PRA. Undated subordinated liabilities Group First call date 2019 £m 2018 10.0625% Exchangeable capital securities n/a 205 205 7.375% 20 Year Step-up 2020 15 16 7.125% 30 Year Step-up 2030 361 353 581 574 In common with other debt securities issued by Santander UK group companies and notwithstanding the issuer’s first call dates in the table above, in the event of certain tax changes affecting the treatment of payments of interest on subordinated liabilities in the UK, the 7.375% 20 Year Step-up Step-up The 10.0625% Exchangeable capital securities are exchangeable into fully paid 10.375% non-cumulative non-redeemable Dated subordinated liabilities Group Maturity 2019 £m 2018 5% Subordinated notes (US$1,500m) 2023 1,132 1,173 4.75% Subordinated notes (US$1,000m) 2025 763 791 7.95% Subordinated notes (US$1,000m) 2029 280 278 6.50% Subordinated notes 2030 40 38 5.875% Subordinated notes 2031 9 9 5.625% Subordinated notes (US$500m) 2045 379 394 2,603 2,683 The dated subordinated liabilities are redeemable in whole at the option of Santander UK plc in the event of certain tax changes affecting the treatment of payments of interest on the subordinated liabilities in the UK, at their principal amount together with any accrued interest.

Provisions

Provisions	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Provisions	27. PROVISIONS Group Conduct remediation PPI Other FSCS and Property Off-balance Regulatory Total At 31 December 2018 246 30 45 37 56 95 509 Adoption of IFRS 16 (see Note 1) — — — 17 — — 17 At 1 January 2019 246 30 45 54 56 95 526 Additional provisions (see Note 8) 169 0 86 44 22 166 487 Provisions released (see Note 8) 0 0 (5 ) (21 ) 0 (4 ) (30 ) Utilisation and other (1) (226 ) (5 ) (90 ) (18 ) 0 (82 ) (421 ) Recharge (2) 0 0 10 0 0 0 10 At 31 December 2019 189 25 46 59 78 175 572 To be settled: - Within 12 months 189 18 46 43 78 171 545 - In more than 12 months 0 7 0 16 0 4 27 189 25 46 59 78 175 572 (1) Utilisation and other included a transfer from ‘PPI’ to ‘Regulatory and other’ in respect of an ongoing legal dispute. No further information has been provided on the basis it would be seriously prejudicial. (2) This relates to a recharge in respect of the UK Bank Levy paid on behalf of other UK entities of Banco Santander SA. a) Conduct remediation The amounts in respect of conduct remediation comprise the estimated cost of making redress payments, including related costs, with respect to the past sales or administration of products. The provision for conduct remediation represents management’s best estimate of the anticipated costs of related customer contact and/or redress, including related costs. (i) Payment Protection Insurance (PPI) The FCA set a deadline of 29 August 2019 for PPI complaints and delivered a nationwide communications campaign to raise awareness of this deadline among consumers. In line with industry experience, we received unprecedented volumes of information requests in August 2019 and saw a significant spike in both these requests and complaints in the final days prior to the complaint deadline, with the processing of these claims ongoing. PPI assumptions A provision for conduct remediation has been recognised to represent management’s best estimate of Santander UK’s liability in respect of misselling of PPI policies. Given the passing of the FCA’s August 2019 time bar, the level of judgment required by management in determining appropriate assumptions has reduced. At 31 December 2019, the key assumption in calculating the provision was around the estimated number of customer complaints that would be received in respect of customers with successful information requests that were still eligible to submit a complaint. The uphold rates are informed by historical experience and the average cost of redress can be predicted reasonably accurately given that management is dealing with a high volume and reasonably homogenous population. Cumulative complaints from the inception of the PPI complaints process to 31 December 2019, regardless of the likelihood of Santander UK incurring a liability and including the specific PPI portfolio of complaints referred to below, were 3.5m. This includes c.327,000 that were still being reviewed. Future expected claims were c.49,000. For every additional 10,000 inbound PPI complaints, we would expect an additional charge in the order of £4m. 2019 compared to 2018 In 2019, we charged an additional £169m in respect of PPI: – In Q2 2019 we reported an additional provision of £70m reflecting an increase in PPI claim volumes, additional industry activities and having considered guidance provided by the FCA and our specific approach to PPI claims, in advance of the PPI claims deadline on 29 August 2019. – In Q3 2019, and in line with industry experience, we received unprecedented volumes of information requests in August 2019 and saw a significant spike in both these requests and complaints in the final days prior to the complaint deadline. Our best estimate of the additional provision required was £99m. (ii) Other products A provision for conduct remediation has also been recognised in respect of sales of other products. A number of uncertainties remain as to the eventual costs with respect to conduct remediation in respect of these products given the inherent difficulties in determining the number of customers involved and the amount of any redress to be provided to them. The remaining provision for other conduct was £25m (2018: £30m), which primarily related to the sale of interest rate derivatives. b) Financial Services Compensation Scheme (FSCS) and Bank Levy (i) FSCS The FSCS is the UK’s independent statutory compensation fund for customers of authorised financial services firms and pays compensation if a firm is unable to pay claims against it. The FSCS is funded by levies on the industry (and recoveries and borrowings where appropriate). Following the default of a number of deposit takers since 2008, the FSCS borrowed funds from HM Treasury to meet the compensation costs for customers of those firms. The remaining debt due to the FSCS, that related to the failure of Bradford & Bingley plc, has now been repaid. This has enabled the FSCS to make a corresponding repayment of the balance of its loan to HM Treasury. As a result, the opening provision of £4m was released in 2019 (2018: £4m release, 2017: £1m charge), to bring the balance to £nil (2018: £4m). (ii) UK Bank Levy In addition to changes in UK corporation tax rates, Finance (No.2) Act 2015 reduced the UK Bank Levy rate from 0.21% via subsequent annual reductions to 0.10% from 1 January 2021. As a result, a rate of 0.15% applies for 2019 (2018: 0.16%). The cost of the UK Bank Levy for 2019 was £86m (2018: £69m, 2017: £92m). The Santander UK group paid £90m in 2019 (2018: £86m) and provided for a liability of £46m at 31 December 2019 (2018: £40m). c) Property Property provisions include vacant property provisions and property dilapidation provisions for leased properties within the scope of IFRS 16. Vacant property provisions are made by reference to an estimate of any expected sub-let Property provisions were impacted by £40m of transformation charges in 2019. These relate to a multi-year project to deliver on our strategic priorities and enhance efficiency in order for us to better serve our customers and meet our medium-term targets. These charges largely related to restructuring of our branch network associated with the announcement made in 2019. d) Off-balance Provisions include expected credit losses relating to guarantees given to third parties and undrawn loan commitments. e) Regulatory and other Regulatory and other provisions principally comprised amounts in respect of regulatory charges (including fines), operational loss and operational risk provisions, restructuring charges and litigation and related expenses. A number of uncertainties exist with respect to these provisions given the uncertainties inherent in operational, restructuring and litigation matters that affect the amount and timing of any potential outflows with respect to which provisions have been established. These provisions are reviewed at least quarterly. At 31 December 2019 the balance included an amount of £68m (2018: £58m) that arose from a systems related historical issue identified by Santander UK, relating to compliance with certain requirements of the Consumer Credit Act. This provision is based on detailed reviews of relevant systems related to consumer credit business operations, supported by external legal and regulatory advice, and reflects our best estimate at 31 December 2019 of potential costs in respect of the identified issue. As detailed in Note 29, there are aspects of the issue which remain under review. The balance also included an amount in respect of our best estimate of liability relating to a legal dispute regarding allocation of responsibility for a specific PPI portfolio of complaints, further described in Note 29. No further information regarding the best estimate is provided on the basis that it would be seriously prejudicial to Santander UK’s interests in connection with the dispute. Regulatory and other provisions charged in 2019 included £65m of transformation charges in 2019, relating to the multi-year project described above in ‘c) Property’. In addition to charges largely related to the restructuring of our branch network, further charges were largely associated with the announced plans to reshape our Corporate & Commercial Banking business. Regulatory and other provisions charged in 2019 also included £68m of operational loss and operational risk provisions.

Retirement Benefit Plans

Retirement Benefit Plans	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Retirement Benefit Plans	28. RETIREMENT BENEFIT PLANS The amounts recognised in the balance sheet were as follows: Group 2019 £m 2018 Assets/(liabilities) Funded defined benefit pension scheme – surplus 669 842 Funded defined benefit pension scheme – deficit (239 ) (75 ) Unfunded pension and post retirement medical benefits (41 ) (39 ) Total net assets 389 728 Remeasurement losses/(gains) recognised in other comprehensive income during the year were as follows: Group 2019 £m 2018 2017 Pension remeasurement 522 (470 ) 103 a) Defined contribution pension plans The Santander UK group operates a number of defined contribution pension plans. The assets of the defined contribution pension plans are held and administered separately from those of the Santander UK group. The majority of employees are members of a defined contribution Master Trust, LifeSight. This Master Trust is the plan into which eligible employees are enrolled automatically. The assets of the LifeSight Master Trust are held in separate trustee-administered funds. An expense of £66m (2018: £67m, 2017: £54m) was recognised for defined contribution plans in the year and is included in staff costs classified within operating expenses (see Note 6). None of this amount was recognised in respect of key management personnel for the years ended 31 December 2019, 2018 and 2017. b) Defined benefit pension schemes The Santander UK group operates a number of defined benefit pension schemes. The main scheme is the Santander (UK) Group Pension Scheme (the Scheme). It comprises seven legally segregated sections. The Scheme covers 11% (2018: 13%) of the Santander UK group’s current employees and is a funded defined benefit scheme which is closed to new members. The corporate trustee of the Scheme is Santander (UK) Group Pension Scheme Trustees Limited (the Trustee), a private limited company incorporated in 1996 and a wholly-owned subsidiary of Santander UK Group Holdings plc. The principal duty of the Trustee is to act in the best interests of the members of the Scheme. The Trustee board comprises five (2018: six) Directors selected by Santander UK Group Holdings plc, plus five (2018: six) member-nominated Directors selected from eligible members who apply for the role. The assets of the funded schemes including the Scheme are held independently of the Santander UK group’s assets in separate trustee administered funds. Investment strategy across the sections of the Scheme remains under regular review. Investment decisions are delegated by the Trustee to a common investment fund, managed by Santander (CF Trustee) Limited, a private limited company owned by five Trustee directors, three appointed by Santander UK plc and two by the Trustee. The Santander (CF Trustee) Limited directors’ principal duty, within the investment powers delegated to them, is to act in the best interest of the members of the Scheme. Ultimate responsibility for investment policy and strategy rests with the Trustee of the Scheme who is required under the Pensions Act 2004 to prepare a statement of investment principles. The defined benefit pension schemes expose the Santander UK group to risks such as investment risk, interest rate risk, longevity risk and inflation risk. The Santander UK group does not hold material insurance policies over the defined benefit pension schemes and has not entered into any significant transactions with them. Formal actuarial valuations of the assets and liabilities of the defined benefit schemes are carried out on at least a triennial basis by independent professionally-qualified actuaries and valued for accounting purposes at each balance sheet date. Each scheme’s trustee is responsible for the actuarial valuations and in doing so considers, or relies in part on, a report of a third-party expert. The latest formal actuarial valuation for the Scheme at 31 March 2019 was finalised in August 2019, with a deficit to be funded of £1,136m. The next triennial funding valuation will be at 31 March 2022. Any funding surpluses can be recovered by Santander UK plc from the Scheme through refunds as the Scheme is run off over time or could be used to pay for the cost of benefits which are accruing. The total amount charged to the income statement was as follows: Group 2019 £m 2018 2017 Net interest income (23 ) (7 ) (5 ) Current service cost 34 41 31 Past service and GMP costs 1 41 1 Administration costs 8 8 8 20 83 35 On 26 October 2018, the High Court handed down a judgement concluding that defined benefit schemes should equalise pension benefits for men and women in relation to GMP and concluded on the methods that were appropriate. The estimated increase in liabilities at the date of the judgement was £40m and was based on a number of assumptions and the actual impact may be different. This was reflected in the income statement and in the closing net accounting surplus of the Scheme in 2018. The allowance included in the Scheme liabilities at 31 December 2019 increased by £5m to £45m (2018: £40m) to reflect the latest assumptions. This change was recognised in other comprehensive income. We continue to await implementation guidance on the judgement from the UK Government and HMRC. The amounts recognised in other comprehensive income were as follows: Group 2019 2018 2017 Return on plan assets (excluding amounts included in net interest expense) (855 ) 246 (435 ) Actuarial losses/(gains) arising from changes in demographic assumptions 42 (56 ) (151 ) Actuarial (gains)/losses arising from experience adjustments (42 ) 15 (11 ) Actuarial losses/(gains) arising from changes in financial assumptions 1,377 (675 ) 700 Pension remeasurement 522 (470 ) 103 Movements in the present value of defined benefit scheme obligations were as follows: Group 2019 £m 2018 At 1 January (10,804 ) (11,583 ) Current service cost paid by Santander UK plc (22 ) (27 ) Current service cost paid by subsidiaries (12 ) (14 ) Current service cost paid by fellow Banco Santander subsidiaries 0 — Interest cost (308 ) (282 ) Employer salary sacrifice contributions (9 ) (6 ) Past service cost (1 ) (1 ) GMP equalisation cost 0 (40 ) Remeasurement due to actuarial movements arising from: - Changes in demographic assumptions (42 ) 56 - Experience adjustments 42 (15 ) - Changes in financial assumptions (1,377 ) 675 Benefits paid 375 433 At 31 December (12,158 ) (10,804 ) Movements in the fair value of the schemes’ assets were as follows: Group 2019 2018 At 1 January 11,532 11,746 Interest income 331 289 Contributions paid by employer and scheme members 212 184 Contributions paid by fellow Banco Santander subsidiaries 0 — Administration costs paid (8 ) (8 ) Return on plan assets (excluding amounts included in net interest expense) 855 (246 ) Benefits paid (375 ) (433 ) At 31 December 12,547 11,532 The composition and fair value of the schemes’ assets by category was: Group Quoted prices Prices not Total 2019 £m % £m % £m % UK equities 128 1 0 0 128 1 Overseas equities 1,742 14 933 7 2,675 21 Corporate bonds 1,333 11 444 4 1,777 15 Government fixed interest bonds 2,710 22 0 0 2,710 22 Government index-linked bonds 4,543 35 0 0 4,543 35 Property 0 0 1,332 11 1,332 11 Derivatives 0 0 94 1 94 1 Cash 0 0 984 8 984 8 Repurchase agreements (1) 0 0 (3,263 ) (26 ) (3,263 ) (26 ) Other 0 0 1,567 12 1,567 12 10,456 83 2,091 17 12,547 100 2018 UK equities 159 1 — — 159 1 Overseas equities 1,854 16 878 8 2,732 24 Corporate bonds 1,536 13 311 3 1,847 16 Government fixed interest bonds 2,636 23 — — 2,636 23 Government index-linked bonds 4,248 37 — — 4,248 37 Property — — 1,143 10 1,143 10 Derivatives — — 65 — 65 — Cash — — 662 6 662 6 Repurchase agreements (1) — — (2,981 ) (26 ) (2,981 ) (26 ) Other — — 1,021 9 1,021 9 10,433 90 1,099 10 11,532 100 (1) Sale and repurchase agreements net of purchase and resale agreements. Scheme assets are stated at fair value based upon quoted prices in active markets except for property, property funds, derivatives, private equity and those classified under ‘Other’. The ‘Other’ category includes of asset-backed securities, annuities and hedge funds. The property funds were valued using market valuations prepared by an independent expert. Investments in absolute return funds that are included in the ‘Other’ category, and investments in foreign exchange, inflation, equity and interest rate derivatives that are included in the ‘Derivatives’ category, were valued by investment managers by reference to market observable data. Private equity funds were valued by reference to their latest published accounts whilst the insured annuities were valued by actuaries based on the liabilities insured. A strategy is in place to manage interest rate and inflation risk relating to the liabilities. The Scheme also has in place an equity collar to manage equity risk and hedges a proportion of its foreign exchange exposure to manage currency risk. At 31 December 2019, the equity collar had a notional value of £1,560m (2018: £1,795m) and the currency futures had a notional value of £2,079m (2018: £2,112m). In 2018, the level of interest rate hedging in the Scheme was increased, and the Scheme moved from using LIBOR-based instruments to gilt-backed instruments, including through the use of total return swaps and repurchase agreements. In addition, repurchase agreements were entered into by the Scheme over an equivalent value of Government fixed interest and index-linked bonds and are therefore included in the table above. The Santander UK group’s pension schemes did not directly hold any equity securities of the Company or any of its related parties at 31 December 2019 and 2018. The Santander UK group’s pension scheme assets do not include any property or other assets that are occupied or used by the Santander UK group. Funding In August 2019, in compliance with the Pensions Act 2004, the Trustee and the Santander UK group agreed to a new recovery plan in respect of the Scheme and schedule of contributions following the finalisation of the 31 March 2019 actuarial valuation. The funding target for this actuarial valuation is for the Scheme to have sufficient assets to make payments to members in respect of the accrued benefits as and when they fall due. In accordance with the terms of the Trustee agreement in place at the time, the Santander UK group contributed £203m in 2019 (2018: £176m) to the Scheme, of which £153m (2018: £123m) was in respect of agreed deficit repair contributions. The agreed schedule of the Santander UK group’s remaining contributions to the Scheme broadly comprises contributions of £187m each year from 30 September 2019 to 31 March 2026. In addition, the Santander UK group has agreed to pay further contingent contributions should the funding position have fallen behind plan. Actuarial assumptions The principal actuarial assumptions used for the defined benefit schemes were: Group 2019 % 2018 2017 To determine benefit obligations: - Discount rate for scheme liabilities 2.1 2.9 2.5 - General price inflation 3.0 3.2 3.2 - General salary increase 1.0 1.0 1.0 - Expected rate of pension increase 2.9 2.9 2.9 Years Years Years Longevity at 60 for current pensioners, on the valuation date: - Males 27.3 27.3 27.4 - Females 29.8 30.1 30.1 Longevity at 60 for future pensioners currently aged 40, on the valuation date: - Males 28.9 28.7 28.9 - Females 31.3 31.6 31.7 Discount rate for scheme liabilities The rate used to discount the retirement benefit obligation for accounting purposes is based on the annual yield at the balance sheet date of high-quality corporate bonds on that date. There are only a limited number of higher quality Sterling-denominated corporate bonds, particularly those that are longer-dated. Therefore, in order to set a suitable discount rate, we need to construct a corporate bond yield curve. The model which we use for constructing the curve uses corporate bond data but excludes most convertible and asset-backed bonds. The curve is then constructed from this data by extrapolating the horizontal forward curve from 30 years, with the level of this forward rate being the average of the fitted forward rates over the 15 to 30 year range. When considering an appropriate assumption, we project forward the expected cash flows of the Scheme and adopt a single equivalent cash flow weighted discount rate, subject to management judgement. General price inflation Consistent with our discount rate methodology, we set the inflation assumption using the expected cash flows of the Scheme, fitting them to an inflation curve to give a weighted average inflation assumption. We then deduct an inflation risk premium to reflect the compensation holders of fixed rate instruments expect to receive for taking on the inflation risk. This premium is subject to a cap, to better reflect management’s view of inflation expectations. General salary increase From 1 March 2015, a cap on pensionable pay increases of 1% each year was applied to staff in the Scheme. Expected rate of pension increase The pension increase assumption methodology uses a stochastic model, which is calibrated to consider both the observed historical volatility term structure and derivative pricing. The model allows for the likelihood that high or low inflation in one-year Mortality assumptions The mortality assumptions are based on an independent analysis of the Scheme’s actual mortality experience, carried out as part of the triennial actuarial valuation, together with recent evidence from the Continuous Mortality Investigation. An allowance is then made for expected future improvements to life expectancy based on the Continuous Mortality Investigation Tables. Following this review the S3 Medium all pensioner mortality table was adopted with appropriate adjustments to reflect the actual mortality experience. For future improvements, the CMI 2018 projection model was adopted, with model parameters selected having had regard to the Scheme’s membership profile with an initial addition to improvements of 0.15% per annum, together with a long-term rate of future improvements to life expectancy of 1.25% for male and female members. Both of these are published by the Continuous Mortality Investigation. In 2019, the methodology for setting the demographic assumptions was changed to better represent current expectations, following a review carried out by the Trustee as part of the 2019 triennial valuation and a separate review conducted on early retirement experience. These reviews resulted in changes in the assumptions for commutation, family statistics and early retirement, in addition to the changes described above for mortality. At 31 December 2019, these changes combined had a negative impact of £44m on the accounting surplus. Actuarial assumption sensitivities The sensitivity analyses below have been determined based on reasonably possible changes of the respective assumptions occurring at the end of the reporting period, while holding all other assumptions constant. (Decrease)/ Assumption Change in pension obligation at year-end 2019 £m 2018 Discount rate 25 bps increase (564 ) (483 ) General price inflation 25 bps increase 407 350 Mortality Each additional year of longevity assumed 419 335 The sensitivity analysis presented above may not be representative of the actual change in the defined benefit obligation as it is unlikely that the changes in assumptions would occur in isolation of one another as some of the assumptions may be correlated. Furthermore, in presenting the sensitivity analysis, the present value of the defined benefit obligation has been calculated using the projected unit credit method at the end of the reporting period, which is the same method used to calculate the defined benefit obligation recognised in the balance sheet. There were no changes in the methods and assumptions used in preparing the sensitivity analyses from prior years. The benefits expected to be paid in each of the next five years, and in the aggregate for the five years thereafter are: Year ending 31 December £m 2020 332 2021 308 2022 330 2023 343 2024 364 Five years ending 2029 2,083 The average duration of the defined benefit obligation at 31 December 2019 was 18.8 years (2018: 19.1 years).

Contingent Liabilities and Comm

Contingent Liabilities and Commitments	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Contingent Liabilities and Commitments	29. CONTINGENT LIABILITIES AND COMMITMENTS Group 2019 2018 Guarantees given to third parties 1,198 1,610 Formal standby facilities, credit lines and other commitments with original term to maturity of: - One year or less 18,248 8,550 - Later than one year 22,149 31,561 41,595 41,721 For segmental and credit risk staging analysis relating to off-balance At 31 December 2019, the Santander UK group had credit impairment loss provisions relating to guarantees given to third parties and undrawn loan commitments. See Note 27 for further details. For segmental and credit risk staging analysis relating to off-balance Where the items set out below can be reliably estimated, they are disclosed in the table above. Capital support arrangements From 1 January 2019, following the implementation of ring-fencing, Santander UK plc, Cater Allen Limited and certain other non-regulated Sub-Group Sub-Group non-regulated Prior to 1 January 2019, Santander UK plc, SFS and Cater Allen Limited, which are the PRA-regulated non-regulated Other than the change of the entities in scope, the purpose of the RFB Sub-Group Liquidity support arrangements From 1 January 2019, following the implementation of ring-fencing, we monitor and manage liquidity risk for the Santander UK plc group and SFS separately. Under this model, and the PRA’s liquidity rules, Santander UK plc and its subsidiary Cater Allen Limited form the RFB Domestic Liquidity Sub-group Prior to 1 January 2019, Santander UK plc, SFS and Cater Allen Limited formed the Domestic Liquidity Sub-group Guarantees given to third parties Guarantees given to third parties consist primarily of letters of credit, bonds and guarantees granted as part of normal product facilities which are offered to customers. Formal standby facilities, credit lines and other commitments Standby facilities, credit lines and other commitments are also granted as part of normal product facilities which are offered to customers. Retail facilities comprise undrawn facilities granted on flexible mortgages, bank overdrafts and credit cards. On flexible mortgages, the credit limit is set at the point of granting the loan through property value and affordability assessments. Ongoing assessments are made to ensure that credit limits remain appropriate considering any change in the security value or the customer’s financial circumstances. For unsecured overdraft facilities and credit cards, the facilities are granted based on new business risk assessment and are reviewed more frequently based on internal, as well as external data. The delinquency status of the account would result in the withdrawal of the facility. Corporate facilities can comprise standby and revolving facilities which are subject to ongoing compliance with covenants and may require the provision of agreed security. Failure to comply with these terms can result in the withdrawal of the unutilised facility headroom. FSCS As described in Note 27, the Santander UK group participates in the UK’s national resolution scheme, the FSCS, and is thus subject to levies to fund the FSCS. If the FSCS significantly increase the levies to be paid by firms, the associated costs to the Santander UK group would rise. Loan representations and warranties In connection with the securitisations and covered bond transactions described in Note 14, the Santander UK group entities selling the relevant loans into the applicable securitisation or covered bond portfolios make representations and warranties with respect to such loans, in each case as of the date of the sale of the loans into the applicable portfolio. These representations and warranties cover, among other things, the ownership of the loan by the relevant Santander UK group entity, absence of a material breach or default by the relevant borrower under the loan, the loan’s compliance with applicable laws and absence of material disputes with respect to the relevant borrower, asset and loan. The specific representations and warranties made by Santander UK group companies which act as sellers of loans in these securitisations and covered bond transactions depend in each case on the nature of the transaction and the requirements of the transaction structure. In addition, market conditions and credit rating agency requirements may affect the representations and warranties required of the relevant Santander UK group companies in these transactions. In the event that there is a material breach of the representations and warranties given by Santander UK plc as seller of loans under the residential mortgage-backed securitisations or the covered bond programmes included in Note 14, or if such representations and warranties prove to be materially untrue as at the date when they were given (being the sale date of the relevant mortgage loans), Santander UK plc may be required to repurchase the affected mortgage loans (generally at their outstanding principal balance plus accrued interest). These securitisations and covered bond programmes are collateralised by prime residential mortgage loans. Santander UK plc is principally a retail prime lender and has no appetite or product offering for any type of sub-prime Similarly, under the auto loan securitisations in Note 14, in the event that there is a breach or inaccuracy in respect of a representation or warranty relating to the loans, the relevant Santander UK group entity who sold the auto loans into the securitisation portfolio will be required to repurchase such loans from the structure (also at their outstanding principal balance plus accrued interest). In addition to breaches of representation and warranties, under the auto loan securitisations, the seller may also have a repurchase obligation if certain portfolio limits are breached (which include, amongst other things, limits as to the size of a loan given to an individual customer, LTV ratio, average term to maturity and average seasoning). In the case of a repurchase of a loan from the relevant securitisation or covered bond programmes, the Santander UK group may bear any subsequent credit loss on such loan. The Santander UK group manages and monitors its securitisation and covered bond activities closely to minimise potential claims. Other legal actions and regulatory matters Santander UK engages in discussion, and co-operates, regulatory reviews, challenges and tax or enforcement investigations or proceedings in various jurisdictions. All such matters are assessed periodically to determine the likelihood of Santander UK incurring a liability. In those instances where it is concluded that it is not yet probable that a quantifiable payment will be made, for example because the facts are unclear or further time is required to fully assess the merits of the case or to reasonably quantify the expected payment, no provision is made. In addition, where it is not currently practicable to estimate the possible financial effect of these matters, no provision is made. Payment Protection Insurance In relation to a specific PPI portfolio of complaints, a legal dispute regarding allocation of liability is ongoing and remains in its early stages. The dispute relates to the liability for PPI mis-selling pre-2005 A related dispute between AXA and (1) Genworth Financial International Holdings, Inc. and (2) Genworth Financial, Inc. (Genworth) concerning, inter alia, the proper construction of an alleged obligation to make payment on demand of a sum equal to 90% of all applicable PPI mis-selling Genworth’s application for permission to appeal was refused by the Court. Genworth made an application for permission to appeal to the Court of Appeal on 10 January 2020. The application for permission to appeal has not yet been determined. Most recently in its US SEC filing of 27 February 2020, Genworth noted that AXA had at that date submitted invoices claiming aggregate losses of approximately US$560 million. More generally, there are ongoing factual issues to be resolved which may have legal consequences including in relation to liability. These issues create uncertainties which mean that it is not currently practicable to reliably predict the resolution of the matter including timing or the significance of the possible impact. The Regulatory and other provision in Note 27 includes our best estimate of Santander UK’s liability to the specific portfolio. Further information has not been provided on the basis that it would be seriously prejudicial to Santander UK’s interests in connection with the dispute. In addition, and in relation to PPI more generally, there are legal claims being made by Claims Management Companies challenging the FCA’s industry guidance on the treatment of Plevin /recurring non-disclosure German dividend tax arbitrage transactions In June 2018 the Cologne Criminal Prosecution Office and the German Federal Tax Office commenced an investigation in relation to the historical involvement of Santander UK plc, Santander Financial Services plc and Cater Allen International Limited (all subsidiaries of Santander UK Group Holdings plc) in German dividend tax arbitrage transactions (known as cum/ex transactions). These transactions allegedly exploited a feature of a specific German settlement mechanism through short-selling and complex derivative structuring which resulted in the German government either refunding withholding tax where such tax had not been paid or refunding it more than once. The German authorities are investigating numerous institutions and individuals in connection with alleged transactions and practices which may be found to be illegal under German law. During 2019 we have continued to cooperate with the German authorities and, with the assistance of external experts, to progress an internal investigation into the matters in question. From Santander UK plc’s perspective the investigation is focused principally on the period 2009-2011 and remains on-going. Consumer credit The Santander UK group’s unsecured lending and other consumer credit business is governed by consumer credit law and related regulations, including the CCA. Claims brought by customers in relation to these requirements, including potential breaches, could result in costs to the Santander UK group where such potential breaches are not found to be de minimis. The CCA includes very detailed and prescriptive requirements for lenders, including in relation to post contractual information. As described in Note 27, other provisions include an amount of £68m arising from a systems-related historical issue identified by Santander UK, relating to compliance with certain requirements of the CCA. This provision has been based on detailed reviews of relevant systems related to consumer credit business operations, supported by external legal and regulatory advice. Reviews of systems, commercial agreements and the legal and regulatory position are ongoing, such that the potential for additional remedial action is still being determined. The Regulatory and other provision in Note 27 includes our best estimate of Santander UK’s liability for the specific issue. The actual cost of customer compensation could differ from the amount provided. It is not currently practicable to provide an estimate of the risk and amount of any further financial impact. Taxation The Santander UK group engages in discussion, and co-operates, Certain leases in which the Santander UK group is or was the lessor are currently under review by HMRC in connection with claims for tax allowances. Under the terms of the lease agreements, the Santander UK group is fully indemnified in all material respects by the respective lessees for any liability arising from the disallowance of tax allowances plus accrued interest, which could be up to £146m. Whilst legal opinions have been obtained to support the Santander UK group’s position, the matter remains uncertain pending formal resolution with HMRC and any subsequent litigation. It is anticipated that the matters will move to formal litigation in 2020 as required under the terms of the leases. Other On 2 November 2015, Visa Europe Ltd agreed to sell 100% of its share capital to Visa Inc. The deal closed on 21 June 2016. As a member and shareholder of Visa Europe Ltd, Santander UK received upfront consideration made up of cash and convertible preferred stock. Conversion of the preferred stock into Class A Common Stock of Visa Inc. depends on the outcome of litigation against Visa involving UK & Ireland (UK&I) multilateral interchange fees (MIFs). Santander UK and certain other UK&I banks have agreed to indemnify Visa Inc. in the event that the preferred stock is insufficient to meet the costs of this litigation. Visa Inc. has recourse to this indemnity once more than €1bn of losses relating to UK&I MIFs have arisen or once the total value of the preferred stock issued to UK&I banks on closing has been reduced to nil. In valuing the preferred stock, Santander UK makes adjustments for illiquidity and the potential for changes in conversion. Visa Inc. may have recourse to a general indemnity in place under Visa Europe Operating Regulations for damages not satisfied through the above mechanism. As part of the sale of subsidiaries, businesses and other entities, and as is normal in such circumstances, Santander UK has given warranties and indemnities to the purchasers. Obligations under stock borrowing and lending agreements Obligations under stock borrowing and lending agreements represent contractual commitments to return stock borrowed. These obligations are offset by a contractual right to receive stock under other contractual agreements. See Note 34. Other off-balance The Santander UK group has commitments to lend at fixed interest rates which expose us to interest rate risk. For more, see the Risk review. Operating lease commitments The table below shows the rental commitments under non-cancellable Group Rental commitments under non-cancellable 2018 Not later than one year 72 Later than one year and not later than five years 114 Later than five years 60 246 The majority of leases are subject to a third party outsourcing contract which expires in December 2020 and the remainder are held directly by the Santander UK group with third party landlords. Where leases subject to the outsourcing contract expire on or after the expiry of the outsourcing contract in December 2020 and occupation is still required, negotiations will be held directly with the landlords of these properties, to agree renewal terms. Negotiations will be in accordance with a conventional landlord and tenant negotiation on lease expiry, subject to a lease renewal being available from the external landlords. Where a freehold interest in the property is held by the outsourcing company, a notice has been served under the contract confirming the properties where a new lease is required post-2020. The terms for the leases of these properties will also be negotiated during 2020. In 2018, rental expense amounted to £61m (2017: £61m), including minimum rentals of £63m (2017: £61m), offset by sub-lease

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2019
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Share Capital	30. SHARE CAPITAL Group Ordinary shares £300m Preference Total Issued and fully paid share capital No. £m No. £m £m At 1 January 2018, 31 December 2018 and 1 January 2019 31,051,768,866 3,105 13,780 14 3,119 Redemption of preference shares 0 0 (13,780 ) (14 ) (14 ) At 31 December 2019 31,051,768,866 3,105 0 0 3,105 Group Share premium 2019 2018 At 1 January and 31 December 5,620 5,620 The Company has one class of ordinary shares which carries no right to fixed income. The Company’s £325m sterling preference shares are classified as Subordinated Liabilities as described in Note 26. Fixed/Floating Rate Non-Cumulative The remaining preference shares were redeemed at the option of Santander UK plc on 24 May 2019.

Other Equity Instruments

Other Equity Instruments	12 Months Ended
	Dec. 31, 2019
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Other Equity Instruments	31. OTHER EQUITY INSTRUMENTS Group Interest rate Next call date 2019 £m 2018 £300m Step-up 7.037 February 2026 235 235 AT1 securities: - £500m Fixed Rate Reset Perpetual AT1 Capital Securities 6.75 June 2024 496 496 - £750m Fixed Rate Reset Perpetual AT1 Capital Securities 7.375 June 2022 750 750 - £300m Fixed Rate Reset Perpetual AT1 Capital Securities 7.60 n/a 0 300 - £500m Fixed Rate Reset Perpetual AT1 Capital Securities 5.18 March 2020 210 210 - £500m Fixed Rate Reset Perpetual AT1 Capital Securities 6.30 March 2025 500 — 2,191 1,991 Step-up These instruments are redeemable by Santander UK plc on 14 February 2026 or on any coupon payment date thereafter, subject to the prior approval of the PRA. They are perpetual and pay interest annually. The coupon rate resets every five years, based on the UK five-year benchmark gilt rate. Interest payments may be deferred by Santander UK plc. The instruments are not redeemable at the option of the holders and the holders do not have any rights against other Santander UK group companies. AT1 securities The AT1 securities issued by the Company were subscribed by its immediate parent company, Santander UK Group Holdings plc. The securities are perpetual and pay a distribution on 24 March, June, September and December. At each distribution payment date, the Company can decide whether to pay the distribution, which is non-cumulative, in whole or in part. The distribution rate resets every five years. The securities will be automatically written down and the investors will lose their entire investment in the securities should the CET1 capital ratio of the Santander UK prudential consolidation group fall below 7%. They are redeemable at the option of the Company on their first call date or on any reset date thereafter in the cases of the 6.75% and 7.375% Fixed Rate Reset Perpetual AT1 Capital Securities, and on any distribution payment date thereafter in the cases of the 5.18% and 6.30% Fixed Rate Reset Perpetual AT1 Capital Securities. No such redemption may be made without the consent of the PRA. In August 2019, as part of a capital management exercise, the Company purchased and redeemed the £300m 7.60% Fixed Rate Reset Perpetual AT1 Capital Securities, and issued a further £500m 6.30% Fixed Rate Reset Perpetual AT1 Capital Securities to Santander UK Group Holdings plc.

Non-Controlling Interests

Non-Controlling Interests	12 Months Ended
	Dec. 31, 2019
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Non-Controlling Interests	32. NON-CONTROLLING INTERESTS 2019 £m 2018 PSA Finance UK Limited 160 151 160 151 PSA Finance UK Limited is the only subsidiary in the Santander UK group that gives rise to significant non-controlling

Changes in Liabilities Arising

Changes in Liabilities Arising from Financing Activities	12 Months Ended
	Dec. 31, 2019
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Changes in Liabilities Arising from Financing Activities	33. CHANGES IN LIABILITIES ARISING FROM FINANCING ACTIVITIES The table below shows the changes in liabilities arising from financing activities. Group 2019 2018 Balance sheet line item Balance sheet line item Debt Subordinated £m Other Dividends £m Total Debt Subordinated Other Dividends Total At 1 January 46,692 3,601 1,991 0 52,284 42,633 3,793 2,281 — 48,707 Cash flows from financing activities (3,839 ) 0 196 (469 ) (4,112 ) 4,615 (277 ) (290 ) (1,318 ) 2,730 Cash flows from operating activities (529 ) 0 0 0 (529 ) (2,522 ) 69 — — (2,453 ) Non-cash – Unrealised foreign exchange (1,320 ) (50 ) 0 0 (1,370 ) 1,371 149 — — 1,520 – Other changes 125 (23 ) 4 469 575 595 (133 ) — 1,318 1,780 At 31 December 41,129 3,528 2,191 0 46,848 46,692 3,601 1,991 — 52,284

Assets Charged As Security For

Assets Charged As Security For Liabilities And Collateral Accepted As Security For Assets	12 Months Ended
	Dec. 31, 2019
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Assets Charged As Security For Liabilities And Collateral Accepted As Security For Assets	34. ASSETS CHARGED AS SECURITY FOR LIABILITIES AND COLLATERAL ACCEPTED AS SECURITY FOR ASSETS The following transactions are conducted under terms that are usual and customary to collateralised transactions including, where relevant, standard securities lending and repurchase agreements. a) Assets charged as security for liabilities The financial assets below are analysed between those assets accounted for on-balance off-balance Group 2019 £m 2018 On-balance Cash and balances at central banks 1,080 1,080 Loans and advances to banks 403 218 Loans and advances to customers – securitisations and covered bonds (See Note 14) 36,225 35,694 Loans and advances to customers – other 16,282 15,175 Other financial assets at amortised cost 3,026 3,763 Financial assets at fair value through other comprehensive income 6,009 5,825 Total on-balance 63,025 61,755 Total off-balance 15,098 15,220 The Santander UK group provides assets as collateral in the following areas of the business. Sale and repurchase agreements The Santander UK group enters into sale and repurchase agreements and similar transactions of debt securities, which are accounted for as secured borrowings. Upon entering into such transactions, the Santander UK group provides collateral in excess of the borrowed amount. The carrying amount of assets that were so provided at 31 December 2019 was £20,686m (2018: £17,485m), of which £2,067m (2018: £2,383m) was classified within ‘Loans and advances to customers – securitisations and covered bonds’ in the table above. Securitisations and covered bonds As described in Note 14, Santander UK plc and certain of its subsidiaries issue securitisations and covered bonds. At 31 December 2019, there were £36,391m (2018: £36,195m) of gross assets in these secured programmes and £166m (2018: £501m) of these related to internally retained issuances that were available for use as collateral for liquidity purposes in the future. At 31 December 2019, a total of £4,728m (2018: £4,039m) of notes issued under securitisation and covered bond programmes had been retained internally, a proportion of which had been used as collateral for raising funds via third party bilateral secured funding transactions, which totalled £1,581m at 31 December 2019 (2018: £1,834m), or for use as collateral for liquidity purposes in the future. Stock borrowing and lending agreements Asset balances under stock borrowing and lending agreements represent stock lent by the Santander UK group. These balances amounted to £21,563m at 31 December 2019 (2018: £24,714m) and are offset by contractual commitments to return stock borrowed or cash received. Derivatives business In addition to the arrangements described, collateral is also provided in the normal course of derivative business to counterparties. At 31 December 2019 £1,716m (2018: £1,465m) of such collateral in the form of cash had been provided by the Santander UK group and is included in the table. b) Collateral accepted as security for assets The collateral held as security for assets, analysed between those liabilities accounted for on balance sheet and off-balance Group 2019 2018 On-balance Deposits by banks 2,169 4,048 Total on-balance 2,169 4,048 Total off-balance 25,120 23,236 Purchase and resale agreements The Santander UK group also enters into purchase and resale agreements and similar transactions of debt securities, which are accounted for as collateralised loans. Upon entering into such transactions, the Santander UK group receives collateral in excess of the loan amount. The level of collateral held is monitored daily and if required, further calls are made to ensure the market values of collateral remains at least equal to the loan balance. The subsidiaries are permitted to sell or repledge the collateral held in the absence of default. At 31 December 2019, the fair value of such collateral received was £20,444m (2018: £15,728m). Of the collateral received, almost all was sold or repledged. The subsidiaries have an obligation to return collateral that they have sold or pledged. Stock borrowing and lending agreements Obligations representing contractual commitments to return stock borrowed by the Santander UK group amounted to £4,676m at 31 December 2019 (2018: £7,508m) and are offset by a contractual right to receive stock lent. Derivatives business In addition to the arrangements described, collateral is also received from counterparties in the normal course of derivative business. At 31 December 2019, £2,169m (2018: £4,048m) of such collateral in the form of cash had been received by the Santander UK group and is included in the table. Lending activities In addition to the collateral held as security for assets, the Santander UK group may obtain a charge over a customer’s property in connection with its lending activities. Details of these arrangements are set out in the ‘Credit risk’ section of the Risk review.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2019
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Share-Based Compensation	35. SHARE-BASED COMPENSATION The Santander UK group operates share schemes and arrangements for eligible employees. The main current schemes are the Sharesave Schemes, the Long-Term Incentive Plan (the LTIP), the Deferred Shares Bonus Plan and the Partnership Shares scheme. All the share options and awards relate to shares in Banco Santander SA. The amount charged to the income statement in respect of share-based payment transactions is set out in Note 6. a) Sharesave Schemes The Santander UK group launched its twelfth HM Revenue & Customs approved Sharesave Scheme under Banco Santander SA ownership in September 2019. The first eleven Sharesave Schemes were launched each year from 2008 to 2018 under broadly similar terms. Under the Sharesave Scheme’s HMRC-approved savings limits, eligible employees may enter into contracts to save between £5 and £500 per month. For all schemes, at the end of a fixed term of three or five years after the grant date, the employees can use these savings to buy shares in Banco Santander SA at a discount, calculated in accordance with the rules of the scheme. The discount is currently 10% of the average middle market quoted price of Banco Santander SA shares over the first three dealing days prior to invitation. The vesting of awards under the scheme depends on continued employment with the Banco Santander SA group. Participants in the scheme have six months from the date of vest to exercise the option. In 2018, as part of the implementation of our ring-fencing plans, the Sharesave Schemes were transferred to SEIL, which was subsequently transferred outside of the Santander UK group, but remained within the Santander UK Group Holdings plc group. Information relating to the Sharesave Schemes administered by SEIL is presented below as employees of the Santander UK group are participants. The table below summarises movements in the number of options, and changes in weighted average exercise price over the same period. 2019 2018 Number of Weighted Number of Weighted Outstanding at 1 January 26,838 3.12 27,201 3.12 Granted 9,594 2.83 6,210 3.46 Exercised (7,978 ) 2.83 (3,340 ) 3.16 Forfeited/expired (5,081 ) 3.42 (3,233 ) 3.76 Outstanding at 31 December 23,373 3.03 26,838 3.12 Exercisable at 31 December 2,519 3.62 10,370 2.81 The weighted average share price at the date the options were exercised was £3.18 (2018: £3.79). The following table summarises the range of exercise prices and weighted average remaining contractual life of the options at 31 December 2019 and 2018. 2019 2018 Range of exercise prices Weighted average Years Weighted Weighted average Weighted £2 to £3 3 2.80 2 2.75 £3 to £4 2 3.38 3 3.36 £4 to £5 2 4.13 3 4.11 The fair value of each option at the date of grant is estimated using a partial differentiation equation model. This model uses assumptions on the share price, the EUR/GBP FX rate, the risk free interest rate, dividend yields, the expected volatility of the underlying shares and the expected lives of options granted. The weighted average grant-date fair value of options granted during the year was £0.49 (2018: £0.53). At 31 December 2019, the carrying amount of liabilities arising from share-based payment transactions in the Santander UK Group Holdings plc group was £2.4m (2018: £7.7m), of which £1.4m had vested at 31 December 2019 (2018: £0.7m). b) LTIP In 2014 and 2015, conditional cash awards were made to certain Executive Directors, Key Management Personnel (as defined in Note 36) and other nominated individuals which are converted into shares in Banco Santander SA at the time of vesting and deferred for three years. There have been no LTIP awards granted since 2015 due to the introduction of a single variable remuneration framework across the Banco Santander group in 2016. The LTIP plans granted in 2014 and 2015 involved a one-year The following table summarises the movement in the value of conditional awards in the LTIPs in 2019 and 2018: 2015 LTIP 2014 LTIP 2019 2018 2019 2018 £000 £000 £000 £000 Outstanding at 1 January 6,374 6,503 0 1,910 Payments made (4,578 ) — 0 — Forfeited/cancelled (1,796 ) (129 ) 0 (1,910 ) Outstanding at 31 December 0 6,374 0 — c) Deferred shares bonus plan Deferred bonus awards are designed to align employee performance with shareholder value and encourage increased retention of senior employees. During 2018 and 2019, conditional share awards were made to employees (designated as Material Risk Takers). Such employees receive part of their annual bonus as a deferred award comprising 50% in shares, and 50% in cash. Any deferred awards are dependent on continued employment or subject to Santander’s discretion for leavers. For 2018 and 2019 bonus awards, deferral of the award is over a three, five or seven-year period from the anniversary of the initial award. Deferred bonus awards in shares are subject to an additional one-year Material Risk Takers are required to defer either 40% or 60% of any annual bonus (40% for variable pay of less than £500,000, 60% for variable pay at or above this amount). Vesting of both deferred bonus awards and long-term bonus awards is subject to risk and performance adjustment in the event of deficient performance and prudent financial control provisions. d) Partnership Shares scheme A Partnership Shares scheme is operated for eligible employees under the Share Incentive Plan (SIP) umbrella. Participants can choose to invest up to £1,800 per tax year (or no more than 10% of an employee’s salary for the tax year) from pre-tax

Transactions With Directors and

Transactions With Directors and Other Key Management Personnel	12 Months Ended
	Dec. 31, 2019
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Transactions With Directors and Other Key Management Personnel	36. TRANSACTIONS WITH DIRECTORS AND OTHER KEY MANAGEMENT PERSONNEL a) Remuneration of Directors and Other Key Management Personnel The remuneration of the Directors and Other Key Management Personnel of the Santander UK group is set out in aggregate below. 2019 2018 2017 Directors’ remuneration £ £ £ Salaries and fees 5,025,665 5,028,434 4,406,908 Performance-related payments (1) 3,864,965 5,194,317 3,685,464 Other fixed remuneration (pension and other allowances & non-cash 1,367,069 1,467,011 1,580,321 Expenses 42,526 25,198 96,358 Total remuneration 10,300,225 11,714,960 9,769,051 2019 2018 2017 Directors’ and Other Key Management Personnel compensation £ £ £ Short-term employee benefits (2) 21,925,975 24,445,189 24,642,085 Post-employment benefits (3) 3,590,466 2,399,261 2,292,857 Total Compensation 25,516,441 26,844,450 26,934,942 (1) In line with the Code, a proportion of the performance-related payment was deferred. Further details can be found in Note 35. (2) There were no buy-outs buy-outs buy-outs (3) Termination payments of £1,076,435 were paid in 2019 to one key management persons (2018: £847,388 for two individuals; 2017: £nil). In 2019, the remuneration, excluding pension contributions, of the highest paid Director, was £3,725,993 (2018: £4,635,497) of which £1,989,900 (2018: £2,317,000) was performance related. In 2019, there was no pension benefit accrued for the highest paid Director but in respect of the qualifying past services to Santander UK to 31 May 2009 he has a deferred pension benefit accruing under a defined benefit scheme of £20,973 p.a. (2018: £20,402 p.a.). b) Retirement benefits Defined benefit pension schemes are provided to certain employees. See Note 28 for details of the schemes and the related costs and obligations. As described above, one director, being the highest paid director, has a deferred pension benefit accruing under a defined benefit scheme. Ex gratia pensions paid to former Directors of Santander UK plc in 2019, which have been provided for previously, amounted to £335,202 (2018: £87,300; 2017: £2,482). In 1992, the Board decided not to award any new such ex gratia pensions. c) Transactions with Directors, Other Key Management Personnel and each of their connected persons Directors, Other Key Management Personnel (Defined as the Executive Committee of Santander UK plc who served during the year) and their connected persons have undertaken the following transactions with the Santander UK group in the ordinary course of business. 2019 2018 No. £000 No. £000 Secured loans, unsecured loans and overdrafts At 1 January 16 3,035 7 1,216 Net movements 2 1,885 9 1,819 At 31 December 18 4,920 16 3,035 Deposit, bank and instant access accounts and investments At 1 January 30 10,963 25 13,184 Net movements 2 1,012 5 (2,221 ) At 31 December 32 11,975 30 10,963 In 2019 and 2018, no Director held any interest in the shares of any company in the Santander UK group and no Director exercised or was granted any rights to subscribe for shares in any company in the Santander UK group. In addition, in 2019 and 2018, no Directors exercised share options over shares in Banco Santander SA, the ultimate parent company of the Company. Secured loans, unsecured loans and overdrafts are made to Directors, Other Key Management Personnel and their connected persons, in the ordinary course of business, with terms prevailing for comparable transactions and on the same terms and conditions as applicable to other employees in the Santander UK group. Such loans do not involve more than the normal risk of collectability or present any unfavourable features. Amounts deposited by Directors, Other Key Management. Personnel and their connected persons earn interest at the same rates as those offered to the market or on the same terms and conditions applicable to other employees in the Santander UK group. Deposits, bank and instant access accounts and investments are entered into by Directors, Other Key Management Personnel and their connected persons on normal market terms and conditions, or on the same terms and conditions as applicable to other employees in Santander UK group. In 2019, loans were made to nine Directors (2018: eight Directors), with a principal amount of £1,767,066 outstanding at 31 December 2019 (2018: £65,232). In 2019, loans were made to nine Other Key Management Personnel (2018: eight), with a principal amount of £3,153,343 outstanding at 31 December 2019 (2018: £2,969,462). In 2019 and 2018, there were no other transactions, arrangements or agreements with Santander UK in which Directors, Other Key Management Personnel or their connected persons had a material interest. In addition, in 2019 and 2018, no Director had a material interest in any contract of significance with Santander UK other than a service contract.

Related Party Disclosures

Related Party Disclosures	12 Months Ended
	Dec. 31, 2019
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Related Party Disclosures	37. RELATED PARTY DISCLOSURES a) Parent undertaking and controlling party The Company’s immediate parent is Santander UK Group Holdings plc, a company incorporated in England and Wales. Its ultimate parent and controlling party is Banco Santander SA, a company incorporated in Spain. The smallest and largest groups into which the Santander UK group’s results are included are the group accounts of Santander UK Group Holdings plc and Banco Santander SA, respectively, copies of which may be obtained from Shareholder Relations, 2 Triton Square, Regent’s Place, London NW1 3AN. b) Transactions with related parties Transactions with related parties during the year and balances outstanding at the year-end: Group Interest, fees and other Interest, fees and other Amounts owed by Amounts owed to 2019 2018 2017 2019 2018 2017 2019 2018 2019 2018 £m £m £m £m £m £m £m £m £m £m Ultimate parent (130 ) (72 ) (60 ) 266 217 321 1,560 2,491 (2,143 ) (3,594 ) Immediate parent (7 ) (3 ) (3 ) 317 275 207 8 — (10,012 ) (10,392 ) Fellow subsidiaries (66 ) (86 ) (76 ) 173 178 491 204 57 (544 ) (689 ) Associates & joint ventures (29 ) (28 ) (20 ) 0 — — 2,194 1,986 (930 ) (718 ) (232 ) (189 ) (159 ) 756 670 1,019 3,966 4,534 (13,629 ) (15,393 ) For more on this, see ‘Balances with other Banco Santander companies’ in the Risk review. In addition, transactions with pension schemes operated by the Santander UK group are described in Note 28. The above transactions were made in the ordinary course of business, except those carried out with Banco Santander SA and subsidiaries of the Company as part of our ring-fencing implementation in 2018, on substantially the same terms as for comparable transactions with third party counterparties, and within limits acceptable to the PRA. Such transactions do not involve more than the normal risk of collectability or present any unfavourable features. In addition, in July 2018 we transferred £1.4bn of customer loans, £21.5bn of other assets and £20.7bn of liabilities from Santander UK to Banco Santander London Branch. Of these transfers, £19.7bn of assets and £18.8bn of liabilities related to derivatives business. These transfers reduced RWAs by £5.5bn and we paid an associated dividend of £668m. Furthermore in 2018, Santander UK plc sold 100% of the share capital of SFS plc to Santander UK Group Holdings plc, for a consideration of £337m, and the business of the Jersey and Isle of Man branches of Santander UK plc was subsequently acquired by SFS plc.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2019
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Financial Instruments	38. FINANCIAL INSTRUMENTS a) Measurement basis of financial assets and liabilities Financial assets and financial liabilities are measured on an ongoing basis either at fair value or at amortised cost. Note 1 describes how the classes of financial instruments are measured, and how income and expenses, including fair value gains and losses, are recognised. b) Fair value measurement and hierarchy (i) Fair value measurement The fair value of financial instruments is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date in the principal, or in its absence, the most advantageous market to which Santander UK has access at that date. The fair value of a liability reflects its non-performance Financial instruments valued using observable market prices If a quoted market price in an active market is available for an instrument, the fair value is calculated as the current bid price multiplied by the number of units of the instrument held. Financial instruments valued using a valuation technique In the absence of a quoted market price in an active market, management uses internal models to make its best estimate of the price that the market would set for that financial instrument. In order to make these estimations, various techniques are employed, including extrapolation from observable market data and observation of similar financial instruments with similar characteristics. Wherever possible, valuation parameters for each product are based on prices directly observable in active markets or that can be derived from directly observable market prices. Chosen valuation techniques incorporate all the factors that market participants would take into account in pricing transactions. Santander UK manages certain groups of financial assets and liabilities on the basis of its net exposure to either market risks or credit risk. As a result it has elected to use the exception under IFRS 13 which permits the fair value measurement of a group of financial assets and financial liabilities on the basis of the price that would be received to sell a net long position for a particular risk exposure or paid to transfer a net short position for a particular risk exposure in an orderly transaction between market participants at the measurement date under current market conditions. (ii) Fair value hierarchy Santander UK applies the following fair value hierarchy that prioritises the inputs to valuation techniques used in measuring fair value. The hierarchy establishes three categories for valuing financial instruments, giving the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities and the lowest priority to unobservable inputs. The three categories are: quoted prices in active markets (Level 1), internal models based on observable market data (Level 2) and internal models based on other than observable market data (Level 3). If the inputs used to measure an asset or a liability fall to different levels within the hierarchy, the classification of the entire asset or liability will be based on the lowest level input that is significant to the overall fair value measurement of the asset or liability. Santander UK categorises assets and liabilities measured at fair value within the fair value hierarchy based on the inputs to the valuation techniques as follows: Level 1 Unadjusted quoted prices for identical assets or liabilities in an active market that Santander UK can access at the measurement date. Active markets are assessed by reference to average daily trading volumes in absolute terms and, where applicable, by reference to market capitalisation for the instrument. Level 2 Quoted prices in inactive markets, quoted prices for similar assets or liabilities, recent market transactions, inputs other than quoted market prices for the asset or liability that are observable either directly or indirectly for substantially the full term, and inputs to valuation techniques that are derived principally from or corroborated by observable market data through correlation or other statistical means for substantially the full term of the asset or liability. Level 3 Significant inputs to the pricing or valuation techniques are unobservable. These unobservable inputs reflect the assumptions that market participants would use when pricing assets or liabilities and are considered significant to the overall valuation. Changes in the observability of significant valuation inputs during the reporting period may result in a transfer of assets and liabilities within the fair value hierarchy. The Santander UK group recognises transfers between levels of the fair value hierarchy when there is a significant change in either its principal market or the level of observability of the inputs to the valuation techniques as at the end of the reporting period. c) Valuation techniques The main valuation techniques employed in internal models to measure the fair value of the financial instruments at 31 December 2019 and 2018 are set out below. In substantially all cases, the principal inputs into these models are derived from observable market data. Santander UK did not make any material changes to the valuation techniques and internal models it used in 2019, 2018 and 2017. A In the valuation of financial instruments requiring static hedging (for example interest rate, currency derivatives and property derivatives) and in the valuation of loans and advances and deposits, the ‘present value’ method is used. Expected future cash flows are discounted using the interest rate curves of the applicable currencies or forward house price index levels, as well as credit spreads. The interest rate curves are generally observable market data and reference yield curves derived from quoted interest rates in appropriate time bandings, which match the timings of the cash flows and maturities of the instruments. The forward commodity house price index levels are generally observable market data. B In the valuation of equity financial instruments requiring dynamic hedging (principally equity securities, options and other structured instruments), proprietary local volatility and stochastic volatility models are used. These types of models are widely accepted in the financial services industry. Observable market inputs used in these models include the bid-offer C In the valuation of financial instruments exposed to interest rate risk that require either static or dynamic hedging (such as interest rate futures, caps and floors, and options), the present value method (futures), Black’s model (caps/floors) and the Hull/White and Markov functional models (Bermudan options) are used. These types of models are widely accepted in the financial services industry. The significant inputs used in these models are observable market data, including appropriate interest rate curves, volatilities, correlations and exchange rates. In limited circumstances, other inputs may be used in these models that are based on unobservable market data, such as HPI volatility, HPI forward growth, HPI spot rate and mortality. D In the valuation of linear instruments such as credit risk and fixed-income derivatives, credit risk is measured using dynamic models similar to those used in the measurement of interest rate risk. In the case of non-linear The fair values of the financial instruments arising from Santander UK’s internal models take into account, among other things, contract terms and observable market data, which include such factors as bid-offer Santander UK believes its valuation methods are appropriate and consistent with other market participants. Nevertheless, the use of different valuation methods or assumptions, including imprecision in estimating unobservable market inputs, to determine the fair value of certain financial instruments could result in different estimates of fair value at the reporting date and the amount of gain or loss recorded for a particular instrument. Most of the valuation models are not significantly subjective, because they can be tested and, if necessary, recalibrated by the internal calculation of and subsequent comparison to market prices of actively traded securities, where available. d) Control framework Fair values are subject to a control framework designed to ensure that they are either determined or validated by a function independent of the risk-taker. To this end, ultimate responsibility for the determination of fair values lies with the Risk Department. For all financial instruments where fair values are determined by reference to externally quoted prices or observable pricing inputs to models, independent price determination or validation is utilised. In inactive markets, direct observation of a traded price may not be possible. In these circumstances, Santander UK will source alternative market information to validate the financial instrument’s fair value, with greater weight given to information that is considered to be more relevant and reliable. The factors that are considered in this regard include: – The extent to which prices may be expected to represent genuine traded or tradeable prices – The degree of similarity between financial instruments – The degree of consistency between different sources – The process followed by the pricing provider to derive the data – The elapsed time between the date to which the market data relates and the balance sheet date – The manner in which the data was sourced. The source of pricing data is considered as part of the process that determines the classification of the level of a financial instrument. Consideration is given to the quality of the information available that provides the current mark-to-model For fair values determined using a valuation model, the control framework may include, as applicable, independent development and / or validation of: (i) the logic within the models; (ii) the inputs to those models; and (iii) any adjustments required outside the models. Internal valuation models are validated independently within the Risk Department. A validation report is produced for each model-derived valuation that assesses the mathematical assumptions behind the model, the implementation of the model and its integration within the trading system. e) Fair values of financial instruments carried at amortised cost The following tables analyse the fair value of the financial instruments carried at amortised cost at 31 December 2019 and 2018, including their levels in the fair value hierarchy – Level 1, Level 2 and Level 3. It does not include fair value information for financial assets and financial liabilities carried at amortised cost if the carrying amount is a reasonable approximation of fair value. Cash and balances at central banks, which consist of demand deposits with the Bank of England, together with cash in tills and ATMs, have been excluded from the table as the carrying amount is deemed an appropriate approximation of fair value. The fair value of the portfolio of UK Government debt securities, included in other financial assets at amortised cost, is the only material financial instrument categorised in Level 1 of the fair value hierarchy. Group 2019 2018 Fair value Carrying Fair value Carrying Level 1 Level 2 Level 3 Total value Level 1 Level 2 Level 3 Total value £m £m £m £m £m £m £m £m £m £m Assets Loans and advances to customers 0 0 211,796 211,796 207,287 — — 204,061 204,061 201,289 Loans and advances to banks 0 1,739 116 1,855 1,855 — 2,739 60 2,799 2,799 Reverse repurchase agreements – non trading 0 23,634 0 23,634 23,636 — 21,130 — 21,130 21,127 Other financial assets at amortised cost 6,575 535 0 7,110 7,056 6,390 721 — 7,111 7,229 6,575 25,908 211,912 244,395 239,834 6,390 24,590 204,121 235,101 232,444 Liabilities Deposits by customers 0 95 181,918 182,013 181,883 — 21 178,160 178,181 178,090 Deposits by banks 0 13,956 407 14,363 14,353 — 16,243 989 17,232 17,221 Repurchase agreements – non trading 0 18,292 0 18,292 18,286 — 10,923 — 10,923 10,910 Debt securities in issue 0 42,694 0 42,694 41,129 — 47,787 — 47,787 46,692 Subordinated liabilities 0 4,220 0 4,220 3,528 — 3,877 — 3,877 3,601 0 79,257 182,325 261,582 259,179 — 78,851 179,149 258,000 256,514 The carrying value above of any financial assets and liabilities that are designated as hedged items in a portfolio (or macro) fair value hedge relationship excludes gains and losses attributable to the hedged risk, as this is included in other assets on the balance sheet. Valuation methodology for financial instruments carried at amortised cost The valuation approach to specific categories of financial instruments is described below. Assets: Loans and advances to customers The approach to estimating the fair value of loans and advances to customers has been determined by discounting expected cash flows to reflect either current market rates or credit spreads relevant to the specific industry of the borrower. The determination of their fair values is an area of considerable estimation and uncertainty as there is no observable market and values are significantly affected by customer behaviour. i) Advances secured on residential property The fair value of the mortgage portfolio is calculated by discounting contractual cash flows by different spreads for each LTV Band, after taking account of expected customer prepayment rates. The spread is based on new business interest rates derived from competitor market information. ii) Corporate loans The determination of the fair values of performing loans takes account of the differential between existing margins and estimated new business rates for similar loans in terms of segment and maturity. Provisions are considered appropriate for the book that is not impaired. A discount has been applied to impaired loans. Although exits have generally been achieved at carrying value, this does not reflect the discount a purchaser would require. A discount has therefore been applied based on the target return sought by distressed bond funds, who are the typical purchaser of the assets. iii) Other loans These consist of unsecured personal loans, credit cards, overdrafts and consumer (auto) finance. The weighted average lives of these portfolios are short and relate to relatively new business. As a result, contractual interest rates approximate new business interest rates, and therefore no mark-to-market Loans and advances to banks These comprise secured loans, short-term placements with banks including collateral and unsettled financial transactions. The secured loans have been valued based on a discounted spread for the term of the loans using valuation technique A as described above. The carrying amount of the other items is deemed a reasonable approximation of their fair value, as the transactions are very short-term in duration. Reverse repurchase agreements – non trading The fair value of the reverse repurchase agreements – non trading has been estimated using valuation technique A as described above, using a spread appropriate to the underlying collateral. Other financial assets at amortised cost These consist of asset backed securities and debt securities. The asset backed securities can be complex products and in some instances are valued with the assistance of an independent, specialist valuation firm. These fair values are determined using industry-standard valuation techniques, including discounted cash flow models. The inputs to these models used in these valuation techniques include quotes from market makers, prices of similar assets, adjustments for differences in credit spreads, and additional quantitative and qualitative research. The debt security investments consist of a portfolio of government debt securities. The fair value of this portfolio has been determined using quoted market prices. Liabilities: Deposits by customers The majority of deposit liabilities are payable on demand and therefore can be deemed short-term in nature with the fair value equal to the carrying value. Certain of the deposit liabilities are at a fixed rate until maturity. The deficit/surplus of fair value over carrying value of these liabilities has been estimated by reference to the market rates available at the balance sheet date for similar deposit liabilities of similar maturities. The fair value of such deposit liabilities has been estimated using valuation technique A as described above. Deposits by banks The fair value of deposits by banks, including repos, has been estimated using valuation technique A as described above, discounted at the appropriate credit spread. Repurchase agreements – non trading The fair value of the repurchase agreements – non trading has been estimated using valuation technique A as described above, discounted at a spread appropriate to the underlying collateral. Debt securities in issue and subordinated liabilities Where reliable prices are available, the fair value of debt securities in issue and subordinated liabilities has been calculated using quoted market prices. f) Fair values of financial instruments measured at fair value The following tables summarise the fair values of the financial assets and liabilities accounted for at fair value at 31 December 2019 and 2018, analysed by their levels in the fair value hierarchy – Level 1, Level 2 and Level 3. Group 2019 2018 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Valuation £m £m £m £m £m £m £m £m technique Assets Derivative financial instruments Exchange rate contracts 0 2,317 6 2,323 — 4,323 25 4,348 A Interest rate contracts 0 1,915 9 1,924 — 2,526 6 2,532 A & C Equity and credit contracts 0 223 60 283 — 188 63 251 B & D Netting 0 (1,214 ) 0 (1,214 ) — (1,872 ) — (1,872 ) 0 3,241 75 3,316 — 5,165 94 5,259 Other financial assets at FVTPL Loans and advances to customers 0 0 92 92 — 12 82 94 A Debt securities 0 0 294 294 18 2,339 894 3,251 A, B & D Equity securities 0 0 0 0 — — — — B Reverse repurchase agreements – non trading 0 0 0 0 — 2,272 — 2,272 A 0 0 386 386 18 4,623 976 5,617 Financial assets at FVOCI Debt securities 9,209 482 0 9,691 12,487 742 — 13,229 D Loans and advances to customers 0 0 56 56 — — 73 73 D 9,209 482 56 9,747 12,487 742 73 13,302 Total assets at fair value 9,209 3,723 517 13,449 12,505 10,530 1,143 24,178 Liabilities Derivative financial instruments Exchange rate contracts 0 660 4 664 — 528 23 551 A Interest rate contracts 0 1,836 2 1,838 — 2,515 7 2,522 A & C Equity and credit contracts 0 134 26 160 — 132 36 168 B & D Netting 0 (1,214 ) 0 (1,214 ) — (1,872 ) — (1,872 ) 0 1,416 32 1,448 — 1,303 66 1,369 Other financial liabilities at FVTPL Debt securities in issue 0 1,099 6 1,105 — 983 7 990 A Structured deposits 0 406 29 435 — 104 29 133 A Repurchase agreements – non trading 0 0 0 0 — 2,110 — 2,110 A Collateral and associated financial guarantees 0 147 26 173 — 3,040 13 3,053 D 0 1,652 61 1,713 — 6,237 49 6,286 Total liabilities at fair value 0 3,068 93 3,161 — 7,540 115 7,655 Transfers between levels of the fair value hierarchy Transfers between levels of the fair value hierarchy are reported regularly throughout the year. In 2019, there were no significant transfers of financial instruments between Levels 1 and 2 or between Levels 2 and 3. In 2018, the main transfers of financial instruments between Levels 2 and 3 were Derivative assets of £35m and Derivative liabilities of £31m which were transferred from Level 2 to Level 3 following enhancements to the fair value hierarchy classification process. g) Fair value adjustments The internal models incorporate assumptions that Santander UK believes would be made by a market participant to establish fair value. Fair value adjustments are adopted when Santander UK considers that there are additional factors that would be considered by a market participant that are not incorporated in the valuation model. Santander UK classifies fair value adjustments as either ‘risk-related’ or ‘model-related’. The fair value adjustments form part of the portfolio fair value and are included in the balance sheet values of the product types to which they have been applied. The magnitude and types of fair value adjustment are listed in the following table: 2019 £m 2018 Risk-related: – Bid-offer (12 ) 13 – Uncertainty 17 36 – Credit risk adjustment 6 9 – Funding fair value adjustment 6 4 17 62 Model-related 0 5 17 67 Risk-related adjustments Risk-related adjustments are driven, in part, by the magnitude of Santander UK’s market or credit risk exposure, and by external market factors, such as the size of market spreads. (i) Bid-offer Portfolios are marked at bid or offer, as appropriate. Valuation models will typically generate mid-market bid-offer bid-offer bid-offer bid-offer (ii) Uncertainty Certain model inputs may be less readily determinable from market data, and/or the choice of model itself may be more subjective. In these circumstances, a range of possible values exists that the financial instrument or market parameter may assume, and an adjustment may be needed to reflect the likelihood that in estimating the fair value of the financial instrument, market participants would adopt more conservative values for uncertain parameters and/or model assumptions than those used in the valuation model. (iii) Credit risk adjustment Credit risk adjustments comprise credit and debit valuation adjustments. The credit valuation adjustment (CVA) is an adjustment to the valuation of OTC derivative contracts to reflect within fair value the possibility that the counterparty may default, and Santander UK may not receive the full market value of the transactions. The debit valuation adjustment (DVA) is an adjustment to the valuation of the OTC derivative contracts to reflect within the fair value the possibility that Santander UK may default, and that Santander UK may not pay full market value of the transactions. Santander UK calculates a separate CVA and DVA for each Santander UK legal entity, and within each entity for each counterparty to which the entity has exposure. Santander UK calculates the CVA by applying the probability of default of the counterparty to the expected positive exposure to the counterparty, and multiplying the result by the loss expected in the event of default i.e. LGD. Conversely, Santander UK calculates the DVA by applying the PD of the Santander UK group, conditional on the non-default For most products Santander UK uses a simulation methodology to calculate the expected positive exposure to a counterparty. This incorporates a range of potential exposures across the portfolio of transactions with the counterparty over the life of the portfolio. The simulation methodology includes credit mitigants such as counterparty netting agreements and collateral agreements with the counterparty. The methodologies do not, in general, account for wrong-way Wrong-way wrong-way wrong-way wrong-way wrong-way (iv) Funding fair value adjustment (FFVA) The FFVA is an adjustment to the valuation of OTC derivative positions to include the net cost of funding uncollateralised derivative positions. This is calculated by applying a suitable funding cost to the expected future funding exposure of any uncollateralised component of the OTC derivative portfolio. Model-related adjustments Models used for portfolio valuation purposes may be based upon a simplifying set of assumptions that do not capture all material market characteristics. Additionally, markets evolve, and models that were adequate in the past may require development to capture all material market characteristics in current market conditions. In these circumstances, model limitation adjustments are adopted. As model development progresses, model limitations are addressed within the core revaluation models and a model limitation adjustment is no longer needed. h) Internal models based on information other than market data (Level 3) The table below provides an analysis of financial instruments valued using internal models based on information other than market data together with further details on the valuation techniques used for each type of instrument. Each instrument is initially valued at transaction price: Balance sheet value Fair value movements recognised Balance sheet line item Category Financial instrument product type 2019 2018 2019 £m 2018 2017 1. Derivative assets Equity and credit contracts Reversionary property interests 52 54 2 30 (6 ) 2. FVTPL assets Loans and advances to customers Roll-up 51 53 0 8 2 3. FVTPL assets Loans and advances to customers Other loans 41 29 1 2 — 4. FVTPL assets Debt securities Reversionary property securities 120 142 (17 ) (28 ) (18 ) 5. FVTPL assets Debt securities Credit linked notes 174 752 7 13 — 6. FVOCI assets Loans and advances to customers Other loans 56 73 (2 ) (5 ) — 7. Derivative liabilities Equity contracts Property options and forwards (26 ) (35 ) 0 — (5 ) 8. FVTPL liabilities Financial guarantees Credit protection guarantee (26 ) (13 ) (7 ) (13 ) — 442 1,055 (16 ) 7 (27 ) Other Level 3 assets 23 40 16 (2 ) (26 ) Other Level 3 liabilities (41 ) (67 ) (5 ) 1 19 Total net assets 424 1,028 0 — — Total (expense)/income (5 ) 6 (34 ) Valuation techniques 1. Derivative assets – Equity and credit contracts These are valued using a probability weighted set of HPI forward prices, which are assumed to be a reasonable representation of the increase in value of the Santander UK group’s reversionary interest portfolio underlying the derivatives. The probability used reflects the likelihood of the home owner vacating the property and is calculated from mortality rates and acceleration rates which are a function of age and gender, obtained from the relevant mortality tables. Indexing is felt to be appropriate due to the size and geographical dispersion of the reversionary interest portfolio. These are determined using HPI spot rates adjusted to reflect estimated forward growth. Non-seasonally The inputs used to determine the value of the reversionary property derivatives are HPI spot, HPI forward growth and mortality rates. The principal pricing parameter is HPI forward growth. 2. FVTPL assets – Loans and advances to customers – roll-up These represent roll-up rolled-up The value of the mortgage ‘rolls up’ or accretes until the owner vacates the property. In order to value the roll-up The inputs used to determine the value of these instruments are HPI spot, HPI forward growth, HPI volatility, mortality rates and repayment rates. The principal pricing parameter is HPI forward growth. The HPI forward growth rate used is unobservable and is the same as used in the valuation of Instrument 1 above. The other parameters do not have a significant effect on the value of the instruments. 3. FVTPL assets – Loans and advances to customers – other loans These relate to loans to transport and education companies. The fair value of these loans is estimated using the ‘present value’ model based on a credit curve derived from current market spreads. Loan specific credit data is unobservable, so a proxy population is applied based on industry sector and credit rating. 4. FVTPL assets – Debt securities These consist of reversionary property securities and are an equity release scheme, where the property owner receives an upfront lump sum in return for paying a fixed percentage of the sales proceeds of the property when the owner vacates the property. These reversionary property securities are valued using a probability-weighted set of HPI forward prices which are assumed to be a reasonable representation of the increase in value of Santander UK’s reversionary interest portfolio underlying the derivatives. The probability weighting used reflects the probability of the home owner vacating the property through death or moving into care and is calculated from mortality rates and acceleration factors which are a function of age and gender, obtained from the relevant mortality table. The inputs used to determine the value of these instruments are HPI spot, HPI forward growth and mortality rates. The principal pricing parameter is HPI forward growth. Discussion of the HPI spot rate, HPI forward growth rate and mortality rates for this financial instrument is the same as Instrument 1 above. An adjustment is also made to reflect the specific property risk. Discussion of the specific property risk adjustment is the same as Instrument 1 above. 5. FVTPL assets – Debt securities (Credit linked notes) These consist of the retained senior tranches of credit linked notes in respect of credit protection vehicles sponsored by Santander UK, and are mandatorily held at fair value through profit or loss. These vehicles provide credit protection on reference portfolios of Santander UK group loans with junior notes sold to external investors. The notes retained by Santander UK are classified as level 3 financial instruments as their valuation depends upon unobservable parameters relating to the underlying reference portfolios of loans, including credit spreads, correlations and prepayment speed, which have a significant effect on the overall valuation. For more information, see ‘Credit protection entities’ in Note 19. 6. FVOCI assets – Loans and advances to customers – other loans These relate to shipping and construction loans. The fair value of these loans is estimated using the ‘present value’ model based on a credit curve derived from current market spreads. Loan specific credit data is unobservable, so a proxy population is applied based on industry sector and credit rating. 7. Derivative liabilities – Equity contracts There are three types of derivatives in this category: European options – These are valued using a modified Black-Scholes model where the HPI is log-normally Asian options – Asian (or average value) options are valued using a modified Black-Scholes model, with an amended strike price and volatility assumption to account for the average exercise period, through a closed form adjustment that reflects the strike price relative to the distribution of stock prices at each relevant date. This is also known as the Curran model. Forward contracts – Forward contracts are valued using a standard forward pricing model. The inputs used to determine the value of the above instruments are HPI spot rate, HPI forward growth rate and HPI volatility. The principal pricing parameter is HPI forward growth rate. 8. FVTPL liabilities – Financial guarantees These relate to credit protection guarantees in respect of the proceeds of the retained senior tranches of credit linked notes described in Instrument 5 above, and have been designated at fair value through profit or loss. These instruments are valued using the same unobservable parameters described in Instrument 5 above, such that changes in the valuation of the senior tranches of the credit linked notes are offset by changes in the value of these credit protection guarantees. For more information, see ‘Credit protection entities’ in Note 19. Reconciliation of fair value measurement in Level 3 of the fair value hierarchy The following table sets out the movements in Level 3 financial instruments in 2019 and 2018: Assets Liabilities Derivatives Other financial Financial Total Derivatives Other financial Total At 1 January 2019 94 976 73 1,143 (66 ) (49 ) (115 ) Total gains/(losses) recognised in profit or loss: – Fair value movements 18 (9 ) (2 ) 7 (6 ) (6 ) (12 ) – Foreign exchange and other movements 0 6 0 6 0 (6 ) (6 ) Transfers in 0 11 0 11 0 0 0 Netting (1) 0 (430 ) 0 (430 ) 0 0 0 Additions 2 188 0 190 0 (3 ) (3 ) Sales 0 0 0 0 0 0 0 Settlements (39 ) (356 ) (15 ) (410 ) 40 3 43 At 31 December 2019 75 386 56 517 (32 ) (61 ) (93 ) Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year 18 (3 ) (2 ) 13 (6 ) (12 ) (18 ) At 1 January 2018 64 838 199 1,101 (63 ) (6 ) (69 ) Total gains/(losses) recognised in profit or loss: – Fair value movements 28 (5 ) (5 ) 18 1 (13 ) (12 ) – Foreign exchange and other movements (5 ) — — (5 ) 5 (1 ) 4 Transfers in 35 18 — 53 (31 ) (29 ) (60 ) Additions — 280 17 297 — — — Sales — (95 ) — (95 ) — — — Settlements (28 ) (60 ) (138 ) (226 ) 22 — 22 At 31 December 2018 94 976 73 1,143 (66 ) (49 ) (115 ) Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year 23 (5 ) (5 ) 13 6 (14 ) (8 ) (1) This relates to the effect of netting on the fair value of the credit linked notes due to a legal right of set-off 19. Effect of changes in significant unobservable assumptions to reasonably possible alternatives (Level 3) As discussed

Offsetting Financial Assets and

Offsetting Financial Assets and Liabilities	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Offsetting Financial Assets and Liabilities	39. OFFSETTING FINANCIAL ASSETS AND LIABILITIES Financial assets and financial liabilities are reported on a net basis on the balance sheet only if there is a legally enforceable right to set off the recognised amounts and there is an intention to settle on a net basis, or to realise the asset and settle the liability simultaneously. The following table shows the impact of netting arrangements on: – All financial assets and liabilities that are reported net on the balance sheet – All derivative financial instruments and repurchase agreements and other similar secured lending and borrowing agreements that are subject to enforceable master netting arrangements or similar agreements, but do not qualify for balance sheet netting. The table identifies the amounts that have been offset in the balance sheet and also those amounts that are covered by enforceable netting arrangements (offsetting arrangements and financial collateral) but do not qualify for netting under the requirements described above. For derivative contracts, the ‘Financial instruments’ column identifies financial assets and liabilities that are subject to set off under netting agreements, such as the ISDA Master Agreement or derivative exchange or clearing counterparty agreements, whereby all outstanding transactions with the same counterparty can be offset and close-out non-cash Santander UK engages in a variety of counterparty credit mitigation strategies in addition to netting and collateral arrangements. Therefore, the net amounts presented in the tables below do not purport to represent Santander UK’s actual credit exposure. Group Amounts subject to enforceable netting arrangements Effects of offsetting on balance sheet Related amounts not offset Assets not 2019 Gross Amounts Net amounts Financial Financial (1) Net enforceable (2) Balance (3) Assets Derivative financial assets 4,446 (1,214 ) 3,232 (768 ) (1,915 ) 549 84 3,316 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 25,312 (1,676 ) 23,636 (537 ) (23,099 ) 0 0 23,636 – Fair value 0 0 0 0 0 0 0 0 Loans and advances to customers and banks (4) 5,247 (1,248 ) 3,999 0 0 3,999 205,143 209,142 35,005 (4,138 ) 30,867 (1,305 ) (25,014 ) 4,548 205,227 236,094 Liabilities Derivative financial liabilities 2,616 (1,214 ) 1,402 (768 ) (572 ) 62 46 1,448 Repurchase, securities lending & similar agreements: – Amortised cost 19,962 (1,676 ) 18,286 (537 ) (17,749 ) 0 0 18,286 – Fair value 0 0 0 0 0 0 0 0 Deposits by customers and banks (4) 11,395 (1,248 ) 10,147 0 (502 ) 9,645 186,089 196,236 33,973 (4,138 ) 29,835 (1,305 ) (18,823 ) 9,707 186,135 215,970 2018 Assets Derivative financial assets 7,026 (1,872 ) 5,154 (933 ) (2,133 ) 2,088 105 5,259 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 24,733 (3,606 ) 21,127 (2,721 ) (18,406 ) — — 21,127 – Fair value 2,272 — 2,272 — (2,272 ) — — 2,272 Loans and advances to customers and banks (4) 6,021 (1,293 ) 4,728 — — 4,728 199,360 204,088 40,052 (6,771 ) 33,281 (3,654 ) (22,811 ) 6,816 199,465 232,746 Liabilities Derivative financial liabilities 3,187 (1,872 ) 1,315 (933 ) (303 ) 79 54 1,369 Repurchase, securities lending & similar agreements: – Amortised cost 14,516 (3,606 ) 10,910 (2,721 ) (8,189 ) — — 10,910 – Fair value 2,110 — 2,110 — (2,110 ) — — 2,110 Deposits by customers and banks (4) 12,174 (1,293 ) 10,881 — (502 ) 10,379 184,430 195,311 31,987 (6,771 ) 25,216 (3,654 ) (11,104 ) 10,458 184,484 209,700 (1) Financial collateral is reflected at its fair value, but has been limited to the net balance sheet exposure so as not to include any over-collateralisation. (2) This column includes contractual rights of set-off (3) The balance sheet total is the sum of ‘Net amounts reported on the balance sheet’ that are subject to enforceable netting arrangements and ‘Amounts not subject to enforceable netting arrangements’. (4) The amounts offset within loans and advances to customers/banks or deposits by customers/banks relate to offset mortgages which are classified as either and that are subject to netting.

Events After the Balance Sheet

Events After the Balance Sheet Date	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Events After the Balance Sheet Date	40. EVENTS AFTER THE BALANCE SHEET DATE Since the balance sheet date there has been a global pandemic arising from an outbreak of respiratory illness known as COVID-19. This is causing disruption to financial markets and business activity in the UK. While it is too early to accurately estimate the financial and business impact of the COVID-19 outbreak, we expect a negative impact on our 2020 financial results.

Accounting Policies (Policies)

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2019
Statement [Line Items]
Basis of preparation	Basis of preparation These financial statements incorporate the financial statements of the Company and entities controlled by the Company (its subsidiaries) made up to 31 December each year. The Consolidated Financial Statements have been prepared on the going concern basis using the historical cost convention, except for financial assets and liabilities that have been measured at fair value. An assessment of the appropriateness of the adoption of the going concern basis of accounting is disclosed in the statement of going concern in the Directors’ Report. Compliance with International Financial Reporting Standards The Santander UK group Consolidated Financial Statements have been prepared in accordance with IFRSs as issued by the IASB, including interpretations issued by the IFRS Interpretations Committee (IFRS IC) of the IASB (together IFRS). The Santander UK group has also complied with its legal obligation to comply with IFRSs as adopted by the European Union as there are no applicable differences between the two frameworks for the periods presented. Disclosures required by IFRS 7 ‘Financial Instruments: Disclosure’ relating to the nature and extent of risks arising from financial instruments, and IAS 1 ‘Presentation of Financial Statements’ relating to objectives, policies and processes for managing capital, can be found in the Risk review. Those disclosures form an integral part of these financial statements. Recent accounting developments IFRS 16 ‘Leases’ (IFRS 16) On 1 January 2019 the Santander UK group adopted IFRS 16 and the revised accounting policies as lessee which have been applied from 1 January 2019 are set out below. Comparatives have not been restated. The impact of applying IFRS 16 is disclosed in section (ii). As described below, IFRS 16 impacted property and equipment leases where the Santander UK group is the lessee. IFRS 16 had no impact for leases where the Santander UK group is the lessor. i) Accounting policy change The Santander UK group as lessee The Santander UK group assesses whether a contract is or contains a lease at the inception of the contract and recognises a right-of-use (ROU) asset representing its right to use the underlying leased asset and a lease liability representing its obligation to make lease payments for all leases, except for short-term leases, being those with a term of 12 months or less, or leases for which the underlying asset is of low value which are expensed in the income statement on a straight-line basis over the lease terms. Lease payments exclude irrecoverable VAT which is expensed in the income statement as lease payments are made. The lease liability, which is included within Other liabilities on the balance sheet, is initially measured at the present value of the lease payments that are not paid at the commencement date, discounted using the incremental borrowing rate appropriate to the lease term. The lease liability is subsequently measured at amortised cost using the effective interest rate method. Remeasurement of the lease liability occurs if there is a change in the lease payments (when a corresponding adjustment is made to the ROU asset), the lease term or in the assessment of an option to purchase the underlying asset. At inception, the ROU asset, which is included within Property, plant and equipment on the balance sheet, comprises the lease liability, initial direct costs and the obligations to restore the asset, less any incentives granted by the lessor. The ROU asset is depreciated over the shorter of the lease term or the useful life of the underlying asset and is reviewed for indications of impairment as for owned assets. The obligation to restore the asset is included within Provisions on the balance sheet. ii) Impact of adoption The Santander UK group elected to apply the modified retrospective approach whereby the ROU asset at the date of initial application was measured at an amount equal to the lease liability. The ROU asset was adjusted for any prepaid lease payments and incentives relating to the relevant leases that were recognised on the balance sheet at 31 December 2018 and included an estimate of the costs of restoring the underlying assets to the condition required by the terms of the lease. In addition, the following practical expedients permitted by the standard were applied: • a single discount rate being the incremental borrowing rate was applied to a portfolio of leases with reasonably similar characteristics; and • operating leases with a remaining lease term of less than 12 months as at 1 January 2019 were treated as short term leases. For the Santander UK group, the application of IFRS 16 at 1 January 2019 increased property, plant and equipment by £210m (being the net increase in ROU assets referred to above), reduced other assets by £12m and increased other liabilities by £181m from recognising lease liabilities. In addition, we also increased provisions by £17m (see Note 27). There was no impact on shareholders’ equity. The amount of the lease liabilities above differed from the amount of operating lease commitments at 31 December 2018 and is reconciled as follows: Group £m Rental commitments under non-cancellable 246 Recognition exemption for short-term leases (72 ) Effect from discounting at the incremental borrowing rate at 1 January 2019 7 Additional liabilities recognised based on the initial application of IFRS 16 at 1 January 2019 181 In addition to the choice of transition approach, the determination of the discount rate is the most significant area of judgement. The Santander UK group applies an incremental borrowing rate (based on 3-month GBP LIBOR plus a credit spread to reflect the cost of raising unsecured funding in the wholesale markets) appropriate to the relevant remaining lease term. IAS 12 The Santander UK group has also applied the amendment to IAS 12 ‘Income Taxes’ (part of ‘Annual Improvements to IFRS Standards 2015-2017 Cycle’) in these Condensed Consolidated Interim Financial Statements. The amendment clarifies that the income tax consequences of dividends on financial instruments classified as equity should be recognised according to where the past transactions or events that generated distributable profits were recognised. This means that, to the extent that profits from which dividends on equity instruments were recognised in the income statement, the income tax consequences would be similarly recognised in the same statement. The amendment, which has been applied retrospectively, reduces the effective tax rate where the tax relief on dividends in respect of other equity instruments is recognised in the income statement rather than as a separate line item within the statement of changes in equity. Overall, there was no impact on shareholders’ equity for the Santander UK group from applying the amendment to IAS 12 at 1 January 2019. For the Santander UK group, the impact of the amendment to IAS 12 on the income statement for the year ended 31 December 2019 was to reduce tax on profit by £39m (2018: £42m, 2017: £46m), increasing profit after tax by the same amount. London Inter-Bank Offered Rate (LIBOR) reform In September 2019, the IASB issued Interest Rate Benchmark Reform: Amendments to IFRS 9 ‘Financial Instruments’, IAS 39 ‘Financial Instruments: Recognition and Measurement’ and IFRS 7 ‘Financial Instruments: Disclosure’. Santander UK applies IAS 39 hedge accounting so the amendments to IFRS 9 do not apply. The IAS 39 amendments provide temporary exceptions from applying specific hedge accounting requirements to hedging relationships that are directly affected by the reform to LIBOR and other Interbank Offered Rates, hereinafter referred to as LIBOR reform. The exceptions have the effect that LIBOR reform should not generally cause hedge accounting to terminate, however any hedge ineffectiveness continues to be recognised in the income statement. The exceptions end at the earlier of: • when the uncertainty regarding the timing and the amount of interest rate benchmark based cash flows is no longer present, and • discontinuance of the hedge relationship (or reclassification of all amounts from the cash flow hedge reserve). The IAS 39 amendments apply to all hedging relationships directly affected by uncertainties related to LIBOR reform and must be applied for annual periods beginning on or after 1 January 2020. However, following their endorsement for use in the European Union, Santander UK has elected to apply the IAS 39 and IFRS 7 amendments in the preparation of the financial statements for the year ended 31 December 2019. The exceptions given by the IAS 39 amendments mean that LIBOR reform had no impact on hedge relationships for affected hedges at and for the year ended 31 December 2019. The main assumptions or judgements made by Santander UK in applying the IAS 39 amendments are outlined below. • For cash flow hedges affected by LIBOR reform, Santander UK management has assumed that the interest rate benchmark on which hedged cash flows are based is not altered as a result of LIBOR reform when assessing whether the future cash flows are highly probable. For discontinued hedging relationships, the same assumption has been applied for determining whether the hedged future cash flows are expected to occur. • In making its prospective hedge effectiveness assessments, Santander UK has assessed whether the economic relationship between the hedged item and the hedging instrument exists based on the assumption that the interest rate benchmark on which the hedged item and the hedging instrument are based is not altered as a result of LIBOR reform. • Santander UK will not discontinue hedge accounting during the period of LIBOR-related uncertainty solely because the retrospective effectiveness falls outside the required 80-125% range. • For hedges of a non-contractually specified benchmark portion of an interest rate, Santander UK only considers at inception of such a hedging relationship whether the separately identifiable requirement is met. Details of the significant interest rate benchmarks to which hedging relationships are exposed, the extent of risk exposure that is affected by LIBOR reform, and how Santander UK’s transition to alternative benchmark interest rates is being managed, are disclosed in the Banking market risk section of the Risk review. The nominal amount of the hedging instruments in hedging relationships directly affected by uncertainties related to LIBOR reform is disclosed in Note 11. Future accounting developments At 31 December 2019, for the Santander UK group, there were no significant new or revised standards and interpretations, and amendments thereto, which have been issued but which are not yet effective or which have otherwise not been early adopted where permitted. Comparative information As required by US public company reporting requirements, these financial statements include two years of comparative information for the consolidated income statement, consolidated statement of comprehensive income, consolidated statement of changes in equity, consolidated statement of cash flows and related Notes.
Consolidation	Consolidation a) Subsidiaries The Consolidated Financial Statements incorporate the financial statements of the Company and entities (including structured entities) controlled by it and its subsidiaries. Control is achieved where the Company (i) has power over the investee; (ii) is exposed, or has rights, to variable returns from its involvement with the investee; and (iii) has the ability to use its power to affect its returns. The Company reassesses whether or not it controls an investee if facts and circumstances indicate that there are changes to one or more of the three elements of control listed above. When the Company has less than a majority of the voting rights of an investee, it has power over the investee when the voting rights are sufficient to give it the practical ability to direct the relevant activities of the investee unilaterally. The Company considers all relevant facts and circumstances in assessing whether or not the Company’s voting rights in an investee are sufficient to give it power, including: • The size of the Company’s holding of voting rights relative to the size and dispersion of holdings of the other vote holders • Potential voting rights held by the Company, other vote holders or other parties • Rights arising from other contractual arrangements • Any additional facts and circumstances that indicate that the Company has, or does not have, the current ability to direct the relevant activities at the time that decisions need to be made, including voting patterns at previous shareholders’ meetings. Consolidation of a subsidiary begins when the Company obtains control over the subsidiary and ceases when the Company loses control of the subsidiary. Specifically, the results of a subsidiary acquired or disposed of during the year are included in the consolidated income statement and the consolidated statement of comprehensive income from the date the Company gains control until the date when the Company ceases to control the subsidiary. Inter-company transactions, balances and unrealised gains on transactions between Santander UK group companies are eliminated; unrealised losses are also eliminated unless the cost cannot be recovered. The acquisition method of accounting is used to account for the acquisition of subsidiaries which meet the definition of a business. The cost of an acquisition is measured at the fair value of the assets given up, shares issued or liabilities undertaken at the date of acquisition. Acquisition-related costs are expensed as incurred. The excess of the cost of acquisition, as well as the fair value of any interest previously held, over the fair value of the Santander UK group’s share of the identifiable net assets of the subsidiary at the date of acquisition is recorded as goodwill. When the Santander UK group loses control of a subsidiary, the profit or loss on disposal is calculated as the difference between (i) the aggregate of the fair value of the consideration received and the fair value of any retained interest and (ii) the previous carrying amount of the assets (including goodwill), less liabilities of the subsidiary and any non-controlling interests. Amounts previously recognised in other comprehensive income in relation to the subsidiary are accounted for (i.e. reclassified to profit or loss or transferred directly to retained earnings) in the same manner as would be required if the relevant assets or liabilities are disposed of. The fair value of any investment retained in a former subsidiary at the date when control is lost is regarded as the fair value on initial recognition for subsequent accounting under IFRS 9 or, when applicable, the costs on initial recognition of an investment in an associate or joint venture. Business combinations between entities under common control (i.e. fellow subsidiaries of Banco Santander SA, the ultimate parent) are outside the scope of IFRS 3 – ‘Business Combinations’, and there is no other guidance for such transactions under IFRS. The Santander UK group elects to account for business combinations between entities under common control at their book values in the acquired entity by including the acquired entity’s results from the date of the business combination and not restating comparatives. Reorganisations of entities within the Santander UK group are also accounted for at their book values. Interests in subsidiaries are eliminated during the preparation of the Consolidated Financial Statements. b) Joint ventures Joint ventures are joint arrangements whereby the parties that have joint control of the arrangement have rights to its net assets. Joint control is the contractually agreed sharing of control of an arrangement, which exists only when decisions about the relevant activities require unanimous consent of the parties sharing control. Accounting policies of joint ventures have been aligned to the extent there are differences from the Santander UK group’s policies. Investments in joint ventures are accounted for by the equity method of accounting and are initially recorded at cost and adjusted each year to reflect the Santander UK group’s share of their post-acquisition results. When the Santander UK group’s share of losses of a joint venture exceed its interest in that joint venture, the Santander UK group discontinues recognising its share of further losses. Further losses are recognised only to the extent that the Santander UK group has incurred legal or constructive obligations or made payments on behalf of the joint venture.
Foreign currency translation	Foreign currency translation Items included in the financial statements of each entity in the Santander UK group are measured using the currency that best reflects the economic substance of the underlying events and circumstances relevant to that entity (the functional currency). The Consolidated Financial Statements are presented in sterling, which is the functional currency of the Company. Income statements and cash flows of foreign entities are translated into the Santander UK group’s presentation currency at average exchange rates for the year and their balance sheets are translated at the exchange rates ruling on 31 December. Exchange differences on the translation of the net investment in foreign entities are recognised in other comprehensive income. When a foreign entity is sold, such exchange differences are recognised in the income statement as part of the gain or loss on sale. Foreign currency transactions are translated into the functional currency of the entity involved at the exchange rates prevailing at the dates of the transactions. Foreign exchange gains and losses resulting from the settlement of such transactions and from the translation of monetary assets and liabilities denominated in foreign currencies are recognised in the income statement unless recognised in other comprehensive income in connection with a cash flow hedge. Non-monetary items denominated in a foreign currency measured at historical cost are not retranslated. Exchange rate differences arising on non-monetary items measured at fair value are recognised in the consolidated income statement except for differences arising on equity securities measured at fair value through other comprehensive income (FVOCI) (2017: available-for-sale asset measured at fair value), which are recognised in other comprehensive income.
Revenue recognition	Revenue recognition a) Interest income and expense Interest and similar income comprises interest income on financial assets measured at amortised cost, investments in debt instruments measured at FVOCI (2017: available-for-sale measured at fair value) and interest income on hedging derivatives. Interest expense and similar charges comprises interest expense on financial liabilities measured at amortised cost, and interest expense on hedging derivatives. Interest income on financial assets measured at amortised cost, investments in debt instruments measured at FVOCI (2017: available-for-sale The effective interest rate is the rate that discounts the estimated future cash payments or receipts over the expected life of the instrument or, when appropriate, a shorter period, to the gross carrying amount of the financial asset (i.e. its amortised cost before any impairment allowance) or to the amortised cost of a financial liability. When calculating the effective interest rate, the future cash flows are estimated after considering all the contractual terms of the instrument excluding expected credit losses. The calculation includes all amounts paid or received by the Santander UK group that are an integral part of the overall return, direct incremental transaction costs related to the acquisition, issue or disposal of the financial instrument and all other premiums or discounts. Interest income is calculated by applying the effective interest rate to the gross carrying amount of financial assets, except for financial assets that have subsequently become credit-impaired (or ‘Stage 3’), for which interest revenue is calculated by applying the effective interest rate to their amortised cost (i.e. net of the ECL provision). For more information on stage allocations of credit risk exposures, see ‘Significant increase in credit risk’ in the ‘Santander UK group level – credit risk management’ section of the Risk Review. b) Fee and commission income and expense Fees and commissions that are not an integral part of the effective interest rate are recognised when the service is performed. Most fee and commission income is recognised at a point in time. Certain commitment, upfront and management fees are recognised over time but are not material. For retail and corporate products, fee and commission income consists principally of collection services fees, commission on foreign currencies, commission and other fees received from retailers for processing credit card transactions, fees received from other credit card issuers for providing cash advances for their customers through the Santander UK group’s branch and ATM networks, annual fees payable by credit card holders and fees for non-banking financial products. For insurance products, fee and commission income consists principally of commissions and profit share arising from the sale of building and contents insurance and life protection insurance. Commissions arising from the sale of buildings and contents insurance are recognised over the period of insurance cover, adjusted to take account of cancelled policies. Profit share income from the sale of buildings and contents insurance which is not subject to any adjustment is recognised when the profit share income is earned. Commissions and profit share arising from the sale of life protection insurance is subject to adjustment for cancellations of policies within 3 years from inception. Fee and commission income which forms an integral part of the effective interest rate of a financial instrument (for example certain loan commitment fees) is recognised as an adjustment to the effective interest rate and recorded in ‘Interest income’. c) Dividend income Except for equity securities classified as trading assets or financial assets held at fair value through profit or loss, described below, dividend income is recognised when the right to receive payment is established. This is the ex-dividend d) Net trading and other income Net trading and other income includes all gains and losses from changes in the fair value of financial assets and liabilities held at fair value through profit or loss (comprising financial assets and liabilities held for trading, trading derivatives and other financial assets and liabilities at fair value through profit or loss), together with related interest income, expense, dividends and changes in fair value of any derivatives managed in conjunction with these assets and liabilities. Changes in fair value of derivatives in a fair value hedging relationship are also recognised in net trading and other income. Net trading and other income also includes income from operating lease assets, and profits and losses arising on the sales of property, plant and equipment and subsidiary undertakings.
Borrowing costs	Borrowing costs Borrowing costs directly attributable to the acquisition, construction or production of qualifying assets, including computer software, which are assets that necessarily take a substantial period of time to develop for their intended use, are added to the cost of those assets, until the assets are substantially ready for their intended use. All other borrowing costs are recognised in profit or loss in the period in which they occur.
Pensions and other post-retirement benefits	Pensions and other post-retirement benefits a) Defined benefit schemes A defined benefit scheme is a pension scheme that guarantees an amount of pension benefit to be provided, usually as a function of one or more factors such as age, years of service or compensation. Pension costs are charged to ‘Administration expenses’, within the line item ‘Operating expenses before impairment losses, provisions and charges’ with the net interest on the defined benefit asset or liability included within ‘Net interest income’ in the income statement. The asset or liability recognised in respect of defined benefit pension schemes is the present value of the defined benefit obligation at the balance sheet date, less the fair value of scheme assets. The defined benefit obligation is calculated annually by independent actuaries using the projected unit credit method. The assets of the schemes are measured at their fair values at the balance sheet date. The present value of the defined benefit obligation is estimated by projecting forward the growth in current accrued pension benefits to reflect inflation and salary growth to the date of pension payment, then discounted to present value using the yield applicable to high-quality AA rated corporate bonds of the same currency and which have terms to maturity closest to the terms of the scheme liabilities, adjusted where necessary to match those terms. In determining the value of scheme liabilities, demographic and financial assumptions are made by management about life expectancy, inflation, discount rates, pension increases and earnings growth, based on past experience and future expectations. Financial assumptions are based on market conditions at the balance sheet date and can generally be derived objectively. Demographic assumptions require a greater degree of estimation and judgement to be applied to externally derived data. Any surplus or deficit of scheme assets over liabilities is recognised in the balance sheet as an asset (surplus) or liability (deficit). An asset is only recognised to the extent that the surplus can be recovered through reduced contributions in the future or through refunds from the scheme. The income statement includes the net interest income/expense on the net defined benefit liability/asset, current service cost and any past service cost and gain or loss on settlement. Remeasurement of defined benefit pension schemes, including return on scheme assets (excludes amounts included in net interest), actuarial gains and losses (arising from changes in demographic assumptions, the impact of scheme experience and changes in financial assumptions) and the effect of the changes to the asset ceiling (if applicable), are recognised in other comprehensive income. Remeasurement recognised in other comprehensive income will not be reclassified to the income statement. Past-service costs are recognised as an expense in the income statement at the earlier of when the scheme amendment or curtailment occurs and when the related restructuring costs or termination benefits are recognised. Curtailments include the impact of significant reductions in the number of employees covered by a scheme, or amendments to the terms of the scheme so that a significant element of future service will no longer qualify for benefits or will qualify only for reduced benefits. Curtailment gains and losses on businesses that meet the definition of discontinued operations are included in profit or loss for the year from discontinued operations. Gains and losses on settlements are recognised when the settlement occurs. b) Defined contribution plans A defined contribution plan is a pension scheme under which the Santander UK group pays fixed contributions as they fall due into a separate entity (a fund). The pension paid to the member at retirement is based on the amount in the separate fund for each member. The Santander UK group has no legal or constructive obligations to pay further contributions into the fund to ‘top up’ benefits to a certain guaranteed level. The regular contributions constitute net periodic costs for the year in which they are due and are included in staff costs within Operating expenses in the income statement. c) Post-retirement medical benefit plans Post-retirement medical benefit liabilities are determined using the projected unit credit method, with actuarial valuations updated at each year-end. The expected benefit costs are accrued over the period of employment using an accounting methodology similar to that for the defined benefit pension scheme.
Share-based payments	Share-based payments The Santander UK group engages in cash-settled and equity-settled Options granted under the Employee Sharesave scheme are accounted for as cash-settled share-based payment transactions. Awards granted under the Long-Term Incentive Plan and Deferred Shares Bonus Plan are accounted for as equity-settled share-based The fair value of the services received is measured by reference to the fair value of the shares or share options initially on the date of the grant for both the cash and equity settled share-based payments and then subsequently at each reporting date for the cash-settled share-based payments. The cost of the employee services received in respect of the shares or share options granted is recognised in the income statement in administration expenses over the period that the services are received i.e. the vesting period. A liability equal to the portion of the services received is recognised at the fair value determined at each balance sheet date for cash-settled share-based The fair value of the options granted under the Employee Sharesave scheme is determined using an option pricing model, which takes into account the exercise price of the option, the current share price, the risk free interest rate, the expected volatility of the Banco Santander SA share price over the life of the option and the dividend growth rate. The fair value of the awards granted for the Long-Term Incentive Plan was determined at the grant date using an option pricing model, which takes into account the share price at grant date, the risk free interest rate, the expected volatility of the Banco Santander SA share price over the life of the award and the dividend growth rate. Vesting conditions included in the terms of the grant are not taken into account in estimating fair value, except for those that include terms related to market conditions. Non-market vesting conditions are taken into account by adjusting the number of shares or share options included in the measurement of the cost of employee service so that, ultimately, the amount recognised in the income statement reflects the number of vested shares or share options. Where vesting conditions are related to market conditions, the charges for the services received are recognised regardless of whether or not the market–related vesting conditions are met, provided that the non-market vesting conditions are met. Where an award has been modified, as a minimum, the expense of the original award continues to be recognised as if it had not been modified. Where the effect of a modification is to increase the fair value of an award or increase the number of equity instruments, the incremental fair value of the award or incremental fair value of the modification of the award is recognised in addition to the expense of the original grant, measured at the date of modification, over the modified vesting period. Cancellations in the vesting period are treated as an acceleration of vesting, and recognised immediately for the amount that would otherwise have been recognised for services over the vesting period.
Goodwill and other intangible assets	Goodwill and other intangible assets Goodwill represents the excess of the cost of an acquisition, as well as the fair value of any interest previously held, over the fair value of the share of the identifiable net assets of the acquired subsidiary, associate, or business at the date of acquisition. Goodwill on the acquisition of subsidiaries and businesses is included in intangible assets. Goodwill on acquisitions of associates is included as part of investment in associates. Goodwill is tested for impairment annually, or more frequently when events or changes in circumstances dictate, and carried at cost less accumulated impairment losses. Gains and losses on the disposal of an entity or business include the carrying amount of goodwill relating to the entity or business sold. Other intangible assets are recognised if they arise from contractual or other legal rights or if they are capable of being separated or divided from the Santander UK group and sold, transferred, licensed, rented or exchanged. The value of such intangible assets is amortised on a straight-line basis over their useful economic life of three to seven years. Other intangible assets are reviewed annually for impairment indicators and tested for impairment where indicators are present. Software development costs are capitalised when they are direct costs associated with identifiable and unique software products that are expected to provide future economic benefits and the cost of those products can be measured reliably. These costs include payroll, materials, services and directly attributable overheads. Internally developed software meeting these criteria and externally purchased software are classified in intangible assets on the balance sheet and amortised on a straight-line
Property, plant and equipment	Property, plant and equipment Property, plant and equipment include owner-occupied properties (including leasehold properties), office fixtures and equipment and computer software. Property, plant and equipment also includes operating leases where the Santander UK group is the lessor and right-of-use assets where the Santander UK group is the lessee, as described further in ‘Leases’ below. Property, plant and equipment are carried at cost less accumulated depreciation and accumulated impairment losses. A review for indications of impairment is carried out at each reporting date. Gains and losses on disposal are determined by reference to the carrying amount and are reported in net trading and other income. Repairs and renewals are charged to the income statement when the expenditure is incurred. Internally developed software meeting the criteria set out in ‘Goodwill and other intangible assets’ above and externally purchased software are classified in property, plant and equipment where the software is an integral part of the related computer hardware (for example operating system of a computer). Classes of property, plant and equipment are depreciated on a straight-line basis over their useful life, as follows: Owner-occupied properties Not exceeding 50 years Office fixtures and equipment 3 to 15 years Computer software 3 to 7 years Right-of-use Shorter of the lease term or the useful life of the underlying asset Depreciation is not charged on freehold land and assets under construction. Depreciation on operating lease assets where the Santander UK group is the lessor is described in ‘Leases’ below.
Financial instruments	Financial instruments a) Initial recognition and measurement Financial assets and liabilities are initially recognised when the Santander UK group becomes a party to the contractual terms of the instrument. The Santander UK group determines the classification of its financial assets and liabilities at initial recognition and measures a financial asset or financial liability at its fair value plus or minus, in the case of a financial asset or financial liability not at FVTPL, transaction costs that are incremental and directly attributable to the acquisition or issue of the financial asset or financial liability. Transaction costs of financial assets and financial liabilities carried at FVTPL are expensed in profit or loss. Immediately after initial recognition, an expected credit loss (ECL) allowance is recognised for financial assets measured at amortised cost and investments in debt instruments measured at FVOCI. A regular way purchase is a purchase of a financial asset under a contract whose terms require delivery of the asset within the timeframe established generally by regulation or convention in the market place concerned. Regular way purchases of financial assets classified as loans and receivables, issues of equity or financial liabilities measured at amortised cost are recognised on settlement date; all other regular way purchases and issues are recognised on trade date. b) Financial assets and liabilities i) Classification and subsequent measurement The Santander UK group classifies its financial assets in the measurement categories of amortised cost, FVOCI and FVTPL. Financial assets and financial liabilities are classified as FVTPL where there is a requirement to do so or where they are otherwise designated at FVTPL on initial recognition. Financial assets and financial liabilities which are required to be held at FVTPL include: • Financial assets and financial liabilities held for trading • Debt instruments that do not have solely payments of principal and interest (SPPI) characteristics. Otherwise, such instruments are measured at amortised cost or FVOCI, and • Equity instruments that have not been designated as held at FVOCI. Financial assets and financial liabilities are classified as held for trading if they are derivatives or if they are acquired or incurred principally for the purpose of selling or repurchasing in the near-term, or form part of a portfolio of financial instruments that are managed together and for which there is evidence of short-term profit taking. In certain circumstances, other financial assets and financial liabilities are designated at FVTPL where this results in more relevant information. This may arise because it significantly reduces a measurement inconsistency that would otherwise arise from measuring assets or liabilities or recognising the gains or losses on them on a different basis, where the assets and liabilities are managed and their performance evaluated on a fair value basis or, in the case of financial liabilities, where it contains one or more embedded derivatives which are not closely related to the host contract. The classification and measurement requirements for financial asset debt and equity instruments and financial liabilities are set out below. a) Financial assets: debt instruments Debt instruments are those instruments that meet the definition of a financial liability from the issuer’s perspective, such as loans and government and corporate bonds. Classification and subsequent measurement of debt instruments depend on the Santander UK group’s business model for managing the asset, and the cash flow characteristics of the asset. Business model The business model reflects how the Santander UK group manages the assets in order to generate cash flows and, specifically, whether the Santander UK group’s objective is solely to collect the contractual cash flows from the assets or is to collect both the contractual cash flows and cash flows arising from the sale of the assets. If neither of these is applicable, such as where the financial assets are held for trading purposes, then the financial assets are classified as part of an ‘other’ business model and measured at FVTPL. Factors considered in determining the business model for a group of assets include past experience on how the cash flows for these assets were collected, how the assets’ performance is evaluated and reported to key management personnel, and how risks are assessed and managed. SPPI Where the business model is to hold assets to collect contractual cash flows or to collect contractual cash flows and sell, the Santander UK group assesses whether the assets’ cash flows represent SPPI. In making this assessment, the Santander UK group considers whether the contractual cash flows are consistent with a basic lending arrangement (i.e. interest includes only consideration for the time value of money, credit risk, other basic lending risks and a profit margin that is consistent with a basic lending arrangement). Where the contractual terms introduce exposure to risk or volatility that is inconsistent with a basic lending arrangement, the related asset is classified and measured at FVTPL. Financial assets with embedded derivatives are considered in their entirety when determining whether their cash flows are SPPI. Based on these factors, the Santander UK group classifies its debt instruments into one of the following measurement categories: • Amortised cost – Financial assets that are held for collection of contractual cash flows where those cash flows represent SPPI, and that are not designated at FVTPL, are measured at amortised cost. The carrying amount of these assets is adjusted by any ECL recognised and measured as presented in Note 13. Interest income from these financial assets is included in ‘Interest and similar income’ using the effective interest rate method. When estimates of future cash flows are revised, the carrying amount of the respective financial assets or financial liabilities is adjusted to reflect the new estimate discounted using the original effective interest rate. Any changes are recognised in the income statement. • FVOCI – Financial assets that are held for collection of contractual cash flows and for selling the assets, where the assets’ cash flows represent SPPI, and that are not designated at FVTPL, are measured at FVOCI. Movements in the carrying amount are recognised in OCI, except for the recognition of impairment gains or losses, interest revenue and foreign exchange gains and losses on the instrument’s amortised cost which are recognised in profit or loss. When the financial asset is derecognised, the cumulative gain or loss previously recognised in OCI is reclassified from equity to profit or loss and recognised in ‘Net trading and other income’. Interest income from these financial assets is included in ‘Interest and similar income’ using the effective interest rate method. • FVTPL – Financial assets that do not meet the criteria for amortised cost or FVOCI are measured at FVTPL. A gain or loss on a debt instrument that is subsequently measured at FVTPL, including any debt instruments designated at fair value, is recognised in profit or loss and presented in the income statement in ‘Net trading and other income’ in the period in which it arises. The Santander UK group reclassifies financial assets when and only when its business model for managing those assets changes. The reclassification takes place from the start of the first reporting period following the change. Such changes are expected to be very infrequent. b) Financial assets: equity instruments Equity instruments are instruments that meet the definition of equity from the issuer’s perspective, being instruments that do not contain a contractual obligation to pay cash and that evidence a residual interest in the issuer’s net assets. All equity investments are subsequently measured at FVTPL, except where management has elected, at initial recognition, to irrevocably designate an equity investment at FVOCI. When this election is used, fair value gains and losses are recognised in OCI and are not subsequently reclassified to profit or loss, including on disposal. ECLs (and reversal of ECLs) are not reported separately from other changes in fair value. Dividends, when representing a return on such investments, continue to be recognised in profit or loss as other income when the right to receive payments is established. Gains and losses on equity investments at FVTPL are included in the ‘Net trading and other income’ line in the income statement. c) Financial liabilities Financial liabilities are classified as subsequently measured at amortised cost, except for: • Financial liabilities at fair value through profit or loss: this classification is applied to derivatives and other financial liabilities designated as such at initial recognition. Gains or losses on financial liabilities designated at fair value through profit or loss are presented partially in other comprehensive income (the amount of change in the fair value of the financial liability that is attributable to changes in the credit risk of that liability) and partially in profit or loss (the remaining amount of change in the fair value of the liability) • Financial liabilities arising from the transfer of financial assets which did not qualify for derecognition, whereby a financial liability is recognised for the consideration received for the transfer. In subsequent periods, the Santander UK group recognises any expense incurred on the financial liability, and • Financial guarantee contracts and loan commitments. Contracts involving the receipt of cash on which customers receive an index-linked return are accounted for as equity index-linked deposits. The principal products are Capital Guaranteed/Protected Products which give the customers a limited participation in the upside growth of an equity index. In the event the index falls in price, a cash principal element is guaranteed/protected. The equity index-linked deposits contain embedded derivatives. These embedded derivatives, in combination with the principal cash deposit element, are designed to replicate the investment performance profile tailored to the return agreed in the contracts with customers. The cash principal element is accounted for as deposits by customers at amortised cost. The embedded derivatives are separated from the host instrument and are separately accounted for as derivatives. d) Sale and repurchase agreements (including stock borrowing and lending) Securities sold subject to a commitment to repurchase them at a predetermined price (repos) under which substantially all the risks and rewards of ownership are retained by the Santander UK group remain on the balance sheet and a liability is recorded in respect of the consideration received. Securities purchased under commitments to resell (reverse repos) are not recognised on the balance sheet and the consideration paid is recorded as an asset. The difference between the sale and repurchase price is treated as trading income in the income statement, except where the repo is not treated as part of the trading book, in which case the difference is recorded in interest income or expense. Securities lending and borrowing transactions are generally secured, with collateral in the form of securities or cash advanced or received. Securities lent or borrowed are not reflected on the balance sheet. Collateral in the form of cash received or advanced is recorded as a deposit or a loan. Collateral in the form of securities is not recognised. e) Day One profit adjustments The fair value of a financial instrument on initial recognition is generally its transaction price (that is, the fair value of the consideration given or received). However, sometimes the fair value will be based on other observable current market transactions in the same instrument, without modification or repackaging, or on a valuation technique whose variables include only data from observable markets, such as interest rate yield curves, option volatilities and currency rates. When such evidence exists, the Santander UK group recognises a trading gain or loss at inception (Day One gain or loss), being the difference between the transaction price and the fair value. When significant unobservable parameters are used, the entire Day One gain or loss is deferred and is recognised in the income statement over the life of the transaction until the transaction matures, is closed out, the valuation inputs become observable or an offsetting transaction is entered into. ii) Impairment of debt instrument financial assets The Santander UK group assesses on a forward-looking • An unbiased and probability-weighted amount that is determined by evaluating a range of possible outcomes • The time value of money, and • Reasonable and supportable information that is available without undue cost or effort at the reporting date about past events, current conditions and forecasts of future economic conditions. Grouping of instruments for losses measured on a collective basis We typically group instruments and assess them for impairment collectively where they share risk characteristics (as described in Retail Banking – credit risk management in the Risk review) using one or more statistical models. Where we have used internal capital or similar models as the basis for our IFRS 9 models, this typically results in a large number of relatively small homogenous groups which are determined by the permutations of the underlying characteristics in the statistical models. We calculate separate collective provisions for instruments in Stages 1, 2 and 3 where the instrument is not individually assessed, as described below. Individually assessed impairments (IAIs) We assess significant Stage 3 cases individually. We do this for CIB and Corporate & Commercial Banking cases, but not for Business Banking cases in Retail Banking which we assess collectively. To calculate the estimated loss, we estimate the future cash flows under several scenarios each of which uses case-specific For more on how ECL is calculated, see the Credit risk section of the Risk review. a) Write-off For secured loans, a write-off There is no threshold based on past due status beyond which all secured loans are written off as there can be significant variations in the time needed to enforce possession and sale of the security, especially due to the different legal frameworks that apply in different regions of the UK. For unsecured loans, a write-off is only made when all internal avenues of collecting the debt have been exhausted. Where appropriate the debt is passed over to external collection agencies. A past due threshold is applied to unsecured debt where accounts that are 180 days past due are written off unless there is a dispute awaiting resolution. Contact is made with customers with the aim to achieve a realistic and sustainable repayment arrangement. Litigation and/or enforcement of security is usually carried out only when the steps described above have been undertaken without success. All write-offs are assessed / made on a case-by-case basis, taking account of the exposure at the date of write-off, after accounting for the value from any collateral or insurance held against the loan. The exception to this is in cases where fraud has occurred, where the exposure is written off once investigations have been completed and the probability of recovery is minimal. The time span between discovery and write-off will be short and may not result in an impairment loss allowance being raised. The write-off Write-offs b) Recoveries Recoveries of credit impairment losses are not included in the impairment loss allowance, but are taken to income and offset against credit impairment losses. Recoveries of credit impairment losses are classified in the income statement as ‘Credit impairment losses’. iii) Modifications of financial assets The treatment of a renegotiation or modification of the contractual cash flows of a financial asset normally depends upon whether the renegotiation or modification is due to financial difficulties of the borrower or for other commercial reasons. • Contractual modifications due to financial difficulties of the borrower • Contractual modifications for other commercial reasons: Any other contractual modifications, such as where a regulatory authority imposes a change in certain contractual terms or due to legal reasons, are assessed on a case-by-case iv) Derecognition other than on a modification Financial assets are derecognised when the rights to receive cash flows have expired or the Santander UK group has transferred its contractual right to receive the cash flows from the assets and either: (1) substantially all the risks and rewards of ownership have been transferred; or (2) the Santander UK group has neither retained nor transferred substantially all of the risks and rewards, but has transferred control. Financial liabilities are derecognised when extinguished, cancelled or expired. c) Financial guarantee contracts and loan commitments Financial guarantee contracts are contracts that require the issuer to make specified payments to reimburse the holder for a loss it incurs because a specified debtor fails to make payments when due, in accordance with the terms of a debt instrument. Such financial guarantees are given to banks, financial institutions and others on behalf of customers to secure loans, overdrafts and other banking facilities. Financial guarantee contracts are initially measured at fair value and subsequently measured at the higher of the amount of the loss allowance, and the premium received on initial recognition less income recognised in accordance with the principles of IFRS 15. Loan commitments are measured as the amount of the loss allowance (determined in accordance with IFRS 9 as described in Credit risk section of the Risk review). The Santander UK group has not provided any commitment to provide loans at a below-market For financial guarantee contracts and loan commitments, the loss allowance is recognised as a provision and charged to credit impairment losses in the income statement. The loss allowance in respect of revolving facilities is classified in loans and advances to customers to the extent of any drawn balances. The loss allowance in respect of undrawn amounts is classified in provisions. When amounts are drawn, any related loss allowance is transferred from provisions to loans and advances to customers.
Derivative financial instruments	Derivative financial instruments (derivatives) Derivatives are contracts or agreements whose value is derived from one or more underlying indices or asset values inherent in the contract or agreement, which require no or little initial net investment and are settled at a future date. Transactions are undertaken in interest rate, cross currency, equity, residential property and other index-related swaps, forwards, caps, floors, swaptions, as well as credit default and total return swaps, equity index contracts and exchange traded interest rate futures, and equity index options. Derivatives are held for risk management purposes. Derivatives are classified as held for trading unless they are designated as being in a hedge accounting relationship. The Santander UK group chooses to designate certain derivatives as in a hedging relationship if they meet specific criteria, as further described in ‘Hedge accounting’ below. Derivatives are recognised initially (on the date on which a derivative contract is entered into), and are subsequently remeasured, at their fair value. Fair values of exchange-traded derivatives are obtained from quoted market prices. Fair values of over-the-counter Certain derivatives may be embedded in hybrid contracts, such as the conversion option in a convertible bond. If the hybrid contract contains a host that is a financial asset, then the Santander UK group assesses the entire contract as described in the financial asset section above for classification and measurement purposes. Otherwise, embedded derivatives are treated as separate derivatives when their economic characteristics and risks are not closely related to those of the host contract; the terms of the embedded derivative would meet the definition of a stand-alone derivative if they were contained in a separate contract; and the combined contract is not held for trading or designated at fair value. These embedded derivatives are measured at fair value with changes in fair value recognised in the income statement. Contracts containing embedded derivatives are not subsequently reassessed for separation unless either there has been a change in the terms of the contract which significantly modifies the cash flows (in which case the contract is reassessed at the time of modification) or the contract has been reclassified (in which case the contract is reassessed at the time of reclassification). All derivatives are carried as assets when their fair value is positive and as liabilities when their fair value is negative, except where netting is permitted. The method of recognising fair value gains and losses depends on whether derivatives are held for trading or are designated as hedging instruments and, if the latter, the nature of the risks being hedged. Gains and losses from changes in the fair value of derivatives held for trading are recognised in the income statement, and included within net trading and other income.
Offsetting financial assets and liabilities	Offsetting financial assets and liabilities Financial assets and liabilities including derivatives are offset and the net amount reported in the balance sheet when there is a legally enforceable right to set off the recognised amounts and there is an intention to settle on a net basis, or realise the asset and settle the liability simultaneously. The Santander UK group is party to a number of arrangements, including master netting arrangements under industry standard agreements which facilitate netting of transactions in jurisdictions where netting agreements are recognised and have legal force. The netting arrangements do not generally result in an offset of balance sheet assets and liabilities for accounting purposes, as transactions are usually settled on a gross basis.
Hedge accounting	Hedge accounting The Santander UK group applies hedge accounting to represent, to the maximum possible extent permitted under accounting standards, the economic effects of its risk management strategies. Derivatives are used to hedge exposures to interest rates, exchange rates and certain indices such as retail price indices. At the time a financial instrument is designated as a hedge (i.e. at the inception of the hedge), the Santander UK group formally documents the relationship between the hedging instrument(s) and hedged item(s), its risk management objective and strategy for undertaking the hedge. The documentation includes the identification of each hedging instrument and respective hedged item, the nature of the risk being hedged (including the benchmark interest rate being hedged in a hedge of interest rate risk) and how the hedging instrument’s effectiveness in offsetting the exposure to changes in the hedged item’s fair value attributable to the hedged risk is to be assessed. Accordingly, the Santander UK group formally assesses, both at the inception of the hedge and on an ongoing basis, whether the hedging derivatives have been and will be highly effective in offsetting changes in the fair value attributable to the hedged risk during the period that the hedge is designated. A hedge is normally regarded as highly effective if, at inception and throughout its life, the Santander UK group can expect, and actual results indicate, that changes in the fair value or cash flow of the hedged items are effectively offset by changes in the fair value or cash flow of the hedging instrument. If at any point it is concluded that it is no longer highly effective in achieving its documented objective, hedge accounting is discontinued. Where derivatives are held for risk management purposes, and when transactions meet the required criteria for documentation and hedge effectiveness, the derivatives may be designated as either: (i) hedges of the change in fair value of recognised assets or liabilities or firm commitments (fair value hedges); (ii) hedges of the variability in highly probable future cash flows attributable to a recognised asset or liability, or a forecast transaction (cash flow hedges); or (iii) a hedge of a net investment in a foreign operation (net investment hedges). The Santander UK group applies fair value and cash flow hedge accounting, but not hedging of a net investment in a foreign operation. a) Fair value hedge accounting Changes in the fair value of derivatives that are designated and qualify as fair value hedges are recorded in the income statement, together with the changes in the fair value of the hedged asset or liability that are attributable to the hedged risk. Where the hedged item is measured at amortised cost, the fair value changes due to the hedged risk adjust the carrying amount of the hedged asset or liability. Changes in the fair value of portfolio hedged items are presented separately in the consolidated balance sheet in macro hedge of interest rate risk and recognised in the income statement within net trading and other income. If the hedge no longer meets the criteria for hedge accounting, changes in the fair value of the hedged item attributable to the hedged risk are no longer recognised in the income statement. For fair value hedges of interest rate risk, the cumulative adjustment that has been made to the carrying amount of the hedged item is amortised to the income statement using the effective interest method over the period to maturity. For portfolio hedged items, the cumulative adjustment is amortised to the income statement using the straight line method over the period to maturity. b) Cash flow hedge accounting The effective portion of changes in the fair value of qualifying cash flow hedges is recognised in other comprehensive income in the cash flow hedging reserve. The gain or loss relating to the ineffective portion is recognised immediately in the income statement. Amounts accumulated in equity are reclassified to the income statement in the periods in which the hedged item affects profit or loss. When a hedging instrument expires or is sold, or when a hedge no longer meets the criteria for hedge accounting, any cumulative gain or loss existing in equity at that time remains in equity and is recognised in the income statement when the forecast transaction is ultimately recognised in the income statement. When a forecast transaction is no longer expected to occur, the cumulative gain or loss that was reported in equity is immediately transferred to the income statement. The Santander UK group is exposed to cash flow interest rate risk on its floating rate assets, foreign currency risk on its fixed rate debt issuances denominated in foreign currency and equity price risk arises from the Santander UK group operating the Employee Sharesave scheme. Cash flow hedging is used to hedge the variability in cash flows arising from these risks.
Securitisation transactions	Securitisation transactions The Santander UK group has entered into arrangements where undertakings have issued mortgage-backed
Impairment of non-financial assets	Impairment of non-financial assets At each balance sheet date, or more frequently when events or changes in circumstances dictate, property plant and equipment (including operating lease assets) and intangible assets (including goodwill) are assessed for indicators of impairment. If indications are present, these assets are subject to an impairment review. The impairment review comprises a comparison of the carrying amount of the asset or cash generating unit with its recoverable amount: the higher of the asset’s or cash-generating The fair value is the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Value in use is calculated by discounting management’s expected future cash flows obtainable as a result of the asset’s continued use, including those resulting from its ultimate disposal, at a market-based discount rate on a pre-tax The carrying values of property, plant and equipment, goodwill and other intangible assets are written down by the amount of any impairment and the loss is recognised in the income statement in the period in which it occurs. A previously recognised impairment loss relating to property, plant and equipment may be reversed in part or in full when a change in circumstances leads to a change in the estimates used to determine the property, plant and equipment’s recoverable amount. The carrying amount of the property, plant and equipment will only be increased up to the amount that would have been had the original impairment not been recognised. Impairment losses on goodwill are not reversed. For conducting goodwill impairment reviews, cash generating units are the lowest level at which management monitors the return on investment on assets.
Leases	Leases a) The Santander UK group as lessor Operating lease assets are recorded at cost and depreciated over the life of the asset after taking into account anticipated residual value (RV). Operating lease rental income and depreciation is recognised on a straight-line basis over the life of the asset. After initial recognition, residual values are reviewed regularly, and any changes are recognised prospectively through remaining depreciation charges. Amounts due from lessees under finance leases and hire purchase contracts are recorded as receivables at the amount of the Santander UK group’s net investment in the leases. Finance lease income is allocated to accounting periods to reflect a constant periodic rate of return on the Santander UK group’s net investment outstanding in respect of the leases and hire purchase contracts. A provision is recognised to reflect a reduction in any anticipated unguaranteed RV. A provision is also recognised for voluntary termination of the contract by the customer, where appropriate. b) The Santander UK group as lessee The Santander UK group assesses whether a contract is or contains a lease at the inception of the contract and recognises a right-of-use (ROU) asset representing its right to use the underlying leased asset and a lease liability representing its obligation to make lease payments for all leases, except for leases with a term of 12 months or less which are expensed in the income statement on a straight-line The lease liability, which is included within Other liabilities on the balance sheet, is initially measured at the present value of the lease payments that are not paid at the commencement date, discounted using the incremental borrowing rate appropriate to the lease term. The lease liability is subsequently measured at amortised cost using the effective interest rate method. Remeasurement of the lease liability occurs if there is a change in the lease payments (when a corresponding adjustment is made to the ROU asset), the lease term or in the assessment of an option to purchase the underlying asset. At inception, the ROU asset, which is included within Property, plant and equipment on the balance sheet, comprises the lease liability, initial direct costs and the obligations to restore the asset, less any incentives granted by the lessor. The ROU asset is depreciated over the shorter of the lease term or the useful life of the underlying asset and is reviewed for indications of impairment as for owned assets. The obligation to restore the asset is included within Provisions on the balance sheet.
Income taxes, including deferred taxes	Income taxes, including deferred taxes The tax expense represents the sum of the income tax currently payable and deferred income tax. Income tax payable on profits, based on the applicable tax law in each jurisdiction, is recognised as an expense in the period in which profits arise. Taxable profit differs from net profit as reported in the income statement because it excludes items of income or expense that are taxable or deductible in other years and it further excludes items that are never taxable or deductible. The liability for current tax is calculated using tax rates that have been enacted or substantively enacted by the balance sheet date. Current taxes associated with the repurchase of equity instruments are reported directly in equity. A current tax liability for the current or prior period is measured at the amount expected to be paid to the tax authorities. Where the amount of the final tax liability is uncertain or where a position is challenged by a taxation authority, the liability recognised is the most likely outcome. Where a most likely outcome cannot be determined, a weighted average basis is applied. Deferred income tax is the tax expected to be payable or recoverable on income tax losses available to carry forward and on temporary differences arising between the tax bases of assets and liabilities and their carrying amounts in the Consolidated Financial Statements and is accounted for using the balance sheet liability method. Deferred tax liabilities are generally recognised for all taxable temporary differences and deferred tax assets are recognised to the extent that it is probable that taxable profits will be available against which the assets may be utilised as they reverse. Such deferred tax liabilities are not recognised if the temporary difference arises from the initial recognition of goodwill. Deferred tax assets and liabilities are not recognised from the initial recognition of other assets (other than in a business combination) and liabilities in a transaction that affects neither the taxable profit nor the accounting profit. Deferred tax is calculated at the tax rates that are expected to apply in the period when the liability is settled or the asset is realised based on rates enacted or substantively enacted at the balance sheet date. Deferred tax is charged or credited in the income statement, except when it relates to items recognised in other comprehensive income or directly in equity, in which case the deferred tax is also recognised in other comprehensive income or directly in equity. Deferred tax liabilities are recognised for taxable temporary differences arising on investments in subsidiaries except where the Santander UK group is able to control reversal of the temporary difference and it is probable that it will not reverse in the foreseeable future. The Santander UK group reviews the carrying amount of deferred tax assets at each balance sheet date and reduces it to the extent that it is no longer probable that sufficient taxable profits will be available to allow all or part of the asset to be recovered. Deferred tax relating to actuarial gains and losses on defined benefits is recognised in other comprehensive income. Deferred tax relating to fair value re-measurements of financial instruments accounted for at FVOCI and cash flow hedging instruments is charged or credited directly to other comprehensive income and is subsequently recognised in the income statement when the deferred fair value gain or loss is recognised in the income statement. Deferred and current tax assets and liabilities are only offset when they arise in the same tax reporting group and where there is both the legal right and the intention to settle on a net basis or to realise the asset and settle the liability simultaneously.
Cash and cash equivalents	Cash and cash equivalents For the purposes of the cash flow statement, cash and cash equivalents comprise balances with less than three months maturity from the date of acquisition, including cash and non-restricted balances with central banks, treasury bills and other eligible bills, loans and advances to banks and short-term investments in securities. Balances with central banks represent amounts held at the Bank of England as part of the Santander UK group’s liquidity management activities. In addition, it includes certain minimum cash balances held for regulatory purposes required to be maintained with the Bank of England.
Provisions	Provisions Provisions are recognised for present obligations arising as consequences of past events where it is more likely than not that a transfer of economic benefits will be necessary to settle the obligation, and it can be reliably estimated. Conduct provisions are made for the estimated cost of making redress payments with respect to the past sales of products, using conclusions such as the number of claims the number of those that will be upheld, the estimated average settlement per case and other related costs. Provision is made for the anticipated cost of restructuring, including redundancy costs, when an obligation exists. An obligation exists when the Santander UK group has a detailed formal plan for restructuring a business, has raised valid expectations in those affected by the restructuring, and has started to implement the plan or announce its main features. When a leasehold property ceases to be used in the business, provision is made where the unavoidable costs of the future obligations relating to the lease are expected to exceed anticipated rental income. The net costs are discounted using market rates of interest to reflect the long-term nature of the cash flows. Loan commitments are measured as the amount of the loss allowance (determined in accordance with IFRS 9 as described in Credit risk section of the Risk review). Contingent liabilities are possible obligations whose existence will be confirmed only by certain future events or present obligations where the transfer of economic benefit is uncertain or cannot be reliably measured. Contingent liabilities are not recognised but are disclosed unless they are remote.
Share capital	Share capital a) Share issue costs Incremental external costs directly attributable to the issue of new shares are deducted from equity net of related income taxes. b) Dividends Dividends on ordinary shares are recognised in equity in the period in which the right to receive payment is established.
Accounting policies relating to comparatives - IAS 39: Financial Instruments: Recognition and Measurement	Accounting policies relating to comparatives – IAS 39 On 1 January 2018, the Santander UK group adopted IFRS 9, which replaced IAS 39. In accordance with the transition requirements of IFRS 9, comparatives were not restated. The principal accounting policies applied in accordance with IAS 39 for periods before the adoption of IFRS 9 are set out below: Classification and measurement of financial assets and liabilities – IAS 39 Financial assets and liabilities are initially recognised when the Santander UK group becomes a party to the contractual terms of the instrument. The Santander UK group determines the classification of its financial assets and liabilities at initial recognition. Financial assets are classified as financial assets at fair value through profit or loss, loans and receivables and available-for-sale Financial assets and financial liabilities classified as FVTPL are initially recognised at fair value and transaction costs are taken directly to the income statement. Gains and losses arising from changes in fair value are included directly in the income statement except for gains and losses on financial liabilities designated at FVTPL relating to own credit which are presented in other comprehensive income. Derivative financial instruments, trading assets and liabilities and financial assets and liabilities designated at fair value are classified as FVTPL. Loans and receivables are initially recognised at fair value including direct and incremental transaction costs. They are subsequently valued at amortised cost, using the effective interest method. Loans and receivables consist of loans and advances to banks, loans and advances to customers, and loans and receivables securities. Available-for-sale financial assets are initially recognised at fair value including direct and incremental transaction costs, and subsequently held at fair value. Gains and losses arising from changes in fair value are recognised in other comprehensive income until sale or until determined to be impaired when the cumulative gain or loss or impairment losses are transferred to the income statement. Impairment losses and foreign exchange translation differences on monetary items are recognised in the income statement. Impairment of financial assets – IAS 39 At each balance sheet date, the Santander UK group assesses whether there is objective evidence that a financial asset or group of financial assets is impaired. A financial asset or a group of financial assets is impaired and impairment losses are incurred only if there is objective evidence of impairment as a result of one or more events that occurred after the initial recognition of the asset (a loss event) and that loss event (or events) has an impact on the estimated future cash flows of the financial asset or group of financial assets that can be reliably estimated. In the case of equity investments classified as available-for-sale, For assets carried at amortised cost, including loans and advances and loans and receivables securities, the amount of the loss is measured as the difference between the asset’s carrying amount and the present value of estimated future cash flows (excluding future credit losses that have not been incurred) discounted at the financial asset’s original effective interest rate. The carrying amount of the asset is reduced and the amount of the loss is recognised in profit or loss. For available-for-sale financial assets, the Santander UK group assesses impairment at each balance sheet date, which involves reviewing the financial circumstances (including creditworthiness) and future prospects of the issuer, assessing the future cash flows expected to be realised and, in the case of equity shares, considering whether there has been a significant or prolonged decline in the fair value of the security below its cost. The cumulative loss is measured as the difference between the acquisition cost and the current fair value, less any impairment loss previously reported in the income statement and is removed from other comprehensive income and recognised in the income statement. IAS 17 On 1 January 2019, Santander UK group adopted IFRS 16, which replaced IAS 17. Having chosen to apply the modified retrospective approach, in accordance with the transition requirements of IFRS 16, comparatives were not restated. The accounting policies for the Santander UK group as lessee applied in accordance with IAS 17 for periods before the adoption of IFRS 16 are set out below: The Santander UK group as lessee – IAS 17 The Santander UK group enters into operating leases for the rental of equipment or real estate. Payments made under such leases are charged to the income statement on a straight-line basis over the period of the lease. When an operating lease is terminated before the lease period has expired, any payment to be made to the lessor by way of penalty is recognised as an expense in the period in which termination takes place. If the lease agreement transfers the risk and rewards of the asset, the lease is recorded as a finance lease and the related asset is capitalised. At inception, the asset is recorded at the lower of the present value of the minimum lease payments or fair value and depreciated over the lower of the estimated useful life and the life of the lease. The corresponding rental obligations are recorded as borrowings. The aggregate benefit of incentives, if any, is recognised as a reduction of rental expense over the lease term on a straight-line basis.
Critical Judgements and Accounting Estimates	CRITICAL JUDGEMENTS AND ACCOUNTING ESTIMATES The preparation of the Consolidated Financial Statements requires management to make judgements and accounting estimates that affect the reported amount of assets and liabilities at the date of the Consolidated Financial Statements and the reported amount of income and expenses during the reporting period. Management evaluates its judgements and accounting estimates, which are based on historical experience and on various other factors that are believed to be reasonable under the circumstances, on an ongoing basis. Actual results may differ from these accounting estimates under different assumptions or conditions. In the course of preparing the Consolidated Financial Statements, no significant judgements have been made in the process of applying the accounting policies, other than those involving estimations about credit impairment losses, conduct remediation and pensions as set out below. The following accounting estimates, as well as the judgements inherent within them, are considered important to the portrayal of the Santander UK group’s financial results and financial condition because: (i) they are highly susceptible to change from period to period as assumptions are made to calculate the estimates, and (ii) any significant difference between the estimated amounts and actual amounts could have a material impact on the Santander UK group’s future financial results and financial condition. In calculating each accounting estimate, a range of outcomes was calculated based principally on management’s conclusions regarding the input assumptions relative to historical experience. The actual estimates were based on what management concluded to be the most probable assumptions within the range of reasonably possible assumptions. a) Credit impairment allowance The application of the ECL impairment methodology for calculating credit impairment allowances is highly susceptible to change from period to period. The methodology requires management to make a number of judgmental assumptions in determining the estimates. Any significant difference between the estimated amounts and actual amounts could have a material impact on the Santander UK group’s future financial results and financial condition. Key areas of judgement in accounting estimates The key judgements made by management in applying the ECL impairment methodology are set out below. • Definition of default • Forward-looking information • Probability weights • SICR • Post model adjustments. For more on each of these key judgements, see the ‘Credit risk – Santander UK group level – credit risk management’ section of the Risk review. Sensitivity of ECL allowance At 31 December 2019, the probability-weighted ECL allowance totalled £863m (2018: £807m), of which £813m (2018: £789m) related to exposures in Retail Banking, Corporate & Commercial Banking and Corporate Centre, and £50m (2018: £18m) related to exposures in Corporate & Investment Banking. The ECL allowance is sensitive to the methods, assumptions and estimates underlying its calculation. For example, management could have applied different probability weights to the economic scenarios and, depending on the weights chosen, this could have a material effect on the ECL allowance. In addition, the ECL allowance for residential mortgages, in particular, is significantly affected by the HPI assumptions which determine the valuation of collateral used in the calculations. Had management used different assumptions on probability weights and HPI, a larger or smaller ECL charge would have resulted that could have had a material impact on the Santander UK group’s reported ECL allowance and profit before tax. Sensitivities to these assumptions are set out below. Probability weights The amounts shown in the tables below illustrate the ECL allowances that would have arisen had management applied a 100% weighting to each economic scenario. The allowances were calculated using a stage allocation appropriate to each economic scenario presented and differs from the probability-weighted As described in more detail in the ‘Santander UK group level – Credit risk management’ section in the Risk review, our CIB segment uses three forward-looking economic scenarios, whereas our other segments use five scenarios. In order to present a consolidated view in a single table, the data for CIB in the table below presents the CIB Upside scenario in the Upside 2 column, the CIB downside scenario in the Downside 2 column, and interpolated data for CIB in the Upside 1 and Downside 1 columns. 2019 Weighted Upside 2 Upside 1 Base case Downside 1 Downside 2 Exposure Retail Banking 206,479 206,479 206,479 206,479 206,479 206,479 - of which: mortgages 178,788 178,788 178,788 178,788 178,788 178,788 CCB 21,855 21,855 21,855 21,855 21,855 21,855 CIB 13,456 13,456 13,456 13,456 13,456 13,456 Corporate Centre 74,532 74,532 74,532 74,532 74,532 74,532 ECL Retail Banking 591 456 467 485 570 1,148 - of which: mortgages 218 122 127 137 196 660 CCB 210 156 169 183 219 317 CIB 50 19 34 48 53 58 Corporate Centre 12 9 10 10 13 18 % % % % % % Proportion of assets in Stage 2 Retail Banking 4.7 3.2 3.3 3.3 3.7 8.3 - of which: mortgages 4.6 3.1 3.1 3.1 3.6 8.7 CCB 10.0 7.4 7.4 7.4 8.5 16.3 CIB 2.9 1.5 1.5 1.5 1.5 1.5 Corporate Centre 0.2 0.1 0.1 0.1 0.2 0.3 2018 £m £m £m £m £m £m Exposure Retail Banking 195,805 195,805 195,805 195,805 195,805 195,805 - of which: mortgages 169,170 169,170 169,170 169,170 169,170 169,170 CCB 22,835 22,835 22,835 22,835 22,835 22,835 CIB 17,618 17,618 17,618 17,618 17,618 17,618 Corporate Centre 74,690 74,690 74,690 74,690 74,690 74,690 ECL Retail Banking 594 431 452 480 637 1,607 - of which: mortgages 237 121 131 137 273 1,105 CCB 182 115 135 157 192 302 CIB 18 8 12 17 22 27 Corporate Centre 13 8 9 11 13 21 % % % % % % Proportion of assets in Stage 2 Retail Banking 5.4 3.4 3.5 3.7 4.7 15.1 - of which: mortgages 5.6 3.4 3.6 3.7 4.9 16.5 CCB 5.5 3.0 3.0 3.1 4.3 10.7 CIB 0.8 0.4 0.4 0.4 0.4 0.4 Corporate Centre 0.2 0.1 0.1 0.1 0.2 0.4 Changes to Stage 3 instruments are excluded from the disclosure because they are not specifically sensitive to changes in macroeconomic assumptions. We have incorporated our post model adjustments into the sensitivity analysis. HPI Given the relative size of our residential mortgage portfolio, management considers that changes in HPI assumptions underpinning the calculation of the ECL allowance for residential mortgages of £218m at 31 December 2019 (2018: £237m) would have the most significant impact on the ECL allowance. The table below shows the impact on profit before tax of applying an immediate and permanent house price increase / decrease to our base case economic scenario, and assumes no changes to the staging allocation of exposures: Increase/decrease in house prices Increase/(decrease) in profit before tax +20% +10% -10% -20% 31 December 2019 16 10 (16 ) (43 ) 31 December 2018 20 12 (20 ) (52 ) b) Provisions and contingent liabilities Significant judgment may be required when accounting for provisions, including in determining whether a present obligation exists and in estimating the probability and amount of any outflows. These judgments are based on the specific facts available and often require specialist professional advice. There can be a wide range of possible outcomes and uncertainties, particularly in relation to legal actions, and regulatory and consumer credit matters. As a result it is often not possible to make reliable estimates of the likelihood and amount of any potential outflows. The main areas of judgement relating to provisions and contingent liabilities are set out below. For more details, see Notes 27 and 29. (i) PPI conduct remediation The most critical factor in determining the level of PPI provision is the volume of claims that fall in scope for Santander UK. The uphold rate is informed by historical experience and the average cost of redress can be predicted reasonably accurately given that management is dealing with a high volume and reasonably homogeneous population. Key areas of judgement in accounting estimates The provision mainly represents management’s best estimate of Santander UK’s future liability in respect of misselling of PPI policies and Plevin complaints. It requires significant judgement by management in determining appropriate assumptions, although the level of judgement has reduced with the passing of the FCA deadline of 29 August 2019 for PPI complaints. The key assumption in calculating the provision was the estimated number of complaints that would be received in respect of customers with successful information requests that were still eligible to make a complaint. Sensitivity of PPI conduct remediation provision Had management used different assumptions, a larger or smaller provision charge would have resulted that could have had a material impact on the Santander UK group’s reported profit before tax. More details can be found in the PPI section of Note 27. (ii) Other Included in Regulatory and other provisions in Note 27 is an amount in respect of management’s best estimate of liability relating to compliance with certain requirements of the Consumer Credit Act. It also includes an amount in respect of management’s best estimate of liability relating to a legal dispute regarding allocation of responsibility for a specific PPI portfolio of complaints. For both items, Note 29 provides disclosure relating to ongoing factual issues and reviews that could impact the timing and amount of any outflows. In addition, Note 29 includes disclosure relating to an investigation in relation to the historical involvement of Santander UK plc, Santander Financial Services plc and Cater Allen International Limited in German dividend tax arbitrage transactions. It also includes disclosure relating to certain leases in which current and former Santander UK group members were the lessor that are currently under review by HMRC in connection with claims for tax allowances. c) Pensions The Santander UK group operates a number of defined benefit pension schemes as described in Note 28 and estimates their position as described in the accounting policy ‘Pensions and other post retirement benefits’. Key areas of judgement in accounting estimates Accounting for defined benefit pension schemes requires management to make assumptions principally about the discount rate adopted, but also about price inflation, pension increases, life expectancy and earnings growth. Management’s assumptions are based on past experience and current economic trends, which are not necessarily an indication of future experience. These are described in more detail in the ‘Actuarial assumptions’ section in Note 28. Sensitivity of defined benefit pension scheme estimates Had management used different assumptions, a larger or smaller pension remeasurement gain or loss would have resulted that could have had a material impact on the Santander UK group’s reported financial position. Detailed disclosures on the actuarial assumption sensitivities of the schemes can be found in the ‘Actuarial assumption sensitivities’ section in Note 28.

Credit risk (Tables)

Credit risk (Tables)	12 Months Ended
	Dec. 31, 2019
Statement [Line Items]
Summary of Probability Weightings Applied to Scenarios	The scenario weights we applied for 2019 and 2018 were: Scenario weights Upside 2 % Upside 1 % Base case % Downside 1 % Downside 2 % 2019 5 10 40 30 15 2018 5 15 40 30 10
Summary of Annual Growth Rates	Our macroeconomic assumptions and their evolution throughout the forecast period for 2019 and 2018 were: 2019 Upside 2 Upside 1 Base case Downside 1 Downside 2 House price growth 5-year 4.90 3.70 1.60 (1.20 ) (9.30 ) Peak/(trough) (1) 8.10 5.80 2.00 (2.80 ) (13.50 ) GDP 5-year 2.40 2.00 1.60 0.70 0.20 Cumulative growth/(fall) to peak/(trough) (2) 1.50 1.00 0.70 (1.10 ) (5.60 ) Unemployment rate 5-year 1.90 2.70 4.00 5.60 7.40 Peak/(trough) at 1.88 2.73 4.10 5.64 7.84 Bank of England base rate 5-year 2.00 2.00 0.75 2.00 2.25 Peak/(trough) at 2.00 2.00 0.75 2.00 3.00 2018 House price growth 5-year 3.40 2.30 2.00 (2.00 ) (9.50 ) Peak/(trough) at 7.40 4.60 2.00 (5.80 ) (15.60 ) GDP 5-year 2.50 2.10 1.60 0.70 0.30 Cumulative growth/(fall) to peak/(trough) 1.60 1.10 0.60 (0.60 ) (6.10 ) Unemployment rate 5-year 2.80 3.80 4.30 6.90 8.60 Peak/(trough) at 2.58 3.71 4.39 7.30 8.65 Bank of England base rate 5-year 1.00 1.25 1.50 2.50 2.25 Peak/(trough) at 2.00 2.00 1.50 2.50 3.00
Summary of Quantitative Criteria to Measure Significant Increase in Credit Risk	For each portfolio, the quantitative criteria we used for 2019 were: Retail Banking (1) Consumer (auto) Other unsecured Corporate & Corporate & Mortgages finance (2) Personal loans Credit cards Overdrafts Commercial Banking Investment Banking 30bps 300bps 30bps 340bps 260bps 30bps Internal rating method
Summary of Qualitative Criteria to Measure Significant Increase in Credit Risk	Qualitative criteria We also use qualitative criteria to identify where an exposure has increased in credit risk, independent of any changes in PD. For each portfolio, the criteria we used for 2019 and 2018 were: Retail Banking (1) Consumer (auto) Other unsecured Corporate & Corporate & Mortgages finance Personal loans Credit cards Overdrafts Commercial Banking Investment Banking In forbearance In forbearance In Collections In forbearance Fees suspended In forbearance Default in last 24m Deceased or Insolvent Default in last 12m Default in last 12m Default in last 12m Default in last 12m >30 Days past due (DPD) in last 12m Court ‘Return of goods’ order or Police watchlist In Collections Debit dormant >35 days Watchlist – proactive management Watchlist – proactive management Bankrupt Agreement terminated Default at proxy origination £100+ arrears Payment holiday Cash Collection £50+ arrears £100+ arrears Any excess in month (1) In Business Banking, for larger customers we apply the same criteria that we use for Corporate & Commercial Banking.
Disclosure of Post Model Adjustment Explanatory	PMAs 2019 2018 Interest-only maturity default risk 51 69 Buy-to-Let 21 20 Long-term indeterminate arrears 19 23 12+ months in arrears 23 11
Summary of Difference Between Maximum and Net Exposure to Credit Risk	The tables below show the main differences between our maximum and net exposure to credit risk. They show the effects of collateral, netting, and risk transfer to mitigate our exposure. The tables only show the financial assets that credit risk affects and to which the impairment requirements in IFRS 9 are applied. Maximum exposure Balance sheet asset Off-balance Collateral (1) 2019 Gross Loss Net Gross Loss Net Cash £bn Non-cash Netting (2) Net Cash and balances at central banks 21.2 0 21.2 0 0 0 0 0 0 21.2 Financial assets at amortised cost: – Loans and advances to customers: (3) – Loans secured on residential (4) 165.4 (0.2 ) 165.2 13.4 0 13.4 0 (168.7 ) 0 9.9 – Corporate loans 27.0 (0.2 ) 26.8 14.3 (0.1 ) (5) 14.2 (0.1 ) (19.4 ) 0 21.5 – Finance leases 6.3 (0.2 ) 6.1 0.3 0 0.3 (0.1 ) (6.3 ) 0 0 – Other unsecured loans 7.1 (0.2 ) 6.9 12.4 0 12.4 0 0 0 19.3 – Amounts due from fellow Banco Santander group subsidiaries and joint ventures 2.4 0 2.4 0 0 0 0 0 0 2.4 Total loans and advances to customers 208.2 (0.8 ) 207.4 40.4 (0.1 ) 40.3 (0.2 ) (194.4 ) 0 53.1 – Loans and advances to banks 1.9 0 1.9 1.2 0 1.2 0 0 0 3.1 – Reverse repurchase agreements – non trading 23.6 0 23.6 0 0 0 0 (23.1 ) (0.5 ) 0 – Other financial assets at amortised cost 7.1 0 7.1 0 0 0 0 0 0 7.1 Total financial assets at amortised cost 240.8 (0.8 ) 240.0 41.6 (0.1 ) 41.5 (0.2 ) (217.5 ) (0.5 ) 63.3 Financial assets at fair value at FVOCI: – Loans and advances to customers 0.1 0 0.1 0 0 0 0 0 0 0.1 – Debt securities 9.6 0 9.6 0 0 0 0 0 0 9.6 Total financial assets at FVOCI 9.7 0 9.7 0 0 0 0 0 0 9.7 Total 271.7 (0.8 ) 270.9 41.6 (0.1 ) 41.5 (0.2 ) (217.5 ) (0.5 ) 94.2 2018 Cash and balances at central banks 19.7 — 19.7 — — — — — — 19.7 Financial assets at amortised cost: – Loans and advances to customers: (3) – Loans secured on residential (4) 157.9 (0.2 ) 157.7 11.2 — 11.2 — (163.8 ) — 5.1 – Corporate loans 27.8 (0.2 ) 27.6 17.0 — 17.0 — (20.2 ) — 24.4 – Finance leases 6.8 (0.1 ) 6.7 0.2 — 0.2 (0.1 ) (6.1 ) — 0.7 – Other unsecured loans 7.6 (0.2 ) 7.4 11.6 (0.1 ) 11.5 — — — 18.9 – Amounts due from fellow Banco Santander group subsidiaries and joint ventures 2.0 — 2.0 — — — — (0.6 ) — 1.4 Total loans and advances to customers 202.1 (0.7 ) 201.4 40.0 (0.1 ) 39.9 (0.1 ) (190.7 ) — 50.5 – Loans and advances to banks 2.8 — 2.8 1.6 — 1.6 — — — 4.4 – Reverse repurchase agreements – non trading 21.1 — 21.1 — — — — (18.4 ) (2.7 ) — – Other financial assets at amortised cost 7.2 — 7.2 — — — — — — 7.2 Total financial assets at amortised cost 233.2 (0.7 ) 232.5 41.6 (0.1 ) 41.5 (0.1 ) (209.1 ) (2.7 ) 62.1 Financial assets at FVOCI: – Loans and advances to customers 0.1 — 0.1 0.1 — 0.1 — — — 0.2 – Debt securities 13.2 — 13.2 — — — — — — 13.2 Total financial assets at FVOCI 13.3 — 13.3 0.1 — 0.1 — — — 13.4 Total 266.2 (0.7 ) 265.5 41.7 (0.1 ) 41.6 (0.1 ) (209.1 ) (2.7 ) 95.2 (1) The forms of collateral we take to reduce credit risk include: residential and commercial property; other physical assets, including motor vehicles; liquid securities, including those transferred under reverse repurchase agreements; cash, including cash used as collateral for derivative transactions; and receivables. Charges on residential property are most of the collateral we take. (2) We can reduce credit risk exposures by applying netting. We do this mainly for derivative and repurchase transactions with financial institutions. For derivatives, we use standard master netting agreements. They allow us to set off our credit risk exposure to a counterparty from a derivative against our obligations to the counterparty in the event of default. This gives us a lower net credit exposure. They may also reduce settlement exposure. For more on this, see ‘Credit risk mitigation’ in the ‘Other business segments – credit risk management’ section. (3) Balances include interest we have charged to the customer’s account and accrued interest that we have not charged to the account yet. (4) The collateral value we have shown against advances secured on residential property is limited to the balance of each associated individual loan. It does not include the impact of over–collateralisation (where the collateral has a higher value than the loan balance) and includes collateral we would receive on draw down of certain off–balance sheet commitments. (5) The total rounds to £0.1bn and is split across all portfolios. In this table, it has been allocated in full to Corporate loans for presentational purposes. For the full detail, see the ‘Credit Quality’ section.
Summary of Difference Between Maximum and Net Exposure to Credit Risk	The tables below show the main differences between our maximum and net exposure to credit risk on the financial assets that credit risk affects and to which the impairment requirements in IFRS 9 are not applied. Balance sheet asset Collateral (1) 2019 gross Cash Non–cash Netting (2) Net Financial assets at FVTPL: – Derivative financial instruments 3.3 0 (1.9 ) (0.8 ) 0.6 – Other financial assets at FVTPL 0.4 0 0 0 0.4 Total 3.7 0 (1.9 ) (0.8 ) 1.0 2018 Financial assets at FVTPL: – Derivative financial instruments 5.3 — (2.1 ) (0.9 ) 2.3 – Other financial assets at FVTPL 5.6 — (2.3 ) — 3.3 Total 10.9 — (4.4 ) (0.9 ) 5.6 (1) The forms of collateral we take to reduce credit risk include: liquid securities, including those transferred under reverse repurchase agreements; cash, including cash used as collateral for derivative transactions; and receivables. (2) We can reduce credit risk exposures by applying netting. We do this mainly for derivative and repurchase transactions with financial institutions. For derivatives, we use standard master netting agreements. They allow us to set off our credit risk exposure to a counterparty from a derivative against our obligations to the counterparty in the event of default. This gives us a lower net credit exposure. They may also reduce settlement exposure. For more on this, see ‘Credit risk mitigation’ in the ‘Other business segments – credit risk management’ section.
Disclosure of Equivalent Credit Rating Grade used by Standard And Poors Ratings Services	In the final column of the table we show the approximate equivalent credit rating grade used by Standard & Poor’s Ratings Services (S&P). PD range Santander UK risk grade Mid % Lower % Upper % S&P equivalent 9 0.010 0.000 0.021 AAA to AA+ 8 0.032 0.021 0.066 AA to AA– 7 0.100 0.066 0.208 A+ to BBB 6 0.316 0.208 0.658 BBB– to BB 5 1.000 0.658 2.081 BB– 4 3.162 2.081 6.581 B+ to B 3 10.000 6.581 20.811 B– 2 31.623 20.811 99.999 CCC to C 1 (Default) 100.000 100.000 100.000 D
Summary of Credit Rating of Financial Assets Subject to Credit Risk	The tables below show the credit rating of our financial assets to which the impairment requirements in IFRS 9 are applied. For more on the credit rating profiles of key portfolios, see the ‘Credit risk – Retail Banking’ and ‘Credit risk – other business segments’ sections. Santander UK risk grade Loss allowance 9 8 7 6 5 4 3 to 1 Other (1) Total 2019 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Exposures On balance sheet Cash and balances at central banks 21.2 0 0 0 0 0 0 0 0 21.2 – Stage 1 21.2 0 0 0 0 0 0 0 0 21.2 Financial assets at amortised cost: – Loans and advances to customers (2) 11.4 30.6 75.4 52.1 18.8 10.9 6.2 2.8 (0.8 ) 207.4 – Stage 1 11.4 30.6 75.0 50.9 16.1 6.2 1.2 2.8 (0.1 ) 194.1 – Stage 2 0 0 0.4 1.2 2.7 4.7 2.7 0 (0.3 ) 11.4 – Stage 3 0 0 0 0 0 0 2.3 0 (0.4 ) 1.9 Of which mortgages: 9.8 25.0 71.9 42.9 7.7 4.2 3.9 0 (0.2 ) 165.2 – Stage 1 9.8 25.0 71.7 42.0 5.7 1.1 0.2 0 0 155.5 – Stage 2 0 0 0.2 0.9 2.0 3.1 2.0 0 (0.1 ) 8.1 – Stage 3 0 0 0 0 0 0 1.7 0 (0.1 ) 1.6 – Loans and advances to banks 0 0.2 0.4 0 0 0 0 1.3 0 1.9 – Stage 1 0 0.2 0.4 0 0 0 0 1.3 0 1.9 – Reverse repo agreements – non trading 15.3 2.4 4.2 1.5 0 0 0 0.2 0 23.6 – Stage 1 15.3 2.4 4.2 1.5 0 0 0 0.2 0 23.6 – Other financial assets at amortised cost 7.1 0 0 0 0 0 0 0 0 7.1 – Stage 1 7.1 0 0 0 0 0 0 0 0 7.1 Total financial assets at amortised cost 33.8 33.2 80.0 53.6 18.8 10.9 6.2 4.3 (0.8 ) 240.0 Financial assets at FVOCI: 6.1 3.2 0.4 0 0 0 0 0 0 9.7 – Stage 1 6.1 3.2 0.4 0 0 0 0 0 0 9.7 Total on balance sheet 61.1 36.4 80.4 53.6 18.8 10.9 6.2 4.3 (0.8 ) 270.9 Total off–balance sheet 0.9 8.5 8.4 8.1 5.0 1.1 0.5 9.1 (0.1 ) (3) 41.5 – Stage 1 0.9 8.5 8.4 8.0 4.7 1.0 0.3 9.1 0 40.9 – Stage 2 0 0 0 0.1 0.3 0.1 0.2 0 (0.1 ) 0.6 – Stage 3 0 0 0 0 0 0 0 0 0 0 Total exposures 62.0 44.9 88.8 61.7 23.8 12.0 6.7 13.4 (0.9 ) 312.4 ECL On balance sheet Cash and balances at central banks 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 Financial assets at amortised cost: – Loans and advances to customers (2) 0 0 0 0 0.1 0.2 0.5 0 0.8 – Stage 1 0 0 0 0 0 0.1 0 0 0.1 – Stage 2 0 0 0 0 0.1 0.1 0.1 0 0.3 – Stage 3 0 0 0 0 0 0 0.4 0 0.4 Of which mortgages: 0 0 0 0 0 0.1 0.1 0 0.2 – Stage 1 0 0 0 0 0 0 0 0 0 – Stage 2 0 0 0 0 0 0.1 0 0 0.1 – Stage 3 0 0 0 0 0 0 0.1 0 0.1 – Loans and advances to banks 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 – Reverse repo agreements – non trading 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 – Other financial assets at amortised cost 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 Total financial assets at amortised cost 0 0 0 0 0.1 0.2 0.5 0 0.8 Financial assets at FVOCI: 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 Total on balance sheet 0 0 0 0 0.1 0.2 0.5 0 0.8 Total off–balance sheet 0 0 0 0 0 0 0.1 0 0.1 – Stage 1 0 0 0 0 0 0 0 0 0 – Stage 2 0 0 0 0 0 0 0.1 0 0.1 – Stage 3 0 0 0 0 0 0 0 0 0 Total ECL 0 0 0 0 0.1 0.2 0.6 0 0.9 Santander UK risk grade 2019 9 % 8 % 7 % 6 % 5 % 4 % 3 to 1 Other (1) % Total % Coverage ratio On balance sheet Cash and balances at central banks 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 Financial assets at amortised cost: – Loans and advances to customers (2) 0 0 0 0 0.5 1.8 8.1 0 0.4 – Stage 1 0 0 0 0 0 1.6 0 0 0.1 – Stage 2 0 0 0 0 3.7 2.1 3.7 0 2.6 – Stage 3 0 0 0 0 0 0 17.4 0 21.1 Of which mortgages: 0 0 0 0 0 2.4 2.6 0 0.1 – Stage 1 0 0 0 0 0 0 0 0 0 – Stage 2 0 0 0 0 0 3.2 0 0 1.2 – Stage 3 0 0 0 0 0 0 5.9 0 6.3 – Loans and advances to banks 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 – Reverse repo agreements – non trading 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 – Other financial assets at amortised cost 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 Total financial assets at amortised cost 0 0 0 0 0.5 1.8 8.1 0 0.3 Financial assets at FVOCI: 0 0 0 0 0 0 0 0 0 – Stage 1 0 0 0 0 0 0 0 0 0 Total on balance sheet 0 0 0 0 0.5 1.8 8.1 0 0.3 Total off–balance sheet 0 0 0 0 0 0 20.0 0 0.2 – Stage 1 0 0 0 0 0 0 0 0 0 – Stage 2 0 0 0 0 0 0 50.0 0 16.7 – Stage 3 0 0 0 0 0 0 0 0 0 Total coverage ratio 0 0 0 0 0.4 1.7 9.0 0 0.3 (1) Includes cash at hand and smaller cases mainly in the consumer (auto) finance and commercial mortgages portfolios. We use scorecards for these items, rather than rating models. (2) Includes interest we have charged to the customer’s account and accrued interest we have not charged to the account yet. Santander UK risk grade Loss allowance £bn Total £bn 2018 9 £bn 8 £bn 7 £bn 6 £bn 5 £bn 4 £bn 3 to 1 Other (1) £bn Exposures On balance sheet Cash and balances at central banks 19.7 — — — — — — — — 19.7 – Stage 1 19.7 — — — — — — — — 19.7 Financial assets at amortised cost: – Loans and advances to customers (2) 10.0 27.4 72.3 51.5 20.3 11.4 6.3 2.9 (0.7 ) 201.4 – Stage 1 10.0 27.4 72.1 50.2 17.6 6.9 1.1 2.8 (0.1 ) 188.0 – Stage 2 — — 0.2 1.3 2.7 4.5 2.8 0.1 (0.3 ) 11.3 – Stage 3 — — — — — — 2.4 — (0.3 ) 2.1 Of which mortgages: 7.7 21.8 69.0 42.8 7.8 4.7 4.2 — (0.2 ) 157.8 – Stage 1 7.7 21.8 68.8 41.6 5.5 1.2 0.2 — — 146.8 – Stage 2 — — 0.2 1.2 2.3 3.5 2.1 — (0.1 ) 9.2 – Stage 3 — — — — — — 1.9 — (0.1 ) 1.8 – Loans and advances to banks 0.8 0.2 0.8 — — — — 1.0 — 2.8 – Stage 1 0.8 0.2 0.8 — — — — 1.0 — 2.8 – Reverse repo agreements – non trading 15.2 3.8 1.3 0.4 — — — 0.4 — 21.1 – Stage 1 15.2 3.8 1.3 0.4 — — — 0.4 — 21.1 – Other financial assets at amortised cost 7.2 — — — — — — — — 7.2 – Stage 1 7.2 — — — — — — — — 7.2 Total financial assets at amortised cost 33 2 31.4 74.4 51.9 20.3 11.4 6.3 4.3 (0.7 ) 232.5 Financial assets at FVOCI: 6.6 5.8 0.7 — — — — 0.2 — 13.3 – Stage 1 6.6 5.8 0.7 — — — — 0.2 — 13.3 Total on balance sheet 59.5 37.2 75.1 51.9 20.3 11.4 6.3 4.5 (0.7 ) 265.5 Total off–balance sheet 0.7 8.0 8.9 9.0 5.4 1.3 0.5 7.9 (0.1 ) (4) 41.6 – Stage 1 0.7 8.0 8.9 8.9 5.3 1.2 0.3 7.9 (0.1 ) 41.1 – Stage 2 — — — 0.1 0.1 0.1 0.1 — — 0.4 – Stage 3 — — — — — — 0.1 — — 0.1 Total exposures 60.2 45.2 84.0 60.9 25.7 12.7 6.8 12.4 (0.8 ) 307.1 Santander UK risk grade 9 8 7 6 5 4 3 to 1 Other (1) Total 2018 £bn £bn £bn £bn £bn £bn £bn £bn £bn ECL On balance sheet Cash and balances at central banks — — — — — — — — — – Stage 1 — — — — — — — — — Financial assets at amortised cost: – Loans and advances to customers (2) — — — — 0.1 0.2 0.4 — 0.7 – Stage 1 — — — — — 0.1 — — 0.1 – Stage 2 — — — — 0.1 0.1 0.1 — 0.3 – Stage 3 — — — — — — 0.3 — 0.3 Of which mortgages: — — — — — 0.1 0.1 — 0.2 – Stage 1 — — — — — — — — — – Stage 2 — — — — — 0.1 — — 0.1 – Stage 3 — — — — — — 0.1 — 0.1 – Loans and advances to banks — — — — — — — — — – Stage 1 — — — — — — — — — – Reverse repo agreements – non trading — — — — — — — — — – Stage 1 — — — — — — — — — – Other financial assets at amortised cost — — — — — — — — — – Stage 1 — — — — — — — — — Total financial assets at amortised cost — — — — 0.1 0.2 0.4 — 0.7 Financial assets at FVOCI: — — — — — — — — — – Stage 1 — — — — — — — — — Total on balance sheet — — — — 0.1 0.2 0.4 — 0.7 Total off-balance sheet — — — — — — 0.1 — 0.1 – Stage 1 — — — — — — 0.1 — 0.1 – Stage 2 — — — — — — — — — – Stage 3 — — — — — — — — — — — — — — — — — Total ECL — — — — 0.1 0.2 0.5 — 0.8 % % % % % % % % % Coverage ratio On balance sheet Cash and balances at central banks — — — — — — — — — – Stage 1 — — — — — — — — — Financial assets at amortised cost: – Loans and advances to customers (2) — — — — 0.5 1.8 6.3 — 0.3 – Stage 1 — — — — — 1.4 — — 0.1 – Stage 2 — — — — 3.7 2.2 3.6 — 2.7 – Stage 3 — — — — — — 12.5 — 14.3 Of which mortgages: — — — — — 2.1 2.4 — 0.1 – Stage 1 — — — — — — — — — – Stage 2 — — — — — 2.9 — — 1.1 – Stage 3 — — — — — — 5.3 — 5.6 – Loans and advances to banks — — — — — — — — — – Stage 1 — — — — — — — — — – Reverse repo agreements – non trading — — — — — — — — — – Stage 1 — — — — — — — — — – Other financial assets at amortised cost — — — — — — — — — – Stage 1 — — — — — — — — — Total financial assets at amortised cost — — — — 0.5 1.8 6.3 — 0.3 Financial assets at FVOCI: — — — — — — — — — – Stage 1 — — — — — — — — — Total on balance sheet — — — — 0.5 1.8 6.3 — 0.3 Total off–balance sheet — — — — — — 20.0 — 0.2 – Stage 1 — — — — — — 33.3 — 0.2 – Stage 2 — — — — — — — — — – Stage 3 — — — — — — — — — Total coverage ratio — — — — 0.4 1.6 7.4 — 0.3 (1) Includes cash at hand and smaller cases mainly in the consumer (auto) finance and commercial mortgages portfolios. We use scorecards for these items, rather than rating models. (2) Includes interest we have charged to the customer’s account and accrued interest we have not charged to the account yet. (3) The total rounds to £0.1bn and is split across all three Stages. In this table, it has been allocated in full to Stage 2 for presentational purposes. For the full detail, see the ‘Credit Quality’ section. (4) The total rounds to £0.1bn and is split across all three Stages. In this table, it has been allocated in full to Stage 1 for presentational purposes. For the full detail, see the ‘Credit Quality’ section.
Summary of Credit Performance	The customer loans in the tables below and in the rest of the ‘Credit risk’ section are presented differently from the balances in the Consolidated Balance Sheet. The main difference is that customer loans exclude interest we have accrued but not charged to customers’ accounts yet. Customer Stage 3 (1)(2) Stage 3 Stage 3 (3) Gross Total 2019 £bn £m £m % £m £m Retail Banking: 180.4 1,936 38 1.09 206 591 – of which mortgages 165.4 1,722 12 1.05 14 218 – of which business banking 1.8 78 1 4.28 24 52 – of which consumer (auto) finance 7.7 42 0 0.55 34 88 – of which other unsecured lending 5.5 94 25 2.15 134 233 Corporate & Commercial Banking 16.3 335 27 2.22 41 210 Corporate & Investment Banking 4.1 0 15 0.36 0 50 Corporate Centre 4.2 17 0 0.40 2 12 205.0 2,288 80 1.15 249 863 2018 Retail Banking: 172.8 2,211 43 1.30 182 594 – of which mortgages 158.0 1,982 17 1.27 18 237 – of which business banking 1.8 89 — 4.99 15 53 – of which consumer (auto) finance 7.3 43 — 0.58 24 85 – of which other unsecured lending 5.7 97 26 2.17 125 219 Corporate & Commercial Banking 17.7 264 12 1.56 97 182 Corporate & Investment Banking 4.6 — 26 0.56 252 (4) 18 Corporate Centre 4.5 16 — 0.36 3 13 199.6 2,491 81 1.29 534 807 Of which: Corporate lending 2019 22.3 413 43 2.04 65 311 2018 24.1 353 38 1.62 364 253 (1) We define Stage 3 in the ‘Credit risk – Santander UK group level’ section. (2) Interest on Stage 3 exposures is derecognised in line with the requirements of IFRS 9. (3) Total Stage 3 exposure as a percentage of customer loans plus undrawn Stage 3 exposures. The way we calculate the Stage 3 ratio was changed from 1 January 2019, and 2018 restated for consistency. See ‘Key metrics’ in the ‘Credit risk – Santander UK group level’ section. (4) Related to Carillion plc write-off
Summary of IFRS 9 Credit Quality	Stage 1 Stage 2 Stage 3 Total 2019 £m £m £m £m Exposures On-balance Retail Banking 169,003 9,459 1,936 180,398 – of which mortgages 155,477 8,157 1,722 165,356 Corporate & Commercial Banking 14,068 1,894 335 16,297 Corporate & Investment Banking 3,916 198 0 4,114 Corporate Centre 67,608 126 17 67,751 Total on-balance 254,595 11,677 2,288 268,560 Off–balance sheet Retail Banking (1) 25,849 194 38 26,081 – of which mortgages (1) 13,353 67 12 13,432 Corporate & Commercial Banking 5,249 282 27 5,558 Corporate & Investment Banking 9,129 198 15 9,342 Corporate Centre 614 0 0 614 Total off–balance sheet (2) 40,841 674 80 41,595 Total exposures 295,436 12,351 2,368 310,155 ECL On-balance Retail Banking 85 255 224 564 – of which mortgages 11 100 103 214 Corporate & Commercial Banking 34 35 126 195 Corporate & Investment Banking 2 12 0 14 Corporate Centre 3 3 6 12 Total on-balance 124 305 356 785 Off–balance sheet Retail Banking 13 13 1 27 – of which mortgages 3 1 0 4 Corporate & Commercial Banking 7 6 2 15 Corporate & Investment Banking 3 24 9 36 Total off–balance sheet 23 43 12 78 Total ECL 147 348 368 863 % % % % Coverage ratio (3) On-balance Retail Banking 0.1 2.7 11.6 0.3 – of which mortgages 0 1.2 5.9 0.1 Corporate & Commercial Banking 0.2 1.8 37.6 1.2 Corporate & Investment Banking 0.1 6.1 0 0.3 Corporate Centre 0 2 4 37.5 0 Total on-balance 0 2.6 15.6 0.3 Off–balance sheet Retail Banking 0.1 6.7 2.6 0.1 – of which mortgages 0 1.5 0 0 Corporate & Commercial Banking 0.1 2.1 7.4 0.3 Corporate & Investment Banking 0 12.1 60.0 0.4 Total off-balance 0.1 6.4 15.0 0.2 Total coverage 0 2.8 15.5 0.3 (1) Off-balance (2) Off-balance (3) ECL as a percentage of the related exposure. Total on-balance Stage 1 Stage 2 Stage 3 Total 2018 £m £m £m £m Exposures On-balance Retail Banking 160,212 10,324 2,211 172,747 – of which mortgages 146,619 9,356 1,982 157,957 Corporate & Commercial Banking 16,394 1,044 264 17,702 Corporate & Investment Banking 4,535 78 — 4,613 Corporate Centre 68,535 131 15 68,681 Total on-balance 249,676 11,577 2,490 263,743 Off–balance sheet Retail Banking 1) 22,819 196 43 23,058 – of which mortgages (1) 11,120 76 17 11,213 Corporate & Commercial Banking 4,939 182 12 5,133 Corporate & Investment Banking 12,923 56 26 13,005 Corporate Centre 525 — — 525 Total off–balance sheet (2) 41,206 434 81 41,721 Total exposures 290,882 12,011 2,571 305,464 ECL On-balance Retail Banking 84 256 228 568 – of which mortgages 10 118 106 234 Corporate & Commercial Banking 31 26 111 168 Corporate & Investment Banking 1 1 — 2 Corporate Centre 5 3 5 13 Total on-balance 121 286 344 751 Off–balance sheet Retail Banking 12 13 1 26 – of which mortgages 2 1 — 3 Corporate & Commercial Banking 6 6 2 14 Corporate & Investment Banking 4 2 10 16 Total off–balance sheet 22 21 13 56 Total ECL 143 307 357 807 % % % % Coverage ratio (3) On-balance Retail Banking 0.1 2.5 10.3 0.3 – of which mortgages — 1.3 5.3 0.1 Corporate & Commercial Banking 0.2 2.5 42.0 0.9 Corporate & Investment Banking — 1.3 — — Corporate Centre — 2.3 33.3 — Total on-balance — 2.5 13.8 0.3 Off–balance sheet Retail Banking 0.1 6.6 2.3 0.1 – of which mortgages — 1.3 — — Corporate & Commercial Banking 0.1 3.3 16.7 0.3 Corporate & Investment Banking — 3.6 38.5 0.1 Total off–balance sheet 0.1 4.8 16.0 0.1 Total coverage — 2.6 13.9 0.3 (1) Off-balance (2) Off-balance (3) ECL as a percentage of the related exposure.
Summary of Stage 2 Decomposition	Stage 2 analysis The following table analyses our Stage 2 exposures and ECL by the reason the exposure is classified as Stage 2. Retail Banking Other business segments Total 2019 Exposure £m ECL £m Coverage % Exposure £m ECL £m Coverage % Exposure £m ECL £m Coverage % PD deterioration 6,844 194 2.8 1,998 25 1.3 8,842 219 2.5 Forbearance 516 4 0.8 45 1 2.2 561 5 0.9 Other 1,239 24 1.9 496 52 10.5 1,735 76 4.4 30 DPD 1,054 46 4.4 159 2 1.3 1,213 48 4.0 9,653 268 2.8 2,698 80 3.0 12,351 348 2.8 2018 PD deterioration 7,854 196 2.5 655 15 2.3 8,509 211 2.5 Forbearance 450 3 0.7 12 1 8.3 462 4 0.9 Other 1,267 31 2.4 813 22 2.7 2,080 53 2.5 30 DPD 949 39 4.1 11 — — 960 39 4.1 10,520 269 2.6 1,491 38 2.5 12,011 307 2.6
Disclosure of Stage Two Decomposition Cure and Not Cure Explanatory	The following table analyses our Stage 2 exposures and the related ECL by whether or not they are in a cure period at the balance sheet date. 2019 2018 Exposure ECL Coverage Exposure ECL Coverage £m £m % £m £m % Stage 2 not in cure period 12,017 342 2.8 11,837 301 2.5 Stage 2 in cure period (for transfer to Stage 1) 334 6 1.8 174 6 3.4 12,351 348 2.8 12,011 307 2.6
Summary of Reconciliation of Exposures, ECL and Net Carrying Amounts	The table below shows the relationships between disclosures in this Credit risk review section which refer to drawn exposures and the associated ECL, and the total assets as presented in the Consolidated Balance Sheet. On-balance Off-balance 2019 Exposures £m Loss allowance £m Net carrying amount £m Exposures £m Loss allowance £m Retail Banking 180,398 564 179,834 26,081 27 – of which mortgages 165,356 214 165,142 13,432 4 Corporate & Commercial Banking 16,297 195 16,102 5,558 15 Corporate & Investment Banking 4,114 14 4,100 9,342 36 Corporate Centre 67,751 12 67,739 614 0 Total exposures presented in Credit Quality tables 268,560 785 267,775 41,595 78 Other items (1) 2,986 Adjusted net carrying amount 270,761 Assets classified at FVTPL 3,702 Non–financial assets 7,239 Total assets per the Consolidated Balance Sheet 281,702 2018 Retail Banking 172,747 568 172,179 23,058 26 – of which mortgages 157,957 234 157,723 11,213 3 Corporate & Commercial Banking 17,702 168 17,534 5,133 14 Corporate & Investment Banking 4,613 2 4,611 13,005 16 Corporate Centre 68,681 13 68,668 525 — Total exposures presented in Credit Quality tables 263,743 751 262,992 41,721 56 Other items (1) 2,501 Adjusted net carrying amount 265,493 Assets classified at FVTPL 10,876 Non–financial assets 7,003 Total assets per the Consolidated Balance Sheet 283,372 (1) These assets mainly relate to loans as part of a JV agreement and the accrued interest on them. They carry low credit risk and therefore have an immaterial ECL.
Summary of ECL Reconciliation	The following table shows changes in total on and off-balance Stage 1 Stage 2 Stage 3 Total Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL £m £m £m £m £m £m £m £m At 1 January 2019 290,882 143 12,011 307 2,571 357 305,464 807 Transfers from Stage 1 to Stage 2 (3) (4,101 ) (11 ) 4,101 11 0 0 0 0 Transfers from Stage 2 to Stage 1 (3) 3,458 74 (3,458 ) (74 ) 0 0 0 0 Transfers to Stage 3 (3) (361 ) (2 ) (595 ) (24 ) 956 26 0 0 Transfers from Stage 3 (3) 10 1 516 23 (526 ) (24 ) 0 08 Transfers of financial instruments (994 ) 62 564 (64 ) 430 2 0 0 Net ECL remeasurement on stage transfer (4) 0 (66 ) 0 130 0 96 0 160 Change in economic scenarios (2) 0 5 0 (15 ) 0 (9 ) 0 (19 ) Changes to model 0 0 0 0 0 13 0 13 New lending and assets purchased (5) (8) 42,415 29 827 32 15 9 43,257 70 Other (6) 3,514 6 294 (14 ) 172 191 3,980 183 Redemptions and repayments (7) (40,380 ) (32 ) (1,344 ) (28 ) (459 ) (42 ) (42,183 ) (102 ) Assets written off (7) (1 ) 0 (1 ) 0 (361 ) (249 ) (363 ) (249 ) At 31 December 2019 295,436 147 12,351 348 2,368 368 310,155 863 Net movement in the year 4,554 4 340 41 (203 ) 11 4,691 56 ECL charge/(release) to the Income Statement 4 41 260 305 Less: ECL relating to derecognised income 0 0 (13 ) (13 ) Less: Recoveries net of collection costs (10 ) (15 ) (46 ) (71 ) Total ECL charge/(release) to the Income Statement (6 ) 26 201 221 2018 At 1 January 2018 285,133 176 12,110 284 3,043 691 300,286 1,151 Transfers from Stage 1 to Stage 2 (3) (4,190 ) (11 ) 4,190 11 — — — — Transfers from Stage 2 to Stage 1 (3) 3,325 68 (3,325 ) (68 ) — — — — Transfers to Stage 3 (3) (445 ) (8 ) (603 ) (23 ) 1,048 31 — — Transfers from Stage 3 (3) 17 6 443 27 (460 ) (33 ) — — Transfers of financial instruments (1,293 ) 55 705 (53 ) 588 (2 ) — — Net remeasurement of ECL on stage transfer (4) — (63 ) — 83 — 79 — 99 Change in economic scenarios (2) — 4 — (12 ) — (8 ) — (16 ) Changes to model — (1 ) — 2 — (8 ) — (7 ) New lending and assets purchased (5) (8) 57,280 43 1,085 33 17 13 58,382 89 Other (6) 5,540 (27 ) (175 ) (15 ) 266 207 5,631 165 Redemptions and repayments (7) (55,778 ) (44 ) (1,714 ) (15 ) (687 ) (81 ) (58,179 ) (140 ) Assets written off (7) — — — — (656 ) (534 ) (656 ) (534 ) At 31 December 2018 290,882 143 12,011 307 2,571 357 305,464 807 Net movement in the year 5,749 (33 ) (99 ) 23 (472 ) (334 ) 5,178 (344 ) ECL charge/(release) to the Income Statement (33 ) 23 200 190 Less: Recoveries net of collection costs — — (36 ) (36 ) Total credit impairment charge/(release) (33 ) 23 164 154 (1) Exposures that have attracted an ECL, and as reported in the Credit Quality table above. (2) Changes to assumptions in the year. Isolates the impact on ECL from changes to the economic variables for each scenario, changes to the scenarios themselves as well as changes in the probability weights from all other movements. The impact of changes in economics on exposure Stage allocations are shown within Transfers of financial instruments. (3) Total impact of facilities that moved Stage(s) in the year. This means, for example, that where risk parameter changes (model inputs) or model changes (methodology) result in a facility moving Stage, the full impact is reflected here (rather than in Other). Stage flow analysis only applies to facilities that existed at both the start and end of the year. Transfers between Stages are based on opening balances and ECL at the start of the period. (4) Relates to the revaluation of ECL following the transfer of an exposure from one Stage to another. (5) Exposures and ECL of facilities that did not exist at the start of the year but did at the end. Amounts in Stage 2 and 3 represent assets which deteriorated in the year after origination in Stage 1. (6) Residual movements on facilities that did not change Stage in the year, and which were neither acquired nor purchased in the year. Includes the impact of changes in risk parameters in the year, unwind of discount rates and increases in ECL requirements of accounts which ultimately were written off in the period. (7) Exposures and ECL for facilities that existed at the start of the year, but not at the end. (8) Basis of preparation for this line item is changed to report new lending for corporate loans at the opening balance rather than the year-end non-customer
Summary of Country Risk Exposures	The tables below exclude balances with other Banco Santander companies. We show them separately in the ‘Balances with other Banco Santander companies’ section. 2019 2018 Governments Government guaranteed Financial Retail Corporate Total (2) Governments Government guaranteed Financial Retail Corporate Total (2) Banks (1) Other Banks (1) Other £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Eurozone Ireland 0 0 0 7.5 0 0.1 7.6 — — — 12.3 — 0.4 12.7 Italy 0 0 0 0.1 0 0 0.1 — — — 0.1 — 0.2 0.3 Spain 0 0 0 0 0 0 0 — — — 0.2 — — 0.2 France 0.1 0 0.6 0.5 0 0 1.2 — — 1.0 — — — 1.0 Germany 0 0 1.3 0 0 0.1 1.4 — — 1.6 — — — 1.6 Luxembourg 0 0 0.1 2.7 0 0.1 2.9 — — — 0.9 — 0.2 1.1 Other (3) 0.3 0 1.0 0.1 0 0 1.4 0.3 — 1.2 0.2 — 1.1 2.8 0.4 0 3.0 10.9 0 0.3 14.6 0.3 — 3.8 13.7 — 1.9 19.7 Other countries UK 28.3 0 3.1 15.0 204.5 38.2 289.1 27.7 — 3.8 15.7 194.3 37.4 278.9 US 1.0 0 1.1 0 0 0.2 2.3 1.1 — 1.5 1.5 — 0.2 4.3 Japan 2.2 0 1.6 0 0 0 3.8 3.8 — 2.6 — — — 6.4 Switzerland 0 0 0 0 0 0 0 — — — — — 0.1 0.1 Denmark 0 0 0 0 0 0.5 0.5 — — 0.2 — — 0.5 0.7 Other 0.2 0 0.5 0.1 0 0.8 1.6 0.1 — 1.9 0.4 — 1.0 3.4 31.7 0 6.3 15.1 204.5 39.7 297.3 32.7 — 10.0 17.6 194.3 39.2 293.8 Total 32.1 0 9.3 26.0 204.5 40.0 311.9 33.0 — 13.8 31.3 194.3 41.1 313.5 (1) Excludes balances with central banks. (2) Excludes cash at hand, interests in other entities, intangible assets, property, plant and equipment, tax assets, retirement benefit assets and other assets. Loans are included gross of credit provisions. (3) Includes The Netherlands of £0.2bn (2018: £1.2bn), Belgium of £0.6bn (2018: £0.9bn), Greece of £nil (2018: £nil).
Summary of Balances with Other Banco Santander Companies	At 31 December 2019 and 2018, we had gross balances with other Banco Santander companies as follows: 2019 2018 Financial institutions Financial institutions Banks £bn Other £bn Corporate £bn Total £bn Banks £bn Other £bn Corporate £bn Total £bn Assets Spain 1.6 0 0 1.6 2.5 — — 2.5 UK 0 2.4 0 2.4 — 2.0 — 2.0 1.6 2.4 0 4.0 2.5 2.0 — 4.5 Liabilities Spain 2.1 0.1 0 2.2 3.6 0.1 — 3.7 UK 0 11.2 0 11.2 — 11.5 — 11.5 Uruguay 0.2 0 0 0.2 0.2 — — 0.2 2.3 11.3 0 13.6 3.8 11.6 — 15.4
Summary of Residential Mortgages by Borrower Profile	In this table, ‘home movers’ include both existing customers moving house and taking out a new mortgage with us, and customers who switch their mortgage to us when they move house. ‘Remortgagers’ are new customers who are taking a new mortgage with us. Stock New business 2019 2018 2019 2018 £m % £m % £m % £m % Home movers 70,860 43 69,198 44 11,192 38 10,854 39 Remortgagers 52,480 32 51,272 32 9,197 31 9,237 34 First-time buyers 32,112 19 29,235 19 6,952 23 4,848 18 Buy-to-let 9,904 6 8,252 5 2,473 8 2,335 9 165,356 100 157,957 100 29,814 100 27,274 100
Summary of Residential Mortgages by Interest Rate Profile	The interest rate profile of our mortgage asset stock was: 2019 2018 £m % £m % Fixed rate 128,798 78 115,178 73 Variable rate 22,116 13 24,396 15 Standard Variable Rate (SVR) 14,442 9 18,383 12 165,356 100 157,957 100
Summary of Residential Mortgages by Geographical Distribution	The geographical distribution of our mortgage asset stock was: Stock New business 2019 2018 2019 2018 Region £bn £bn £bn £bn London 41.4 39.0 7.5 7.1 Midlands and East Anglia 22.1 21.1 4.3 3.8 North 22.7 22.2 3.8 3.4 Northern Ireland 3.3 3.4 0.3 0.2 Scotland 6.8 6.7 1.2 1.0 South East excluding London 51.7 48.7 9.7 9.0 South West, Wales and other 17.4 16.9 3.0 2.8 165.4 158.0 29.8 27.3
Summary of Residential Mortgages by Average Loan Size for New Business	Average loan size for new business £’000 £’000 South East including London 277 270 Rest of the UK 154 150 UK as a whole 207 203
Summary of Residential Mortgages by Loan Size	The mortgage asset stock of larger loans was: South East including London UK 2019 2018 2019 2018 Individual mortgage loan size £m £m £m £m <£0.25m 45,828 45,851 105,855 105,181 £0.25m to £0.50m 34,027 30,488 44,549 39,841 £0.50m to £1.0m 11,471 10,103 13,114 11,551 £1.0m to £2.0m 1,538 1,168 1,644 1,236 >£2.0m 186 146 194 148 93,050 87,756 165,356 157,957
Summary of Residential Mortgages by Loan to Value	This table shows the LTV distribution for the gross carrying amount and the related ECL of our total mortgage portfolio and Stage 3 mortgages, as well as the LTV distribution for new business. We also show the collateral value and simple average LTV for our mortgage stock, Stage 3 stock and new business. We use our estimate of the property value at the balance sheet date. We include fees that have been added to the loan in the LTV calculation. For flexible products, we only include the drawn amount, not undrawn limits. 2019 2018 Stock Stage 3 New Stock Stage 3 New Total ECL Total ECL business Total ECL Total ECL business LTV £m £m £m £m £m £m £m £m £m £m Up to 50% 70,714 24 743 11 5,113 72,613 25 872 11 5,124 >50-75% 67,311 65 626 24 11,876 63,505 67 698 24 11,512 >75- 17,436 31 136 13 6,130 14,191 32 156 13 5,955 >85-100% 9,011 34 110 17 6,650 6,508 36 125 16 4,648 >100% 884 64 107 38 45 1,140 77 131 42 35 165,356 218 1,722 103 29,814 157,957 237 1,982 106 27,274 Collateral value of residential properties (1) 165,229 1,702 29,813 157,787 1,850 27,274 % % % % % % Simple average (2) 43 42 65 42 43 63 (1) Collateral value shown is limited to the balance of each related loan. Excludes the impact of over-collateralisation (where the collateral is higher than the loan). Includes collateral against loans in negative equity of £757m (2018: £969m). (2) Total of all LTV% divided by the total of all accounts.
Summary of Residential Mortgages by Credit Performance	Credit performance 2019 2018 £m £m Mortgage loans and advances to customers of which: 165,356 157,957 – Stage 1 155,477 146,619 – Stage 2 8,157 9,356 – Stage 3 1,722 1,982 Loss allowances (3) 218 234 % % Stage 1 ratio (1) 94.03 92.82 Stage 2 ratio (1) 4.93 5.92 Stage 3 ratio (2) 1.05 1.27 (1) Stage 1/Stage 2 exposures as a percentage of customer loans. (2) Total Stage 3 exposure as a percentage of customer loans plus undrawn Stage 3 exposures. The way we calculate the Stage 3 ratio was changed from 1 January 2019, and 2018 restated for consistency. See ‘Key metrics’ in the ‘Credit risk – Santander UK group level’ section. (3) The ECL allowance is for both on and off–balance sheet exposures.
Summary of Residential Mortgages Portfolios of Particular Interest by Credit Performance	Credit performance Portfolio of particular interest (1) Part interest- only, part Other Total Interest-only repayment (2) (3) Flexible (3) LTV >100% Buy-to-let portfolio 2019 £m £m £m £m £m £m £m Mortgage portfolio 165,356 38,062 13,247 11,273 884 9,904 109,234 – Stage 1 155,477 33,739 12,112 10,183 594 9,593 105,114 – Stage 2 8,157 3,502 888 873 183 285 3,526 – Stage 3 1,722 821 247 217 107 26 594 Stage 3 ratio (4) 1.05 % 2.17 % 1.87 % 2.03 % 12.11 % 0.26 % 0.54 % PIPs 32 14 9 2 13 1 8 Simple average LTV (indexed) 43 % 45 % 45 % 28 % 117 % 60 % 44 % 2018 Mortgage portfolio 157,957 38,035 13,201 12,926 1,140 8,252 101,158 – Stage 1 146,619 33,001 11,824 11,558 740 7,906 96,767 – Stage 2 9,356 4,029 1,115 1,082 273 317 3,802 – Stage 3 1,982 1,005 262 286 127 29 589 Stage 3 ratio (4) 1.27 % 2.67 % 1.99 % 2.34 % 11.18 % 0.35 % 0.58 % PIPs 25 12 5 3 8 — 7 Simple average LTV (indexed) 42 % 44 % 44 % 29 % 118 % 58 % 43 % (1) Where a loan falls into more than one category, we include it in all the categories that apply. As a result, the sum of the mortgages in the segments of particular interest and the other portfolio does not agree to the total mortgage portfolio. (2) Mortgage balance includes both the interest-only part of £9,823m (2018: £9,756m) and the non-interest-only (3) Includes legacy Alliance & Leicester flexible loans that work in a more limited way than our current Flexi loan product. (4) Total Stage 3 exposure as a percentage of customer loans plus undrawn Stage 3 exposures. The way we calculate the Stage 3 ratio was changed from 1 January 2019, and 2018 restated for consistency. See ‘Key metrics’ in the ‘Credit risk – Santander UK group level’ section.
Summary of Full interest-only new business in the year	Full interest-only new business in the year 2019 2018 £m £m Full interest-only loans 4,000 3,810
Summary of Detailed Information of Interest only Loan Maturity Analysis	Full interest-only maturity profile Term Within Between Between Greater than expired 2 years 2-5 years 5-15 years 15 years Total 2019 £m £m £m £m £m £m Full interest-only portfolio 338 1,541 3,706 20,984 11,493 38,062 – of which value weighted average LTV (indexed) is>75% 11 111 219 1,793 1,051 3,185 2018 Full interest-only portfolio 541 1,346 3,761 21,711 10,676 38,035 – of which value weighted average LTV (indexed) is>75% 43 110 265 2,029 642 3,089
Summary of Residential Mortgages Portfolios of Particular Interest by Forbearance Applied	Forbearance (1) The balances at 31 December 2019 and 2018 were: Interest-only (2) Flexible LTV >100% Buy-to-Let 2019 £m £m £m £m Total 392 73 17 10 – Stage 2 285 56 8 8 – Stage 3 107 17 9 2 2018 Total 229 32 10 9 – Stage 2 136 18 3 6 – Stage 3 93 14 7 3 (1) Where a loan falls into more than one category, we have included it in all the categories that apply. (2) Comprises full interest-only loans and part interest-only, part repayment loans.
Summary of Consumer (Auto) Finance and Other Unsecured Lending by Credit Performance	Credit performance Other unsecured 2019 Consumer (auto) finance £m Personal loans £m Credit cards £m Overdrafts £m Total other unsecured £m Total Loans and advances to customers of which: 7,684 2,135 2,788 590 5,513 13,197 – Stage 1 7,038 2,020 2,473 404 4,897 11,935 – Stage 2 604 95 267 160 522 1,126 – Stage 3 42 20 48 26 94 136 Loss allowances (2) 88 51 120 62 233 321 Stage 3 undrawn exposures 0 25 Stage 3 ratio (1) 0.55 % 2.15 % 1.21 % Gross write-offs 34 134 168 2018 Loans and advances to customers of which: 7,347 2,182 2,865 593 5,640 12,987 – Stage 1 6,950 2,113 2,560 422 5,095 12,045 – Stage 2 354 48 256 144 448 802 – Stage 3 43 21 49 27 97 140 Loss allowances (2) 85 47 112 61 220 305 Stage 3 undrawn exposures — 26 Stage 3 ratio (1) 0.58 % 2.17 % 1.28 % Gross write-offs 24 125 149 (1) Total Stage 3 exposure as a percentage of loans and advances to customers plus undrawn Stage 3 exposures. The way we calculate the Stage 3 ratio was changed from 1 January 2019, and 2018 restated for consistency. See ‘Key metrics’ in the ‘Credit risk – Santander UK group level’ section. (2) The ECL allowance is for both on and off–balance sheet exposures.
Summary of Consumer (Auto) Finance and Other Unsecured Lending By Forbearance	Forbearance The balances at 31 December 2019 and 2018 were: Other unsecured 2019 Consumer (auto) finance £m Personal loans £m Credit cards £m Overdrafts £m Total other unsecured £m Total £m Total 7 0 51 25 76 83 – Stage 2 5 0 10 7 17 22 – Stage 3 2 0 41 18 59 61 2018 Total 6 — 53 26 79 85 – Stage 2 4 — 10 7 17 21 – Stage 3 2 — 43 19 62 64
Summary of Business Banking by Credit Performance	Credit performance 2019 2018 £m £m Loans and advances to customers of which: 1,845 1,802 – Stage 1 1,590 1,548 – Stage 2 177 165 – Stage 3 78 89 Loss allowances (2) 52 53 Stage 3 undrawn exposures 1 — Stage 3 ratio (1) 4.28 % 4.99 % Gross write offs 24 15 (1) Total Stage 3 exposure as a percentage of customer loans plus undrawn Stage 3 exposures. The way we calculate the Stage 3 ratio was changed from 1 January 2019, and 2018 restated for consistency. See ‘Key metrics’ in the ‘Credit risk – Santander UK group level’ section (2) The ECL allowance is for both on and off–balance sheet exposures.
Summary of Business Banking by Forbearance	Forbearance The balances at 31 December 2019 and 2018 were: 2019 2018 £m £m Total 67 74 – Stage 2 26 20 – Stage 3 41 54
Summary of Other Segments Exposures By Credit Rating	Rating distribution These tables show our credit risk exposure according to our internal rating scale (see ‘Credit quality’ in the ‘Santander UK group level – credit risk review’ section) for each portfolio. On this scale, the higher the rating, the better the quality of the counterparty. Santander UK risk grade 9 8 7 6 5 4 3 to 1 Other (1) Total 2019 £m £m £m £m £m £m £m £m £m Corporate & Commercial Banking SME and mid corporate 0 25 790 1,914 4,414 3,348 946 32 11,469 Commercial Real Estate 0 0 0 426 3,708 1,363 94 0 5,591 Social Housing 1,231 3,650 26 0 0 2 4 0 4,913 1,231 3,675 816 2,340 8,122 4,713 1,044 32 21,973 Corporate & Investment Banking Large Corporate 281 2,356 4,419 4,558 842 75 115 0 12,646 Financial Institutions 383 822 703 11 0 0 0 0 1,919 664 3,178 5,122 4,569 842 75 115 0 14,565 Corporate Centre Sovereign and Supranational 32,145 2,255 0 0 0 0 0 0 34,400 Structured Products 1,166 981 396 29 0 0 0 0 2,572 Social Housing 934 3,036 90 0 0 0 0 0 4,060 Financial Institutions 542 246 43 25 1 0 0 0 857 Legacy Portfolios in run–off (2) 0 0 0 130 27 98 140 303 698 34,787 6,518 529 184 28 98 140 303 42,587 Total 36,682 13,371 6,467 7,093 8,992 4,886 1,299 335 79,125 Of which: Stage 1 36,682 13,371 6,441 6,901 8,263 3,586 465 320 76,029 Stage 2 0 0 26 192 729 1,300 439 15 2,701 Stage 3 0 0 0 0 0 0 395 0 395 2018 Corporate & Commercial Banking SME and mid corporate — — 66 1,745 5,749 3,426 886 36 11,908 Commercial Real Estate — — — 302 4,564 1,846 31 — 6,743 Social Housing 680 3,899 138 — — 2 24 — 4,743 680 3,899 204 2,047 10,313 5,274 941 36 23,394 Corporate & Investment Banking Large Corporate 12 3,187 5,535 6,361 888 3 78 — 16,064 Financial Institutions 480 1,010 1,432 55 — — — — 2,977 492 4,197 6,967 6,416 888 3 78 — 19,041 Corporate Centre Sovereign and Supranational 30,467 3,898 — 1 — — — — 34,366 Structured Products 2,431 2,062 318 24 — — — — 4,835 Social Housing 1,377 2,839 76 43 — — — — 4,335 Financial Institutions 356 345 47 21 — — — — 769 Legacy Portfolios in run–off (2) — — — 203 35 137 126 357 858 Derivatives — 147 — — — — — — 147 34,631 9,291 441 292 35 137 126 357 45,310 Total 35,803 17,387 7,612 8,755 11,236 5,414 1,145 393 87,745 Of which: Stage 1 35,803 17,387 7,612 8,682 10,788 4,772 521 377 85,942 Stage 2 — — — 73 448 635 318 16 1,490 Stage 3 — — — — — 7 306 — 313 (1) Smaller exposures mainly in the commercial mortgage portfolio. We use scorecards for them, instead of a rating model. (2) Commercial mortgages and residual structured and asset finance loans (shipping, aviation, and structured finance).
Summary of Other Segments Exposures by Geographical Distribution	Geographical distribution We typically classify geographical location according to the counterparty’s country of domicile unless a full risk transfer guarantee is in place, in which case we use the guarantor’s country of domicile instead. 2019 2018 UK £m Europe US Rest of Total UK £m Europe US Rest of Total Corporate & Commercial Banking SME and mid corporate 11,384 84 0 1 11,469 11,833 74 — 1 11,908 Commercial Real Estate 5,591 0 0 0 5,591 6,743 — — — 6,743 Social Housing 4,913 0 0 0 4,913 4,743 — — — 4,743 21,888 84 0 1 21,973 23,319 74 — 1 23,394 Corporate & Investment Banking Large Corporate 10,665 1,922 2 57 12,646 13,080 2,752 124 108 16,064 Financial Institutions 604 841 169 305 1,919 870 1,520 163 424 2,977 11,269 2,763 171 362 14,565 13,950 4,272 287 532 19,041 Corporate Centre Sovereign and Supranational 27,987 1,549 856 4,008 34,400 26,154 1,802 960 5,450 34,366 Structured Products 1,710 811 0 51 2,572 2,574 1,139 — 1,122 4,835 Social Housing 4,060 0 0 0 4,060 4,335 — — — 4,335 Financial Institutions 329 335 157 36 857 346 358 11 54 769 Legacy Portfolios in run-off 587 0 0 111 698 744 — — 114 858 Derivatives 0 0 0 0 0 — — 147 — 147 34,673 2,695 1,013 4,206 42,587 34,153 3,299 1,118 6,740 45,310
Summary of Detailed Information about Gross and Net Credit Exposure	Credit risk mitigation 2019 Gross Collateral Net Corporate & Commercial Banking SME and mid corporate 279 51 228 Commercial Real Estate 83 56 27 362 107 255 Corporate & Investment Banking Large Corporate 15 0 15 15 0 15 Corporate Centre Legacy Portfolios in run–off 17 11 6 17 11 6 2018 Corporate & Commercial Banking SME and mid corporate 253 55 198 Commercial Real Estate 23 14 9 276 69 207 Corporate & Investment Banking Large Corporate 26 — 26 26 — 26 Corporate Centre Legacy Portfolios in run–off 16 9 6 16 9 6
Summary of Other Segments Exposures by Credit Performance	We monitor exposures that show potentially higher risk characteristics using our Watchlist process (described in ‘Monitoring’ in the ‘Credit risk management’ section). The table below shows the exposures we monitor, and those we classify as Stage 3 by portfolio at 31 December 2019 and 2018. Committed exposure Watchlist 2019 Fully Enhanced Proactive Stage 3 Total (1) Loss Corporate & Commercial Banking SME and mid corporate 9,864 1,056 270 279 11,469 164 Commercial Real Estate 5,338 89 81 83 5,591 46 Social Housing 4,823 90 0 0 4,913 0 20,025 1,235 351 362 21,973 210 Corporate & Investment Banking Large Corporate 11,833 252 546 15 12,646 50 Financial Institutions 1,909 0 10 0 1,919 0 13,742 252 556 15 14,565 50 Corporate Centre Sovereign and Supranational 34,400 0 0 0 34,400 0 Structured Products 2,572 0 0 0 2,572 0 Social Housing 4,047 13 0 0 4,060 0 Financial Institutions 854 0 3 0 857 0 Legacy Portfolios in run–off 656 17 8 17 698 12 Derivatives 0 0 0 0 0 0 42,529 30 11 17 42,587 12 Total loss allowances 272 2018 Corporate & Commercial Banking SME and mid corporate 10,350 972 333 253 11,908 160 Commercial Real Estate 6,426 247 47 23 6,743 22 Social Housing 4,626 117 — — 4,743 — 21,402 1,336 380 276 23,394 182 Corporate & Investment Banking Large Corporate 15,304 548 186 26 16,064 18 Financial Institutions 2,977 — — — 2,977 — 18,281 548 186 26 19,041 18 Corporate Centre Sovereign and Supranational 34,366 — — — 34,366 — Structured Products 4,835 — — — 4,835 — Social Housing 4,313 22 — — 4,335 — Financial Institutions 769 — — — 769 — Legacy Portfolios in run–off 809 26 7 16 858 13 Derivatives 147 — — — 147 — 45,239 48 7 16 45,310 13 Total loss allowances 213 (1) Includes committed facilities and derivatives. We define ‘Enhanced Monitoring’ and ‘Proactive Management’ in the ‘Monitoring’ section.
Summary of Other Segments by Forbearance Applied	Forbearance We only make forbearance arrangements for lending to customers. The balances at 31 December 2019 and 2018, analysed by their staging at the year–end and the forbearance we applied, were: 2019 2018 Corporate & £m Corporate & £m Corporate Corporate & £m Corporate & £m Corporate Stock: (1) – Term extension 60 42 0 67 42 — – Interest–only 110 0 13 112 — 8 – Other payment rescheduling 192 15 9 163 26 10 362 57 22 342 68 18 Of which: – Stage 1 57 42 1 43 — 3 – Stage 2 75 0 11 78 42 8 – Stage 3 230 15 10 221 26 7 362 57 22 342 68 18 Proportion of portfolio 1.6 % 0.4 % 3.2 % 1.5 % 0.4 % 2.1 % (1) We base forbearance type on the first forbearance we applied. Tables only show accounts open at the year-end.
Summary of Commercial Real Estate by Credit Performance	Customer (1) £m Stage 3 (2) Stage 3 (3) Gross Total loss 2019 5,350 89 1.55 8 49 2018 6,459 29 0.41 23 26 (1) CRE drawn loans in the business banking portfolio of our Retail Banking segment of £241m (2018: £257m) and in the CRE portfolio of our Corporate & Commercial Banking segment of £5,109m (2018: £6,202m). (2) We define Stage 3 in the ‘Credit risk management’ section. (3) Total Stage 3 exposure as a percentage of customer loans plus undrawn Stage 3 exposures. The way we calculate the Stage 3 ratio was changed from 1 January 2019, and 2018 restated for consistency. See ‘Key metrics’ in the ‘Credit risk – Santander UK group level’ section.
Summary of Commercial Real Estate by Loan to Value	The table below shows the LTV distribution for our CRE total stock and Stage 3 stock (based on the drawn balance and our latest estimate of the property’s current value) of the portfolio at 31 December 2019 and 2018. 2019 2018 Stock Stage 3 Stock Stage 3 LTV Total ECL Total ECL Total ECL Total ECL Up to 50% 3,133 17 15 8 3,663 5 3 — >50–70% 1,557 24 63 17 2,039 4 4 — >70–100% 29 1 1 0 47 2 1 1 >100% 9 1 3 1 18 7 16 7 Standardised portfolio (1) 617 6 7 3 631 7 5 2 Total with collateral 5,345 49 89 29 6,398 25 29 10 Development loans 5 0 0 0 61 1 — — 5,350 49 89 29 6,459 26 29 10 (1) Smaller value transactions, mainly commercial mortgages.
Summary of Commercial Real Estate by Sector	2019 2018 Sector £m % £m % Office 1,262 24 1,556 24 Retail 850 16 1,004 16 Industrial 699 13 888 14 Residential 757 14 927 14 Mixed use 759 14 932 14 Student accommodation 85 2 123 2 Hotels and leisure 268 5 309 5 Other 53 1 89 1 Standardised portfolio (1) 617 11 631 10 5,350 100 6,459 100 (1) Smaller value transactions, mainly commercial mortgages.
Social Housing Exposure	At 31 December 2019 and 2018, our total Social Housing exposure was: 2019 2018 On-balance £m Total Total loss On-balance £m Total Total loss Corporate & Commercial Banking 2,794 4,913 0 2,844 4,743 — Corporate Centre 3,585 4,060 0 3,780 4,335 — 6,379 8,973 0 6,624 9,078 —
Corporate and investment banking [member]
Statement [Line Items]
Summary of Probability Weightings Applied to Scenarios	The scenario weights we applied to the scenarios for our CIB portfolio for 2019 and 2018 were: Upside Base case Downside Scenario weights % % % 2019 30 40 30 2018 20 60 20
Summary of Annual Growth Rates	Our macroeconomic assumptions and their evolution throughout the forecast period for our CIB portfolio for 2019 and 2018 were: Upside Base case Downside GDP assumption % % % 2019 5 year average increase/decrease 3.7 3.5 3.0 Cumulative growth/(fall) to peak/(trough) (1) 0.3 0.5 (1.2 ) 2018 5 year average increase/decrease 4.2 3.6 2.7 Cumulative growth/(fall) to peak/(trough) 0.4 0.3 (0.8 ) (1) Cumulative growth/(fall) refers to the cumulative change from the last historical data point for GDP growth to the peak (for upside scenarios) or to the trough (for downside scenarios).
Retail banking [member]
Statement [Line Items]
Summary of ECL Reconciliation	The following table shows changes in total on and off-balance Stage 1 Stage 2 Stage 3 Total Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL £m £m £m £m £m £m £m £m At 1 January 2019 183,031 96 10,520 269 2,254 229 195,805 594 Transfers from Stage 1 to Stage 2 (3) (3,132 ) (8 ) 3,132 8 0 0 0 0 Transfers from Stage 2 to Stage 1 ((3) 3,289 69 (3,289 ) (69 ) 0 0 0 0 Transfers to Stage 3 (3) (322 ) (2 ) (500 ) (20 ) 822 22 0 0 Transfers from Stage 3 (3) 11 1 509 23 (520 ) (24 ) 0 0 Transfers of financial instruments (154 ) 60 (148 ) (58 ) 302 (2 ) 0 0 Net ECL remeasurement on stage transfer (4) 0 (61 ) 0 76 0 63 0 78 Change in economic scenarios (2) 0 (3 ) 0 (24 ) 0 (9 ) 0 (36 ) Changes to model 0 0 0 0 0 13 0 13 New lending and assets purchased (5) 37,230 23 479 27 14 9 37,723 59 Other (6) 2,670 6 68 (2 ) 128 162 2,866 166 Redemptions and repayments (7) (27,924 ) (23 ) (1,265 ) (20 ) (449 ) (34 ) (29,638 ) (77 ) Assets written off (7) (1 ) 0 (1 ) 0 (275 ) (206 ) (277 ) (206 ) At 31 December 2019 194,852 98 9,653 268 1,974 225 206,479 591 Net movement in the year 11,821 2 (867 ) (1 ) (280 ) (4 ) 10,674 (3 ) ECL charge/(release) to the Income Statement 2 (1 ) 202 203 Less: ECL relating to derecognised income 0 0 (9 ) (9 ) Less: Recoveries net of collection costs (2 ) 0 (32 ) (34 ) Income statement charge/(release) for the year 0 (1 ) 161 160 2018 At 1 January 2018 178,978 110 10,885 247 2,263 268 192,126 625 Transfers from Stage 1 to Stage 2 (3) (3,407 ) (7 ) 3,407 7 — — — — Transfers from Stage 2 to Stage 1 (3) 2,992 58 (2,992 ) (58 ) — — — — Transfers to Stage 3 (3) (403 ) (7 ) (569 ) (22 ) 972 29 — — Transfers from Stage 3 (3) 15 5 438 26 (453 ) (31 ) — — Transfers of financial instruments (803 ) 49 284 (47 ) 519 (2 ) — — Net ECL remeasurement on stage transfer (4) — (54 ) — 73 — 60 — 79 Change in economic scenarios (2) — (1 ) — (9 ) — (8 ) — (18 ) Changes to model — (1 ) — 2 — 1 — 2 New lending and assets purchased (5) 33,366 26 670 26 15 11 34,051 63 Other (6) (27 ) (19 ) (125 ) (14 ) 143 100 (9 ) 67 Redemptions and repayments (7) (28,483 ) (14 ) (1,194 ) (9 ) (436 ) (19 ) (30,113 ) (42 ) Assets written off (7) — — — — (250 ) (182 ) (250 ) (182 ) At 31 December 2018 183,031 96 10,520 269 2,254 229 195,805 594 Net movement in the year 4,053 (14 ) (365 ) 22 (9 ) (39 ) 3,679 (31 ) ECL charge/(release) to the Income Statement (14 ) 22 143 151 Less: Recoveries net of collection costs — — (27 ) (27 ) Income statement charge/(release) for the year (14 ) 22 116 124 (1) Exposures that have attracted an ECL, and as reported in the Credit Quality table above. (2) Changes to assumptions from the start of the year to the end of the year. Includes changes to the economic variables for each scenario, changes to the scenarios themselves as well as changes in the probability weightings. Also includes changes in risk parameters and model changes. (3) Total impact of facilities that moved stage(s) in the year. This means, for example, that where risk parameter changes (model inputs) or model changes (methodology) result in a facility moving stage, the full impact is reflected here (rather than in Other). Stage flow analysis only applies to facilities that existed at both the start and end of the year. Transfers from each stage are based on opening balances, and transfers in are based on closing balances, giving rise to a net movement on transfer. (4) Relates to the revaluation of ECL following the transfer of an exposure from one stage to another. (5) Exposures and ECL at reporting date of facilities that did not exist at the start of the year, but did at the end. Amounts in Stage 2 and 3 represent assets which have deteriorated during the year subsequent to origination in Stage 1. (6) Residual movements on facilities that did not change stage in the year, and which were neither acquired nor purchased in the year. (7) Exposures and ECL for facilities that existed at the start of the year, but not at the end.
Mortgages [member]
Statement [Line Items]
Summary of ECL Reconciliation	The following table shows changes in total on and off-balance Stage 1 Stage 2 Stage 3 Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Mortgages £m £m £m £m £m £m £m £m At 1 January 2019 157,739 12 9,432 119 1,999 106 169,170 237 Transfers from Stage 1 to Stage 2 (3) (2,345 ) (1 ) 2,345 1 0 0 0 0 Transfers from Stage 2 to Stage 1 ((3) 2,921 24 (2,921 ) (24 ) 0 0 0 0 Transfers to Stage 3 (3) (231 ) 0 (429 ) (8 ) 660 8 0 0 Transfers from Stage 3 (3) 5 (1 ) 485 16 (490 ) (15 ) 0 0 Transfers of financial instruments 350 22 (520 ) (15 ) 170 (7 ) 0 0 Net ECL remeasurement on stage transfer (4) 0 (23 ) 0 16 0 12 0 5 Change in economic scenarios (2) 0 (5 ) 0 (22 ) 0 (9 ) 0 (36 ) Changes to model 0 0 0 0 0 13 0 13 New lending and assets purchased (5) 31,090 5 198 3 2 0 31,290 8 Other (6) 2,090 4 153 6 31 14 2,274 24 Redemptions and repayments (7) (22,439 ) (1 ) (1,039 ) (6 ) (396 ) (12 ) (23,874 ) (19 ) Assets written off (7) 0 0 0 0 (72 ) (14 ) (72 ) (14 ) At 31 December 2019 168,830 14 8,224 101 1,734 103 178,788 218 Net movement in the year 11,091 2 (1,208 ) (18 ) (265 ) (3 ) 9,618 (19 ) Charge/(release) to the Income Statement 2 (17 ) 11 (4 ) Less: ECL relating to derecognised income 0 0 (2 ) (2 ) Less: Recoveries net of collection costs 0 0 (2 ) (2 ) Income statement charge/(release) for the year 2 (17 ) 7 (8 ) 2018 At 1 January 2018 155,155 20 9,884 131 2,004 121 167,043 272 Transfers from Stage 1 to Stage 2 (3) (2,941 ) (1 ) 2,941 1 — — — — Transfers from Stage 2 to Stage 1 ((3) (329 ) (6 ) (512 ) (12 ) 841 18 — — Transfers to Stage 3 (3) 2,628 21 (2,628 ) (21 ) — — — — Transfers from Stage 3 (3) 4 — 405 14 (409 ) (14 ) — — Transfers of financial instruments (638 ) 14 206 (18 ) 432 4 — — Net ECL remeasurement on stage transfer (4) — (20 ) — 20 — 14 — 14 Change in economic scenarios (2) — (6 ) — (7 ) — (8 ) — (21 ) Changes to model — — — 2 — 2 — 4 New lending and assets purchased (5) 28,330 2 446 5 3 1 28,779 8 Other (6) (249 ) 6 (81 ) (5 ) (5 ) 1 (335 ) 2 Redemptions and repayments (7) (24,859 ) (4 ) (1,023 ) (9 ) (358 ) (11 ) (26,240 ) (24 ) Assets written off (7) — — — — (77 ) (18 ) (77 ) (18 ) At 31 December 2018 157,739 12 9,432 119 1,999 106 169,170 237 Net movement in the year 2,584 (8 ) (452 ) (12 ) (5 ) (15 ) 2,127 (35 ) Charge/(release) to the Income Statement (8 ) (12 ) 3 (17 ) Less: Recoveries net of collection costs — — (4 ) (4 ) Income statement charge/(release) for the year (8 ) (12 ) (1 ) (21 )
Summary of Modification of Loan Terms	The following table sets out the financial assets that were forborne while they had a loss allowance measured at lifetime ECL. 2019 2018 £m £m Financial assets modified in the year: – Amortised cost before modification 384 207 – Net modification loss 7 3 Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the loss allowance changed to 12m ECL in the year 89 158
Summary of Residential Mortgages by Forbearance Applied	The balances at 31 December 2019 and 2018, analysed by their staging at the year-end Capitalisation Term Interest-only Concessionary Total Loss 2019 £m £m £m £m £m £m Stage 2 405 338 342 1 1,086 12 Stage 3 197 91 97 10 395 24 602 429 439 11 1,481 36 Proportion of portfolio 0.4 % 0.3 % 0.3 % 0.0 % 0.9 % 2018 Stage 2 375 161 389 — 925 9 Stage 3 212 95 113 — 420 20 587 256 502 — 1,345 29 Proportion of portfolio 0.4 % 0.2 % 0.3 % 0.0 % 0.9 % (1) We base forbearance type on the first forbearance on the accounts.
Consumer (auto) finance [member]
Statement [Line Items]
Summary of Modification of Loan Terms	The following table sets out the financial assets that were forborne while they had a loss allowance measured at lifetime ECL. 2019 Credit cards £m Overdrafts £m Total other unsecured £m Financial assets modified in the year: – Amortised cost before modification 23 15 38 – Net modification loss 12 8 20 Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the loss allowance changed to 12m ECL in the year 3 2 5 2018 Financial assets modified in the year: – Amortised cost before modification 26 17 43 – Net modification loss 12 8 20 Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the loss allowance changed to 12m ECL in the year 2 3 5
Business Banking [member]
Statement [Line Items]
Summary of Modification of Loan Terms	The following table provides information on financial assets that were forborne while they had a loss allowance measured at an amount equal to lifetime ECL. 2019 2018 £m £m Financial assets modified in the year: – Amortised cost before modification 15 14 – Net modification loss 0 1 Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the ECL allowance changed to 12-month 2 3
Other business segments [member]
Statement [Line Items]
Summary of ECL Reconciliation	The following tables show changes in total on and off-balance Stage 1 Stage 2 Stage 3 Total Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Corporate & Commercial Banking £m £m £m £m £m £m £m £m At 1 January 2019 21,333 37 1,226 32 276 113 22,835 182 Transfers from Stage 1 to Stage 2 (3) (747 ) (3 ) 747 3 0 0 0 0 Transfers from Stage 2 to Stage 1 ((3) 120 5 (120 ) (5 ) 0 0 0 0 Transfers to Stage 3 (3) (33 ) 0 (92 ) (3 ) 125 3 0 0 Transfers from Stage 3 (3) 0 0 6 0 (6 ) 0 0 0 Transfers of financial instruments (660 ) 2 541 (5 ) 119 3 0 0 Net ECL remeasurement on stage transfer (4) 0 (4 ) 0 17 0 32 0 45 Change in economic scenarios (2) 0 7 0 9 0 0 0 16 New lending and assets purchased (5) 5,129 4 350 6 2 1 5,481 11 Other (6) 1,293 4 63 (11 ) 49 29 1,405 22 Redemptions and repayments (7) (7,778 ) (9 ) (4 ) (7 ) (3 ) (9 ) (7,785 ) (25 ) Assets written off (7) 0 0 0 0 (81 ) (41 ) (81 ) (41 ) At 31 December 2019 19,317 41 2,176 41 362 128 21,855 210 Net movement in the year (2,016 ) 4 950 9 86 15 (980 ) 28 ECL charge/(release) to the Income Statement 4 9 56 69 Less: ECL relating to derecognised income 0 0 (4 ) (4 ) Less: Recoveries net of collection costs (8 ) (8 ) (12 ) (28 ) Income statement charge/(release) for the year (4 ) 1 40 37 Corporate & Investment Banking £m £m £m £m £m £m £m £m At 1 January 2019 17,458 5 134 3 26 10 17,618 18 Transfers from Stage 1 to Stage 2 (3) (208 ) 0 208 0 0 0 0 0 Transfers from Stage 2 to Stage 1 ((3) 41 0 (41 ) 0 0 0 0 0 Transfers to Stage 3 (3) 0 0 0 0 0 0 0 0 Transfers from Stage 3 (3) 0 0 0 0 0 0 0 0 Transfers of financial instruments (167 ) 0 167 0 0 0 0 0 Net ECL remeasurement on stage transfer (4) 0 0 0 37 0 0 0 37 Changes to model 0 0 0 0 0 0 0 0 New lending and assets purchased (5) 54 0 0 0 0 0 54 0 Other (6) 376 0 171 (1 ) (6 ) (1 ) 541 (2 ) Redemptions and repayments (7) (4,676 ) 0 (76 ) (3 ) (5 ) 0 (4,757 ) (3 ) Assets written off (7) 0 0 0 0 0 0 0 0 At 31 December 2019 13,045 5 396 36 15 9 13,456 50 Net movement in the year (4,413 ) 0 262 33 (11 ) (1 ) (4,162 ) 32 ECL charge/(release) to the Income Statement 0 33 (1 ) 32 Less: ECL relating to derecognised income 0 0 0 0 Less: Recoveries net of collection costs 0 (8 ) (2 ) (10 ) Income statement charge/(release) for the year 0 25 (3 ) 22 Corporate Centre £m £m £m £m £m £m £m £m At 1 January 2019 69,060 5 131 3 15 5 69,206 13 Transfers from Stage 1 to Stage 2 (3) (15 ) 0 15 0 0 0 0 0 Transfers from Stage 2 to Stage 1 ((3) 7 0 (7 ) 0 0 0 0 0 Transfers to Stage 3 (3) (3 ) 0 (4 ) 0 7 0 0 0 Transfers from Stage 3 (3) 0 0 0 0 0 0 0 0 Transfers of financial instruments (11 ) 0 4 0 7 0 0 0 Net ECL remeasurement on stage transfer (4) 0 0 0 0 0 2 0 2 Change in economic scenarios (2) 0 1 0 0 0 0 0 1 Changes to model 0 0 0 0 0 0 0 0 New lending and assets purchased (5) (8) 0 0 0 0 0 0 0 0 Other (6) (827 ) (3 ) (9 ) 0 0 1 (836 ) (2 ) Redemptions and repayments (7) 0 0 0 0 0 0 0 0 Assets written off (7) 0 0 0 0 (5 ) (2 ) (5 ) (2 ) At 31 December 2019 68,222 3 126 3 17 6 68,365 12 Net movement in the year (838 ) (2 ) (5 ) 0 2 1 (841 ) (1 ) ECL charge/(release) to the Income Statement (2 ) 0 3 1 Less: ECL relating to derecognised income 0 0 (1 ) (1 ) Less: Recoveries net of collection costs 0 0 0 0 Income statement charge/(release) for the year (2 ) 0 2 0 Stage 1 Stage 2 Stage 3 Total Corporate & Commercial Banking Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL At 1 January 2018 22,417 43 866 33 388 173 23,671 249 Transfers from Stage 1 to Stage 2 (3) (670 ) (3 ) 670 3 — — — — Transfers from Stage 2 to Stage 1 ((3) 200 8 (200 ) (8 ) — — — — Transfers to Stage 3 (3) (41 ) — (31 ) (1 ) 72 1 — — Transfers from Stage 3 (3) 2 1 2 1 (4 ) (2 ) — — Transfers of financial instruments (509 ) 6 441 (5 ) 68 (1 ) — — Net ECL remeasurement on stage transfer (4) — (7 ) — 10 — 18 — 21 Change in economic scenarios (2) — 5 — (3 ) — — — 2 New lending and assets purchased (5) 9,115 12 281 5 3 1 9,399 18 Other (6) 1,642 (5 ) (37 ) (4 ) 23 33 1,628 24 Redemptions and repayments (7) (11,332 ) (17 ) (325 ) (4 ) (101 ) (14 ) (11,758 ) (35 ) Assets written off (7) — — — — (105 ) (97 ) (105 ) (97 ) At 31 December 2018 21,333 37 1,226 32 276 113 22,835 182 Net movement in the year (1,084 ) (6 ) 360 (1 ) (112 ) (60 ) (836 ) (67 ) ECL charge/(release) to the Income Statement (6 ) (1 ) 37 30 Less: Recoveries net of collection costs — — (7 ) (7 ) Income statement charge/(release) for the year (6 ) (1 ) 30 23 Corporate & Investment Banking £m £m £m £m £m £m £m £m At 1 January 2018 20,503 16 109 — 372 242 20,984 258 Transfers from Stage 1 to Stage 2 (3) (2 ) — 2 — — — — — Changes to model — — — — — (10 ) — (10 ) New lending and assets purchased (5) 14,799 4 133 3 — — 14,932 7 Other (6) (1,876 ) (1 ) 83 1 103 76 (1,690 ) 76 Redemptions and repayments (7) (15,966 ) (14 ) (193 ) (1 ) (150 ) (46 ) (16,309 ) (61 ) Assets written off (7) — — — — (299 ) (252 ) (299 ) (252 ) At 31 December 2018 17,458 5 134 3 26 10 17,618 18 Net movement in the year (3,045 ) (11 ) 25 3 (346 ) (232 ) (3,366 ) (240 ) ECL charge/(release) to the Income Statement (11 ) 3 20 12 Less: Recoveries net of collection costs — — 2 2 Income statement charge/(release) for the year (11 ) 3 22 14 Corporate Centre £m £m £m £m £m £m £m £m At 1 January 2018 63,236 7 250 4 20 8 63,506 19 Transfers from Stage 1 to Stage 2 (3) (111 ) (1 ) 111 1 — — — — Transfers from Stage 2 to Stage 1 ((3) 133 3 (133 ) (3 ) — — — — Transfers to Stage 3 (3) — — (4 ) — 4 — — — Transfers from Stage 3 (3) — — 3 1 (3 ) (1 ) — — Transfers of financial instruments 22 2 (23 ) (1 ) 1 (1 ) — — Net ECL remeasurement on stage (4) — (2 ) — — — 1 — (1 ) Change in economic scenarios (2) — — — — — — — — Changes to model — — — — — — — — New lending and assets purchased (5) (8) — — — — — — — — Other (6) 5,802 (2 ) (96 ) — (3 ) — 5,703 (2 ) Redemptions and repayments (7) — — — — — — — — Assets written off (7) — — — — (3 ) (3 ) (3 ) (3 ) At 31 December 2018 69,060 5 131 3 15 5 69,206 13 Net movement in the year 5,824 (2 ) (119 ) (1 ) (5 ) (3 ) 5,700 (6 ) ECL charge/(release) to the Income Statement (2 ) (1 ) — (3 ) Less: Recoveries net of collection costs — — (3 ) (3 ) Income statement charge/(release) for the year (2 ) (1 ) (3 ) (6 )
Summary of Modification of Loan Terms	The following table sets out the financial assets that were forborne while they had a loss allowance measured at lifetime ECL. 2019 2018 Corporate & £m Corporate & £m Corporate £m Corporate & £m Corporate & £m Corporate £m Financial assets modified in the year: – Amortised cost before modification 135 0 10 104 — 2 – Net modification loss 8 0 1 10 — — Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the loss allowance changed to 12m ECL in the year 34 0 2 8 7 4

Market risk (Tables)

Market risk (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of NIM and EVE Sensitivity of Interest Rate Risk	2019 2018 +50bps -50bps +50bps -50bps NIM sensitivity 99 56 207 (23 ) EVE sensitivity (unaudited) 10 (88 ) 162 (124 )
Disclosure Of Detailed Information About Basis Risk Under EAR Approach Explanatory	We report basis risk using the EaR approach. 2019 2018 £m £m Basis risk EaR 18 25
Disclosure Of Detailed Information About Interest Pricing Gap Balance Sheet Disclosure Explanatory	The table below shows the interest rate repricing gap of our balance sheet by repricing buckets. 3 months 1 year 3 years 5 years >5 years Not sensitive Total 2019 £m £m £m £m £m £m £m Assets 107,155 50,284 67,439 32,918 12,561 16,539 286,896 Liabilities 188,773 17,513 22,774 12,892 21,900 24,064 287,916 Off-balance 14,945 (18,495 ) 4,481 (1,516 ) 1,605 0 1,020 Net gap (66,673 ) 14,276 49,146 18,510 (7,734 ) (7,525 ) 0 2018 Assets 128,173 46,354 61,946 26,048 13,705 16,607 292,833 Liabilities 194,362 16,762 23,987 13,508 23,345 23,845 295,809 Off-balance 11,096 (12,204 ) (2,731 ) 6,870 (55 ) — 2,976 Net gap (55,093 ) 17,388 35,228 19,410 (9,695 ) (7,238 ) —
Disclosure Of Detailed Information About Risk Metrics Covering The Portfolio Of Securities Held For Liquidity And Investment Purpose Explanatory	The table below shows the risk metrics covering the portfolios of securities we hold for liquidity and investment purposes. 2019 2018 £m £m VaR 3 4 Worst three month stressed loss 1 3 190
Summary of Internal VaR for Exposure to Main Classes of Risk	This table and graph show our Internal VaR for exposure to each of the main classes of risk for 2019 and 2018. The VaR figures show how much the fair values of all our tradeable instruments could have changed. Since trading instruments are recorded at fair value, these are also the amounts by which they could have increased or reduced our net income. Year-end exposure Average exposure Highest exposure Lowest exposure 2019 2018 2019 2018 2019 2018 2019 2018 Trading instruments £m £m £m £m £m £m £m £m Interest rate risks 0.2 0.5 0.4 1.4 0.6 3.9 0.1 0.2 Equity risks 0.0 — 0.0 0.2 0.1 0.6 0.0 — Foreign exchange risks 0.4 0.1 0.2 0.3 0.4 0.9 0.1 — Diversification offsets (1) (0.3 ) (0.2 ) (0.3 ) (0.5 ) (0.5 ) — (0.0 ) — Total correlated one-day 0.3 0.4 0.3 1.4 0.6 3.8 0.2 0.3 (1) The highest and lowest exposures for each risk type did not necessarily happen on the same day as the highest and lowest total correlated one-day

Liquidity risk (Tables)

Liquidity risk (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Detailed Information About Liquidity Coverage Ratio Explanatory	This table shows our LCR and LRA at 31 December 2019 and 2018. The LCR at 31 December 2019 reflects the RFB DoLSub, and at 31 December 2018 reflects the previous DoLSub. The LRA data reflect the stress testing methodology in place at that time. LCR RFB DoLSub (1) LRA RFB (2) 2019 2018 2019 2018 £bn £bn £bn £bn Eligible liquidity pool (liquidity value) 41.6 53.0 40.6 52.2 Net stress outflows (29.3 ) (32.4 ) (31.7 ) (32.1 ) Surplus 12.3 20.6 8.9 20.1 Eligible liquidity pool as a percentage of anticipated net cash flows 142 % 164 % 128 % 163 % (1) For 2019, in accordance with our ring-fence structure, data is for the RFB DoLSub. For 2018, i.e. before the implementation of ring-fencing, data is for the previous DoLSub. The RFB LCR was 146%. (2) The LRA is calculated for the Santander UK plc group (the RFB Group) and is a three-month Santander UK specific requirement.
Summary of Detailed Information About For Liquidity Pool of Carrying value And Weighted Average Explanatory	This table shows the carrying value and liquidity value of our eligible liquidity pool assets at 31 December 2019 for the RFB DoLSub and 31 December 2018 for the previous DoLSub. It also shows the weighted average carrying value in the year. RFB DoLSub Weighted average carrying Carrying value Liquidity value (1) value in the year 2019 2018 2019 2018 2019 2018 £bn £bn £bn £bn £bn £bn Cash and balances at central banks 19.3 22.4 19.3 22.4 19.1 24.4 Government bonds 17.9 26.1 17.7 25.7 20.8 16.8 Supranational bonds and multilateral development banks 2.9 1.1 2.9 1.1 2.9 1.1 Covered bonds 1.5 2.7 1.4 2.5 2.4 2.6 Asset-backed securities 0.4 1.7 0.3 1.3 1.4 1.4 Equities 0 0.1 0 — 0 2.1 42.0 54.1 41.6 53.0 46.6 48.4 (1) Liquidity value is the carrying value with the applicable LCR haircut applied.
Summary of Detailed Information About Weighted Average Carrying Value In The Year The Composition Of The Pool Is Consistent With The Currency Profile Of Our Net Liquidity Outflows Explanatory	This table shows the carrying value of our eligible liquidity pool by major currencies at 31 December 2019 for the RFB DoLSub and 31 December 2018 for the previous DoLSub. The composition of the pool is consistent with the currency profile of our net liquidity outflows. RFB DoLSub US Dollar Euro Sterling Other Total £bn £bn £bn £bn £bn 2019 3.6 1.2 36.1 1.1 42.0 2018 5.3 3.9 42.2 2.7 54.1
Summary of Detailed Information About Allocation Of The Carrying Value Of The Assets In Our Eligible Liquidity Pool For LRa And LCR Explanatory	This table shows the allocation of the carrying value of the assets in our eligible liquidity pool for LRA and LCR purposes at 31 December 2019 for the RFB DoLSub and 31 December 2018 for the previous DoLSub. RFB DoLSub 2019 2018 LCR eligible liquidity pool LCR eligible liquidity pool Level 1 Level 2A Level 2B Total Of which LRA eligible Level 1 Level 2A Level 2B Total Of which LRA eligible £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Cash and balances at central banks 19.3 0 0 19.3 19.3 22.4 — — 22.4 21.8 Government bonds: – AAA to AA- 16.7 0 0 16.7 16.7 23.6 — — 23.6 23.3 – A+ to A 0 1.2 0 1.2 1.2 — 2.5 — 2.5 2.5 Supranational bonds and multilateral development banks: – AAA to AA- 2.9 0 0 2.9 2.5 1.1 — — 1.1 1.1 Covered bonds: – AAA to AA- 1.4 0.1 0 1.5 1.5 1.6 1.1 — 2.7 2.7 Asset-backed securities: – AAA to AA- 0 0 0.4 0.4 0.4 — — 1.7 1.7 1.7 Equities 0 0 0 0 — — 0.1 0.1 0.1 40.3 1.3 0.4 42.0 41.6 48.7 3.6 1.8 54.1 53.2 2019 compared to 2018
Summary of Reconciliation of Wholesale Funding to Balance Sheet	This table reconciles our wholesale funding to our balance sheet at 31 December 2019 and 2018. Balance sheet line item Financial Repurchase liabilities Debt Funding Deposits Deposits agreements – designated securities Subordinated Other equity analysis by banks by customers (1) non trading at fair value in issue liabilities instruments (2) 2019 £bn £bn £bn £bn £bn £bn £bn £bn Deposits 0.3 0.3 0 0 0 0 0 0 Certificates of deposit and commercial paper 5.8 0 0 0 0 5.8 0 0 Senior unsecured – public benchmark 18.8 0 8.6 0 0 10.2 0 0 – privately placed 2.7 0 0.1 0 1.0 1.6 0 0 Covered bonds 18.2 0 0 0 0 18.2 0 0 Securitisation and structured issuance 5.6 0 0 1.4 0.5 3.7 0 0 Term Funding Scheme 10.8 10.8 0 0 0 0 0 0 Subordinated liabilities and equity 5.2 0 0 0 0 0 3.0 2.2 Total wholesale funding 67.4 11.1 8.7 1.4 1.5 39.5 3.0 2.2 Repos 16.9 0 0 16.9 0 0 0 0 Foreign exchange and hedge accounting 2.5 0 0.4 0 0 1.6 0.5 0 Other 3.5 3.3 (3) 0 0 0.2 0 0 0 Balance sheet total 90.3 14.4 9.1 18.3 1.7 41.1 3.5 2.2 2018 Deposits by banks 1.0 1.0 — — — — — — Certificates of deposit and commercial paper 6.4 — — — — 6.4 — — Senior unsecured – public benchmark 21.2 — 8.6 — — 12.6 — — – privately placed 4.0 — 0.1 — 1.0 2.9 — — Covered bonds 16.6 — — — — 16.6 — — Securitisation and structured issuance 7.8 — 0.5 2.2 — 5.1 — — Term Funding Scheme 10.8 10.8 — — — — — — Subordinated liabilities and equity 5.0 — — — — — 3.0 2.0 Total wholesale funding 72.8 11.8 9.2 2.2 1.0 43.6 3.0 2.0 Repos 10.8 — — 8.7 2.1 — — — Foreign exchange and hedge accounting 4.2 — 0.5 — — 3.1 0.6 — Other 8.6 5.4 (3) — — 3.2 — — — Balance sheet total 96.4 17.2 9.7 10.9 6.3 46.7 3.6 2.0 (1) This is included in our balance sheet total of £181,883 m (2018: £178,090 m). (2) Consists of £nil (2018: £14m) fixed/floating rate non-cumulative Step-up (3) Other consists of items in the course of transmission and other deposits, excluding the TFS. See Note 23 to the Consolidated Financial Statements.
Summary of Sources of Wholesale Funding by Maturity	This table shows our main sources of wholesale funding. It does not include securities finance agreements. The table is based on exchange rates at issue and scheduled repayments and call dates. It does not reflect the final contractual maturity of the funding. £ 1 >1 and £ 3 >3 and £ >6 and £ 9 >9 and £ 12 Sub-total >1 and >2 and month months 6 months months months £ 1 year £ 2 years £ 5 years >5 years Total 2019 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Downstreamed from Santander UK Group Holdings plc to Santander UK plc (1) Senior unsecured – public benchmark 0 0 0 0 0.8 0.8 1.8 4.2 1.7 8.5 – privately placed 0 0 0 0 0 0 0 0 0.1 0.1 Subordinated liabilities and equity (incl. AT1) 0 0 0 0 0 0 0 1.0 2.0 3.0 0 0 0 0 0.8 0.8 1.8 5.2 3.8 11.6 Other Santander UK plc Deposits by banks 0.1 0 0 0.2 0 0.3 0 0 0 0.3 Certificates of deposit and commercial paper 0.6 3.1 2.0 0.1 0 5.8 0 0 0 5.8 Senior unsecured – public benchmark 0.8 1.4 0 0.6 1.9 4.7 2.9 1.9 0.8 10.3 – privately placed 0 0.9 0 0.9 0 1.8 0.4 0.1 0.3 2.6 Covered bonds 0 0 1.8 0 1.0 2.8 5.6 6.2 3.6 18.2 Securitisation and structured (2) 0.2 0 0.8 0.2 0.2 1.4 1.3 1.3 0 4.0 Term Funding Scheme 0 0 0 0 4.5 4.5 4.0 2.3 0 10.8 Subordinated liabilities 0 0 0 0 0 0 0 0.9 1.3 2.2 1.7 5.4 4.6 2.0 7.6 21.3 14.2 12.7 6.0 54.2 Other group entities Securitisation & structured (3) 0 0.1 0.1 0.1 0.1 0.4 0.6 0.6 0 1.6 Total at 31 December 2019 1.7 5.5 4.7 2.1 8.5 22.5 16.6 18.5 9.8 67.4 Of which: – Secured 0.2 0.1 2.7 0.3 5.8 9.1 11.5 10.4 3.6 34.6 – Unsecured 1.5 5.4 2.0 1.8 2.7 13.4 5.1 8.1 6.2 32.8 1.7 5.5 4.7 2.1 8.5 22.5 16.6 18.5 9.8 67.4 2018 Total at 31 December 2018 3.1 6.8 3.0 2.7 0.9 16.5 15.9 30.1 10.3 72.8 Of which: – Secured 0.8 0.7 0.7 1.7 0.5 4.4 8.5 18.3 4.0 35.2 – Unsecured 2.3 6.1 2.3 1.0 0.4 12.1 7.4 11.8 6.3 37.6 (1) 94% of Senior Unsecured debt issued from Santander UK Group Holdings plc has been downstreamed to Santander UK plc as ‘secondary non-preferential (2) Includes funding from mortgage-backed securitisation vehicles where Santander UK plc is the asset originator. (3) Includes funding from asset-backed securitisation vehicles where entities other than Santander UK plc are the asset originator.
Summary of Wholesale Funding by Currency	This table shows our wholesale funding by major currency at 31 December 2019 and 2018. 2019 2018 Sterling US Dollar Euro Other Sterling US Dollar Euro Other % % % % % % % % Downstreamed from Santander UK Group Holdings plc to Santander UK plc Senior unsecured – public benchmark 11 65 22 2 11 65 22 2 – privately placed 0 0 0 100 — — — 100 Subordinated liabilities and equity (incl. AT1) 67 33 0 0 64 36 — — 25 56 16 3 23 57 17 3 Other Santander UK plc Deposits by banks 3 97 0 0 3 97 — — Certificates of deposit and commercial paper 45 54 1 0 48 52 — — Senior unsecured – public benchmark 14 54 32 0 11 56 33 — – privately placed 21 15 59 5 13 12 72 3 Covered bonds 54 0 45 1 50 — 49 1 Securitisation & structured issuance 72 28 0 0 61 35 4 — Term Funding Scheme 100 0 0 0 100 — — — Subordinated liabilities 49 51 0 0 49 51 — — 54 22 24 0 48 25 26 1 Other group entities Securitisation & structured issuance 95 5 0 0 89 11 — — Total 50 27 22 1 46 30 24 —
Summary of External Term Issuance (Sterling Equivalent)	In 2019, our external term issuance (sterling equivalent) was: Sterling US Dollar Euro Other Total 2019 Total 2018 £bn £bn £bn £bn £bn £bn Downstreamed from Santander UK Group Holdings plc to Santander UK plc Senior unsecured – public benchmark 0 0 0 0 0 2.7 Subordinated debt and equity (inc. AT1) 0.5 0 0 0 0.5 0 0.5 0 0 0 0.5 2.7 Other Santander UK plc Securitisations and other secured funding 0 0 0 0 0 2.9 Covered bonds 2.0 0 0.9 0 2.9 4.3 Senior unsecured – public benchmark 0.1 0.8 0 0 0.9 2.9 – privately placed 0 0 0 0 0 1.6 Term Funding Scheme 0 0 0 0 0 2.3 2.1 0.8 0.9 0 3.8 14.0 Other group entities Securitisations 0.2 0 0 0 0.2 0.4 Total gross issuances 2.8 0.8 0.9 0 4.5 17.1
Summary of Balance Sheet Encumbered And Unencumbered Assets Explanatory	On-balance Encumbered with counterparties other than Unencumbered assets not pre-positioned central banks with central banks Covered bonds Securitis- ations Other Total Assets positioned at central banks (3) Readily available Other available assets Cannot be encumbered Total Total assets 2019 £m £m £m £m £m £m £m £m £m £m Cash and balances at central banks (1)(2) 0 0 1,080 1,080 707 19,393 0 0 20,100 21,180 Financial assets at FVTPL: – Derivative financial instruments 0 0 0 0 0 0 0 3,316 3,316 3,316 – Other financial assets at FVTPL 0 0 0 0 0 0 0 386 386 386 Financial assets at amortised cost: – Loans and advances to customers 23,310 12,915 332 36,557 55,273 76,567 22,875 16,015 170,730 207,287 – Loans and advances to banks 0 0 403 403 0 0 0 1,452 1,452 1,855 – Repurchase agreements – non trading 0 0 0 0 0 0 0 23,636 23,636 23,636 – Other financial assets at amortised cost 0 0 3,026 3,026 0 4,030 0 0 4,030 7,056 Financial assets at FVOCI 0 0 6,009 6,009 0 3,738 0 0 3,738 9,747 Interests in other entities 0 0 0 0 0 0 0 117 117 117 Intangible assets 0 0 0 0 0 0 0 1,766 1,766 1,766 Property, plant and equipment 0 0 0 0 0 0 1,967 0 1,967 1,967 Current tax assets 0 0 0 0 0 0 0 200 200 200 Retirement benefit assets 0 0 0 0 0 0 0 669 669 669 Other assets 0 0 0 0 0 0 0 2,520 2,520 2,520 Total assets 23,310 12,915 10,850 47,075 55,980 103,728 24,842 50,077 234,627 281,702 2018 Cash and balances at central banks (1)(2) — — 1,080 1,080 636 18,031 — — 18,667 19,747 Financial assets at FVTPL: – Derivative financial instruments — — — — — — — 5,259 5,259 5,259 – Other financial assets at FVTPL — — — — — — — 5,617 5,617 5,617 Financial assets at amortised cost: – Loans and advances to customers 21,240 14,454 256 35,950 52,497 71,941 20,943 19,958 165,339 201,289 – Loans and advances to banks — — 218 218 — — — 2,581 2,581 2,799 – Repurchase agreements – non trading — — — — — — — 21,127 21,127 21,127 – Other financial assets at amortised cost — — 3,763 3,763 — 3,466 — — 3,466 7,229 Financial assets at FVOCI — — 5,825 5,825 — 7,477 — — 7,477 13,302 Interests in other entities — — — — — — — 88 88 88 Intangible assets — — — — — — — 1,808 1,808 1,808 Property, plant and equipment — — — — — — 1,832 — 1,832 1,832 Current tax assets — — — — — — — 153 153 153 Retirement benefit assets — — — — — — — 842 842 842 Other assets — — — — — — — 2,280 2,280 2,280 Total assets 21,240 14,454 11,142 46,836 53,133 100,915 22,775 59,713 236,536 283,372 (1) Encumbered cash and balances at central banks include minimum cash balances we have to hold at central banks for regulatory purposes. (2) Readily realisable cash and balances at central banks are amounts held at central banks as part of our liquidity management activities. (3) Comprises pre-positioned

Capital risk (Tables)

Capital risk (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Detailed Information About Capital Ratio In Current MDA Explanatory	Current MDA % Pillar 1 4.5 Pillar 2A (1) 3.2 CCB 2.5 CCyB (2) 1.0 SRB 1.0 Current MDA trigger 12.2 Distance to current MDA 2.1 Total CET1 capital ratio 14.3
Summary of Detailed Information About Recapitalisation For Holdings Group Explanatory	2019 2018 CET1 capital ratio 14.3 13.2 AT1 2.7 2.2 Grandfathered Tier 1 0.7 0.8 Tier 2 4.0 4.1 Total capital ratio 21.7 20.3
Summary of Regulatory Capital Resources	Regulatory capital resources This table shows our qualifying regulatory capital. 2019 2018 CET1 capital 10,419 10,374 AT1 capital 2,443 2,349 Tier 1 capital 12,862 12,723 Tier 2 capital 2,925 3,223 Total regulatory capital (1) 15,787 15,946 (1) Capital resources include a transitional IFRS 9 benefit at 31 December 2019 of £16m (2018: £21m).
Summary of Detailed Information About For Additional Capital And Risk Management Explanatory	The tables below are consistent with our regulatory filings for 2019 and 2018. 2019 2018 Total RWAs 72.6 78.5

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Detailed Information Of Effect Of New Lease Accounting Standard Explanatory	The amount of the lease liabilities above differed from the amount of operating lease commitments at 31 December 2018 and is reconciled as follows: Group £m Rental commitments under non-cancellable 246 Recognition exemption for short-term leases (72 ) Effect from discounting at the incremental borrowing rate at 1 January 2019 7 Additional liabilities recognised based on the initial application of IFRS 16 at 1 January 2019 181
Schedule of Useful Lives or Depreciation Rates Used for Property, Plant and Equipment	Classes of property, plant and equipment are depreciated on a straight-line basis over their useful life, as follows: Owner-occupied properties Not exceeding 50 years Office fixtures and equipment 3 to 15 years Computer software 3 to 7 years Right-of-use Shorter of the lease term or the useful life of the underlying asset
Summary of Probability Weights Applied for Each Scenario of Expected Credit Losses Allowance	2019 Weighted Upside 2 Upside 1 Base case Downside 1 Downside 2 Exposure Retail Banking 206,479 206,479 206,479 206,479 206,479 206,479 - of which: mortgages 178,788 178,788 178,788 178,788 178,788 178,788 CCB 21,855 21,855 21,855 21,855 21,855 21,855 CIB 13,456 13,456 13,456 13,456 13,456 13,456 Corporate Centre 74,532 74,532 74,532 74,532 74,532 74,532 ECL Retail Banking 591 456 467 485 570 1,148 - of which: mortgages 218 122 127 137 196 660 CCB 210 156 169 183 219 317 CIB 50 19 34 48 53 58 Corporate Centre 12 9 10 10 13 18 % % % % % % Proportion of assets in Stage 2 Retail Banking 4.7 3.2 3.3 3.3 3.7 8.3 - of which: mortgages 4.6 3.1 3.1 3.1 3.6 8.7 CCB 10.0 7.4 7.4 7.4 8.5 16.3 CIB 2.9 1.5 1.5 1.5 1.5 1.5 Corporate Centre 0.2 0.1 0.1 0.1 0.2 0.3 2018 £m £m £m £m £m £m Exposure Retail Banking 195,805 195,805 195,805 195,805 195,805 195,805 - of which: mortgages 169,170 169,170 169,170 169,170 169,170 169,170 CCB 22,835 22,835 22,835 22,835 22,835 22,835 CIB 17,618 17,618 17,618 17,618 17,618 17,618 Corporate Centre 74,690 74,690 74,690 74,690 74,690 74,690 ECL Retail Banking 594 431 452 480 637 1,607 - of which: mortgages 237 121 131 137 273 1,105 CCB 182 115 135 157 192 302 CIB 18 8 12 17 22 27 Corporate Centre 13 8 9 11 13 21 % % % % % % Proportion of assets in Stage 2 Retail Banking 5.4 3.4 3.5 3.7 4.7 15.1 - of which: mortgages 5.6 3.4 3.6 3.7 4.9 16.5 CCB 5.5 3.0 3.0 3.1 4.3 10.7 CIB 0.8 0.4 0.4 0.4 0.4 0.4 Corporate Centre 0.2 0.1 0.1 0.1 0.2 0.4
Schedule Of Impact On Profit Before Tax Of Applying An Immediate And Permanent House Price Increase Or Decrease To Our Base Case Economic Scenario Explanatory	The table below shows the impact on profit before tax of applying an immediate and permanent house price increase / decrease to our base case economic scenario, and assumes no changes to the staging allocation of exposures: Increase/decrease in house prices Increase/(decrease) in profit before tax +20% +10% -10% -20% 31 December 2019 16 10 (16 ) (43 ) 31 December 2018 20 12 (20 ) (52 )

Segments (Tables)

Segments (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Results by Segment	Results by segment 2019 Retail Corporate & £m Corporate & £m Corporate Total £m Net interest income/(expense) 2,876 359 63 (6 ) 3,292 Non-interest 698 78 112 (7 ) 881 Total operating income/(expense) 3,574 437 175 (13 ) 4,173 Operating expenses before credit impairment losses, provisions and charges (1,994 ) (264 ) (171 ) (70 ) (2,499 ) Credit impairment losses (160 ) (37 ) (22 ) (2 ) (221 ) Provisions for other liabilities and charges (292 ) (20 ) (17 ) (112 ) (441 ) Total operating credit impairment losses, provisions and charges (1) (452 ) (57 ) (39 ) (114 ) (662 ) Profit/(loss) before tax 1,128 116 (35 ) (197 ) 1,012 Revenue from external customers 4,311 530 181 (849 ) 4,173 Inter-segment revenue (737 ) (93 ) (6 ) 836 0 Total operating income/(expense) 3,574 437 175 (13 ) 4,173 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) - Current account and debit card fees 702 27 29 0 758 - Insurance, protection and investments 76 0 0 1 77 - Credit cards 86 0 0 0 86 - Non-banking (3) 61 56 71 3 191 Total fee and commission income 925 83 100 4 1,112 Fee and commission expense (373 ) (23 ) (17 ) (13 ) (426 ) Net fee and commission income/(expense) 552 60 83 (9 ) 686 Customer loans 180,398 16,297 4,114 4,199 205,008 Total assets (4) 187,556 16,297 4,727 73,122 281,702 Customer deposits 145,050 18,234 6,101 2,331 171,716 Total liabilities 145,917 18,260 6,500 95,008 265,685 Average number of staff 20,832 1,796 901 41 23,570 (1) Credit impairment losses for 2018 and later are calculated on an IFRS 9 basis and for 2017 on an IAS 39 basis. (2) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (3) Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance. (4) Includes customer loans, net of credit impairment loss allowances. 2018 Retail Corporate & Corporate & (5) Corporate (5) Total Net interest income 3,126 403 69 5 3,603 Non-interest 638 82 183 28 931 Total operating income 3,764 485 252 33 4,534 Operating expenses before credit impairment losses, provisions and charges (1,929 ) (258 ) (250 ) (142 ) (2,579 ) Credit impairment (losses)/releases (124 ) (23 ) (14 ) 8 (153 ) Provisions for other liabilities and charges (230 ) (14 ) (8 ) (5 ) (257 ) Total operating credit impairment losses, provisions and (charges)/releases (1) (354 ) (37 ) (22 ) 3 (410 ) Profit/(loss) before tax 1,481 190 (20 ) (106 ) 1,545 Revenue from external customers 4,421 638 297 (822 ) 4,534 Inter-segment revenue (657 ) (153 ) (45 ) 855 — Total operating income 3,764 485 252 33 4,534 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) - Current account and debit card fees 697 27 29 — 753 - Insurance, protection and investments 105 — — — 105 - Credit cards 85 — — — 85 - Non-banking (3) 75 62 87 3 227 Total fee and commission income 962 89 116 3 1,170 Fee and commission expense (382 ) (25 ) (14 ) — (421 ) Net fee and commission income 580 64 102 3 749 Customer loans 172,747 17,702 4,613 4,524 199,586 Total assets (4) 179,572 17,702 8,607 77,491 283,372 Customer deposits 142,065 17,606 4,853 2,791 167,315 Total liabilities 142,839 17,634 8,885 98,105 267,463 Average number of staff 21,215 1,732 1,083 175 24,205 2017 Net interest income 3,270 391 67 75 3,803 Non-interest 615 74 261 159 1,109 Total operating income 3,885 465 328 234 4,912 Operating expenses before credit impairment losses, provisions and charges (1,856 ) (223 ) (292 ) (128 ) (2,499 ) Credit impairment (losses)/ releases (1) (36 ) (13 ) (174 ) 20 (203 ) Provisions for other liabilities and charges (342 ) (55 ) (11 ) 15 (393 ) Total operating credit impairment losses, provisions and (charges)/releases (378 ) (68 ) (185 ) 35 (596 ) Profit/(loss) before tax 1,651 174 (149 ) 141 1,817 Revenue from external customers 4,534 639 396 (657 ) 4,912 Inter-segment revenue (649 ) (174 ) (68 ) 891 — Total operating income 3,885 465 328 234 4,912 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) - Current account and debit card fees 737 27 27 — 791 - Insurance, protection and investments 100 — — — 100 - Credit cards 92 — — — 92 - Non-banking (3) 45 63 123 8 239 Total fee and commission income 974 90 150 8 1,222 Fee and commission expense (367 ) (31 ) (17 ) — (415 ) Net fee and commission income 607 59 133 8 807 Customer loans 168,729 19,391 6,037 6,167 200,324 Total assets (4) 174,524 19,391 25,368 95,482 314,765 Customer deposits 143,834 17,760 4,546 9,781 175,921 Total liabilities 150,847 18,697 24,388 104,628 298,560 Average number of staff 17,194 1,240 1,006 119 19,559 (1) Credit impairment losses for 2018 and later are calculated on an IFRS 9 basis and for 2017 on an IAS 39 basis. (2) The disaggregation of fees and commission income as shown above is not included in reports provided to the chief operating decision maker but is provided to show the split by reportable segments. (3) Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance. (4) Includes customer loans, net of credit impairment loss allowances. (5) The re-segmentation of our short term markets business has resulted in profit before tax of £77m being re-presented in Corporate Centre rather than Corporate & Investment Banking in 2018 (2017: £98m).

Net Interest Income (Tables)

Net Interest Income (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Net Interest Income	Group 2019 2018 2017 Interest and similar income: Loans and advances to customers 5,230 5,458 5,494 Loans and advances to banks 137 202 164 Reverse repurchase agreements – non trading 244 124 20 Other 306 282 227 Total interest and similar income (1) 5,917 6,066 5,905 Interest expense and similar charges: Deposits by customers (1,540 ) (1,433 ) (1,330 ) Deposits by banks (134 ) (117 ) (35 ) Repurchase agreements – non trading (126 ) (42 ) (5 ) Debt securities in issue (678 ) (721 ) (590 ) Subordinated liabilities (137 ) (142 ) (134 ) Other (10 ) (8 ) (8 ) Total interest expense and similar charges (2) (2,625 ) (2,463 ) (2,102 ) Net interest income 3,292 3,603 3,803 (1) This includes £203m (2018: £209m) of interest income on financial assets at fair value through other comprehensive income. (2) This includes £310m (2018: £298m) of interest expense on financial assets at fair value through other comprehensive income.

Net Fee and Commission Income (

Net Fee and Commission Income (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Net Fee and Commission Income	Group 2019 2018 2017 Fee and commission income: Current account and debit card fees 758 753 791 Insurance, protection and investments 77 105 100 Credit cards 86 85 92 Non-banking (1) 191 227 239 Total fee and commission income 1,112 1,170 1,222 Total fee and commission expense (426 ) (421 ) (415 ) Net fee and commission income 686 749 807 (1) Non-banking and other fees include mortgages, consumer finance, commitment commission, asset finance, invoice finance and trade finance.

Net Trading and Other Income (T

Net Trading and Other Income (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Net Trading and Other Income	Group 2019 2018 2017 Net trading and funding of other items by the trading book 6 245 205 Net gains/(losses) on other financial assets at fair value through profit or loss 19 (6 ) 80 Net losses on other financial liabilities at fair value through profit or loss (83 ) (44 ) (97 ) Net gains/(losses) on derivatives managed with assets/liabilities held at fair value through profit or loss 69 (128 ) (17 ) Hedge ineffectiveness 8 34 5 Net profit on sale of available-for-sale 54 Net profit on sale of financial assets at fair value through other comprehensive income 15 19 Income from operating lease assets 124 86 44 Other 37 (24 ) 28 195 182 302

Operating Expenses Before Cre_2

Operating Expenses Before Credit Impairment Losses, Provisions and Charges (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Operating Expenses Before Credit Impairment Losses, Provisions and Charges	Group 2019 2018 2017 Staff costs: Wages and salaries 852 898 743 Performance-related payments 159 159 157 Social security costs 111 111 93 Pensions costs – defined contribution plans 66 67 54 – defined benefit plans 35 79 32 Other share-based payments 0 3 10 Other personnel costs 40 52 45 1,263 1,369 1,134 Other administration expenses 693 835 1,011 Depreciation, amortisation and impairment 543 375 354 2,499 2,579 2,499
Summary of Deferred Performance Awards	Costs recognised in 2019 Costs expected to be recognised in 2020 or later Arising from Arising from Total Arising from Arising from Total Cash 3 7 10 7 10 17 Shares 3 6 9 6 9 15 6 13 19 13 19 32
Summary of Amount of Bonus Awarded to Employees	Expenses charged in the year Expenses deferred to future periods Total 2019 £m 2018 2019 £m 2018 2019 2018 Cash award – not deferred 130 123 0 — 130 123 – deferred 10 12 17 20 27 32 Shares award – not deferred 10 11 0 — 10 11 – deferred 9 13 15 17 24 30 Total discretionary bonus 159 159 32 37 191 196

Audit and Other Services (Table

Audit and Other Services (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Audit and Other Services	Group 2019 2018 2017 £m £m £m Audit fees: Fees payable to the Company’s auditor and its associates for the audit of the Santander UK group’s annual accounts 8.0 7.2 7.4 Fees payable to the Company’s auditor and its associates for other services to the Santander UK group: - Audit of the Santander UK group’s subsidiaries 1.3 1.1 1.4 Total audit fees (1) 9.3 8.3 8.8 Non-audit Audit-related assurance services (2) 0.8 0.7 0.7 Other assurance services 0.2 0.1 0.1 Other non-audit 0.2 1.0 0.4 Total non-audit 1.2 1.8 1.2 (1) 2019 audit fees included £0.1m (2018: £nil) which related to the prior year. (2) 2019 audit-related assurance services included £0.1m (2018: £0.1m) which related to the prior year.

Credit Impairment Losses and _2

Credit Impairment Losses and Provisions (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Impairment Losses and Provisions	Group 2019 2018 2017 £m £m £m Credit impairment losses: (1) Loans and advances to customers 239 189 257 Recoveries of loans and advances, net of collection costs (40 ) (42 ) (54 ) Off-balance 22 6 221 153 203 Provisions for other liabilities and charges (excluding off-balance 435 257 385 Provisions for RV and voluntary termination 6 — 8 441 257 393 662 410 596 (1) Credit impairment losses for 2018 and later are calculated on an IFRS 9 basis and for 2017 and earlier on an IAS 39 basis.

Taxation (Tables)

Taxation (Tables)	12 Months Ended
	Dec. 31, 2019
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Disclosure of Tax on Profit	Group 2019 2018 (1) 2017 (1) £m £m £m Current tax: UK corporation tax on profit for the year 265 408 510 Adjustments in respect of prior years (25 ) (20 ) (27 ) Total current tax 240 388 483 Deferred tax: Charge for the year 46 16 23 Adjustments in respect of prior years (7 ) (5 ) 9 Total deferred tax 39 11 32 Tax on profit 279 399 515 (1) Adjusted to reflect the amendment to IAS 12, as described in Note 1.
Schedule of Tax on Profit Before Tax Differs from Theoretical Amount that Arise Using Basic Corporation Tax Rate	The Santander UK group’s effective tax rate for 2019, based on profit before tax, was 27.6% (2018: 25.8%, 2017: 28.3%). The tax on profit before tax differs from the theoretical amount that would arise using the basic corporation tax rate of the Company as follows: Group 2019 2018 (1) 2017 (1) £m £m £m Profit before tax 1,012 1,545 1,817 Tax calculated at a tax rate of 19% (2018: 19%, 2017: 19.25%) 192 294 350 Bank surcharge on profits 65 109 132 Non-deductible 8 8 9 Non-deductible 24 20 25 Non-deductible 44 6 35 Other non-deductible non-taxable 31 30 30 Effect of change in tax rate on deferred tax provision (14 ) (1 ) (2 ) Tax relief on dividends in respect of other equity instruments (39 ) (42 ) (46 ) Adjustment to prior year provisions (32 ) (25 ) (18 ) Tax charge 279 399 515 (1) Adjusted to reflect the amendment to IAS 12, as described in Note 1.
Disclosure of Movements in Current Tax Assets and Liabilities	Movements in current tax assets and liabilities during the year were as follows: Group 2019 2018 (1) £m £m Assets 153 — Liabilities 0 (3 ) At 1 January 153 (3 ) Income statement charge (240 ) (388 ) Other comprehensive income (charge)/credit (4 ) 34 Corporate income tax paid 292 391 Other movements (1 ) 119 200 153 Assets 200 153 Liabilities 0 — At 31 December 200 153 (1) Adjusted to reflect the amendment to IAS 12, as described in Note 1.
Disclosure of Deferred Tax Assets and Liabilities Including Movement in Deferred Tax Account	The table below shows the deferred tax assets and liabilities including the movement in the deferred tax account during the year. Deferred tax balances are presented in the balance sheet after offsetting assets and liabilities where the Santander UK group has the legal right to offset and intends to settle on a net basis. Group Fair value of Pension Cash flow Available- for-sale Fair value Tax losses Accelerated tax Other Total At 1 January 2019 (51 ) (183 ) (43 ) (13 ) 20 (6 ) 53 (223 ) Income statement (charge)/credit (1 ) (44 ) 0 0 (7 ) 23 (10 ) (39 ) Transfers/reclassifications 0 0 22 5 0 0 (27 ) 0 Credited/(charged) to other comprehensive income 0 131 (37 ) 0 0 0 19 113 At 31 December 2019 (52 ) (96 ) (58 ) (8 ) 13 17 35 (149 ) At 31 December 2017 (41 ) (41 ) 3 (26 ) 25 (4 ) (4 ) (88 ) Adoption of IFRS 9 — — — 26 (26 ) — — 68 68 At 1 January 2018 (41 ) (41 ) 3 (26 ) 25 (4 ) 64 (20 ) Income statement (charge)/credit (10 ) (24 ) — — (5 ) — 28 (11 ) Transfers/reclassifications — — — — — (2 ) (18 ) (20 ) Credited/(charged) to other comprehensive income — (118 ) (46 ) 13 — — (21 ) (172 ) At 31 December 2018 (51 ) (183 ) (43 ) (13 ) 20 (6 ) 53 (223 )

Dividends on Ordinary Shares (T

Dividends on Ordinary Shares (Tables)	12 Months Ended
	Dec. 31, 2019
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Disclosure of Dividends on Ordinary Shares Declared and Paid	Dividends on ordinary shares declared and paid in the year were as follows: Group Group 2019 2018 2017 2019 2018 2017 In respect of current year - first interim 0.53 0.81 1.04 164 250 323 - second interim 0.49 2.15 0.74 151 668 230 - third interim 0 0.71 — 0 221 — 1.02 3.67 1.78 315 1,139 553

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
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Notional Amounts and Fair Values of Derivatives	The table below includes the notional amounts of transactions outstanding at the balance sheet date; they do not represent actual exposures. Group 2019 2018 Fair value Fair value Notional Assets Liabilities Notional Assets Liabilities Derivatives held for trading: Exchange rate contracts 14,149 134 200 13,830 454 351 Interest rate contracts 46,564 718 315 79,038 1,421 1,105 Equity and credit contracts 2,474 283 160 2,762 251 168 Total derivatives held for trading 63,187 1,135 675 95,630 2,126 1,624 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 1,482 166 2 3,010 357 — Interest rate contracts 94,550 1,022 1,488 86,422 1,065 1,315 96,032 1,188 1,490 89,432 1,422 1,315 Designated as cash flow hedges: Exchange rate contracts 28,502 2,023 462 33,901 3,537 200 Interest rate contracts 17,451 184 35 18,808 46 102 Equity derivative contracts 0 0 0 — — — 45,953 2,207 497 52,709 3,583 302 Total derivatives held for hedging 141,985 3,395 1,987 142,141 5,005 1,617 Derivative netting (1) (1,214 ) (1,214 ) (1,872 ) (1,872 ) Total derivatives 205,172 3,316 1,448 237,771 5,259 1,369 (1) Derivative netting excludes the effect of cash collateral, which is offset against the gross derivative position. The amount of cash collateral received that had been offset against the gross derivative assets was £222m (2018: £9m) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was £629m (2018: £354m).
Analysis of the Notional and Fair Values of Derivatives by Trading and Settlement Method	The table below analyses the notional and fair values of derivatives by trading and settlement method. Notional Traded over the counter Asset Liability Traded on recognised exchanges Settled by central counterparties Not settled by central counterparties Total Traded on recognised exchanges Traded over the counter Traded on recognised exchanges Traded over the counter 2019 £m £m £m £m £m £m £m £m Exchange rate contracts 0 0 44,133 44,133 0 2,324 0 663 Interest rate contracts 0 131,538 27,027 158,565 0 709 0 625 Equity and credit contracts 0 0 2,474 2,474 0 283 0 160 0 131,538 73,634 205,172 0 3,316 0 1,448 2018 Exchange rate contracts — — 50,741 50,741 — 4,349 — 551 Interest rate contracts — 154,106 30,162 184,268 — 659 — 650 Equity and credit contracts — — 2,762 2,762 — 251 — 168 — 154,106 83,665 237,771 — 5,259 — 1,369
Summary of Nominal Value in Hedging Instruments	Group GBP LIBOR £m USD LIBOR £m Other £m Total £m 2019 Total notional value of hedging instruments: - Cash flow hedges 23,396 8,001 0 31,397 - Fair value hedges 53,244 5,070 1,187 59,501 76,640 13,071 1,187 90,898 Maturing after 31 December 2021: - Cash flow hedges 11,773 2,644 0 14,417 - Fair value hedges 16,455 1,897 740 19,092 28,228 4,541 740 33,509
Summary of Maturity Profile and Average Price/Rate of Hedging Instruments Used in Hedging Strategies	The following table sets out the maturity profile and average price/rate of the hedging instruments used in the Santander UK group’s hedging strategies: Group 2019 Hedging Instruments £ >1 and £ >3 and £ >1 and £ >5 years Total Fair value hedges: Interest rate risk Interest rate contracts – Notional amount (£m) 4,354 5,804 27,405 43,652 13,099 94,314 Average fixed interest rate – GBP 0.77 % 0.90 % 0.88 % 1.33 % 3.00 % Average fixed interest rate – EUR (0.41 )% 0.29 % 2.21 % 1.36 % 2.36 % Average fixed interest rate – USD 0 1.54 % 1.99 % 2.69 % 4.56 % Interest rate/FX risk Exchange rate contracts – Notional amount (£m) 0 755 0 317 410 1,482 Interest rate contracts – Notional amount (£m) 0 0 0 18 218 236 Average GBP – EUR exchange rate 0 0 0 1.1781 1.1603 Average GBP – USD exchange rate 0 1.5110 0 0 0 Average fixed interest rate – EUR 0 0 0 3.52 % 2.12 % Average fixed interest rate – USD 0 2.38 % 0 0 0 Cash flow hedges: Interest rate risk Interest rate contracts – Notional amount (£m) 0 339 1,066 4,671 500 6,576 Average fixed interest rate – GBP 0 0.76 % 0.82 % 1.46 % 0.40 % FX risk Exchange rate contracts – Notional amount (£m) 1,187 2,119 3,758 5,217 0 12,281 Interest rate contracts – Notional amount (£m) 0 0 0 755 0 755 Average GBP – JPY exchange rate 0 145.9275 143.0857 140.8152 0 Average GBP – EUR exchange rate 0 1.1444 1.1167 1.1526 0 Average GBP – USD exchange rate 1.2856 1.2624 1.2925 1.2991 0 Interest rate/FX risk Exchange rate contracts – Notional amount (£m) 812 0 3,367 8,009 4,033 16,221 Interest rate contracts – Notional amount (£m) 0 0 3,121 4,829 2,170 10,120 Average GBP – EUR exchange rate 1.2742 0 1.1689 1.3114 1.2090 Average GBP – USD exchange rate 0 0 1.5357 1.5811 1.4499 Average fixed interest rate – GBP 2.49 % 0 2.16 % 2.87 % 2.96 % 2018 Fair value hedges: Interest rate risk Interest rate contracts – Notional amount (£m) 6,162 8,411 14,611 39,508 15,652 84,344 Average fixed interest rate – GBP 0.63 % 0.79 % 1.06 % 1.59 % 2.85 % Average fixed interest rate – EUR (0.22 )% 0.67 % 0.91 % 1.09 % 1.26 % Average fixed interest rate – USD 1.51 % 1.31 % 1.34 % 2.68 % 2.18 % Interest rate/FX risk Exchange rate contracts – Notional amount (£m) 392 1,295 — 1,101 222 3,010 Interest rate contracts – Notional amount (£m) 392 1,295 — 90 301 2,078 Average GBP – EUR exchange rate — — — 1.1827 1.1682 Average GBP – USD exchange rate 1.5800 1.3325 — 1.5110 — Average fixed interest rate – EUR — — — 3.89 % 3.92 % Average fixed interest rate – USD 3.62 % 2.50 % — 2.38 % 7.95 % Cash flow hedges: Interest rate risk Interest rate contracts – Notional amount (£m) — 1,715 1,991 3,100 — 6,806 Average fixed interest rate – GBP — 0.73 % 0.73 % 1.33 % — FX risk Exchange rate contracts – Notional amount (£m) 3,916 2,552 2,961 5,596 — 15,025 Interest rate contracts – Notional amount (£m) — — — 785 — 785 Average GBP – JPY exchange rate — 147.2149 146.3718 145.3191 — Average GBP – EUR exchange rate — — 1.2803 1.1349 — Average GBP – USD exchange rate 1.3035 1.3067 1.3099 1.3049 — Interest rate/FX risk Exchange rate contracts – Notional amount (£m) — — 1,773 11,481 5,622 18,876 Interest rate contracts – Notional amount (£m) — — 784 7,562 2,871 11,217 Average GBP – EUR exchange rate — — 1.2523 1.2707 1.2167 Average GBP – USD exchange rate — — 1.6333 1.5447 1.5109 Average fixed interest rate – GBP — — 2.34 % 2.66 % 2.90 %
Summary of Net Gains Or Losses Arising from Fair Value and Cash Flow Hedges Included in Net Trading and Other Income	Net gains or losses arising from fair value and cash flow hedges included in net trading and other income Group 2019 2018 2017 Fair value hedging: (Losses)/gains on hedging instruments (360 ) 4 56 Gains/(losses) on hedged items attributable to hedged risks 414 75 (2 ) Fair value hedging ineffectiveness 54 79 54 Cash flow hedging ineffectiveness (46 ) (45 ) (49 ) 8 34 5
Summary of Information About Hedging Ineffectiveness by Risk Category	Hedge ineffectiveness can be analysed by risk category as follows: Group 2019 2018 Change in FV Change in FV Recognised Change in FV Change in FV Recognised Fair value hedges: Interest rate risk (264 ) 284 20 26 15 41 Interest rate/FX risk (96 ) 130 34 (22 ) 60 38 (360 ) 414 54 4 75 79 Group 2019 2018 Hedging Instruments Hedging Instruments Income statement line item Change Recognised Recognised Reclassified Change Recognised Recognised Reclassified Cash flow hedges: Interest rate risk Net interest income 34 (33 ) 1 13 20 (14 ) 6 26 FX risk Net interest income/net trading and other income (333 ) 329 (4 ) (316 ) 18 (20 ) (2 ) 9 Equity risk Operating expenses 0 0 0 0 (12 ) 12 — (9 ) Interest rate/FX risk Net interest income/net trading and other income (604 ) 561 (43 ) (709 ) 722 (771 ) (49 ) 726 (903 ) 857 (46 ) (1,012 ) 748 (793 ) (45 ) 752
Summary of Reconciliation by Risk Category of Components of Equity and Analysis of Other Comprehensive Income Items Resulting from Hedge Accounting	Group 2019 2018 Balance at 1 January 326 285 Effective portion of changes in fair value: - Interest rate risk 33 14 - Foreign currency risk (329 ) 20 - Equity risk 0 (12 ) - Interest rate/foreign currency risk (561 ) 771 (857 ) 793 Income statement transfers: - Interest rate risk (13 ) (26 ) - Foreign currency risk 316 (9 ) - Equity risk 0 9 - Interest rate/foreign currency risk 709 (726 ) 1,012 (752 ) Balance at 31 December 481 326
Summary of Details of Hedged Exposures by Hedging Strategies	Santander UK hedges its exposures to various risks, including interest rate risk and foreign currency risk, as set out in the following table. Group 2019 2018 Carrying Accumulated amount of FV hedge Change in value to calculate hedge Carrying Accumulated amount of FV hedge Change in Hedged Portfolio rate risks Of which Hedged Portfolio Of which Fair value hedges Interest rate risk: Loans and advances to customers 43,098 0 870 630 258 42,075 — 638 729 (149 ) Other financial assets at amortised cost 6,627 0 142 121 83 6,640 — 59 — 59 Reverse repos – non trading 17,121 0 (2 ) 0 (2 ) 10,954 — — — — Other financial assets at FVOCI 5,944 102 0 82 125 7,429 10 — 123 (46 ) Deposits by customers (9,944 ) (85 ) 4 (11 ) (110 ) (702 ) — 1 — — Deposits by banks (517 ) (16 ) 0 (17 ) (1 ) (516 ) (15 ) — (23 ) 9 Debt securities in issue (8,099 ) (303 ) (166 ) (300 ) (50 ) (11,920 ) (199 ) (191 ) (369 ) 121 Subordinated liabilities (707 ) (181 ) (48 ) (204 ) (19 ) (694 ) (161 ) (52 ) (223 ) 21 Interest rate/FX risk: Other financial assets at FVOCI 241 3 0 0 (4 ) 18 — — — — Debt securities in issue (1,396 ) (135 ) 0 (122 ) 136 (3,192 ) (170 ) — (179 ) 37 Subordinated liabilities 7 7 0 7 (2 ) 9 9 — 9 23 52,375 (608 ) 800 186 414 50,101 (526 ) 455 67 75 Group 2019 2018 Hedged item balance sheet line item Change in value to Cash flow Balances on cash Change in value Cash flow Balances on cash Cash flow hedges: Interest rate risk: Loans and advances to customers (34 ) 21 (11 ) (19 ) (4 ) (2 ) Loans and advances to banks (2 ) 0 0 — (2 ) — Deposits by banks 3 (2 ) 0 6 (1 ) — Debt securities in issue 0 0 0 (1 ) — — FX risk: Other financial assets at FVOCI (122 ) 3 0 199 (1 ) — Not applicable – highly probable forecast transactions 267 2 0 (1 ) — — Deposits by customers 3 0 0 — — — Deposits by banks 4 0 0 — — — Debt securities in issue 177 (3 ) 0 (218 ) 22 3 Equity risk: Other liabilities 0 0 (1 ) 12 — — Interest rate/FX risk: Debt securities in issue/loans and advances to customers 630 280 20 (564 ) 233 50 Subordinated liabilities/loans and advances to customers (69 ) 180 0 (207 ) 79 — 857 481 8 (793 ) 326 51

Other Financial Assets At Fai_2

Other Financial Assets At Fair Value Through Profit Or Loss (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Other Financial Assets at Fair Value Through Profit or Loss	Group 2019 £m 2018 Loans and advances to customers: Loans to housing associations 12 13 Other loans 80 81 92 94 Debt securities 294 3,251 Equity securities 0 — Reverse repurchase agreements – non trading 0 2,272 386 5,617

Loans and Advances to Custome_2

Loans and Advances to Customers (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Net Loans and Advances to Customers	Group 2019 £m 2018 Loans secured on residential properties 165,356 157,957 Corporate loans 27,043 27,763 Finance leases 6,264 6,821 Secured advances 0 — Other unsecured loans 7,096 7,554 Amounts due from fellow Banco Santander subsidiaries and joint ventures 2,366 1,997 Amounts due from Santander UK Group Holdings plc 8 17 Amounts due from subsidiaries 0 — Loans and advances to customers 208,133 202,109 Credit impairment loss allowances on loans and advances to customers (785 ) (751 ) RV and voluntary termination provisions on finance leases (61 ) (69 ) Net loans and advances to customers 207,287 201,289
Summary of Finance Lease and Hire Purchase Contract Receivables	Finance lease and hire purchase contract receivables may be analysed as follows: Group 2019 2018 Gross investment £m Unearned finance income £m Net investment £m Gross Unearned Net No later than one year 2,650 (371 ) 2,279 3,730 (210 ) 3,520 Later than one year and not later than two years 1,829 (207 ) 1,622 1,839 (148 ) 1,691 Later than two years and not later than three years 1,047 (119 ) 928 1,056 (87 ) 969 Later than three years and not later than four years 473 (54 ) 419 488 (39 ) 449 Later than four years and not later than five years 41 (4 ) 37 32 (4 ) 28 Later than five years 1,116 (137 ) 979 210 (46 ) 164 7,156 (892 ) 6,264 7,355 (534 ) 6,821

Securitisations and Covered B_2

Securitisations and Covered Bonds (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Analysis of Securitisations and Covered Bonds	The Santander UK group’s principal securitisation programmes and covered bond programme, together with the balances of the advances subject to securitisation (or for the covered bond programme assigned) and the carrying value of the notes in issue at 31 December 2019 and 2018 are listed below. Gross assets External notes Notes issued to Santander UK 2019 2018 2019 2018 2019 2018 Mortgage-backed master trust structures: - Holmes 4,262 4,414 1,931 3,182 463 463 - Fosse 3,708 4,646 295 199 1,404 34 - Langton 3,076 3,034 0 — 2,354 2,354 11,046 12,094 2,226 3,381 4,221 2,851 Other asset-backed securitisation structures: - Motor 490 1,055 324 738 197 374 - Auto ABS UK Loans 1,532 1,468 1,229 1,212 368 316 2,022 2,523 1,553 1,950 565 690 Total securitisation programmes 13,068 14,617 3,779 5,331 4,786 3,541 Covered bond programmes: - Euro 35bn Global Covered Bond Programme 23,323 21,578 19,004 18,653 0 — Total securitisation and covered bond programmes 36,391 36,195 22,783 23,984 4,786 3,541 Less: held by Santander UK group: - Euro 35bn Global Covered Bond Programme 0 (539 ) Total securitisation and covered bond programmes (See Note 25) 22,783 23,445
Summary of Issuances and Redemptions of Securitisation and Covered Bond Programme	The following table sets out the internal and external issuances and redemptions in 2019 and 2018 for each securitisation and covered bond programme. Internal issuances External issuances Internal redemptions External redemptions 2019 2018 2019 2018 2019 2018 2019 2018 Mortgage-backed master trust structures: - Holmes 0 0.1 0 1.8 0 — 1.1 0.1 - Fosse 1.4 — 0.1 — 0 — 0 0.4 Other asset-backed securitisation structures: - Motor 0 — 0 — 0.2 0.1 0.4 0.1 - Auto ABS UK Loans 0.1 — 0.2 0.4 0.1 — 0.2 0.4 Covered bond programme 0 — 2.9 4.3 0.5 0.5 1.5 1.9 1.5 0.1 3.2 6.5 0.8 0.6 3.2 2.9

Transfers of Financial Assets_2

Transfers of Financial Assets Not Qualifying for Derecognition (Tables)	12 Months Ended
	Dec. 31, 2019
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Carrying Amount of Financial Assets that Did Not Qualify for Derecognition and their Associated Financial Liabilities	The following table analyses the carrying amount of financial assets that did not qualify for derecognition and their associated financial liabilities: Group 2019 2018 Nature of transaction Assets Liabilities Assets Liabilities Sale and repurchase agreements 7,592 (6,739 ) 7,642 (7,188 ) Securities lending agreements 195 (143 ) 144 (120 ) Securitisations (See Notes 14 and 25) 9,992 (3,779 ) 11,583 (5,331 ) 17,779 (10,661 ) 19,369 (12,639 )

Reverse Repurchase Agreements_2

Reverse Repurchase Agreements - Non Trading (Tables)	12 Months Ended
	Dec. 31, 2019
Reverse repurchase agreements - non-trading [member]
Statement [Line Items]
Summary of Reverse Repurchase Agreements - Non Trading	Group 2019 2018 Agreements with banks 2,161 3,254 Agreements with customers 21,475 17,873 23,636 21,127

Other Financial Assets At Amo_2

Other Financial Assets At Amortised Cost (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Other Financial Assets at Amortised Cost	Group 2019 2018 Asset backed securities 532 720 Debt securities 6,524 6,509 7,056 7,229

Financial Assets At Fair Valu_2

Financial Assets At Fair Value Through Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Financial Assets at Fair Value Through Other Comprehensive Income	Group 2019 2018 Debt securities 9,691 13,229 Loans and advances to customers 56 73 9,747 13,302

Interests in Other Entities (Ta

Interests in Other Entities (Tables)	12 Months Ended
	Dec. 31, 2019
Statement [Line Items]
Schedule of Interests in Other Entities	Group 2019 2018 Subsidiaries 0 — Joint ventures 117 88 117 88
Schedule of Subsidiaries With Significant Non-Controlling Interests	2019 2018 Profit attributable to non-controlling 19 22 Accumulated non-controlling 160 151 Dividends paid to non-controlling 12 22 Summarised financial information: - Total assets 3,228 3,289 - Total liabilities 2,905 2,987 - Profit for the year 40 43 - Total comprehensive income for the year 40 43

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2019
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Schedule of Goodwill	a) Goodwill Group Cost Accumulated Net book At 31 December 2018, 1 January 2019 and 31 December 2019 1,269 (66 ) 1,203
Schedule of Goodwill for Cash Generating Units	The following CGUs include in their carrying values goodwill that comprises the goodwill reported by Santander UK. The CGUs do not carry on their balance sheets any other intangible assets with indefinite useful lives. The calculations have been based on value in use using cash flows based on the five-year plan. Goodwill Discount rate Growth rate (1) CGU 2019 2018 2019 2018 2019 2018 Personal financial services 1,169 1,169 9.8 10.5 3 2 Private banking 30 30 9.8 10.5 4 2 Other 4 4 9.8 10.5 3 2 1,203 1,203
Schedule of Other Intangibles	b) Other intangibles Group Cost Accumulated Net book At January 2019 1,090 (485 ) 605 Additions 173 0 173 Disposals (14 ) 0 (14 ) Charge 0 (191 ) (191 ) Impairment 0 (10 ) (10 ) At 31 December 2019 1,249 (686 ) 563 At 1 January 2018 962 (423 ) 539 Additions 204 — 204 Write offs (76 ) 76 — Charge — (138 ) (138 ) Sales — — — At 31 December 2018 1,090 (485 ) 605

Other Financial Liabilities a_2

Other Financial Liabilities at Fair Value Through Profit or Loss (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Other Financial Liabilities at Fair Value Through Profit or Loss	Group 2019 £m 2018 US$30bn Euro Medium Term Note Programme 159 165 Structured Notes Programmes 809 696 Eurobonds 137 129 Structured deposits 435 133 Collateral and associated financial guarantees 173 3,053 Repurchase agreements – non trading 0 2,110 1,713 6,286 For the Santander UK group, all (2018: all) of the other financial liabilities at fair value through profit or loss were designated as such.

Deposits by Customers (Tables)

Deposits by Customers (Tables)	12 Months Ended
	Dec. 31, 2019
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Schedule of Deposits by Customers	Group 2019 £m 2018 Current and demand accounts 89,221 86,207 Savings accounts (1) 65,835 66,039 Time deposits 16,680 15,485 Amounts due to other Santander UK Group Holdings plc subsidiaries 44 83 Amounts due to Santander UK Group Holdings plc (2) 8,869 9,206 Amounts due to fellow Banco Santander subsidiaries and joint ventures 1,234 1,070 181,883 178,090 (1) Includes equity index-linked deposits of £1,139m (2018: £1,176m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,139m and £18m (2018: £1,176m and £28m) respectively. (2) Includes downstreamed funding from our immediate parent company Santander UK Group Holdings plc.

Deposits by Banks (Tables)

Deposits by Banks (Tables)	12 Months Ended
	Dec. 31, 2019
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Schedule of Deposits by Banks	Group 2019 £m 2018 Items in the course of transmission 337 262 Deposits held as collateral 2,169 4,048 Other deposits (1) 11,847 12,891 Amounts due to Santander UK subsidiaries 0 20 14,353 17,221 (1) Includes drawdown from the TFS of £10.8bn (2018: £10.8bn).

Repurchase Agreements - Non T_2

Repurchase Agreements - Non Trading (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Repurchase Agreements - Non Trading	Group 2019 £m 2018 Agreements with banks 10,227 5,865 Agreements with customers 8,059 5,045 18,286 10,910

Debt Securities in Issue (Table

Debt Securities in Issue (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Debt Securities in Issue	Group 2019 £m 2018 Medium-term notes: - US$30bn Euro Medium Term Note Programme 4,679 7,229 - Euro 30bn Euro Medium Term Note Programme 1,896 1,975 - US SEC-registered 5,891 7,649 - US$20bn Commercial Paper Programmes 3,014 3,131 15,480 19,984 Euro 35bn Global Covered Bond Programme (See Note 14) 19,004 18,114 Certificates of deposit 2,806 3,221 Credit linked notes 60 42 Securitisation programmes (See Note 14) 3,779 5,331 41,129 46,692

Subordinated Liabilities (Table

Subordinated Liabilities (Tables)	12 Months Ended
	Dec. 31, 2019
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Schedule of Subordinated Liabilities	Group 2019 2018 £325m Sterling Preference Shares 344 344 Undated subordinated liabilities 581 574 Dated subordinated liabilities 2,603 2,683 3,528 3,601
Summary of Undated Subordinated Liabilities	Group First call date 2019 £m 2018 10.0625% Exchangeable capital securities n/a 205 205 7.375% 20 Year Step-up 2020 15 16 7.125% 30 Year Step-up 2030 361 353 581 574
Summary of Dated Subordinated Liabilities	Group Maturity 2019 £m 2018 5% Subordinated notes (US$1,500m) 2023 1,132 1,173 4.75% Subordinated notes (US$1,000m) 2025 763 791 7.95% Subordinated notes (US$1,000m) 2029 280 278 6.50% Subordinated notes 2030 40 38 5.875% Subordinated notes 2031 9 9 5.625% Subordinated notes (US$500m) 2045 379 394 2,603 2,683

Provisions (Tables)

Provisions (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Provisions Reconciliation	Group Conduct remediation PPI Other FSCS and Property Off-balance Regulatory Total At 31 December 2018 246 30 45 37 56 95 509 Adoption of IFRS 16 (see Note 1) — — — 17 — — 17 At 1 January 2019 246 30 45 54 56 95 526 Additional provisions (see Note 8) 169 0 86 44 22 166 487 Provisions released (see Note 8) 0 0 (5 ) (21 ) 0 (4 ) (30 ) Utilisation and other (1) (226 ) (5 ) (90 ) (18 ) 0 (82 ) (421 ) Recharge (2) 0 0 10 0 0 0 10 At 31 December 2019 189 25 46 59 78 175 572 To be settled: - Within 12 months 189 18 46 43 78 171 545 - In more than 12 months 0 7 0 16 0 4 27 189 25 46 59 78 175 572 (1) Utilisation and other included a transfer from ‘PPI’ to ‘Regulatory and other’ in respect of an ongoing legal dispute. No further information has been provided on the basis it would be seriously prejudicial. (2) This relates to a recharge in respect of the UK Bank Levy paid on behalf of other UK entities of Banco Santander SA.

Retirement Benefit Plans (Table

Retirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Retirement Benefit Plans	The amounts recognised in the balance sheet were as follows: Group 2019 £m 2018 Assets/(liabilities) Funded defined benefit pension scheme – surplus 669 842 Funded defined benefit pension scheme – deficit (239 ) (75 ) Unfunded pension and post retirement medical benefits (41 ) (39 ) Total net assets 389 728
Summary of Pension Remeasurement Losses/(Gains) Recognised In Other Comprehensive Income	Remeasurement losses/(gains) recognised in other comprehensive income during the year were as follows: Group 2019 £m 2018 2017 Pension remeasurement 522 (470 ) 103
Total defined benefit plan amount charged to the income statement	The total amount charged to the income statement was as follows: Group 2019 £m 2018 2017 Net interest income (23 ) (7 ) (5 ) Current service cost 34 41 31 Past service and GMP costs 1 41 1 Administration costs 8 8 8 20 83 35
Summary of Amounts Recognised in Other Comprehensive Income	The amounts recognised in other comprehensive income were as follows: Group 2019 2018 2017 Return on plan assets (excluding amounts included in net interest expense) (855 ) 246 (435 ) Actuarial losses/(gains) arising from changes in demographic assumptions 42 (56 ) (151 ) Actuarial (gains)/losses arising from experience adjustments (42 ) 15 (11 ) Actuarial losses/(gains) arising from changes in financial assumptions 1,377 (675 ) 700 Pension remeasurement 522 (470 ) 103
Disclosure of Movements in Present Value of Defined Benefit Obligations	Movements in the present value of defined benefit scheme obligations were as follows: Group 2019 £m 2018 At 1 January (10,804 ) (11,583 ) Current service cost paid by Santander UK plc (22 ) (27 ) Current service cost paid by subsidiaries (12 ) (14 ) Current service cost paid by fellow Banco Santander subsidiaries 0 — Interest cost (308 ) (282 ) Employer salary sacrifice contributions (9 ) (6 ) Past service cost (1 ) (1 ) GMP equalisation cost 0 (40 ) Remeasurement due to actuarial movements arising from: - Changes in demographic assumptions (42 ) 56 - Experience adjustments 42 (15 ) - Changes in financial assumptions (1,377 ) 675 Benefits paid 375 433 At 31 December (12,158 ) (10,804 )
Disclosure of Movements in Fair Value of Schemes' Assets	Movements in the fair value of the schemes’ assets were as follows: Group 2019 2018 At 1 January 11,532 11,746 Interest income 331 289 Contributions paid by employer and scheme members 212 184 Contributions paid by fellow Banco Santander subsidiaries 0 — Administration costs paid (8 ) (8 ) Return on plan assets (excluding amounts included in net interest expense) 855 (246 ) Benefits paid (375 ) (433 ) At 31 December 12,547 11,532
Summary of Composition and Fair Value of Plan Assets	The composition and fair value of the schemes’ assets by category was: Group Quoted prices Prices not Total 2019 £m % £m % £m % UK equities 128 1 0 0 128 1 Overseas equities 1,742 14 933 7 2,675 21 Corporate bonds 1,333 11 444 4 1,777 15 Government fixed interest bonds 2,710 22 0 0 2,710 22 Government index-linked bonds 4,543 35 0 0 4,543 35 Property 0 0 1,332 11 1,332 11 Derivatives 0 0 94 1 94 1 Cash 0 0 984 8 984 8 Repurchase agreements (1) 0 0 (3,263 ) (26 ) (3,263 ) (26 ) Other 0 0 1,567 12 1,567 12 10,456 83 2,091 17 12,547 100 2018 UK equities 159 1 — — 159 1 Overseas equities 1,854 16 878 8 2,732 24 Corporate bonds 1,536 13 311 3 1,847 16 Government fixed interest bonds 2,636 23 — — 2,636 23 Government index-linked bonds 4,248 37 — — 4,248 37 Property — — 1,143 10 1,143 10 Derivatives — — 65 — 65 — Cash — — 662 6 662 6 Repurchase agreements (1) — — (2,981 ) (26 ) (2,981 ) (26 ) Other — — 1,021 9 1,021 9 10,433 90 1,099 10 11,532 100 (1) Sale and repurchase agreements net of purchase and resale agreements.
Summary of Principal Actuarial Assumptions Used for Defined Benefit Schemes	The principal actuarial assumptions used for the defined benefit schemes were: Group 2019 % 2018 2017 To determine benefit obligations: - Discount rate for scheme liabilities 2.1 2.9 2.5 - General price inflation 3.0 3.2 3.2 - General salary increase 1.0 1.0 1.0 - Expected rate of pension increase 2.9 2.9 2.9 Years Years Years Longevity at 60 for current pensioners, on the valuation date: - Males 27.3 27.3 27.4 - Females 29.8 30.1 30.1 Longevity at 60 for future pensioners currently aged 40, on the valuation date: - Males 28.9 28.7 28.9 - Females 31.3 31.6 31.7
Summary of Actuarial Assumption Sensitivities	The sensitivity analyses below have been determined based on reasonably possible changes of the respective assumptions occurring at the end of the reporting period, while holding all other assumptions constant. (Decrease)/ Assumption Change in pension obligation at year-end 2019 £m 2018 Discount rate 25 bps increase (564 ) (483 ) General price inflation 25 bps increase 407 350 Mortality Each additional year of longevity assumed 419 335
Disclosure of Benefits Expected To Be Paid	The benefits expected to be paid in each of the next five years, and in the aggregate for the five years thereafter are: Year ending 31 December £m 2020 332 2021 308 2022 330 2023 343 2024 364 Five years ending 2029 2,083

Contingent Liabilities and Co_2

Contingent Liabilities and Commitments (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Contingent Liabilities and Commitments	Group 2019 2018 Guarantees given to third parties 1,198 1,610 Formal standby facilities, credit lines and other commitments with original term to maturity of: - One year or less 18,248 8,550 - Later than one year 22,149 31,561 41,595 41,721
Operating Lease Commitments	Group Rental commitments under non-cancellable 2018 Not later than one year 72 Later than one year and not later than five years 114 Later than five years 60 246

Share Capital (Tables)

Share Capital (Tables)	12 Months Ended
	Dec. 31, 2019
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Schedule of Share Capital Issued and Fully Paid	Group Ordinary shares £300m Preference Total Issued and fully paid share capital No. £m No. £m £m At 1 January 2018, 31 December 2018 and 1 January 2019 31,051,768,866 3,105 13,780 14 3,119 Redemption of preference shares 0 0 (13,780 ) (14 ) (14 ) At 31 December 2019 31,051,768,866 3,105 0 0 3,105
Summary of Share Premium	Group Share premium 2019 2018 At 1 January and 31 December 5,620 5,620

Other Equity Instruments (Table

Other Equity Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of other equity instruments	Group Interest rate Next call date 2019 £m 2018 £300m Step-up 7.037 February 2026 235 235 AT1 securities: - £500m Fixed Rate Reset Perpetual AT1 Capital Securities 6.75 June 2024 496 496 - £750m Fixed Rate Reset Perpetual AT1 Capital Securities 7.375 June 2022 750 750 - £300m Fixed Rate Reset Perpetual AT1 Capital Securities 7.60 n/a 0 300 - £500m Fixed Rate Reset Perpetual AT1 Capital Securities 5.18 March 2020 210 210 - £500m Fixed Rate Reset Perpetual AT1 Capital Securities 6.30 March 2025 500 — 2,191 1,991

Non-Controlling Interests (Tabl

Non-Controlling Interests (Tables)	12 Months Ended
	Dec. 31, 2019
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Schedule of Amounts Attributable to Non-Controlling Interests	2019 £m 2018 PSA Finance UK Limited 160 151 160 151

Changes in Liabilities Arisin_2

Changes in Liabilities Arising from Financing Activities (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Changes in Liabilities Arising from Financing Activities	The table below shows the changes in liabilities arising from financing activities. Group 2019 2018 Balance sheet line item Balance sheet line item Debt Subordinated £m Other Dividends £m Total Debt Subordinated Other Dividends Total At 1 January 46,692 3,601 1,991 0 52,284 42,633 3,793 2,281 — 48,707 Cash flows from financing activities (3,839 ) 0 196 (469 ) (4,112 ) 4,615 (277 ) (290 ) (1,318 ) 2,730 Cash flows from operating activities (529 ) 0 0 0 (529 ) (2,522 ) 69 — — (2,453 ) Non-cash – Unrealised foreign exchange (1,320 ) (50 ) 0 0 (1,370 ) 1,371 149 — — 1,520 – Other changes 125 (23 ) 4 469 575 595 (133 ) — 1,318 1,780 At 31 December 41,129 3,528 2,191 0 46,848 46,692 3,601 1,991 — 52,284

Assets Charged As Security Fo_2

Assets Charged As Security For Liabilities And Collateral Accepted As Security For Assets (Tables)	12 Months Ended
	Dec. 31, 2019
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Financial Assets Charged as Security Under On-Balance Sheet and Off-Balance	The financial assets below are analysed between those assets accounted for on-balance off-balance Group 2019 £m 2018 On-balance Cash and balances at central banks 1,080 1,080 Loans and advances to banks 403 218 Loans and advances to customers – securitisations and covered bonds (See Note 14) 36,225 35,694 Loans and advances to customers – other 16,282 15,175 Other financial assets at amortised cost 3,026 3,763 Financial assets at fair value through other comprehensive income 6,009 5,825 Total on-balance 63,025 61,755 Total off-balance 15,098 15,220
Schedule of Collateral Held as Security For Assets	The collateral held as security for assets, analysed between those liabilities accounted for on balance sheet and off-balance Group 2019 2018 On-balance Deposits by banks 2,169 4,048 Total on-balance 2,169 4,048 Total off-balance 25,120 23,236

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2019
Statement [Line Items]
Summary of Movement in Share Options	The table below summarises movements in the number of options, and changes in weighted average exercise price over the same period. 2019 2018 Number of Weighted Number of Weighted Outstanding at 1 January 26,838 3.12 27,201 3.12 Granted 9,594 2.83 6,210 3.46 Exercised (7,978 ) 2.83 (3,340 ) 3.16 Forfeited/expired (5,081 ) 3.42 (3,233 ) 3.76 Outstanding at 31 December 23,373 3.03 26,838 3.12 Exercisable at 31 December 2,519 3.62 10,370 2.81
Summary of Range of Exercise Prices and Weighted Average Remaining Contractual Life of the Options Outstanding	The following table summarises the range of exercise prices and weighted average remaining contractual life of the options at 31 December 2019 and 2018. 2019 2018 Range of exercise prices Weighted average Years Weighted Weighted average Weighted £2 to £3 3 2.80 2 2.75 £3 to £4 2 3.38 3 3.36 £4 to £5 2 4.13 3 4.11
2015 LTIP [member]
Statement [Line Items]
Summary of Movement in Value of Conditional Awards in LTIPs	The following table summarises the movement in the value of conditional awards in the LTIPs in 2019 and 2018: 2015 LTIP 2014 LTIP 2019 2018 2019 2018 £000 £000 £000 £000 Outstanding at 1 January 6,374 6,503 0 1,910 Payments made (4,578 ) — 0 — Forfeited/cancelled (1,796 ) (129 ) 0 (1,910 ) Outstanding at 31 December 0 6,374 0 —

Transactions With Directors a_2

Transactions With Directors and Other Key Management Personnel (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Remuneration of the Directors and Other Key Management Personnel	The remuneration of the Directors and Other Key Management Personnel of the Santander UK group is set out in aggregate below. 2019 2018 2017 Directors’ remuneration £ £ £ Salaries and fees 5,025,665 5,028,434 4,406,908 Performance-related payments (1) 3,864,965 5,194,317 3,685,464 Other fixed remuneration (pension and other allowances & non-cash 1,367,069 1,467,011 1,580,321 Expenses 42,526 25,198 96,358 Total remuneration 10,300,225 11,714,960 9,769,051 2019 2018 2017 Directors’ and Other Key Management Personnel compensation £ £ £ Short-term employee benefits (2) 21,925,975 24,445,189 24,642,085 Post-employment benefits (3) 3,590,466 2,399,261 2,292,857 Total Compensation 25,516,441 26,844,450 26,934,942 (1) In line with the Code, a proportion of the performance-related payment was deferred. Further details can be found in Note 35. (2) There were no buy-outs buy-outs buy-outs (3) Termination payments of £1,076,435 were paid in 2019 to one key management persons (2018: £847,388 for two individuals; 2017: £nil).
Summary of Transactions with Directors, Other Key Management Personnel	Directors, Other Key Management Personnel (Defined as the Executive Committee of Santander UK plc who served during the year) and their connected persons have undertaken the following transactions with the Santander UK group in the ordinary course of business. 2019 2018 No. £000 No. £000 Secured loans, unsecured loans and overdrafts At 1 January 16 3,035 7 1,216 Net movements 2 1,885 9 1,819 At 31 December 18 4,920 16 3,035 Deposit, bank and instant access accounts and investments At 1 January 30 10,963 25 13,184 Net movements 2 1,012 5 (2,221 ) At 31 December 32 11,975 30 10,963

Related Party Disclosures (Tabl

Related Party Disclosures (Tables)	12 Months Ended
	Dec. 31, 2019
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Summary of Transactions With Related Parties	Transactions with related parties during the year and balances outstanding at the year-end: Group Interest, fees and other Interest, fees and other Amounts owed by Amounts owed to 2019 2018 2017 2019 2018 2017 2019 2018 2019 2018 £m £m £m £m £m £m £m £m £m £m Ultimate parent (130 ) (72 ) (60 ) 266 217 321 1,560 2,491 (2,143 ) (3,594 ) Immediate parent (7 ) (3 ) (3 ) 317 275 207 8 — (10,012 ) (10,392 ) Fellow subsidiaries (66 ) (86 ) (76 ) 173 178 491 204 57 (544 ) (689 ) Associates & joint ventures (29 ) (28 ) (20 ) 0 — — 2,194 1,986 (930 ) (718 ) (232 ) (189 ) (159 ) 756 670 1,019 3,966 4,534 (13,629 ) (15,393 )

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2019
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Fair Values of Financial Instruments Carried at Amortised Cost	Group 2019 2018 Fair value Carrying Fair value Carrying Level 1 Level 2 Level 3 Total value Level 1 Level 2 Level 3 Total value £m £m £m £m £m £m £m £m £m £m Assets Loans and advances to customers 0 0 211,796 211,796 207,287 — — 204,061 204,061 201,289 Loans and advances to banks 0 1,739 116 1,855 1,855 — 2,739 60 2,799 2,799 Reverse repurchase agreements – non trading 0 23,634 0 23,634 23,636 — 21,130 — 21,130 21,127 Other financial assets at amortised cost 6,575 535 0 7,110 7,056 6,390 721 — 7,111 7,229 6,575 25,908 211,912 244,395 239,834 6,390 24,590 204,121 235,101 232,444 Liabilities Deposits by customers 0 95 181,918 182,013 181,883 — 21 178,160 178,181 178,090 Deposits by banks 0 13,956 407 14,363 14,353 — 16,243 989 17,232 17,221 Repurchase agreements – non trading 0 18,292 0 18,292 18,286 — 10,923 — 10,923 10,910 Debt securities in issue 0 42,694 0 42,694 41,129 — 47,787 — 47,787 46,692 Subordinated liabilities 0 4,220 0 4,220 3,528 — 3,877 — 3,877 3,601 0 79,257 182,325 261,582 259,179 — 78,851 179,149 258,000 256,514
Fair Values of Financial Instruments Measured at Fair Value on a Recurring Basis	The following tables summarise the fair values of the financial assets and liabilities accounted for at fair value at 31 December 2019 and 2018, analysed by their levels in the fair value hierarchy – Level 1, Level 2 and Level 3. Group 2019 2018 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Valuation £m £m £m £m £m £m £m £m technique Assets Derivative financial instruments Exchange rate contracts 0 2,317 6 2,323 — 4,323 25 4,348 A Interest rate contracts 0 1,915 9 1,924 — 2,526 6 2,532 A & C Equity and credit contracts 0 223 60 283 — 188 63 251 B & D Netting 0 (1,214 ) 0 (1,214 ) — (1,872 ) — (1,872 ) 0 3,241 75 3,316 — 5,165 94 5,259 Other financial assets at FVTPL Loans and advances to customers 0 0 92 92 — 12 82 94 A Debt securities 0 0 294 294 18 2,339 894 3,251 A, B & D Equity securities 0 0 0 0 — — — — B Reverse repurchase agreements – non trading 0 0 0 0 — 2,272 — 2,272 A 0 0 386 386 18 4,623 976 5,617 Financial assets at FVOCI Debt securities 9,209 482 0 9,691 12,487 742 — 13,229 D Loans and advances to customers 0 0 56 56 — — 73 73 D 9,209 482 56 9,747 12,487 742 73 13,302 Total assets at fair value 9,209 3,723 517 13,449 12,505 10,530 1,143 24,178 Liabilities Derivative financial instruments Exchange rate contracts 0 660 4 664 — 528 23 551 A Interest rate contracts 0 1,836 2 1,838 — 2,515 7 2,522 A & C Equity and credit contracts 0 134 26 160 — 132 36 168 B & D Netting 0 (1,214 ) 0 (1,214 ) — (1,872 ) — (1,872 ) 0 1,416 32 1,448 — 1,303 66 1,369 Other financial liabilities at FVTPL Debt securities in issue 0 1,099 6 1,105 — 983 7 990 A Structured deposits 0 406 29 435 — 104 29 133 A Repurchase agreements – non trading 0 0 0 0 — 2,110 — 2,110 A Collateral and associated financial guarantees 0 147 26 173 — 3,040 13 3,053 D 0 1,652 61 1,713 — 6,237 49 6,286 Total liabilities at fair value 0 3,068 93 3,161 — 7,540 115 7,655
Summary of Fair Value Adjustment	The magnitude and types of fair value adjustment are listed in the following table: 2019 £m 2018 Risk-related: – Bid-offer (12 ) 13 – Uncertainty 17 36 – Credit risk adjustment 6 9 – Funding fair value adjustment 6 4 17 62 Model-related 0 5 17 67
Analysis of Financial Instruments Valued Using Internal Models Based on Information Other Than Market Data	The table below provides an analysis of financial instruments valued using internal models based on information other than market data together with further details on the valuation techniques used for each type of instrument. Each instrument is initially valued at transaction price: Balance sheet value Fair value movements recognised Balance sheet line item Category Financial instrument product type 2019 2018 2019 £m 2018 2017 1. Derivative assets Equity and credit contracts Reversionary property interests 52 54 2 30 (6 ) 2. FVTPL assets Loans and advances to customers Roll-up 51 53 0 8 2 3. FVTPL assets Loans and advances to customers Other loans 41 29 1 2 — 4. FVTPL assets Debt securities Reversionary property securities 120 142 (17 ) (28 ) (18 ) 5. FVTPL assets Debt securities Credit linked notes 174 752 7 13 — 6. FVOCI assets Loans and advances to customers Other loans 56 73 (2 ) (5 ) — 7. Derivative liabilities Equity contracts Property options and forwards (26 ) (35 ) 0 — (5 ) 8. FVTPL liabilities Financial guarantees Credit protection guarantee (26 ) (13 ) (7 ) (13 ) — 442 1,055 (16 ) 7 (27 ) Other Level 3 assets 23 40 16 (2 ) (26 ) Other Level 3 liabilities (41 ) (67 ) (5 ) 1 19 Total net assets 424 1,028 0 — — Total (expense)/income (5 ) 6 (34 )
Reconciliation of fair value measurement in Level 3 of the fair value hierarchy	The following table sets out the movements in Level 3 financial instruments in 2019 and 2018: Assets Liabilities Derivatives Other financial Financial Total Derivatives Other financial Total At 1 January 2019 94 976 73 1,143 (66 ) (49 ) (115 ) Total gains/(losses) recognised in profit or loss: – Fair value movements 18 (9 ) (2 ) 7 (6 ) (6 ) (12 ) – Foreign exchange and other movements 0 6 0 6 0 (6 ) (6 ) Transfers in 0 11 0 11 0 0 0 Netting (1) 0 (430 ) 0 (430 ) 0 0 0 Additions 2 188 0 190 0 (3 ) (3 ) Sales 0 0 0 0 0 0 0 Settlements (39 ) (356 ) (15 ) (410 ) 40 3 43 At 31 December 2019 75 386 56 517 (32 ) (61 ) (93 ) Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year 18 (3 ) (2 ) 13 (6 ) (12 ) (18 ) At 1 January 2018 64 838 199 1,101 (63 ) (6 ) (69 ) Total gains/(losses) recognised in profit or loss: – Fair value movements 28 (5 ) (5 ) 18 1 (13 ) (12 ) – Foreign exchange and other movements (5 ) — — (5 ) 5 (1 ) 4 Transfers in 35 18 — 53 (31 ) (29 ) (60 ) Additions — 280 17 297 — — — Sales — (95 ) — (95 ) — — — Settlements (28 ) (60 ) (138 ) (226 ) 22 — 22 At 31 December 2018 94 976 73 1,143 (66 ) (49 ) (115 ) Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year 23 (5 ) (5 ) 13 6 (14 ) (8 ) (1) This relates to the effect of netting on the fair value of the credit linked notes due to a legal right of set-off 19.
Effects of Changes in Significant Unobservable Assumptions to Reasonably Possible Alternatives (Level 3)	Significant unobservable input Sensitivity Assumption value Favourable Unfavourable 2019 Fair value Assumption description Range (1) Weighted Shift 1. Derivative assets 52 HPI Forward growth rate 0% - 5% 2.57 % 1 % 8 (8 ) – Reversionary property derivatives HPI Spot rate (2) n/a 802 10 % 7 (7 ) 2. FVTPL 51 HPI Forward growth rate 0% - 5% 2.69 % 1 % 2 (2 ) – Roll-up mortgage portfolio 3. FVTPL 41 Credit spreads 0% - 1% 0.35 % 20 % 0 0 – Other loans 4. FVTPL 120 HPI Forward growth rate 0% - 5% 2.57 % 1 % 0 0 – Reversionary property securities HPI Spot rate (2) n/a 802 10 % 6 (6 ) 6. FVOCI 56 Credit spreads 0% - 1% 0.51 % 20 % 0 0 – Other loans 7. Derivative liabilities (26 ) HPI Forward growth rate 0% - 5% 2.44 % 1 % 2 (2 ) – Property-related options and forwards HPI Spot rate (2) n/a 758 10 % 3 (3 ) 2018 1. Derivative assets 54 HPI Forward growth rate 0% - 5% 2.68 % 1 % 8 (8 ) – Reversionary property derivatives HPI Spot rate (2) n/a 783 10 % 7 (7 ) 2. FVTPL 53 HPI Forward growth rate 0% - 5% 2.77 % 1 % 2 (2 ) – Roll-up 3. FVTPL 29 Credit spreads 0% - 1% 0.52 % 20 % — — – Other loans 4. FVTPL 142 HPI Forward growth rate 0% - 5% 2.68 % 1 % 6 (6 ) – Reversionary property securities HPI Spot rate (2) n/a 783 10 % 10 (10 ) 6. FVOCI 73 Credit spreads 0% - 2% 0.80 % 20 % — — – Other loans 7. Derivative liabilities (35 ) HPI Forward growth rate 0% - 5% 2.59 % 1 % 2 (2 ) – Property-related options and forwards HPI Spot rate (2) n/a 722 10 % 3 (4 ) (1) The range of actual assumption values used to calculate the weighted average disclosure. (2) The HPI spot rate in the weighted average column represents the HPI spot rate index level at 31 December 2019 and 2018.
Maturities of Undiscounted Cash Flows for Financial Liabilities and Off Balance Sheet Commitments	Group 2019 On demand Not later than Later than Later than Later than Total Financial liabilities Derivative financial instruments 9 243 293 418 532 1,495 Other financial liabilities at fair value through profit or loss 1 6 203 617 969 1,796 Deposits by customers 160,833 2,531 6,476 9,770 3,045 182,655 Deposits by banks 2,711 486 4,764 6,338 220 14,519 Repurchase agreements – non trading 6 15,878 1,578 846 0 18,308 Debt securities in issue 0 7,129 8,702 18,100 8,897 42,828 Subordinated liabilities 0 239 131 1,539 3,961 5,870 Total financial liabilities 163,560 26,512 22,147 37,628 17,624 267,471 Off-balance 18,907 7,829 840 11,490 1,278 40,344 2018 Financial liabilities Derivative financial instruments — 431 57 41 1,003 1,532 Other financial liabilities at fair value through profit or loss 11 2,146 76 408 3,855 6,496 Deposits by customers 159,009 3,422 9,491 5,216 1,305 178,443 Deposits by banks 5,096 1,100 90 11,100 52 17,438 Repurchase agreements – non trading 2 9,101 972 849 517 11,441 Debt securities in issue — 9,157 5,520 23,051 10,921 48,649 Subordinated liabilities — 255 134 709 5,279 6,377 Total financial liabilities 164,118 25,612 16,340 41,374 22,932 270,376 Off-balance 18,667 5,843 670 13,413 1,426 40,019

Offsetting Financial Assets a_2

Offsetting Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2019
Text block [abstract]
Summary of Information about Impact of Offsetting of Financial Assets and Liabilities	Group Amounts subject to enforceable netting arrangements Effects of offsetting on balance sheet Related amounts not offset Assets not 2019 Gross Amounts Net amounts Financial Financial (1) Net enforceable (2) Balance (3) Assets Derivative financial assets 4,446 (1,214 ) 3,232 (768 ) (1,915 ) 549 84 3,316 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 25,312 (1,676 ) 23,636 (537 ) (23,099 ) 0 0 23,636 – Fair value 0 0 0 0 0 0 0 0 Loans and advances to customers and banks (4) 5,247 (1,248 ) 3,999 0 0 3,999 205,143 209,142 35,005 (4,138 ) 30,867 (1,305 ) (25,014 ) 4,548 205,227 236,094 Liabilities Derivative financial liabilities 2,616 (1,214 ) 1,402 (768 ) (572 ) 62 46 1,448 Repurchase, securities lending & similar agreements: – Amortised cost 19,962 (1,676 ) 18,286 (537 ) (17,749 ) 0 0 18,286 – Fair value 0 0 0 0 0 0 0 0 Deposits by customers and banks (4) 11,395 (1,248 ) 10,147 0 (502 ) 9,645 186,089 196,236 33,973 (4,138 ) 29,835 (1,305 ) (18,823 ) 9,707 186,135 215,970 2018 Assets Derivative financial assets 7,026 (1,872 ) 5,154 (933 ) (2,133 ) 2,088 105 5,259 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 24,733 (3,606 ) 21,127 (2,721 ) (18,406 ) — — 21,127 – Fair value 2,272 — 2,272 — (2,272 ) — — 2,272 Loans and advances to customers and banks (4) 6,021 (1,293 ) 4,728 — — 4,728 199,360 204,088 40,052 (6,771 ) 33,281 (3,654 ) (22,811 ) 6,816 199,465 232,746 Liabilities Derivative financial liabilities 3,187 (1,872 ) 1,315 (933 ) (303 ) 79 54 1,369 Repurchase, securities lending & similar agreements: – Amortised cost 14,516 (3,606 ) 10,910 (2,721 ) (8,189 ) — — 10,910 – Fair value 2,110 — 2,110 — (2,110 ) — — 2,110 Deposits by customers and banks (4) 12,174 (1,293 ) 10,881 — (502 ) 10,379 184,430 195,311 31,987 (6,771 ) 25,216 (3,654 ) (11,104 ) 10,458 184,484 209,700 (1) Financial collateral is reflected at its fair value, but has been limited to the net balance sheet exposure so as not to include any over-collateralisation. (2) This column includes contractual rights of set-off (3) The balance sheet total is the sum of ‘Net amounts reported on the balance sheet’ that are subject to enforceable netting arrangements and ‘Amounts not subject to enforceable netting arrangements’. (4) The amounts offset within loans and advances to customers/banks or deposits by customers/banks relate to offset mortgages which are classified as either and that are subject to netting.

Credit Risk - Summary of Exposu

Credit Risk - Summary of Exposures to Credit Risk in Business Segments (Detail) - Credit risk [member]	12 Months Ended
	Dec. 31, 2019
Retail banking [member]
Disclosure of credit risk exposure [line items]
Description of exposure to risk in business segments	Residential mortgages, business banking, consumer (auto) finance and other unsecured lending (credit cards, personal loans and overdrafts). We provide these to individuals and small businesses.
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Description of exposure to risk in business segments	Loans, bank accounts, treasury services, invoice discounting, cash transmission, trade finance and asset finance. We provide these to SMEs and mid corporates, Commercial Real Estate and Social Housing associations.
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Description of exposure to risk in business segments	Loans, bank accounts, treasury services, treasury markets activities, trade finance, receivables discounting and cash transmission. We provide these to large corporates and financial institutions.
Corporate centre [member]
Disclosure of credit risk exposure [line items]
Description of exposure to risk in business segments	Asset and liability management of our balance sheet, as well as our non-core and Legacy Portfolios being run down. Exposures include sovereign and other international organisation assets that we hold for liquidity.

Credit Risk - Summary of Key Me

Credit Risk - Summary of Key Metrics to Measure and Control Credit Risk (Detail) - Credit risk [member]	12 Months Ended
	Dec. 31, 2019
Expected credit losses [member]
Disclosure of credit risk exposure [line items]
Metric	Expected Credit Loss (ECL)
Description	ECL tells us what credit risk is likely to cost us either over the next 12 months on qualifying exposures, or defaults over the lifetime of the exposure where there is evidence of a SICR since origination. We explain how we calculate ECL below.
Stages 1, 2 and 3 [member]
Disclosure of credit risk exposure [line items]
Metric	Stages 1, 2 and 3
Description	We assess each facility’s credit risk profile to determine which stage to allocate them to, and we monitor where there is a SICR and transfers between the Stages including monitoring of coverage ratios for each stage. We explain how we allocate a facility to Stage 1, 2 or 3 below.
Stage 3 ratio [member]
Disclosure of credit risk exposure [line items]
Metric	Stage 3 ratio
Description	The Stage 3 ratio is total Stage 3 exposure as a percentage of customer loans plus undrawn Stage 3 exposures. We changed our definition of the Stage 3 ratio in 2019 and restated 2018 for consistency. The Stage 3 ratio was previously calculated as Stage 3 exposures as a percentage of customer loans. The Stage 3 ratio at 31 December 2018 using the new definition was 1.29%, compared to 1.20% using the previous definition.
Expected Loss [member]
Disclosure of credit risk exposure [line items]
Metric	Expected Loss (EL)
Description	EL is based on the regulatory capital rules of CRD IV and gives us another view of credit risk. It is the product of the probability of default, exposure at default and loss given default. We calculate each factor in accordance with CRD IV and include direct and indirect costs. We base them on our risk models and our assessment of each customer’s credit quality. There are differences between regulatory EL and IFRS 9 ECL, which we set out below. For the rest of our Risk review, impairments, losses and loss allowances refer to calculations in accordance with IFRS, unless we specifically say they relate to CRD IV. For our IFRS accounting policy on impairment, see Note 1 to the Consolidated Financial Statements.

Credit Risk - Summary of Probab

Credit Risk - Summary of Probability Weightings Applied to Scenarios (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Upside 2 [member]
Disclosure of probability weightings of scenarios [line items]
Probability %	5.00%	5.00%
Upside 1 [member]
Disclosure of probability weightings of scenarios [line items]
Probability %	10.00%	15.00%
Base case [member]
Disclosure of probability weightings of scenarios [line items]
Probability %	40.00%	40.00%
Downside 1 [member]
Disclosure of probability weightings of scenarios [line items]
Probability %	30.00%	30.00%
Downside 2 [member]
Disclosure of probability weightings of scenarios [line items]
Probability %	15.00%	10.00%

Credit Risk - Summary of Compou

Credit Risk - Summary of Compound Annual Growth Rates Over 5 Year Forecast (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Upside 2 [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House Price Index Five Year Average Increase Decrease	4.90%	3.40%
House Price Growth Peak/Trough	8.10%	7.40%
Gross Domestic product Five Year Average Increase Decrease	2.40%	2.50%
Gross Domestic Product Peak/Trough Rate	1.50%	1.60%
Unemployement Five Year Average end period	1.90%	2.80%
Unemployment Peak/Trough Rate	1.88%	2.58%
Bank of England Base Rate Five Year end period	2.00%	1.00%
Bank of England Base Rate Peak/Trough	2.00%	2.00%
Upside 1 [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House Price Index Five Year Average Increase Decrease	3.70%	2.30%
House Price Growth Peak/Trough	5.80%	4.60%
Gross Domestic product Five Year Average Increase Decrease	2.00%	2.10%
Gross Domestic Product Peak/Trough Rate	1.00%	1.10%
Unemployement Five Year Average end period	2.70%	3.80%
Unemployment Peak/Trough Rate	2.73%	3.71%
Bank of England Base Rate Five Year end period	2.00%	1.25%
Bank of England Base Rate Peak/Trough	2.00%	2.00%
Base case [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House Price Index Five Year Average Increase Decrease	1.60%	2.00%
House Price Growth Peak/Trough	2.00%	2.00%
Gross Domestic product Five Year Average Increase Decrease	1.60%	1.60%
Gross Domestic Product Peak/Trough Rate	0.70%	0.60%
Unemployement Five Year Average end period	4.00%	4.30%
Unemployment Peak/Trough Rate	4.10%	4.39%
Bank of England Base Rate Five Year end period	0.75%	1.50%
Bank of England Base Rate Peak/Trough	0.75%	1.50%
Downside 1 [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House Price Index Five Year Average Increase Decrease	(1.20%)	(2.00%)
House Price Growth Peak/Trough	(2.80%)	(5.80%)
Gross Domestic product Five Year Average Increase Decrease	0.70%	0.70%
Gross Domestic Product Peak/Trough Rate	(1.10%)	(0.60%)
Unemployement Five Year Average end period	5.60%	6.90%
Unemployment Peak/Trough Rate	5.64%	7.30%
Bank of England Base Rate Five Year end period	2.00%	2.50%
Bank of England Base Rate Peak/Trough	2.00%	2.50%
Downside 2 [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House Price Index Five Year Average Increase Decrease	(9.30%)	(9.50%)
House Price Growth Peak/Trough	(13.50%)	(15.60%)
Gross Domestic product Five Year Average Increase Decrease	0.20%	0.30%
Gross Domestic Product Peak/Trough Rate	(5.60%)	(6.10%)
Unemployement Five Year Average end period	7.40%	8.60%
Unemployment Peak/Trough Rate	7.84%	8.65%
Bank of England Base Rate Five Year end period	2.25%	2.25%
Bank of England Base Rate Peak/Trough	3.00%	3.00%

Credit Risk - Summary of Comp_2

Credit Risk - Summary of Compound Annual Growth Rates Over 5 Year Forecast (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
House Price Index [Member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
Forecasting period for macroeconomic assumptions	5 years	5 years
GDP [Member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
Forecasting period for macroeconomic assumptions	5 years	5 years
Unemployment Rate [Member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
Forecasting period for macroeconomic assumptions	5 years	5 years
Bank Of England Base Rate [Member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
Forecasting period for macroeconomic assumptions	5 years	5 years

Credit Risk - Summary of Prob_2

Credit Risk - Summary of Probability Weightings Applied to Scenarios for CIB Portfolio (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Base case [member]
Disclosure of probability weightings of scenarios [line items]
Probability %	40.00%	40.00%
Corporate and investment banking [member] | Upside Scenario [member]
Disclosure of probability weightings of scenarios [line items]
Probability %	30.00%	20.00%
Corporate and investment banking [member] | Base case [member]
Disclosure of probability weightings of scenarios [line items]
Probability %	40.00%	60.00%
Corporate and investment banking [member] | Downside Scenario [member]
Disclosure of probability weightings of scenarios [line items]
Probability %	30.00%	20.00%

Credit Risk - Summary of Annual

Credit Risk - Summary of Annual Growth Rates over 4 Year Forecast for CIB portfolio (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Upside Scenario [member] | 5 year average increase/decrease
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	3.70%	4.20%
Upside Scenario [member] | Cumulative growth/(fall) to peak/(trough)
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	0.30%	0.40%
Base case [member] | 5 year average increase/decrease
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	3.50%	3.60%
Base case [member] | Cumulative growth/(fall) to peak/(trough)
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	0.50%	0.30%
Downside Scenario [member] | 5 year average increase/decrease
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	3.00%	2.70%
Downside Scenario [member] | Cumulative growth/(fall) to peak/(trough)
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	(1.20%)	(0.80%)

Credit Risk - Summary of Annu_2

Credit Risk - Summary of Annual Growth Rates over 4 Year Forecast for CIB portfolio (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
GDP [Member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
Forecasting period for macroeconomic assumptions	5 years	5 years

Credit Risk - Disclosure of Qua

Credit Risk - Disclosure of Quantitative Criteria of Credit Risk Exposure (Detail) - Probability of default [member]	12 Months Ended
	Dec. 31, 2019
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Other unsecured loans	0.30%
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Corporate & Investment Banking	Internal rating method
Mortgages [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Other unsecured loans	0.30%
Consumer (auto) finance [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Other unsecured loans	3.00%
Personal loans [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Other unsecured loans	0.30%
Credit cards [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Other unsecured loans	3.40%
Overdrafts [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Other unsecured loans	2.60%

Credit Risk - Disclosure of Q_2

Credit Risk - Disclosure of Qualitative Criteria of Credit Risk Exposure (Detail)	12 Months Ended
	Dec. 31, 2019
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Qualitative Criteria For Measuring SICR	In forbearance Default in last 12m Watchlist – proactive management Default at proxy origination
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Qualitative Criteria For Measuring SICR	Watchlist – proactive management
Mortgages [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Qualitative Criteria For Measuring SICR	In forbearance Default in last 24m >30 Days past due (DPD) in last 12m Bankrupt £100+ arrears
Consumer (auto) finance [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Qualitative Criteria For Measuring SICR	In forbearance Deceased or Insolvent Court 'Return of goods' order or Police watchlist Agreement terminated Payment holiday Cash Collection
Personal loans [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Qualitative Criteria For Measuring SICR	In Collections Default in last 12m £50+ arrears
Credit cards [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Qualitative Criteria For Measuring SICR	In forbearance Default in last 12m In Collections £100+ arrears
Overdrafts [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Qualitative Criteria For Measuring SICR	Fees suspended Default in last 12m Debit dormant >35 days Any excess in month

Credit Risk - Disclosure of Pos

Credit Risk - Disclosure of Post Model Adjustments Explanatory (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Interest-only maturity default risk [member]
Statement [Line Items]
Post Model Adjustments	£ 51	£ 69
Buy-To-Let [member]
Statement [Line Items]
Post Model Adjustments	21	20
Long-term indeterminate arrears [member]
Statement [Line Items]
Post Model Adjustments	19	23
12+ months in arrears
Statement [Line Items]
Post Model Adjustments	£ 23	£ 11

Credit Risk - Summary of Differ

Credit Risk - Summary of Difference Between Maximum and Net Exposure to Credit Risk - IFRS 9 (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	£ 79,125	£ 87,745
Collateral cash	(18,823)	(11,104)
Netting	(1,305)	(3,654)
Net exposure	310,155	305,464
Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	270,900	265,500
Collateral cash	(200)	(100)
Collateral non-cash	(217,500)	(209,100)
Netting	(500)	(2,700)
Net exposure	94,200	95,200
Credit risk [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	271,700	266,200
Credit risk [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(800)	(700)
Credit risk [member] | Cash and balances at central banks [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	21,200	19,700
Collateral cash	0
Collateral non-cash	0
Netting	0
Net exposure	21,200	19,700
Credit risk [member] | Cash and balances at central banks [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	21,200	19,700
Credit risk [member] | Cash and balances at central banks [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Credit risk [member] | Financial assets at FVOCI [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	9,700	13,300
Collateral cash	0
Collateral non-cash	0
Netting	0
Net exposure	9,700	13,400
Credit risk [member] | Financial assets at FVOCI [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	9,700	13,300
Credit risk [member] | Financial assets at FVOCI [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Off-Balance Sheet [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	41,500	41,600
Off-Balance Sheet [member] | Credit risk [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	41,600	41,700
Off-Balance Sheet [member] | Credit risk [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(100)	(100)
Off-Balance Sheet [member] | Credit risk [member] | Cash and balances at central banks [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Off-Balance Sheet [member] | Credit risk [member] | Cash and balances at central banks [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Off-Balance Sheet [member] | Credit risk [member] | Cash and balances at central banks [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	100
Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	100
Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	240,000	232,500
Collateral cash	(200)	(100)
Collateral non-cash	(217,500)	(209,100)
Netting	(500)	(2,700)
Net exposure	63,300	62,100
Financial assets at amortised cost [member] | Credit risk [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	240,800	233,200
Financial assets at amortised cost [member] | Credit risk [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(800)	(700)
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	207,400	201,400
Collateral cash	(200)	(100)
Collateral non-cash	(194,400)	(190,700)
Netting	0
Net exposure	53,100	50,500
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Advances secured on residential property [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	165,200	157,700
Collateral cash	0
Collateral non-cash	(168,700)	(163,800)
Netting	0
Net exposure	9,900	5,100
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Corporate loans [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	26,800	27,600
Collateral cash	(100)
Collateral non-cash	(19,400)	(20,200)
Netting	0
Net exposure	21,500	24,400
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Finance leases [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	6,100	6,700
Collateral cash	(100)	(100)
Collateral non-cash	(6,300)	(6,100)
Netting	0
Net exposure	0	700
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Other unsecured advances [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	6,900	7,400
Collateral cash	0
Collateral non-cash	0
Netting	0
Net exposure	19,300	18,900
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Amounts due from fellow banco santander group subsidiaries and joint ventures [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	2,400	2,000
Collateral cash	0
Collateral non-cash	0	(600)
Netting	0
Net exposure	2,400	1,400
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	208,200	202,100
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Advances secured on residential property [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	165,400	157,900
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Corporate loans [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	27,000	27,800
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Finance leases [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	6,300	6,800
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Other unsecured advances [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	7,100	7,600
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Amounts due from fellow banco santander group subsidiaries and joint ventures [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	2,400	2,000
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(800)	(700)
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Advances secured on residential property [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(200)	(200)
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Corporate loans [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(200)	(200)
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Finance leases [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(200)	(100)
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Other unsecured advances [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(200)	(200)
Financial assets at amortised cost [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Amounts due from fellow banco santander group subsidiaries and joint ventures [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Credit risk [member] | Loans and advances to banks [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	1,900	2,800
Collateral cash	0
Collateral non-cash	0
Netting	0
Net exposure	3,100	4,400
Financial assets at amortised cost [member] | Credit risk [member] | Loans and advances to banks [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	1,900	2,800
Financial assets at amortised cost [member] | Credit risk [member] | Loans and advances to banks [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Credit risk [member] | Reverse repurchase agreements - non-trading [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	23,600	21,100
Collateral cash	0
Collateral non-cash	(23,100)	(18,400)
Netting	(500)	(2,700)
Net exposure	0
Financial assets at amortised cost [member] | Credit risk [member] | Reverse repurchase agreements - non-trading [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	23,600	21,100
Financial assets at amortised cost [member] | Credit risk [member] | Reverse repurchase agreements - non-trading [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Credit risk [member] | Other financial assets at amortised cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	7,100	7,200
Collateral cash	0
Collateral non-cash	0
Netting	0
Net exposure	7,100	7,200
Financial assets at amortised cost [member] | Credit risk [member] | Other financial assets at amortised cost [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	7,100	7,200
Financial assets at amortised cost [member] | Credit risk [member] | Other financial assets at amortised cost [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	41,500	41,500
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	41,600	41,600
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(100)	(100)
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	40,300	39,900
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Advances secured on residential property [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	13,400	11,200
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Corporate loans [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	14,200	17,000
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Finance leases [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	300	200
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Other unsecured advances [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	12,400	11,500
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Amounts due from fellow banco santander group subsidiaries and joint ventures [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	40,400	40,000
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Advances secured on residential property [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	13,400	11,200
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Corporate loans [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	14,300	17,000
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Finance leases [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	300	200
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Other unsecured advances [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	12,400	11,600
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Cost [member] | Amounts due from fellow banco santander group subsidiaries and joint ventures [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(100)	(100)
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Advances secured on residential property [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Corporate loans [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(100)
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Finance leases [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Other unsecured advances [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	(100)
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member] | Amounts due from fellow banco santander group subsidiaries and joint ventures [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and advances to banks [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	1,200	1,600
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and advances to banks [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	1,200	1,600
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Loans and advances to banks [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Reverse repurchase agreements - non-trading [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Reverse repurchase agreements - non-trading [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Reverse repurchase agreements - non-trading [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Other financial assets at amortised cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Other financial assets at amortised cost [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Financial assets at amortised cost [member] | Off-Balance Sheet [member] | Credit risk [member] | Other financial assets at amortised cost [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Loans and Advances to Customers [member] | Credit risk [member] | Financial assets at FVOCI [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	100	100
Collateral cash	0
Collateral non-cash	0
Netting	0
Net exposure	100	200
Loans and Advances to Customers [member] | Credit risk [member] | Financial assets at FVOCI [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	100	100
Loans and Advances to Customers [member] | Credit risk [member] | Financial assets at FVOCI [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Loans and Advances to Customers [member] | Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	100
Loans and Advances to Customers [member] | Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0	100
Loans and Advances to Customers [member] | Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Debt Securities [member] | Credit risk [member] | Financial assets at FVOCI [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	9,600	13,200
Collateral cash	0
Collateral non-cash	0
Netting	0
Net exposure	9,600	13,200
Debt Securities [member] | Credit risk [member] | Financial assets at FVOCI [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	9,600	£ 13,200
Debt Securities [member] | Credit risk [member] | Financial assets at FVOCI [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Debt Securities [member] | Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Debt Securities [member] | Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	0
Debt Securities [member] | Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	£ 0

Credit Risk - Summary of Diff_2

Credit Risk - Summary of Difference Between Maximum and Net Exposure to Credit Risk (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	£ 79,125	£ 87,745
Collateral cash	18,823	11,104
Netting	(1,305)	(3,654)
Net exposure	310,155	305,464
Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	270,900	265,500
Collateral cash	200	100
Collateral non-cash	(217,500)	(209,100)
Netting	(500)	(2,700)
Net exposure	94,200	95,200
Derivative Financial Instruments [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	3,300	5,300
Collateral cash	0
Collateral non-cash	(1,900)	(2,100)
Netting	(800)	(900)
Net exposure	600	2,300
Other financial assets at fair value through profit loss [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	400	5,600
Collateral cash	0
Collateral non-cash	0	(2,300)
Netting	0
Net exposure	400	3,300
Financial assets at fair value through profit loss [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	3,700	10,900
Collateral cash	0
Collateral non-cash	(1,900)	(4,400)
Netting	(800)	(900)
Net exposure	£ 1,000	£ 5,600

Credit Risk - Disclosure of Equ

Credit Risk - Disclosure of Equivalent Credit Rating Grade used by Standard and Poors Ratings Services (Detail)	12 Months Ended
	Dec. 31, 2019
Santander UK risk grade 9 [member]
Statement [Line Items]
Description of rating agencies used	AAA to AA+
Santander UK risk grade 8 [member]
Statement [Line Items]
Description of rating agencies used	AA to AA–
Santander UK risk grade 7 [member]
Statement [Line Items]
Description of rating agencies used	A+ to BBB
Santander UK risk grade 6 [member]
Statement [Line Items]
Description of rating agencies used	BBB– to BB
Santander UK risk grade 5 [member]
Statement [Line Items]
Description of rating agencies used	BB–
Santander UK risk grade 4 [member]
Statement [Line Items]
Description of rating agencies used	B+ to B
Santander UK risk grade 3 [member]
Statement [Line Items]
Description of rating agencies used	B–
Santander UK risk grade 2 [member]
Statement [Line Items]
Description of rating agencies used	CCC to C
Santander UK risk grade 1 [member]
Statement [Line Items]
Description of rating agencies used	D
Mid range [member] | Santander UK risk grade 9 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.01%
Mid range [member] | Santander UK risk grade 8 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.032%
Mid range [member] | Santander UK risk grade 7 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.10%
Mid range [member] | Santander UK risk grade 6 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.316%
Mid range [member] | Santander UK risk grade 5 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	1.00%
Mid range [member] | Santander UK risk grade 4 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	3.162%
Mid range [member] | Santander UK risk grade 3 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	10.00%
Mid range [member] | Santander UK risk grade 2 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	31.623%
Mid range [member] | Santander UK risk grade 1 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	100.00%
Lower range [member] | Santander UK risk grade 9 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.00%
Lower range [member] | Santander UK risk grade 8 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.021%
Lower range [member] | Santander UK risk grade 7 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.066%
Lower range [member] | Santander UK risk grade 6 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.208%
Lower range [member] | Santander UK risk grade 5 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.658%
Lower range [member] | Santander UK risk grade 4 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	2.081%
Lower range [member] | Santander UK risk grade 3 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	6.581%
Lower range [member] | Santander UK risk grade 2 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	20.811%
Lower range [member] | Santander UK risk grade 1 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	100.00%
Upper range [member] | Santander UK risk grade 9 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.021%
Upper range [member] | Santander UK risk grade 8 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.066%
Upper range [member] | Santander UK risk grade 7 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.208%
Upper range [member] | Santander UK risk grade 6 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	0.658%
Upper range [member] | Santander UK risk grade 5 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	2.081%
Upper range [member] | Santander UK risk grade 4 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	6.581%
Upper range [member] | Santander UK risk grade 3 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	20.811%
Upper range [member] | Santander UK risk grade 2 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	99.999%
Upper range [member] | Santander UK risk grade 1 [member]
Statement [Line Items]
Standard and poors rating probability of default percent	100.00%

Credit Risk - Summary of Credit

Credit Risk - Summary of Credit Rating of Financial Assets Subject to Credit Risk (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of internal credit grades [line items]
Loss allowance	£ (785)	£ (751)
Coverage	0.30%	0.30%
Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 310,155	£ 305,464	£ 300,286
Credit risk [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Loss allowance	(218)	(234)
Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	(900)	(800)
Financial assets	£ 312,400	£ 307,100
Coverage	0.30%	0.30%
Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 900	£ 800
Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 62,000	60,200
Coverage	0.00%
Internal grade 9 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 44,900	45,200
Coverage	0.00%
Internal grade 8 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 88,800	84,000
Coverage	0.00%
Internal grade 7 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 61,700	60,900
Coverage	0.00%
Internal grade 6 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 23,800	£ 25,700
Coverage	0.40%	0.40%
Internal grade 5 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 12,000	£ 12,700
Coverage	1.70%	1.60%
Internal grade 4 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200	£ 200
Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 6,700	£ 6,800
Coverage	9.00%	7.40%
Internal grade 3 to 1 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 600	£ 500
Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 13,400	12,400
Coverage	0.00%
Other [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	(800)	(700)
Financial assets	£ 270,900	£ 265,500
Coverage	0.30%	0.30%
Balance sheet exposures [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 800
Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	(800)	£ (700)
Financial assets	£ 240,000	£ 232,500
Coverage	0.30%	0.30%
Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Loss allowance	£ (200)	£ (200)
Financial assets	£ 165,200	£ 157,800
Coverage	0.10%	0.10%
Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 800	£ 700
Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	200	200
Balance sheet exposures [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 21,200	19,700
Coverage	0.00%
Balance sheet exposures [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	(800)	(700)
Financial assets	£ 207,400	£ 201,400
Coverage	0.40%	0.30%
Balance sheet exposures [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 800	£ 700
Balance sheet exposures [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 1,900	2,800
Coverage	0.00%
Balance sheet exposures [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 23,600	21,100
Coverage	0.00%
Balance sheet exposures [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 7,100	7,200
Coverage	0.00%
Balance sheet exposures [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 9,700	13,300
Coverage	0.00%
Balance sheet exposures [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	700
Balance sheet exposures [member] | Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 61,100	59,500
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 9 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 33,800	332,000
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 9,800	7,700
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Balance sheet exposures [member] | Internal grade 9 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 21,200	19,700
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 9 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 11,400	10,000
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 9 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	800
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 9 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 9 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 15,300	15,200
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 9 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 9 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 7,100	7,200
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 9 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 6,100	6,600
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 36,400	37,200
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 8 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 33,200	31,400
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 25,000	21,800
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Balance sheet exposures [member] | Internal grade 8 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 8 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 30,600	27,400
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 8 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200	200
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 8 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 8 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 2,400	3,800
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 8 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 8 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 8 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 3,200	5,800
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 80,400	75,100
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 7 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 80,000	74,400
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 71,900	69,000
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Balance sheet exposures [member] | Internal grade 7 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 7 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 75,400	72,300
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 7 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 400	800
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 7 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 7 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 4,200	1,300
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 7 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 7 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 7 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 400	700
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 53,600	51,900
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 6 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 53,600	51,900
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 42,900	42,800
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Balance sheet exposures [member] | Internal grade 6 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 6 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 52,100	51,500
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 6 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 6 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 6 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 1,500	400
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 6 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 6 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 6 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 18,800	£ 20,300
Coverage	0.50%	0.50%
Balance sheet exposures [member] | Internal grade 5 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100
Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 18,800	£ 20,300
Coverage	0.50%	0.50%
Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 7,700	£ 7,800
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	100
Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Balance sheet exposures [member] | Internal grade 5 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 5 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 18,800	£ 20,300
Coverage	0.50%	0.50%
Balance sheet exposures [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Balance sheet exposures [member] | Internal grade 5 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 5 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 5 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 5 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 5 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 5 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	100
Balance sheet exposures [member] | Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 10,900	£ 11,400
Coverage	1.80%	1.80%
Balance sheet exposures [member] | Internal grade 4 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200
Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 10,900	£ 11,400
Coverage	1.80%	1.80%
Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 4,200	£ 4,700
Coverage	2.40%	2.10%
Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200	£ 200
Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	100	100
Balance sheet exposures [member] | Internal grade 4 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 4 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 10,900	£ 11,400
Coverage	1.80%	1.80%
Balance sheet exposures [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200	£ 200
Balance sheet exposures [member] | Internal grade 4 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 4 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 4 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 4 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 4 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 4 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	200
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 6,200	£ 6,300
Coverage	8.10%	6.30%
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 500
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 6,200	£ 6,300
Coverage	8.10%	6.30%
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 3,900	£ 4,200
Coverage	2.60%	2.40%
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 500	£ 400
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	100	100
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 6,200	£ 6,300
Coverage	8.10%	6.30%
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 500	£ 400
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	400
Balance sheet exposures [member] | Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 4,300	4,500
Coverage	0.00%
Balance sheet exposures [member] | Other [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 4,300	4,300
Coverage	0.00%
Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Balance sheet exposures [member] | Other [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Other [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 2,800	2,900
Coverage	0.00%
Balance sheet exposures [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Other [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 1,300	1,000
Coverage	0.00%
Balance sheet exposures [member] | Other [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Other [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200	400
Coverage	0.00%
Balance sheet exposures [member] | Other [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Other [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Balance sheet exposures [member] | Other [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Balance sheet exposures [member] | Other [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	200
Coverage	0.00%
Balance sheet exposures [member] | Other [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Off-Balance Sheet [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	(100)	(100)
Financial assets	£ 41,500	£ 41,600
Coverage	0.20%	0.20%
Off-Balance Sheet [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Off-Balance Sheet [member] | Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 900	700
Coverage	0.00%
Off-Balance Sheet [member] | Internal grade 9 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Off-Balance Sheet [member] | Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 8,500	8,000
Coverage	0.00%
Off-Balance Sheet [member] | Internal grade 8 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Off-Balance Sheet [member] | Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 8,400	8,900
Coverage	0.00%
Off-Balance Sheet [member] | Internal grade 7 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Off-Balance Sheet [member] | Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 8,100	9,000
Coverage	0.00%
Off-Balance Sheet [member] | Internal grade 6 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Off-Balance Sheet [member] | Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 5,000	5,400
Coverage	0.00%
Off-Balance Sheet [member] | Internal grade 5 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Off-Balance Sheet [member] | Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 1,100	1,300
Coverage	0.00%
Off-Balance Sheet [member] | Internal grade 4 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Off-Balance Sheet [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 500	£ 500
Coverage	20.00%	20.00%
Off-Balance Sheet [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Off-Balance Sheet [member] | Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 9,100	7,900
Coverage	0.00%
Off-Balance Sheet [member] | Other [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance		(100)
Financial assets		£ 41,100
Coverage	0.00%	0.20%
Stage 1 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 100
Stage 1 [member] | Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		700
Coverage	0.00%
Stage 1 [member] | Internal grade 9 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		8,000
Coverage	0.00%
Stage 1 [member] | Internal grade 8 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		8,900
Coverage	0.00%
Stage 1 [member] | Internal grade 7 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		8,900
Coverage	0.00%
Stage 1 [member] | Internal grade 6 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		5,300
Coverage	0.00%
Stage 1 [member] | Internal grade 5 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		1,200
Coverage	0.00%
Stage 1 [member] | Internal grade 4 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		£ 300
Coverage	0.00%	33.30%
Stage 1 [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	£ 100
Stage 1 [member] | Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		7,900
Coverage	0.00%
Stage 1 [member] | Other [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	21,200
Stage 1 [member] | Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 155,500	146,800
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		19,700
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	(100)	(100)
Financial assets	£ 194,100	£ 188,000
Coverage	0.10%	0.10%
Stage 1 [member] | Balance sheet exposures [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Stage 1 [member] | Balance sheet exposures [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 1,900	2,800
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 23,600	21,100
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 7,100	7,200
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	£ 9,700	13,300
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	21,200
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 9,800	7,700
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		19,700
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 11,400	10,000
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	800
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 15,300	15,200
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 7,100	7,200
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 6,100	6,600
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 25,000	21,800
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 30,600	27,400
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200	200
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 2,400	3,800
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 3,200	5,800
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 71,700	68,800
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 75,000	72,100
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 400	800
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 4,200	1,300
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 400	700
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 42,000	41,600
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 50,900	50,200
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 1,500	400
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 5,700	5,500
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 16,100	17,600
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 1,100	1,200
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 6,200	£ 6,900
Coverage	1.60%	1.40%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200	200
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 1,200	1,100
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Cash and balances at central banks [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Cash and balances at central banks [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 2,800	2,800
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 1,300	1,000
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200	400
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	200
Coverage	0.00%
Stage 1 [member] | Balance sheet exposures [member] | Other [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 1 [member] | Off-Balance Sheet [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	40,900
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	900
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	8,500
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	8,400
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	8,000
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	4,700
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	1,000
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	300
Stage 1 [member] | Off-Balance Sheet [member] | Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 9,100
Stage 2 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		400
Coverage	16.70%
Stage 2 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100
Stage 2 [member] | Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 2 [member] | Internal grade 9 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 2 [member] | Internal grade 8 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 2 [member] | Internal grade 7 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Coverage	0.00%
Stage 2 [member] | Internal grade 6 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Coverage	0.00%
Stage 2 [member] | Internal grade 5 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Coverage	0.00%
Stage 2 [member] | Internal grade 4 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Coverage	50.00%
Stage 2 [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100
Stage 2 [member] | Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 2 [member] | Other [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Loss allowance	(100)	(100)
Financial assets	£ 8,100	£ 9,200
Coverage	1.20%	1.10%
Stage 2 [member] | Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Stage 2 [member] | Balance sheet exposures [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	(300)	(300)
Financial assets	£ 11,400	£ 11,300
Coverage	2.60%	2.70%
Stage 2 [member] | Balance sheet exposures [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 300	£ 300
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 200	200
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 400	200
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 900	1,200
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 1,200	1,300
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 2,000	2,300
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 2,700	£ 2,700
Coverage	3.70%	3.70%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 3,100	£ 3,500
Coverage	3.20%	2.90%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 4,700	£ 4,500
Coverage	2.10%	2.20%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 2,000	2,100
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 2,700	£ 2,800
Coverage	3.70%	3.60%
Stage 2 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Stage 2 [member] | Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Balance sheet exposures [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0	100
Coverage	0.00%
Stage 2 [member] | Balance sheet exposures [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 2 [member] | Off-Balance Sheet [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	(100)
Financial assets	600
Stage 2 [member] | Off-Balance Sheet [member] | Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 2 [member] | Off-Balance Sheet [member] | Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 2 [member] | Off-Balance Sheet [member] | Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 2 [member] | Off-Balance Sheet [member] | Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	100
Stage 2 [member] | Off-Balance Sheet [member] | Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	300
Stage 2 [member] | Off-Balance Sheet [member] | Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	100
Stage 2 [member] | Off-Balance Sheet [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	200
Stage 2 [member] | Off-Balance Sheet [member] | Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Coverage	0.00%
Stage 3 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 3 [member] | Internal grade 9 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 3 [member] | Internal grade 8 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 3 [member] | Internal grade 7 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 3 [member] | Internal grade 6 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 3 [member] | Internal grade 5 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 3 [member] | Internal grade 4 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Coverage	0.00%
Stage 3 [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Coverage	0.00%
Stage 3 [member] | Other [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Loss allowance	(100)	(100)
Financial assets	£ 1,600	£ 1,800
Coverage	6.30%	5.60%
Stage 3 [member] | Balance sheet exposures [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Stage 3 [member] | Balance sheet exposures [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	(400)	(300)
Financial assets	£ 1,900	£ 2,100
Coverage	21.10%	14.30%
Stage 3 [member] | Balance sheet exposures [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 400	£ 300
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 1,700	£ 1,900
Coverage	5.90%	5.30%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100	£ 100
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 2,300	£ 2,400
Coverage	17.40%	12.50%
Stage 3 [member] | Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 400	£ 300
Stage 3 [member] | Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Other [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member] | Mortgages [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Balance sheet exposures [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Coverage	0.00%
Stage 3 [member] | Balance sheet exposures [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member] | Expected credit loss [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0
Stage 3 [member] | Off-Balance Sheet [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Loss allowance	0
Financial assets	0
Stage 3 [member] | Off-Balance Sheet [member] | Internal grade 9 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 3 [member] | Off-Balance Sheet [member] | Internal grade 8 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 3 [member] | Off-Balance Sheet [member] | Internal grade 7 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 3 [member] | Off-Balance Sheet [member] | Internal grade 6 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 3 [member] | Off-Balance Sheet [member] | Internal grade 5 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 3 [member] | Off-Balance Sheet [member] | Internal grade 4 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 3 [member] | Off-Balance Sheet [member] | Internal grade 3 to 1 [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	0
Stage 3 [member] | Off-Balance Sheet [member] | Other [member] | Credit risk [member] | Total exposure [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 0

Credit Risk - Summary of Cred_2

Credit Risk - Summary of Credit Performance (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Customer loans	£ 207,287	£ 201,289
Exposure	310,155	305,464
Loss allowances	785	751
Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	268,560	263,743
Loss allowances	785	751
Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	205,000	199,600
Gross write-offs	249	534
Loss allowances	£ 863	£ 807
Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	1.15%	1.29%
Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 2,288	£ 2,491
Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	80	81
Retail banking [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	180,398	172,747
Loss allowances	564	568
Retail banking [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	180,400	172,800
Gross write-offs	206	182
Loss allowances	£ 591	£ 594
Retail banking [member] | Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	1.09%	1.30%
Retail banking [member] | Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 1,936	£ 2,211
Retail banking [member] | Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	38	43
Corporate and commercial banking [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	16,297	17,702
Loss allowances	195	168
Corporate and commercial banking [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	16,300	17,700
Gross write-offs	41	97
Loss allowances	£ 210	£ 182
Corporate and commercial banking [member] | Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	2.22%	1.56%
Corporate and commercial banking [member] | Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 335	£ 264
Corporate and commercial banking [member] | Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	27	12
Corporate and investment banking [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	4,114	4,613
Loss allowances	14	2
Corporate and investment banking [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	4,100	4,600
Gross write-offs	0	252
Loss allowances	£ 50	£ 18
Corporate and investment banking [member] | Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	0.36%	0.56%
Corporate and investment banking [member] | Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 0
Corporate and investment banking [member] | Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	15	£ 26
Corporate centre [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	67,751	68,681
Loss allowances	12	13
Corporate centre [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	4,200	4,500
Gross write-offs	2	3
Loss allowances	£ 12	£ 13
Corporate centre [member] | Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	0.40%	0.36%
Corporate centre [member] | Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 17	£ 16
Corporate centre [member] | Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	0
Business Banking [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	1,800	1,800
Gross write-offs	24	15
Loss allowances	£ 52	£ 53
Business Banking [member] | Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	4.28%	4.99%
Business Banking [member] | Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 78	£ 89
Business Banking [member] | Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	1
Consumer (auto) finance [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	7,700	7,300
Gross write-offs	34	24
Loss allowances	£ 88	£ 85
Consumer (auto) finance [member] | Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	0.55%	0.58%
Consumer (auto) finance [member] | Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 42	£ 43
Consumer (auto) finance [member] | Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	0
Other unsecured lending [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	5,500	5,700
Gross write-offs	134	125
Loss allowances	£ 233	£ 219
Other unsecured lending [member] | Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	2.15%	2.17%
Other unsecured lending [member] | Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 94	£ 97
Other unsecured lending [member] | Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	25	26
Mortgages [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	165,400	158,000
Gross write-offs	14	18
Loss allowances	£ 218	£ 237
Mortgages [member] | Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	1.05%	1.27%
Mortgages [member] | Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 1,722	£ 1,982
Mortgages [member] | Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	12	17
Corporate loans [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	22,300	24,100
Gross write-offs	65	364
Loss allowances	£ 311	£ 253
Corporate loans [member] | Loans to Customers [member] | Stage three [member]
Disclosure of credit risk exposure [line items]
Exposure ratio	2.04%	1.62%
Corporate loans [member] | Loans to Customers [member] | Stage three [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 413	£ 353
Corporate loans [member] | Loans to Customers [member] | Stage three [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 43	£ 38

Credit Risk - Summary of IFRS 9

Credit Risk - Summary of IFRS 9 Credit Quality (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Total exposures	£ 310,155	£ 305,464
Loss Impairment: On Balance Sheet ECL	785	751
Loss Impairment: Off Balance Sheet ECL	572	509
Total ECL	£ 863	£ 807
Coverage	0.30%	0.30%
Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 268,560	£ 263,743
Loss Impairment: On Balance Sheet ECL	£ 785	£ 751
Coverage	0.30%	0.30%
Drawn exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 180,398	£ 172,747
Loss Impairment: On Balance Sheet ECL	£ 564	£ 568
Coverage	0.30%	0.30%
Drawn exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 165,356	£ 157,957
Loss Impairment: On Balance Sheet ECL	£ 214	£ 234
Coverage	0.10%	0.10%
Drawn exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 16,297	£ 17,702
Loss Impairment: On Balance Sheet ECL	£ 195	£ 168
Coverage	1.20%	0.90%
Drawn exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 4,114	£ 4,613
Loss Impairment: On Balance Sheet ECL	£ 14	2
Coverage	0.30%
Drawn exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 67,751	68,681
Loss Impairment: On Balance Sheet ECL	£ 12	13
Coverage	0.00%
Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 41,595	41,721
Loss Impairment: Off Balance Sheet ECL	£ 78	£ 56
Coverage	0.20%	0.10%
Off-Balance Sheet Exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 26,081	£ 23,058
Loss Impairment: Off Balance Sheet ECL	£ 27	£ 26
Coverage	0.10%	0.10%
Off-Balance Sheet Exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 13,432	£ 11,213
Loss Impairment: Off Balance Sheet ECL	£ 4	3
Coverage	0.00%
Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 5,558	5,133
Loss Impairment: Off Balance Sheet ECL	£ 15	£ 14
Coverage	0.30%	0.30%
Off-Balance Sheet Exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 9,342	£ 13,005
Loss Impairment: Off Balance Sheet ECL	£ 36	£ 16
Coverage	0.40%	0.10%
Off-Balance Sheet Exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 614	£ 525
Stage 1 [member]
Disclosure of credit risk exposure [line items]
Total exposures	295,436	290,882
Total ECL	£ 147	143
Coverage	0.00%
Stage 1 [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 254,595	249,676
Loss Impairment: On Balance Sheet ECL	£ 124	121
Coverage	0.00%
Stage 1 [member] | Drawn exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 169,003	160,212
Loss Impairment: On Balance Sheet ECL	£ 85	£ 84
Coverage	0.10%	0.10%
Stage 1 [member] | Drawn exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 155,477	£ 146,619
Loss Impairment: On Balance Sheet ECL	£ 11	10
Coverage	0.00%
Stage 1 [member] | Drawn exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 14,068	16,394
Loss Impairment: On Balance Sheet ECL	£ 34	£ 31
Coverage	0.20%	0.20%
Stage 1 [member] | Drawn exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 3,916	£ 4,535
Loss Impairment: On Balance Sheet ECL	£ 2	1
Coverage	0.10%
Stage 1 [member] | Drawn exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 67,608	68,535
Loss Impairment: On Balance Sheet ECL	£ 3	5
Coverage	0.00%
Stage 1 [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 40,841	41,206
Loss Impairment: Off Balance Sheet ECL	£ 23	£ 22
Coverage	0.10%	0.10%
Stage 1 [member] | Off-Balance Sheet Exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 25,849	£ 22,819
Loss Impairment: Off Balance Sheet ECL	£ 13	£ 12
Coverage	0.10%	0.10%
Stage 1 [member] | Off-Balance Sheet Exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 13,353	£ 11,120
Loss Impairment: Off Balance Sheet ECL	£ 3	2
Coverage	0.00%
Stage 1 [member] | Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 5,249	4,939
Loss Impairment: Off Balance Sheet ECL	£ 7	£ 6
Coverage	0.10%	0.10%
Stage 1 [member] | Off-Balance Sheet Exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 9,129	£ 12,923
Loss Impairment: Off Balance Sheet ECL	£ 3	4
Coverage	0.00%
Stage 1 [member] | Off-Balance Sheet Exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 614	525
Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total exposures	12,351	12,011
Total ECL	£ 348	£ 307
Coverage	2.80%	2.60%
Stage 2 [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 9,653	£ 10,520
Coverage	2.80%	2.60%
Stage 2 [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 11,677	£ 11,577
Loss Impairment: On Balance Sheet ECL	£ 305	£ 286
Coverage	2.60%	2.50%
Stage 2 [member] | Drawn exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 9,459	£ 10,324
Loss Impairment: On Balance Sheet ECL	£ 255	£ 256
Coverage	2.70%	2.50%
Stage 2 [member] | Drawn exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 8,157	£ 9,356
Loss Impairment: On Balance Sheet ECL	£ 100	£ 118
Coverage	1.20%	1.30%
Stage 2 [member] | Drawn exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 1,894	£ 1,044
Loss Impairment: On Balance Sheet ECL	£ 35	£ 26
Coverage	1.80%	2.50%
Stage 2 [member] | Drawn exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 198	£ 78
Loss Impairment: On Balance Sheet ECL	£ 12	£ 1
Coverage	6.10%	1.30%
Stage 2 [member] | Drawn exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 126	£ 131
Loss Impairment: On Balance Sheet ECL	£ 3	£ 3
Coverage	24.00%	2.30%
Stage 2 [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 674	£ 434
Loss Impairment: Off Balance Sheet ECL	£ 43	£ 21
Coverage	6.40%	4.80%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 194	£ 196
Loss Impairment: Off Balance Sheet ECL	£ 13	£ 13
Coverage	6.70%	6.60%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 67	£ 76
Loss Impairment: Off Balance Sheet ECL	£ 1	£ 1
Coverage	1.50%	1.30%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 282	£ 182
Loss Impairment: Off Balance Sheet ECL	£ 6	£ 6
Coverage	2.10%	3.30%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 198	£ 56
Loss Impairment: Off Balance Sheet ECL	£ 24	£ 2
Coverage	12.10%	3.60%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 0
Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total exposures	2,368	£ 2,571
Total ECL	£ 368	£ 357
Coverage	15.50%	13.90%
Stage 3 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 362	£ 276
Stage 3 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	15	26
Stage 3 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	17	16
Stage 3 [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	2,288	2,490
Loss Impairment: On Balance Sheet ECL	£ 356	£ 344
Coverage	15.60%	13.80%
Stage 3 [member] | Drawn exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 1,936	£ 2,211
Loss Impairment: On Balance Sheet ECL	£ 224	£ 228
Coverage	11.60%	10.30%
Stage 3 [member] | Drawn exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 1,722	£ 1,982
Loss Impairment: On Balance Sheet ECL	£ 103	£ 106
Coverage	5.90%	5.30%
Stage 3 [member] | Drawn exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 335	£ 264
Loss Impairment: On Balance Sheet ECL	£ 126	£ 111
Coverage	37.60%	42.00%
Stage 3 [member] | Drawn exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 0
Loss Impairment: On Balance Sheet ECL	£ 0
Coverage	0.00%
Stage 3 [member] | Drawn exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 17	£ 15
Loss Impairment: On Balance Sheet ECL	£ 6	£ 5
Coverage	37.50%	33.30%
Stage 3 [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 80	£ 81
Loss Impairment: Off Balance Sheet ECL	£ 12	£ 13
Coverage	15.00%	16.00%
Stage 3 [member] | Off-Balance Sheet Exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 38	£ 43
Loss Impairment: Off Balance Sheet ECL	£ 1	£ 1
Coverage	2.60%	2.30%
Stage 3 [member] | Off-Balance Sheet Exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 12	£ 17
Loss Impairment: Off Balance Sheet ECL	£ 0
Coverage	0.00%
Stage 3 [member] | Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 27	12
Loss Impairment: Off Balance Sheet ECL	£ 2	£ 2
Coverage	7.40%	16.70%
Stage 3 [member] | Off-Balance Sheet Exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 15	£ 26
Loss Impairment: Off Balance Sheet ECL	£ 9	£ 10
Coverage	60.00%	38.50%
Stage 3 [member] | Off-Balance Sheet Exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 0

Credit Risk - Summary of IFRS_2

Credit Risk - Summary of IFRS 9 Credit Quality (Parenthetical) (Detail) - GBP (£) £ in Billions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [abstract]
Retail mortgage offers in pipeline	£ 7.6	£ 6.2

Credit Risk - Summary of Stage

Credit Risk - Summary of Stage 2 Decomposition (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Exposure	£ 310,155	£ 305,464
Coverage	0.30%	0.30%
Stage 2 [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 12,351	£ 12,011
ECL	£ 348	£ 307
Coverage	2.80%	2.60%
Stage 2 [member] | Retail Banking [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 9,653	£ 10,520
ECL	£ 268	£ 269
Coverage	2.80%	2.60%
Stage 2 [member] | Other Business Segments [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 2,698	£ 1,491
ECL	£ 80	£ 38
Coverage	3.00%	2.50%
Deterioation in probability of default [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 8,842	£ 8,509
ECL	£ 219	£ 211
Coverage	2.50%	2.50%
Deterioation in probability of default [member] | Stage 2 [member] | Retail Banking [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 6,844	£ 7,854
ECL	£ 194	£ 196
Coverage	2.80%	2.50%
Deterioation in probability of default [member] | Stage 2 [member] | Other Business Segments [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 1,998	£ 655
ECL	£ 25	£ 15
Coverage	1.30%	2.30%
Forbearance support provided [Member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 561	£ 462
ECL	£ 5	£ 4
Coverage	0.90%	0.90%
Forbearance support provided [Member] | Stage 2 [member] | Retail Banking [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 516	£ 450
ECL	£ 4	£ 3
Coverage	0.80%	0.70%
Forbearance support provided [Member] | Stage 2 [member] | Other Business Segments [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 45	£ 12
ECL	£ 1	£ 1
Coverage	2.20%	8.30%
30 DPD [Member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 1,213	£ 960
ECL	£ 48	£ 39
Coverage	4.00%	4.10%
30 DPD [Member] | Stage 2 [member] | Retail Banking [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 1,054	£ 949
ECL	£ 46	£ 39
Coverage	4.40%	4.10%
30 DPD [Member] | Stage 2 [member] | Other Business Segments [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 159	£ 11
ECL	£ 2
Coverage	1.30%
Other [Member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 1,735	2,080
ECL	£ 76	£ 53
Coverage	4.40%	2.50%
Other [Member] | Stage 2 [member] | Retail Banking [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 1,239	£ 1,267
ECL	£ 24	£ 31
Coverage	1.90%	2.40%
Other [Member] | Stage 2 [member] | Other Business Segments [Member]
Disclosure of credit risk exposure [line items]
Exposure	£ 496	£ 813
ECL	£ 52	£ 22
Coverage	10.50%	2.70%

Credit Risk - Disclosure of Sta

Credit Risk - Disclosure of Stage 2 Decomposition Cure and Not Cure Explanatory (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Exposure	£ 310,155	£ 305,464
Coverage	0.30%	0.30%
Stage Two [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 12,351	£ 12,011
ECL	£ 348	£ 307
Coverage	2.80%	2.60%
Stage 2 not in cure period [member] | Stage Two [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 12,017	£ 11,837
ECL	£ 342	£ 301
Coverage	2.80%	2.50%
Stage 2 in cure period (for transfer to Stage 1) [member] | Stage Two [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 334	£ 174
ECL	£ 6	£ 6
Coverage	1.80%	3.40%

Credit Risk - Summary of Reconc

Credit Risk - Summary of Reconciliation of Exposures, ECL and Net Carrying Amounts (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Total exposures	£ 310,155	£ 305,464
Total ECL on drawn exposures	785	751
Total ECL on off-balance sheet exposures	572	509
Assets classified at FVTPL	374	4,522
Total assets	281,702	283,372	£ 314,765
Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	268,560	263,743
Total ECL on drawn exposures	785	751
On-balance sheet net carrying amount	267,775	262,992
Other items	2,986	2,501
Adjusted net carrying amount	270,761	265,493
Assets classified at FVTPL	3,702	10,876
Non-financial assets	7,239	7,003
Total assets	281,702	283,372
Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	41,595	41,721
Total ECL on off-balance sheet exposures	78	56
Retail banking [member]
Disclosure of credit risk exposure [line items]
Total assets	187,556	179,572	174,524
Retail banking [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	180,398	172,747
Total ECL on drawn exposures	564	568
On-balance sheet net carrying amount	179,834	172,179
Retail banking [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	26,081	23,058
Total ECL on off-balance sheet exposures	27	26
Mortgages [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	165,356	157,957
Total ECL on drawn exposures	214	234
On-balance sheet net carrying amount	165,142	157,723
Mortgages [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	13,432	11,213
Total ECL on off-balance sheet exposures	4	3
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total assets	16,297	17,702	19,391
Corporate and commercial banking [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	16,297	17,702
Total ECL on drawn exposures	195	168
On-balance sheet net carrying amount	16,102	17,534
Corporate and commercial banking [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	5,558	5,133
Total ECL on off-balance sheet exposures	15	14
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total assets	4,727	8,607	25,368
Corporate and investment banking [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	4,114	4,613
Total ECL on drawn exposures	14	2
On-balance sheet net carrying amount	4,100	4,611
Corporate and investment banking [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	9,342	13,005
Total ECL on off-balance sheet exposures	36	16
Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total assets	73,122	77,491	£ 95,482
Corporate centre [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	67,751	68,681
Total ECL on drawn exposures	12	13
On-balance sheet net carrying amount	67,739	68,668
Corporate centre [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	614	£ 525
Total ECL on off-balance sheet exposures	£ 0

Credit Risk - Summary of ECL Re

Credit Risk - Summary of ECL Reconciliation (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	£ 807
Ending balance	863	£ 807
Less: Recoveries net of collection costs	(40)	(42)		£ (54)
Total credit impairment charge/(release)	221	153	[1]	203	[1]
Total exposure [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	305,464	300,286
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfer of financial instruments	0
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	43,257	58,382
Other	3,980	5,631
Assets derecognised - Redemptions and repayments	(42,183)	(58,179)
Assets derecognised - written off	(363)	(656)
Ending balance	310,155	305,464		300,286
Net movement in the year	4,691	5,178
Expected credit loss [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	807	1,151
Change in economic scenarios	(19)	(16)
Changes to model	13	(7)
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	8
Transfer of financial instruments	0
Net remeasurement of ECL on stage transfer	160	99
New lending and assets purchased	70	89
Other	183	165
Assets derecognised - Redemptions and repayments	(102)	(140)
Assets derecognised - written off	(249)	(534)
Ending balance		807		1,151
Net movement in the year	56	(344)
Income Statement ECL charge/(release)	305	190
Less: ECL relating to derecognised income	(13)
Less: Recoveries net of collection costs	(71)	(36)
Total credit impairment charge/(release)	221	154
Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	143
Ending balance	147	143
Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	307
Ending balance	348	307
Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	357
Ending balance	368	357
Financial instruments not credit-impaired [member] | Subject to 12-month ECL [member] | Stage 1 ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	143	176
Change in economic scenarios	5	4
Changes to model	0	(1)
Transfers from Stage 1 to Stage 2	(11)	(11)
Transfers from Stage 2 to Stage 1	74	68
Transfers to Stage 3	(2)	(8)
Transfers from Stage 3	1	6
Transfer of financial instruments	62	55
Net remeasurement of ECL on stage transfer	(66)	(63)
New lending and assets purchased	29	43
Other	6	(27)
Assets derecognised - Redemptions and repayments	(32)	(44)
Assets derecognised - written off	0
Ending balance	147	143		176
Net movement in the year	4	(33)
Income Statement ECL charge/(release)	4	(33)
Less: ECL relating to derecognised income	0
Less: Recoveries net of collection costs	(10)
Total credit impairment charge/(release)	(6)	(33)
Financial instruments not credit-impaired [member] | Subject to 12-month ECL [member] | Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	290,882	285,133
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	(4,101)	(4,190)
Transfers from Stage 2 to Stage 1	3,458	3,325
Transfers to Stage 3	(361)	(445)
Transfers from Stage 3	10	17
Transfer of financial instruments	(994)	(1,293)
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	42,415	57,280
Other	3,514	5,540
Assets derecognised - Redemptions and repayments	(40,380)	(55,778)
Assets derecognised - written off	(1)
Ending balance	295,436	290,882		285,133
Net movement in the year	4,554	5,749
Financial instruments not credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 2 ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	307	284
Change in economic scenarios	(15)	(12)
Changes to model	0	2
Transfers from Stage 1 to Stage 2	11	11
Transfers from Stage 2 to Stage 1	(74)	(68)
Transfers to Stage 3	(24)	(23)
Transfers from Stage 3	23	27
Transfer of financial instruments	(64)	(53)
Net remeasurement of ECL on stage transfer	130	83
New lending and assets purchased	32	33
Other	(14)	(15)
Assets derecognised - Redemptions and repayments	(28)	(15)
Assets derecognised - written off	0
Ending balance	348	307		284
Net movement in the year	41	23
Income Statement ECL charge/(release)	41	23
Less: ECL relating to derecognised income	0
Less: Recoveries net of collection costs	(15)
Total credit impairment charge/(release)	26	23
Financial instruments not credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	12,011	12,110
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	4,101	4,190
Transfers from Stage 2 to Stage 1	(3,458)	(3,325)
Transfers to Stage 3	(595)	(603)
Transfers from Stage 3	516	443
Transfer of financial instruments	564	705
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	827	1,085
Other	294	(175)
Assets derecognised - Redemptions and repayments	(1,344)	(1,714)
Assets derecognised - written off	(1)
Ending balance	12,351	12,011		12,110
Net movement in the year	340	(99)
Financial instruments credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 3 ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	357	691
Change in economic scenarios	(9)	(8)
Changes to model	13	(8)
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	26	31
Transfers from Stage 3	(24)	(33)
Transfer of financial instruments	2	(2)
Net remeasurement of ECL on stage transfer	96	79
New lending and assets purchased	9	13
Other	191	207
Assets derecognised - Redemptions and repayments	(42)	(81)
Assets derecognised - written off	(249)	(534)
Ending balance	368	357		691
Net movement in the year	11	(334)
Income Statement ECL charge/(release)	260	200
Less: ECL relating to derecognised income	(13)
Less: Recoveries net of collection costs	(46)	(36)
Total credit impairment charge/(release)	201	164
Financial instruments credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	2,571	3,043
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	956	1,048
Transfers from Stage 3	(526)	(460)
Transfer of financial instruments	430	588
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	15	17
Other	172	266
Assets derecognised - Redemptions and repayments	(459)	(687)
Assets derecognised - written off	(361)	(656)
Ending balance	2,368	2,571		£ 3,043
Net movement in the year	£ (203)	£ (472)
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Credit Risk - Summary of Countr

Credit Risk - Summary of Country Risk Exposure (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Risk exposures	£ 310,155	£ 305,464
Governments [member]
Disclosure of credit risk exposure [line items]
Risk exposures	32,100	33,000
Government Guaranteed [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Banks [member]
Disclosure of credit risk exposure [line items]
Risk exposures	9,300	13,800
Other Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Risk exposures	26,000	31,300
Retail [member]
Disclosure of credit risk exposure [line items]
Risk exposures	204,500	194,300
Corporate counterparty [member]
Disclosure of credit risk exposure [line items]
Risk exposures	40,000	41,100
Eurozone Countries [member]
Disclosure of credit risk exposure [line items]
Risk exposures	14,600	19,700
Eurozone Countries [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	7,600	12,700
Eurozone Countries [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100	300
Eurozone Countries [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0	200
Eurozone Countries [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,200	1,000
Eurozone Countries [member] | Germany [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,400	1,600
Eurozone Countries [member] | Luxembourg [member]
Disclosure of credit risk exposure [line items]
Risk exposures	2,900	1,100
Eurozone Countries [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,400	2,800
Eurozone Countries [member] | Governments [member]
Disclosure of credit risk exposure [line items]
Risk exposures	400	300
Eurozone Countries [member] | Governments [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Governments [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Governments [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Governments [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100
Eurozone Countries [member] | Governments [member] | Germany [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Governments [member] | Luxembourg [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Governments [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	300	300
Eurozone Countries [member] | Government Guaranteed [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Government Guaranteed [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Government Guaranteed [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Government Guaranteed [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Government Guaranteed [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Government Guaranteed [member] | Germany [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Government Guaranteed [member] | Luxembourg [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Government Guaranteed [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Banks [member]
Disclosure of credit risk exposure [line items]
Risk exposures	3,000	3,800
Eurozone Countries [member] | Banks [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Banks [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Banks [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Banks [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures	600	1,000
Eurozone Countries [member] | Banks [member] | Germany [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,300	1,600
Eurozone Countries [member] | Banks [member] | Luxembourg [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100
Eurozone Countries [member] | Banks [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,000	1,200
Eurozone Countries [member] | Other Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Risk exposures	10,900	13,700
Eurozone Countries [member] | Other Financial Institutions [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	7,500	12,300
Eurozone Countries [member] | Other Financial Institutions [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100	100
Eurozone Countries [member] | Other Financial Institutions [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0	200
Eurozone Countries [member] | Other Financial Institutions [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures	500
Eurozone Countries [member] | Other Financial Institutions [member] | Germany [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Other Financial Institutions [member] | Luxembourg [member]
Disclosure of credit risk exposure [line items]
Risk exposures	2,700	900
Eurozone Countries [member] | Other Financial Institutions [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100	200
Eurozone Countries [member] | Retail [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Retail [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Retail [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Retail [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Retail [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Retail [member] | Germany [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Retail [member] | Luxembourg [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Retail [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Corporate counterparty [member]
Disclosure of credit risk exposure [line items]
Risk exposures	300	1,900
Eurozone Countries [member] | Corporate counterparty [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100	400
Eurozone Countries [member] | Corporate counterparty [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0	200
Eurozone Countries [member] | Corporate counterparty [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Corporate counterparty [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
Eurozone Countries [member] | Corporate counterparty [member] | Germany [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100
Eurozone Countries [member] | Corporate counterparty [member] | Luxembourg [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100	200
Eurozone Countries [member] | Corporate counterparty [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0	1,100
All Other Countries [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,600	3,400
All Other Countries [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	289,100	278,900
All Other Countries [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	2,300	4,300
All Other Countries [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	3,800	6,400
All Other Countries [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0	100
All Other Countries [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	500	700
All Other Countries [member] | Governments [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	200	100
All Other Countries [member] | Governments [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	28,300	27,700
All Other Countries [member] | Governments [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,000	1,100
All Other Countries [member] | Governments [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	2,200	3,800
All Other Countries [member] | Governments [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Governments [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Government Guaranteed [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Government Guaranteed [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Government Guaranteed [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Government Guaranteed [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Government Guaranteed [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Government Guaranteed [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Banks [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	500	1,900
All Other Countries [member] | Banks [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	3,100	3,800
All Other Countries [member] | Banks [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,100	1,500
All Other Countries [member] | Banks [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,600	2,600
All Other Countries [member] | Banks [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Banks [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0	200
All Other Countries [member] | Other Financial Institutions [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100	400
All Other Countries [member] | Other Financial Institutions [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	15,000	15,700
All Other Countries [member] | Other Financial Institutions [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0	1,500
All Other Countries [member] | Other Financial Institutions [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Other Financial Institutions [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Other Financial Institutions [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Retail [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Retail [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	204,500	194,300
All Other Countries [member] | Retail [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Retail [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Retail [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Retail [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Corporate counterparty [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	800	1,000
All Other Countries [member] | Corporate counterparty [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	38,200	37,400
All Other Countries [member] | Corporate counterparty [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	200	200
All Other Countries [member] | Corporate counterparty [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Other Countries [member] | Corporate counterparty [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0	100
All Other Countries [member] | Corporate counterparty [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	500	500
All Countries Excluding Eurozone Countries [member]
Disclosure of credit risk exposure [line items]
Risk exposures	297,300	293,800
All Countries Excluding Eurozone Countries [member] | Governments [member]
Disclosure of credit risk exposure [line items]
Risk exposures	31,700	32,700
All Countries Excluding Eurozone Countries [member] | Government Guaranteed [member]
Disclosure of credit risk exposure [line items]
Risk exposures	0
All Countries Excluding Eurozone Countries [member] | Banks [member]
Disclosure of credit risk exposure [line items]
Risk exposures	6,300	10,000
All Countries Excluding Eurozone Countries [member] | Other Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Risk exposures	15,100	17,600
All Countries Excluding Eurozone Countries [member] | Retail [member]
Disclosure of credit risk exposure [line items]
Risk exposures	204,500	194,300
All Countries Excluding Eurozone Countries [member] | Corporate counterparty [member]
Disclosure of credit risk exposure [line items]
Risk exposures	£ 39,700	£ 39,200

Credit Risk - Summary of Coun_2

Credit Risk - Summary of Country Risk Exposure (Parenthetical) (Detail) - GBP (£)	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Risk exposures	£ 310,155,000,000	£ 305,464,000,000
Eurozone Countries [member] | Netherlands [member]
Disclosure of credit risk exposure [line items]
Risk exposures	200,000,000	1,200,000,000
Eurozone Countries [member] | Belgium [Member]
Disclosure of credit risk exposure [line items]
Risk exposures	600,000,000	900,000,000
Eurozone Countries [member] | Greece [member]
Disclosure of credit risk exposure [line items]
Risk exposures	£ 0	£ 0

Credit Risk - Summary of Balanc

Credit Risk - Summary of Balances with Other Banco Santander Companies (Detail) - Santander UK Group Holdings plc [member] - GBP (£) £ in Billions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of detailed information about financial instruments [line items]
Financial assets	£ 4	£ 4.5
Financial liabilities	13.6	15.4
Spain (excl. Banco Santander) [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	1.6	2.5
Financial liabilities	2.2	3.7
UK [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	2.4	2
Financial liabilities	11.2	11.5
Uruguay [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0.2	0.2
Banks [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	1.6	2.5
Financial liabilities	2.3	3.8
Banks [member] | Spain (excl. Banco Santander) [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	1.6	2.5
Financial liabilities	2.1	3.6
Banks [member] | UK [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	0
Financial liabilities	0
Banks [member] | Uruguay [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0.2	0.2
Other Financial Institutions [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	2.4	2
Financial liabilities	11.3	11.6
Other Financial Institutions [member] | Spain (excl. Banco Santander) [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	0
Financial liabilities	0.1	0.1
Other Financial Institutions [member] | UK [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	2.4	2
Financial liabilities	11.2	£ 11.5
Other Financial Institutions [member] | Uruguay [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0
Corporate counterparty [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	0
Financial liabilities	0
Corporate counterparty [member] | Spain (excl. Banco Santander) [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	0
Financial liabilities	0
Corporate counterparty [member] | UK [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	0
Financial liabilities	0
Corporate counterparty [member] | Uruguay [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	£ 0

Credit Risk - Summary of Types

Credit Risk - Summary of Types of Credit Risk Mitigation (Detail)	12 Months Ended
	Dec. 31, 2019
Residential mortgages [member]
Disclosure of credit risk exposure [line items]
Types of credit risk mitigation, including collateral, across portfolios	Collateral is in the form of a first legal charge over the property. Before we grant a mortgage, we have the property valued. We have our own guidelines for surveyor valuations, which build on guidance from the Royal Institution of Chartered Surveyors (RICS). But we also make use of automated valuation methodologies where our confidence in the accuracy of this method is high.
Unsecured Lending [member]
Disclosure of credit risk exposure [line items]
Types of credit risk mitigation, including collateral, across portfolios	Unsecured lending means there is no collateral or security tied to the loan that can be used to mitigate any potential loss if the customer does not pay us back.
Consumer (auto) finance [member]
Disclosure of credit risk exposure [line items]
Types of credit risk mitigation, including collateral, across portfolios	Collateral is in the form of legal ownership of the vehicle for most consumer (auto) finance loans, with the customer being the registered keeper. Only a very small proportion of the consumer (auto) finance business is underwritten as a personal loan. In these cases, there is no collateral or security tied to the loan. We use a leading vehicle valuation company to assess the LTV at the proposal stage.
Business Banking [member]
Disclosure of credit risk exposure [line items]
Types of credit risk mitigation, including collateral, across portfolios	Includes secured and unsecured lending. We can take mortgage debentures as collateral if the business is incorporated. These are charges over a company’s assets. We can also take guarantees, but we do not treat them as collateral and we do not put a cash value on them unless they are supported by a tangible asset which is charged to us. If a customer defaults, we work with them to consider debt restructuring options. We generally do not enforce our security over their assets except as a last resort. In which case we might appoint an administrator or receiver.

Credit Risk - Summary of ECL _2

Credit Risk - Summary of ECL Reconciliation for Retail Segment (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	£ 807
Ending balance	863	£ 807
Recoveries net of collection costs	(40)	(42)		£ (54)
Income statement charge/(release) for the year	221	153	[1]	203	[1]
Retail banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Income statement charge/(release) for the year	160	124		36
Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	143
Ending balance	147	143
Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	307
Ending balance	348	307
Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	357
Ending balance	368	357
Total exposure [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	305,464	300,286
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	43,257	58,382
Other	3,980	5,631
Assets derecognised - Redemptions and repayments	(42,183)	(58,179)
Assets derecognised - written off	(363)	(656)
Ending balance	310,155	305,464		300,286
Net movement in the year	4,691	5,178
Total exposure [member] | Retail banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	195,805	192,126
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	37,723	34,051
Other	2,866	(9)
Assets derecognised - Redemptions and repayments	(29,638)	(30,113)
Assets derecognised - written off	(277)	(250)
Ending balance	206,479	195,805		192,126
Net movement in the year	10,674	3,679
Expected credit loss [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	807	1,151
Change in economic scenarios	(19)	(16)
Changes to model	13	(7)
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	8
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	160	99
New lending and assets purchased	70	89
Other	183	165
Assets derecognised - Redemptions and repayments	(102)	(140)
Assets derecognised - written off	(249)	(534)
Ending balance		807		1,151
Net movement in the year	56	(344)
Charge/(release) to the Income Statement	305	190
Less: ECL relating to derecognised income	(13)
Recoveries net of collection costs	(71)	(36)
Income statement charge/(release) for the year	221	154
Expected credit loss [member] | Retail banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	594	625
Change in economic scenarios	(36)	(18)
Changes to model	13	2
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	78	79
New lending and assets purchased	59	63
Other	166	67
Assets derecognised - Redemptions and repayments	(77)	(42)
Assets derecognised - written off	(206)	(182)
Ending balance	591	594		625
Net movement in the year	(3)	(31)
Charge/(release) to the Income Statement	203	151
Less: ECL relating to derecognised income	(9)
Recoveries net of collection costs	(34)	(27)
Income statement charge/(release) for the year	160	124
Financial instruments not credit-impaired [member] | Subject to 12-month ECL [member] | Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	290,882	285,133
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	(4,101)	(4,190)
Transfers from Stage 2 to Stage 1	3,458	3,325
Transfers to Stage 3	(361)	(445)
Transfers from Stage 3	10	17
Transfers of financial instruments	(994)	(1,293)
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	42,415	57,280
Other	3,514	5,540
Assets derecognised - Redemptions and repayments	(40,380)	(55,778)
Assets derecognised - written off	(1)
Ending balance	295,436	290,882		285,133
Net movement in the year	4,554	5,749
Financial instruments not credit-impaired [member] | Subject to 12-month ECL [member] | Stage 1 [member] | Retail banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	183,031	178,978
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	(3,132)	(3,407)
Transfers from Stage 2 to Stage 1	3,289	2,992
Transfers to Stage 3	(322)	(403)
Transfers from Stage 3	11	15
Transfers of financial instruments	(154)	(803)
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	37,230	33,366
Other	2,670	(27)
Assets derecognised - Redemptions and repayments	(27,924)	(28,483)
Assets derecognised - written off	(1)
Ending balance	194,852	183,031		178,978
Net movement in the year	11,821	4,053
Financial instruments not credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	12,011	12,110
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	4,101	4,190
Transfers from Stage 2 to Stage 1	(3,458)	(3,325)
Transfers to Stage 3	(595)	(603)
Transfers from Stage 3	516	443
Transfers of financial instruments	564	705
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	827	1,085
Other	294	(175)
Assets derecognised - Redemptions and repayments	(1,344)	(1,714)
Assets derecognised - written off	(1)
Ending balance	12,351	12,011		12,110
Net movement in the year	340	(99)
Financial instruments not credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 2 [member] | Retail banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	10,520	10,885
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	3,132	3,407
Transfers from Stage 2 to Stage 1	(3,289)	(2,992)
Transfers to Stage 3	(500)	(569)
Transfers from Stage 3	509	438
Transfers of financial instruments	(148)	284
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	479	670
Other	68	(125)
Assets derecognised - Redemptions and repayments	(1,265)	(1,194)
Assets derecognised - written off	(1)
Ending balance	9,653	10,520		10,885
Net movement in the year	(867)	(365)
Financial instruments not credit-impaired [member] | Stage 1 ECL [member] | Subject to 12-month ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	143	176
Change in economic scenarios	5	4
Changes to model	0	(1)
Transfers from Stage 1 to Stage 2	(11)	(11)
Transfers from Stage 2 to Stage 1	74	68
Transfers to Stage 3	(2)	(8)
Transfers from Stage 3	1	6
Transfers of financial instruments	62	55
Net remeasurement of ECL on stage transfer	(66)	(63)
New lending and assets purchased	29	43
Other	6	(27)
Assets derecognised - Redemptions and repayments	(32)	(44)
Assets derecognised - written off	0
Ending balance	147	143		176
Net movement in the year	4	(33)
Charge/(release) to the Income Statement	4	(33)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(10)
Income statement charge/(release) for the year	(6)	(33)
Financial instruments not credit-impaired [member] | Stage 1 ECL [member] | Subject to 12-month ECL [member] | Stage 1 [member] | Retail banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	96	110
Change in economic scenarios	(3)	(1)
Changes to model	0	(1)
Transfers from Stage 1 to Stage 2	(8)	(7)
Transfers from Stage 2 to Stage 1	69	58
Transfers to Stage 3	(2)	(7)
Transfers from Stage 3	1	5
Transfers of financial instruments	60	49
Net remeasurement of ECL on stage transfer	(61)	(54)
New lending and assets purchased	23	26
Other	6	(19)
Assets derecognised - Redemptions and repayments	(23)	(14)
Assets derecognised - written off	0
Ending balance	98	96		110
Net movement in the year	2	(14)
Charge/(release) to the Income Statement	2	(14)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(2)
Income statement charge/(release) for the year	0	(14)
Financial instruments not credit-impaired [member] | Stage 2 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	307	284
Change in economic scenarios	(15)	(12)
Changes to model	0	2
Transfers from Stage 1 to Stage 2	11	11
Transfers from Stage 2 to Stage 1	(74)	(68)
Transfers to Stage 3	(24)	(23)
Transfers from Stage 3	23	27
Transfers of financial instruments	(64)	(53)
Net remeasurement of ECL on stage transfer	130	83
New lending and assets purchased	32	33
Other	(14)	(15)
Assets derecognised - Redemptions and repayments	(28)	(15)
Assets derecognised - written off	0
Ending balance	348	307		284
Net movement in the year	41	23
Charge/(release) to the Income Statement	41	23
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(15)
Income statement charge/(release) for the year	26	23
Financial instruments not credit-impaired [member] | Stage 2 ECL [member] | Subject to Lifetime ECL [member] | Stage 2 [member] | Retail banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	269	247
Change in economic scenarios	(24)	(9)
Changes to model	0	2
Transfers from Stage 1 to Stage 2	8	7
Transfers from Stage 2 to Stage 1	(69)	(58)
Transfers to Stage 3	(20)	(22)
Transfers from Stage 3	23	26
Transfers of financial instruments	(58)	(47)
Net remeasurement of ECL on stage transfer	76	73
New lending and assets purchased	27	26
Other	(2)	(14)
Assets derecognised - Redemptions and repayments	(20)	(9)
Assets derecognised - written off	0
Ending balance	268	269		247
Net movement in the year	(1)	22
Charge/(release) to the Income Statement	(1)	22
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	0
Income statement charge/(release) for the year	(1)	22
Financial instruments credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	2,571	3,043
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	956	1,048
Transfers from Stage 3	(526)	(460)
Transfers of financial instruments	430	588
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	15	17
Other	172	266
Assets derecognised - Redemptions and repayments	(459)	(687)
Assets derecognised - written off	(361)	(656)
Ending balance	2,368	2,571		3,043
Net movement in the year	(203)	(472)
Financial instruments credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 3 [member] | Retail banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	2,254	2,263
Change in economic scenarios	0
Changes to model	0
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	822	972
Transfers from Stage 3	(520)	(453)
Transfers of financial instruments	302	519
Net remeasurement of ECL on stage transfer	0
New lending and assets purchased	14	15
Other	128	143
Assets derecognised - Redemptions and repayments	(449)	(436)
Assets derecognised - written off	(275)	(250)
Ending balance	1,974	2,254		2,263
Net movement in the year	(280)	(9)
Financial instruments credit-impaired [member] | Stage 3 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	357	691
Change in economic scenarios	(9)	(8)
Changes to model	13	(8)
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	26	31
Transfers from Stage 3	(24)	(33)
Transfers of financial instruments	2	(2)
Net remeasurement of ECL on stage transfer	96	79
New lending and assets purchased	9	13
Other	191	207
Assets derecognised - Redemptions and repayments	(42)	(81)
Assets derecognised - written off	(249)	(534)
Ending balance	368	357		691
Net movement in the year	11	(334)
Charge/(release) to the Income Statement	260	200
Less: ECL relating to derecognised income	(13)
Recoveries net of collection costs	(46)	(36)
Income statement charge/(release) for the year	201	164
Financial instruments credit-impaired [member] | Stage 3 ECL [member] | Subject to Lifetime ECL [member] | Stage 3 [member] | Retail banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	229	268
Change in economic scenarios	(9)	(8)
Changes to model	13	1
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	22	29
Transfers from Stage 3	(24)	(31)
Transfers of financial instruments	(2)	(2)
Net remeasurement of ECL on stage transfer	63	60
New lending and assets purchased	9	11
Other	162	100
Assets derecognised - Redemptions and repayments	(34)	(19)
Assets derecognised - written off	(206)	(182)
Ending balance	225	229		£ 268
Net movement in the year	(4)	(39)
Charge/(release) to the Income Statement	202	143
Less: ECL relating to derecognised income	(9)
Recoveries net of collection costs	(32)	(27)
Income statement charge/(release) for the year	£ 161	£ 116
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Credit Risk - Summary of Reside

Credit Risk - Summary of Residential Mortgages by Borrower Profile (Detail) - Credit risk [member] - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 165,356	£ 157,957
Percentage of residential mortgage loans	100.00%	100.00%
New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 29,814	£ 27,274
Percentage of residential mortgage loans	100.00%	100.00%
First-Time Buyers [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 32,112	£ 29,235
Percentage of residential mortgage loans	19.00%	19.00%
First-Time Buyers [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 6,952	£ 4,848
Percentage of residential mortgage loans	23.00%	18.00%
Home Movers [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 70,860	£ 69,198
Percentage of residential mortgage loans	43.00%	44.00%
Home Movers [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 11,192	£ 10,854
Percentage of residential mortgage loans	38.00%	39.00%
Remortgagers [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 52,480	£ 51,272
Percentage of residential mortgage loans	32.00%	32.00%
Remortgagers [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 9,197	£ 9,237
Percentage of residential mortgage loans	31.00%	34.00%
Buy-To-Let [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 9,904	£ 8,252
Percentage of residential mortgage loans	6.00%	5.00%
Buy-To-Let [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 2,473	£ 2,335
Percentage of residential mortgage loans	8.00%	9.00%

Credit Risk - Additional Inform

Credit Risk - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)MortgageLoan	Dec. 31, 2018GBP (£)MortgageLoan
Disclosure of internal credit grades [line items]
Advances and flexible mortgage drawdowns	£ 1,300	£ 1,500
Maximum exposure to credit risk	£ 79,125	87,745
Percenatage of reverse repos to exposure	100.00%
Credit risk [member]
Disclosure of internal credit grades [line items]
Maximum exposure to credit risk	£ 270,900	265,500
Credit risk [member] | Accumulated impairment [member]
Disclosure of internal credit grades [line items]
Maximum exposure to credit risk	(800)	(700)
Credit risk [member] | Off Balance Sheet [member]
Disclosure of internal credit grades [line items]
Maximum exposure to credit risk	41,500	41,600
Credit risk [member] | Off Balance Sheet [member] | Accumulated impairment [member]
Disclosure of internal credit grades [line items]
Maximum exposure to credit risk	(100)	(100)
Mortgages [member]
Disclosure of internal credit grades [line items]
Parts of the loans in negative equity that were effectively uncollateralised	127	170
Consumer loans	2	2
Corporate loans [member] | Loans and advances to customers [Member] | Off Balance Sheet [member] | Accumulated impairment [member]
Disclosure of internal credit grades [line items]
Maximum exposure to credit risk	100
Internal Remortgages [member]
Disclosure of internal credit grades [line items]
Internal remortgages	£ 31,600	£ 27,200
Greater Than 2.0m [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Number of individual mortgage loans | MortgageLoan	76	57
New business number of individual mortgage loans | MortgageLoan	32	9

Credit Risk - Summary of Resi_2

Credit Risk - Summary of Residential Mortgages by Interest Rate Profile (Detail) - Stock [member] - Credit risk [member] - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 165,356	£ 157,957
Percentage of residential mortgage loans	100.00%	100.00%
Fixed Rate [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 128,798	£ 115,178
Percentage of residential mortgage loans	78.00%	73.00%
Variable Rate [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 22,116	£ 24,396
Percentage of residential mortgage loans	13.00%	15.00%
Standard Variable Rate [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 14,442	£ 18,383
Percentage of residential mortgage loans	9.00%	12.00%

Credit Risk - Summary of Resi_3

Credit Risk - Summary of Residential Mortgages by Geographical Distribution (Detail) - Credit risk [member] - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 165,356	£ 157,957
New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	29,814	27,274
London [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	41,400	39,000
London [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	7,500	7,100
Midlands and East Anglia [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	22,100	21,100
Midlands and East Anglia [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	4,300	3,800
North UK [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	22,700	22,200
North UK [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	3,800	3,400
Northern Ireland [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	3,300	3,400
Northern Ireland [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	300	200
Scotland [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	6,800	6,700
Scotland [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	1,200	1,000
South East Excluding London [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	51,700	48,700
South East Excluding London [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	9,700	9,000
South West and Wales and Other [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	17,400	16,900
South West and Wales and Other [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 3,000	£ 2,800

Credit Risk - Summary of Resi_4

Credit Risk - Summary of Residential Mortgages by Average Loan Size for New Business (Detail) - GBP (£) £ in Thousands	Dec. 31, 2019	Dec. 31, 2018
South East Including London [member]
Disclosure of credit risk exposure [line items]
New business residential mortgage loans average size	£ 277	£ 270
Rest of UK [member]
Disclosure of credit risk exposure [line items]
New business residential mortgage loans average size	154	150
UK [member]
Disclosure of credit risk exposure [line items]
New business residential mortgage loans average size	£ 207	£ 203

Credit Risk - Summary of Resi_5

Credit Risk - Summary of Residential Mortgages by Loan Size (Detail) - Credit risk [member] - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 93,050	£ 87,756
UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	165,356	157,957
Less Than 0.25m [member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	45,828	45,851
Less Than 0.25m [member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	105,855	105,181
0.25m-0.50m[member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	34,027	30,488
0.25m-0.50m[member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	44,549	39,841
0.50m-1.0m [member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	11,471	10,103
0.50m-1.0m [member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	13,114	11,551
1.0m-2.0m [member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	1,538	1,168
1.0m-2.0m [member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	1,644	1,236
Greater Than 2.0m [member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	186	146
Greater Than 2.0m [member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 194	£ 148

Credit Risk - Summary of Resi_6

Credit Risk - Summary of Residential Mortgages by Loan to Value (Detail) - Credit risk [member] - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	£ 165,356	£ 157,957
Collateral value of residential properties, Stock	165,229	157,787
Loan-to-value, Stage 3	1,722	1,982
Collateral value of residential properties, Stage 3	1,702	1,850
Loan-to-value, New business	29,814	27,274
Collateral value of residential properties, New business	29,813	27,274
ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	218	237
Loan-to-value, Stage 3	103	106
Up to 50% [member]
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	70,714	72,613
Loan-to-value, Stage 3	743	872
Loan-to-value, New business	5,113	5,124
Up to 50% [member] | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	24	25
Loan-to-value, Stage 3	11	11
50 - 75% [member]
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	67,311	63,505
Loan-to-value, Stage 3	626	698
Loan-to-value, New business	11,876	11,512
50 - 75% [member] | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	65	67
Loan-to-value, Stage 3	24	24
75 - 85% [member]
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	17,436	14,191
Loan-to-value, Stage 3	136	156
Loan-to-value, New business	6,130	5,955
75 - 85% [member] | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	31	32
Loan-to-value, Stage 3	13	13
85 - 100% [member]
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	9,011	6,508
Loan-to-value, Stage 3	110	125
Loan-to-value, New business	6,650	4,648
85 - 100% [member] | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	34	36
Loan-to-value, Stage 3	17	16
Greater Than 100% [member]
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	884	1,140
Loan-to-value, Stage 3	107	131
Loan-to-value, New business	45	35
Greater Than 100% [member] | ECL
Disclosure of credit risk exposure [line items]
Loan-to-value, Stock	64	77
Loan-to-value, Stage 3	£ 38	£ 42
Simple Average [member]
Disclosure of credit risk exposure [line items]
Percentage of loan to value, Stock	43.00%	42.00%
Percentage of loan to value, Stage 3	42.00%	43.00%
Percentage of loan to value, New business	65.00%	63.00%

Credit Risk - Summary of Resi_7

Credit Risk - Summary of Residential Mortgages by Loan to Value (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Credit risk [member]
Disclosure of credit risk exposure [line items]
Collateral against loans in negative equity	£ 757	£ 969

Credit Risk - Summary of Resi_8

Credit Risk - Summary of Residential Mortgages by Credit Performance (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 207,287	£ 201,289
Impairment loss allowances	785	751
Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	165,356	157,957
Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	165,356	157,957
Impairment loss allowances	£ 218	£ 234
Stage 1 ratio	94.03%	92.82%
Stage 2 ratio	4.93%	5.92%
Stage 3 ratio	1.05%	1.27%
Stage 1 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 155,477	£ 146,619
Stage 1 [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	155,477	146,619
Stage 2 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	8,157	9,356
Stage 2 [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	8,157	9,356
Stage 3 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 1,722	£ 1,982
Stage 3 ratio	1.05%	1.27%
Stage 3 [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 1,722	£ 1,982

Credit Risk - Summary of ECL _3

Credit Risk - Summary of ECL Reconciliation (Residential Mortgages) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	£ 807
Ending balance	863	£ 807
Recoveries net of collection costs	(40)	(42)		£ (54)
Income statement charge/(release) for the year	221	153	[1]	203	[1]
Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	143
Ending balance	147	143
Stage 1 [member] | Subject to 12-month ECL [member] | Financial instruments not credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	290,882	285,133
Transfers from Stage 1 to Stage 2	(4,101)	(4,190)
Transfers from Stage 2 to Stage 1	3,458	3,325
Transfers to Stage 3	(361)	(445)
Transfers from Stage 3	10	17
Transfers of financial instruments	(994)	(1,293)
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	42,415	57,280
Other	3,514	5,540
Assets derecognised - Redemptions and repayments	(40,380)	(55,778)
Assets derecognised - written off	(1)
Ending balance	295,436	290,882		285,133
Net movement in the year	4,554	5,749
Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	307
Ending balance	348	307
Stage 2 [member] | Subject to Lifetime ECL [member] | Financial instruments not credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	12,011	12,110
Transfers from Stage 1 to Stage 2	4,101	4,190
Transfers from Stage 2 to Stage 1	(3,458)	(3,325)
Transfers to Stage 3	(595)	(603)
Transfers from Stage 3	516	443
Transfers of financial instruments	564	705
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	827	1,085
Other	294	(175)
Assets derecognised - Redemptions and repayments	(1,344)	(1,714)
Assets derecognised - written off	(1)
Ending balance	12,351	12,011		12,110
Net movement in the year	340	(99)
Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	357
Ending balance	368	357
Stage 3 [member] | Subject to Lifetime ECL [member] | Financial instruments credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	2,571	3,043
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	956	1,048
Transfers from Stage 3	(526)	(460)
Transfers of financial instruments	430	588
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	15	17
Other	172	266
Assets derecognised - Redemptions and repayments	(459)	(687)
Assets derecognised - written off	(361)	(656)
Ending balance	2,368	2,571		3,043
Net movement in the year	(203)	(472)
Stage 1 ECL [member] | Subject to 12-month ECL [member] | Financial instruments not credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	143	176
Transfers from Stage 1 to Stage 2	(11)	(11)
Transfers from Stage 2 to Stage 1	74	68
Transfers to Stage 3	(2)	(8)
Transfers from Stage 3	1	6
Transfers of financial instruments	62	55
Net remeasurement of ECL on stage transfer	(66)	(63)
Change in economic scenarios	5	4
Changes to model	0	(1)
New lending and assets purchased	29	43
Other	6	(27)
Assets derecognised - Redemptions and repayments	(32)	(44)
Assets derecognised - written off	0
Ending balance	147	143		176
Net movement in the year	4	(33)
Charge/(release) to the Income Statement	4	(33)
Recoveries net of collection costs	(10)
Income statement charge/(release) for the year	(6)	(33)
Stage 2 ECL [member] | Subject to Lifetime ECL [member] | Financial instruments not credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	307	284
Transfers from Stage 1 to Stage 2	11	11
Transfers from Stage 2 to Stage 1	(74)	(68)
Transfers to Stage 3	(24)	(23)
Transfers from Stage 3	23	27
Transfers of financial instruments	(64)	(53)
Net remeasurement of ECL on stage transfer	130	83
Change in economic scenarios	(15)	(12)
Changes to model	0	2
New lending and assets purchased	32	33
Other	(14)	(15)
Assets derecognised - Redemptions and repayments	(28)	(15)
Assets derecognised - written off	0
Ending balance	348	307		284
Net movement in the year	41	23
Charge/(release) to the Income Statement	41	23
Recoveries net of collection costs	(15)
Income statement charge/(release) for the year	26	23
Stage 3 ECL [member] | Subject to Lifetime ECL [member] | Financial instruments credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	357	691
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	26	31
Transfers from Stage 3	(24)	(33)
Transfers of financial instruments	2	(2)
Net remeasurement of ECL on stage transfer	96	79
Change in economic scenarios	(9)	(8)
Changes to model	13	(8)
New lending and assets purchased	9	13
Other	191	207
Assets derecognised - Redemptions and repayments	(42)	(81)
Assets derecognised - written off	(249)	(534)
Ending balance	368	357		691
Net movement in the year	11	(334)
Charge/(release) to the Income Statement	260	200
Recoveries net of collection costs	(46)	(36)
Income statement charge/(release) for the year	201	164
Total exposure [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	305,464	300,286
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	43,257	58,382
Other	3,980	5,631
Assets derecognised - Redemptions and repayments	(42,183)	(58,179)
Assets derecognised - written off	(363)	(656)
Ending balance	310,155	305,464		300,286
Net movement in the year	4,691	5,178
Expected credit loss [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	807	1,151
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	8
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	160	99
Change in economic scenarios	(19)	(16)
Changes to model	13	(7)
New lending and assets purchased	70	89
Other	183	165
Assets derecognised - Redemptions and repayments	(102)	(140)
Assets derecognised - written off	(249)	(534)
Ending balance		807		1,151
Net movement in the year	56	(344)
Charge/(release) to the Income Statement	305	190
Recoveries net of collection costs	(71)	(36)
Income statement charge/(release) for the year	221	154
Residential mortgages [member] | Stage 1 [member] | Subject to 12-month ECL [member] | Financial instruments not credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	157,739	155,155
Transfers from Stage 1 to Stage 2	(2,345)	(2,941)
Transfers from Stage 2 to Stage 1	2,921	(329)
Transfers to Stage 3	(231)	2,628
Transfers from Stage 3	5	4
Transfers of financial instruments	350	(638)
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	31,090	28,330
Other	2,090	(249)
Assets derecognised - Redemptions and repayments	(22,439)	(24,859)
Assets derecognised - written off	0
Ending balance	168,830	157,739		155,155
Net movement in the year	11,091	2,584
Residential mortgages [member] | Stage 2 [member] | Subject to Lifetime ECL [member] | Financial instruments not credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	9,432	9,884
Transfers from Stage 1 to Stage 2	2,345	2,941
Transfers from Stage 2 to Stage 1	(2,921)	(512)
Transfers to Stage 3	(429)	(2,628)
Transfers from Stage 3	485	405
Transfers of financial instruments	(520)	206
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	198	446
Other	153	(81)
Assets derecognised - Redemptions and repayments	(1,039)	(1,023)
Assets derecognised - written off	0
Ending balance	8,224	9,432		9,884
Net movement in the year	(1,208)	(452)
Residential mortgages [member] | Stage 3 [member] | Subject to Lifetime ECL [member] | Financial instruments credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	1,999	2,004
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0	841
Transfers to Stage 3	660	0
Transfers from Stage 3	(490)	(409)
Transfers of financial instruments	170	432
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	2	3
Other	31	(5)
Assets derecognised - Redemptions and repayments	(396)	(358)
Assets derecognised - written off	(72)	(77)
Ending balance	1,734	1,999		2,004
Net movement in the year	(265)	(5)
Residential mortgages [member] | Stage 1 ECL [member] | Stage 1 [member] | Subject to 12-month ECL [member] | Financial instruments not credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	12	20
Transfers from Stage 1 to Stage 2	(1)	(1)
Transfers from Stage 2 to Stage 1	24	(6)
Transfers to Stage 3	0	21
Transfers from Stage 3	(1)
Transfers of financial instruments	22	14
Net remeasurement of ECL on stage transfer	(23)	(20)
Change in economic scenarios	(5)	(6)
Changes to model	0
New lending and assets purchased	5	2
Other	4	6
Assets derecognised - Redemptions and repayments	(1)	(4)
Assets derecognised - written off	0
Ending balance	14	12		20
Net movement in the year	2	(8)
Charge/(release) to the Income Statement	2	(8)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	0
Income statement charge/(release) for the year	2	(8)
Residential mortgages [member] | Stage 2 ECL [member] | Stage 2 [member] | Subject to Lifetime ECL [member] | Financial instruments not credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	119	131
Transfers from Stage 1 to Stage 2	1	1
Transfers from Stage 2 to Stage 1	(24)	(12)
Transfers to Stage 3	(8)	(21)
Transfers from Stage 3	16	14
Transfers of financial instruments	(15)	(18)
Net remeasurement of ECL on stage transfer	16	20
Change in economic scenarios	(22)	(7)
Changes to model	0	2
New lending and assets purchased	3	5
Other	6	(5)
Assets derecognised - Redemptions and repayments	(6)	(9)
Assets derecognised - written off	0
Ending balance	101	119		131
Net movement in the year	(18)	(12)
Charge/(release) to the Income Statement	(17)	(12)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	0
Income statement charge/(release) for the year	(17)	(12)
Residential mortgages [member] | Stage 3 ECL [member] | Stage 3 [member] | Subject to Lifetime ECL [member] | Financial instruments credit-impaired [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	106	121
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0	18
Transfers to Stage 3	8
Transfers from Stage 3	(15)	(14)
Transfers of financial instruments	(7)	4
Net remeasurement of ECL on stage transfer	12	14
Change in economic scenarios	(9)	(8)
Changes to model	13	2
New lending and assets purchased	0	1
Other	14	1
Assets derecognised - Redemptions and repayments	(12)	(11)
Assets derecognised - written off	(14)	(18)
Ending balance	103	106		121
Net movement in the year	(3)	(15)
Charge/(release) to the Income Statement	11	3
Less: ECL relating to derecognised income	(2)
Recoveries net of collection costs	(2)	(4)
Income statement charge/(release) for the year	7	(1)
Residential mortgages [member] | Total exposure [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	169,170	167,043
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	31,290	28,779
Other	2,274	(335)
Assets derecognised - Redemptions and repayments	(23,874)	(26,240)
Assets derecognised - written off	(72)	(77)
Ending balance	178,788	169,170		167,043
Net movement in the year	9,618	2,127
Residential mortgages [member] | Expected credit loss [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	237	272
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	5	14
Change in economic scenarios	(36)	(21)
Changes to model	13	4
New lending and assets purchased	8	8
Other	24	2
Assets derecognised - Redemptions and repayments	(19)	(24)
Assets derecognised - written off	(14)	(18)
Ending balance	218	237		£ 272
Net movement in the year	(19)	(35)
Charge/(release) to the Income Statement	(4)	(17)
Less: ECL relating to derecognised income	(2)
Recoveries net of collection costs	(2)	(4)
Income statement charge/(release) for the year	£ (8)	£ (21)
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Credit Risk - Summary of Modifi

Credit Risk - Summary of Modification of Loan Terms (Residential Mortgages) (Detail) - Mortgages [member] - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Amortised cost before modification	£ 384	£ 207
Net modification loss	7	3
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	£ 89	£ 158

Credit Risk - Summary of Resi_9

Credit Risk - Summary of Residential Mortgages by Forbearance Applied (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Capitalisation	£ 602	£ 587
Term extension	429	256
Interest-only	439	502
Concessionary interest rate	11
Total	1,481	1,345
Impairment loss allowances	£ 36	£ 29
Loans capitalisation forbearance Percentage	0.40%	0.40%
Loans term extension forbearance percentage	0.30%	0.20%
Loans interest only forbearance percentage	0.30%	0.30%
Loans forbearance percentage	0.90%	0.90%
Loans Concessionary interest rate forbearance percentage	0.00%	0.00%
Stage 2 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Capitalisation	£ 405	£ 375
Term extension	338	161
Interest-only	342	389
Concessionary interest rate	1
Total	1,086	925
Impairment loss allowances	12	9
Stage 3 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Capitalisation	197	212
Term extension	91	95
Interest-only	97	113
Concessionary interest rate	10
Total	395	420
Impairment loss allowances	£ 24	£ 20

Credit Risk - Summary of Res_10

Credit Risk - Summary of Residential Mortgages Portfolios of Particular Interest by Credit Performance (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 207,287	£ 201,289
Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	165,356	157,957
PIPs	£ 32	£ 25
Percenatge of simple average loan to value	43.00%	42.00%
Mortgages [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 38,062	£ 38,035
PIPs	£ 14	£ 12
Percenatge of simple average loan to value	45.00%	44.00%
Mortgages [member] | Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 13,247	£ 13,201
PIPs	£ 9	£ 5
Percenatge of simple average loan to value	45.00%	44.00%
Mortgages [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 11,273	£ 12,926
PIPs	£ 2	£ 3
Percenatge of simple average loan to value	28.00%	29.00%
Mortgages [member] | Loan To Value Greater Than 100% Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 884	£ 1,140
PIPs	£ 13	£ 8
Percenatge of simple average loan to value	117.00%	118.00%
Mortgages [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 9,904	£ 8,252
PIPs	£ 1
Percenatge of simple average loan to value	60.00%	58.00%
Mortgages [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 109,234	£ 101,158
PIPs	£ 8	£ 7
Percenatge of simple average loan to value	44.00%	43.00%
Mortgages [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 155,477	£ 146,619
Mortgages [member] | Stage 1 [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	33,739	33,001
Mortgages [member] | Stage 1 [member] | Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	12,112	11,824
Mortgages [member] | Stage 1 [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	10,183	11,558
Mortgages [member] | Stage 1 [member] | Loan To Value Greater Than 100% Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	594	740
Mortgages [member] | Stage 1 [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	9,593	7,906
Mortgages [member] | Stage 1 [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	105,114	96,767
Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	8,157	9,356
Mortgages [member] | Stage 2 [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	3,502	4,029
Mortgages [member] | Stage 2 [member] | Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	888	1,115
Mortgages [member] | Stage 2 [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	873	1,082
Mortgages [member] | Stage 2 [member] | Loan To Value Greater Than 100% Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	183	273
Mortgages [member] | Stage 2 [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	285	317
Mortgages [member] | Stage 2 [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	3,526	3,802
Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 1,722	£ 1,982
Stage 3 ratio	1.05%	1.27%
Mortgages [member] | Stage 3 [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 821	£ 1,005
Stage 3 ratio	2.17%	2.67%
Mortgages [member] | Stage 3 [member] | Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 247	£ 262
Stage 3 ratio	1.87%	1.99%
Mortgages [member] | Stage 3 [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 217	£ 286
Stage 3 ratio	2.03%	2.34%
Mortgages [member] | Stage 3 [member] | Loan To Value Greater Than 100% Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 107	£ 127
Stage 3 ratio	12.11%	11.18%
Mortgages [member] | Stage 3 [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 26	£ 29
Stage 3 ratio	0.26%	0.35%
Mortgages [member] | Stage 3 [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 594	£ 589
Stage 3 ratio	0.54%	0.58%

Credit Risk - Summary of Res_11

Credit Risk - Summary of Residential Mortgages Portfolios of Particular Interest by Credit Performance (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Mortgage loan including interest-only part	£ 9,823	£ 9,756

Credit Risk - Summary of Res_12

Credit Risk - Summary of Residential Mortgages Portfolios of Particular Interest by Forbearance Applied (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Total value	£ 1,481	£ 1,345
Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	1,086	925
Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	395	420
Interest Only Loan [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Total value	392	229
Interest Only Loan [member] | Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	285	136
Interest Only Loan [member] | Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	107	93
Flexible Interest Loan [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Total value	73	32
Flexible Interest Loan [member] | Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	56	18
Flexible Interest Loan [member] | Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	17	14
Loan To Value Greater Than 100% Loan [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Total value	17	10
Loan To Value Greater Than 100% Loan [member] | Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	8	3
Loan To Value Greater Than 100% Loan [member] | Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	9	7
Buy To Let Loan [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Total value	10	9
Buy To Let Loan [member] | Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	8	6
Buy To Let Loan [member] | Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	£ 2	£ 3

Credit Risk - Summary of Consum

Credit Risk - Summary of Consumer (Auto) Finance and Other Unsecured Lending by Credit Performance (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 207,287	£ 201,289
Loss allowances	785	751
Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	13,197	12,987
Loss allowances	321	305
Gross write-offs	168	149
Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	11,935	12,045
Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,126	802
Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 136	£ 140
Stage 3 ratio	1.21%	1.28%
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 7,684	£ 7,347
Loss allowances	£ 88	£ 85
Stage 3 ratio	0.55%	0.58%
Gross write-offs	£ 34	£ 24
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	7,038	6,950
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	604	354
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	42	43
Personal loans [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,135	2,182
Loss allowances	51	47
Personal loans [member] | Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,020	2,113
Personal loans [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	95	48
Personal loans [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	20	21
Credit Card [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,788	2,865
Loss allowances	120	112
Credit Card [member] | Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,473	2,560
Credit Card [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	267	256
Credit Card [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	48	49
Overdrafts [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	590	593
Loss allowances	62	61
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	404	422
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	160	144
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	26	27
Other unsecured advances [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	5,513	5,640
Loss allowances	233	£ 220
Stage 3 undrawn exposures	£ 0
Stage 3 ratio	2.15%	2.17%
Gross write-offs	£ 134	£ 125
Other unsecured advances [member] | Consumer finance and unsecured lending [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Stage 3 undrawn exposures	25	26
Other unsecured advances [member] | Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	4,897	5,095
Other unsecured advances [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	522	448
Other unsecured advances [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 94	£ 97

Credit Risk - Summary of Modi_2

Credit Risk - Summary of Modification of Loan Terms ( Consumer (Auto) Finance and Other Unsecured Lending) (Detail) - Consumer finance and unsecured lending [member] - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Amortised cost before modification	£ 38	£ 43
Net modification loss	20	20
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	5	5
Credit cards [member]
Disclosure of credit risk exposure [line items]
Amortised cost before modification	23	26
Net modification loss	12	12
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	3	2
Overdrafts [member]
Disclosure of credit risk exposure [line items]
Amortised cost before modification	15	17
Net modification loss	8	8
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	£ 2	£ 3

Credit Risk - Summary of Cons_2

Credit Risk - Summary of Consumer (Auto) Finance and Other Unsecured Lending by Forbearance (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Forbearance	£ 1,481	£ 1,345
Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	83	85
Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	22	21
Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	61	64
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	7	6
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	5	4
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	2	2
Personal loans [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	0
Personal loans [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	0
Personal loans [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	0
Credit cards [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	51	53
Credit cards [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	10	10
Credit cards [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	41	43
Overdrafts [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	25	26
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	7	7
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	18	19
Total other unsecured [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	76	79
Total other unsecured [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	17	17
Total other unsecured [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	£ 59	£ 62

Credit Risk - Summary of Full I

Credit Risk - Summary of Full Interest-Only New Business in the Year (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Information Related To Full Interest Only Loans [Abstract]
Full interest-only loans	£ 4,000	£ 3,810

Credit Risk - Summary of Detail

Credit Risk - Summary of Detailed Information of Interest only Loan Maturity Analysis (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Interest Only Loans [Line Items]
carrying amount of interest-only loans	£ 38,062	£ 38,035
Term expired [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	338	541
Within 2 years [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	1,541	1,346
Between 2-5 years [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	3,706	3,761
Between 5-15 years [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	20,984	21,711
Greater than 15 years [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	11,493	10,676
Weighted average LTV [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	3,185	3,089
Weighted average LTV [member] | Term expired [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	11	43
Weighted average LTV [member] | Within 2 years [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	111	110
Weighted average LTV [member] | Between 2-5 years [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	219	265
Weighted average LTV [member] | Between 5-15 years [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	1,793	2,029
Weighted average LTV [member] | Greater than 15 years [member]
Interest Only Loans [Line Items]
carrying amount of interest-only loans	£ 1,051	£ 642

Credit Risk - Summary of Busine

Credit Risk - Summary of Business Banking by Credit Performance (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 207,287	£ 201,289
Loss allowances	785	751
Stage 3 undrawn exposures	310,155	305,464
Stage 1 [member]
Disclosure of credit risk exposure [line items]
Stage 3 undrawn exposures	295,436	290,882
Stage 2 [member]
Disclosure of credit risk exposure [line items]
Stage 3 undrawn exposures	12,351	12,011
Stage 3 [member]
Disclosure of credit risk exposure [line items]
Stage 3 undrawn exposures	2,368	2,571
Credit risk [member]
Disclosure of credit risk exposure [line items]
Stage 3 undrawn exposures	94,200	95,200
Credit risk [member] | Business Banking [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,845	1,802
Loss allowances	52	53
Gross write offs	24	15
Credit risk [member] | Business Banking [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,590	1,548
Credit risk [member] | Business Banking [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	177	165
Credit risk [member] | Business Banking [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 78	£ 89
Stage 3 ratio	4.28%	4.99%
Credit risk [member] | Business Banking [member] | Stage 3 [member] | Undrawn Exposures [Member]
Disclosure of credit risk exposure [line items]
Stage 3 undrawn exposures	£ 1

Credit Risk - Summary of Modi_3

Credit Risk - Summary of Modification of Loan Terms (Business Banking) (Detail) - Business Banking [member] - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Amortised cost before modification	£ 15	£ 14
Net modification loss	0	1
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	£ 2	£ 3

Credit Risk - Summary of Busi_2

Credit Risk - Summary of Business Banking by Forbearance (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Total value	£ 1,481	£ 1,345
Business Banking [member]
Disclosure of credit risk exposure [line items]
Total value	67	74
Business Banking [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	26	20
Business Banking [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	£ 41	£ 54

Credit Risk - Summary of ECL _4

Credit Risk - Summary of ECL Reconciliation For Other Business Segments (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	£ 807
Ending balance	863	£ 807
Recoveries net of collection costs	(40)	(42)		£ (54)
Income statement charge/(release) for the year	221	153	[1]	203	[1]
Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	143
Ending balance	147	143
Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	307
Ending balance	348	307
Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	357
Ending balance	368	357
Total exposure [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	305,464	300,286
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	43,257	58,382
Other	3,980	5,631
Redemptions and repayments	(42,183)	(58,179)
Assets written off	(363)	(656)
Ending balance	310,155	305,464		300,286
Net movement in the year	4,691	5,178
Expected credit loss [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	807	1,151
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	8
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	160	99
Change in economic scenarios	(19)	(16)
Changes to model	13	(7)
New lending and assets purchased	70	89
Other	183	165
Redemptions and repayments	(102)	(140)
Assets written off	(249)	(534)
Ending balance		807		1,151
Net movement in the year	56	(344)
Charge/(release) to the Income Statement	305	190
Less: ECL relating to derecognised income	(13)
Recoveries net of collection costs	(71)	(36)
Income statement charge/(release) for the year	221	154
Corporate and commercial banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Income statement charge/(release) for the year	37	23		13
Corporate and commercial banking [member] | Total exposure [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	22,835	23,671
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
New lending and assets purchased	5,481	9,399
Other	1,405	1,628
Redemptions and repayments	(7,785)	(11,758)
Assets written off	(81)	(105)
Ending balance	21,855	22,835		23,671
Net movement in the year	(980)	(836)
Corporate and commercial banking [member] | Expected credit loss [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	182	249
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	45	21
Change in economic scenarios	16	2
New lending and assets purchased	11	18
Other	22	24
Redemptions and repayments	(25)	(35)
Assets written off	(41)	(97)
Ending balance	210	182		249
Net movement in the year	28	(67)
Charge/(release) to the Income Statement	69	30
Less: ECL relating to derecognised income	(4)
Recoveries net of collection costs	(28)	(7)
Income statement charge/(release) for the year	37	23
Corporate and investment banking [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Income statement charge/(release) for the year	22	14		174
Corporate and investment banking [member] | Total exposure [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	17,618	20,984
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
Changes to model	0
New lending and assets purchased	54	14,932
Other	541	(1,690)
Redemptions and repayments	(4,757)	(16,309)
Assets written off	0	(299)
Ending balance	13,456	17,618		20,984
Net movement in the year	(4,162)	(3,366)
Corporate and investment banking [member] | Expected credit loss [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	18	258
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	37
Changes to model	0	(10)
New lending and assets purchased	0	7
Other	(2)	76
Redemptions and repayments	(3)	(61)
Assets written off	0	(252)
Ending balance	50	18		258
Net movement in the year	32	(240)
Charge/(release) to the Income Statement	32	12
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(10)	2
Income statement charge/(release) for the year	22	14
Corporate centre [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Income statement charge/(release) for the year	2	(8)		(20)
Corporate centre [member] | Total exposure [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	69,206	63,506
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	0
Other	(836)	5,703
Redemptions and repayments	0
Assets written off	(5)	(3)
Ending balance	68,365	69,206		63,506
Net movement in the year	(841)	5,700
Corporate centre [member] | Expected credit loss [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	13	19
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	2	(1)
Change in economic scenarios	1
Changes to model	0
New lending and assets purchased	0
Other	(2)	(2)
Redemptions and repayments	0
Assets written off	(2)	(3)
Ending balance	12	13		19
Net movement in the year	(1)	(6)
Charge/(release) to the Income Statement	1	(3)
Less: ECL relating to derecognised income	(1)
Recoveries net of collection costs	0	(3)
Income statement charge/(release) for the year	0	(6)
Financial instruments not credit-impaired [member] | Subject to 12-month ECL [member] | Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	290,882	285,133
Transfers from Stage 1 to Stage 2	(4,101)	(4,190)
Transfers from Stage 2 to Stage 1	3,458	3,325
Transfers to Stage 3	(361)	(445)
Transfers from Stage 3	10	17
Transfers of financial instruments	(994)	(1,293)
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	42,415	57,280
Other	3,514	5,540
Redemptions and repayments	(40,380)	(55,778)
Assets written off	(1)
Ending balance	295,436	290,882		285,133
Net movement in the year	4,554	5,749
Financial instruments not credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	12,011	12,110
Transfers from Stage 1 to Stage 2	4,101	4,190
Transfers from Stage 2 to Stage 1	(3,458)	(3,325)
Transfers to Stage 3	(595)	(603)
Transfers from Stage 3	516	443
Transfers of financial instruments	564	705
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	827	1,085
Other	294	(175)
Redemptions and repayments	(1,344)	(1,714)
Assets written off	(1)
Ending balance	12,351	12,011		12,110
Net movement in the year	340	(99)
Financial instruments not credit-impaired [member] | Stage 1 ECL [member] | Subject to 12-month ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	143	176
Transfers from Stage 1 to Stage 2	(11)	(11)
Transfers from Stage 2 to Stage 1	74	68
Transfers to Stage 3	(2)	(8)
Transfers from Stage 3	1	6
Transfers of financial instruments	62	55
Net remeasurement of ECL on stage transfer	(66)	(63)
Change in economic scenarios	5	4
Changes to model	0	(1)
New lending and assets purchased	29	43
Other	6	(27)
Redemptions and repayments	(32)	(44)
Assets written off	0
Ending balance	147	143		176
Net movement in the year	4	(33)
Charge/(release) to the Income Statement	4	(33)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(10)
Income statement charge/(release) for the year	(6)	(33)
Financial instruments not credit-impaired [member] | Stage 2 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	307	284
Transfers from Stage 1 to Stage 2	11	11
Transfers from Stage 2 to Stage 1	(74)	(68)
Transfers to Stage 3	(24)	(23)
Transfers from Stage 3	23	27
Transfers of financial instruments	(64)	(53)
Net remeasurement of ECL on stage transfer	130	83
Change in economic scenarios	(15)	(12)
Changes to model	0	2
New lending and assets purchased	32	33
Other	(14)	(15)
Redemptions and repayments	(28)	(15)
Assets written off	0
Ending balance	348	307		284
Net movement in the year	41	23
Charge/(release) to the Income Statement	41	23
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(15)
Income statement charge/(release) for the year	26	23
Financial instruments not credit-impaired [member] | Corporate and commercial banking [member] | Subject to 12-month ECL [member] | Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	21,333	22,417
Transfers from Stage 1 to Stage 2	(747)	(670)
Transfers from Stage 2 to Stage 1	120	200
Transfers to Stage 3	(33)	(41)
Transfers from Stage 3	0	2
Transfers of financial instruments	(660)	(509)
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
New lending and assets purchased	5,129	9,115
Other	1,293	1,642
Redemptions and repayments	(7,778)	(11,332)
Assets written off	0
Ending balance	19,317	21,333		22,417
Net movement in the year	(2,016)	(1,084)
Financial instruments not credit-impaired [member] | Corporate and commercial banking [member] | Subject to Lifetime ECL [member] | Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	1,226	866
Transfers from Stage 1 to Stage 2	747	670
Transfers from Stage 2 to Stage 1	(120)	(200)
Transfers to Stage 3	(92)	(31)
Transfers from Stage 3	6	2
Transfers of financial instruments	541	441
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
New lending and assets purchased	350	281
Other	63	(37)
Redemptions and repayments	(4)	(325)
Assets written off	0
Ending balance	2,176	1,226		866
Net movement in the year	950	360
Financial instruments not credit-impaired [member] | Corporate and commercial banking [member] | Stage 1 ECL [member] | Subject to 12-month ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	37	43
Transfers from Stage 1 to Stage 2	(3)	(3)
Transfers from Stage 2 to Stage 1	5	8
Transfers to Stage 3	0
Transfers from Stage 3	0	1
Transfers of financial instruments	2	6
Net remeasurement of ECL on stage transfer	(4)	(7)
Change in economic scenarios	7	5
New lending and assets purchased	4	12
Other	4	(5)
Redemptions and repayments	(9)	(17)
Assets written off	0
Ending balance	41	37		43
Net movement in the year	4	(6)
Charge/(release) to the Income Statement	4	(6)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(8)
Income statement charge/(release) for the year	(4)	(6)
Financial instruments not credit-impaired [member] | Corporate and commercial banking [member] | Stage 2 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	32	33
Transfers from Stage 1 to Stage 2	3	3
Transfers from Stage 2 to Stage 1	(5)	(8)
Transfers to Stage 3	(3)	(1)
Transfers from Stage 3	0	1
Transfers of financial instruments	(5)	(5)
Net remeasurement of ECL on stage transfer	17	10
Change in economic scenarios	9	(3)
New lending and assets purchased	6	5
Other	(11)	(4)
Redemptions and repayments	(7)	(4)
Assets written off	0
Ending balance	41	32		33
Net movement in the year	9	(1)
Charge/(release) to the Income Statement	9	(1)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(8)
Income statement charge/(release) for the year	1	(1)
Financial instruments not credit-impaired [member] | Corporate and investment banking [member] | Subject to 12-month ECL [member] | Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	17,458	20,503
Transfers from Stage 1 to Stage 2	(208)	(2)
Transfers from Stage 2 to Stage 1	41
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	(167)
Net remeasurement of ECL on stage transfer	0
Changes to model	0
New lending and assets purchased	54	14,799
Other	376	(1,876)
Redemptions and repayments	(4,676)	(15,966)
Assets written off	0
Ending balance	13,045	17,458		20,503
Net movement in the year	(4,413)	(3,045)
Financial instruments not credit-impaired [member] | Corporate and investment banking [member] | Subject to Lifetime ECL [member] | Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	134	109
Transfers from Stage 1 to Stage 2	208
Transfers from Stage 2 to Stage 1	(41)
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	167
Net remeasurement of ECL on stage transfer	0
Changes to model	0
New lending and assets purchased	0	133
Other	171	83
Redemptions and repayments	(76)	(193)
Assets written off	0
Ending balance	396	134		109
Net movement in the year	262	25
Financial instruments not credit-impaired [member] | Corporate and investment banking [member] | Stage 1 ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	5	16
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
Changes to model	0
New lending and assets purchased	0	4
Other	0	(1)
Redemptions and repayments	0	(14)
Assets written off	0
Ending balance	5	5		16
Net movement in the year	0	(11)
Charge/(release) to the Income Statement	0	(11)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	0
Income statement charge/(release) for the year	0	(11)
Financial instruments not credit-impaired [member] | Corporate and investment banking [member] | Stage 2 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	3
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	37
Changes to model	0
New lending and assets purchased	0	3
Other	(1)	1
Redemptions and repayments	(3)	(1)
Assets written off	0
Ending balance	36	3
Net movement in the year	33	3
Charge/(release) to the Income Statement	33	3
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(8)
Income statement charge/(release) for the year	25	3
Financial instruments not credit-impaired [member] | Corporate centre [member] | Subject to 12-month ECL [member] | Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	69,060	63,236
Transfers from Stage 1 to Stage 2	(15)	(111)
Transfers from Stage 2 to Stage 1	7	133
Transfers to Stage 3	(3)
Transfers from Stage 3	0
Transfers of financial instruments	(11)	22
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	0
Other	(827)	5,802
Redemptions and repayments	0
Assets written off	0
Ending balance	68,222	69,060		63,236
Net movement in the year	(838)	5,824
Financial instruments not credit-impaired [member] | Corporate centre [member] | Subject to Lifetime ECL [member] | Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	131	250
Transfers from Stage 1 to Stage 2	15	111
Transfers from Stage 2 to Stage 1	(7)	(133)
Transfers to Stage 3	(4)	(4)
Transfers from Stage 3	0	3
Transfers of financial instruments	4	(23)
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	0
Other	(9)	(96)
Redemptions and repayments	0
Assets written off	0
Ending balance	126	131		250
Net movement in the year	(5)	(119)
Financial instruments not credit-impaired [member] | Corporate centre [member] | Stage 1 ECL [member] | Subject to 12-month ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	5	7
Transfers from Stage 1 to Stage 2	0	(1)
Transfers from Stage 2 to Stage 1	0	3
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0	2
Net remeasurement of ECL on stage transfer	0	(2)
Change in economic scenarios	1
Changes to model	0
New lending and assets purchased	0
Other	(3)	(2)
Redemptions and repayments	0
Assets written off	0
Ending balance	3	5		7
Net movement in the year	(2)	(2)
Charge/(release) to the Income Statement	(2)	(2)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	0
Income statement charge/(release) for the year	(2)	(2)
Financial instruments not credit-impaired [member] | Corporate centre [member] | Stage 2 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	3	4
Transfers from Stage 1 to Stage 2	0	1
Transfers from Stage 2 to Stage 1	0	(3)
Transfers to Stage 3	0
Transfers from Stage 3	0	1
Transfers of financial instruments	0	(1)
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	0
Other	0
Redemptions and repayments	0
Assets written off	0
Ending balance	3	3		4
Net movement in the year	0	(1)
Charge/(release) to the Income Statement	0	(1)
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	0
Income statement charge/(release) for the year	0	(1)
Financial instruments credit-impaired [member] | Subject to Lifetime ECL [member] | Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	2,571	3,043
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	956	1,048
Transfers from Stage 3	(526)	(460)
Transfers of financial instruments	430	588
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	15	17
Other	172	266
Redemptions and repayments	(459)	(687)
Assets written off	(361)	(656)
Ending balance	2,368	2,571		3,043
Net movement in the year	(203)	(472)
Financial instruments credit-impaired [member] | Stage 3 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	357	691
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	26	31
Transfers from Stage 3	(24)	(33)
Transfers of financial instruments	2	(2)
Net remeasurement of ECL on stage transfer	96	79
Change in economic scenarios	(9)	(8)
Changes to model	13	(8)
New lending and assets purchased	9	13
Other	191	207
Redemptions and repayments	(42)	(81)
Assets written off	(249)	(534)
Ending balance	368	357		691
Net movement in the year	11	(334)
Charge/(release) to the Income Statement	260	200
Less: ECL relating to derecognised income	(13)
Recoveries net of collection costs	(46)	(36)
Income statement charge/(release) for the year	201	164
Financial instruments credit-impaired [member] | Corporate and commercial banking [member] | Subject to Lifetime ECL [member] | Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	276	388
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	125	72
Transfers from Stage 3	(6)	(4)
Transfers of financial instruments	119	68
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
New lending and assets purchased	2	3
Other	49	23
Redemptions and repayments	(3)	(101)
Assets written off	(81)	(105)
Ending balance	362	276		388
Net movement in the year	86	(112)
Financial instruments credit-impaired [member] | Corporate and commercial banking [member] | Stage 3 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	113	173
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	3	1
Transfers from Stage 3	0	(2)
Transfers of financial instruments	3	(1)
Net remeasurement of ECL on stage transfer	32	18
Change in economic scenarios	0
New lending and assets purchased	1	1
Other	29	33
Redemptions and repayments	(9)	(14)
Assets written off	(41)	(97)
Ending balance	128	113		173
Net movement in the year	15	(60)
Charge/(release) to the Income Statement	56	37
Less: ECL relating to derecognised income	(4)
Recoveries net of collection costs	(12)	(7)
Income statement charge/(release) for the year	40	30
Financial instruments credit-impaired [member] | Corporate and investment banking [member] | Subject to Lifetime ECL [member] | Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	26	372
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
Changes to model	0
New lending and assets purchased	0
Other	(6)	103
Redemptions and repayments	(5)	(150)
Assets written off	0	(299)
Ending balance	15	26		372
Net movement in the year	(11)	(346)
Financial instruments credit-impaired [member] | Corporate and investment banking [member] | Stage 3 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	10	242
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0
Transfers of financial instruments	0
Net remeasurement of ECL on stage transfer	0
Changes to model	0	(10)
New lending and assets purchased	0
Other	(1)	76
Redemptions and repayments	0	(46)
Assets written off	0	(252)
Ending balance	9	10		242
Net movement in the year	(1)	(232)
Charge/(release) to the Income Statement	(1)	20
Less: ECL relating to derecognised income	0
Recoveries net of collection costs	(2)	2
Income statement charge/(release) for the year	(3)	22
Financial instruments credit-impaired [member] | Corporate centre [member] | Subject to Lifetime ECL [member] | Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	15	20
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	7	4
Transfers from Stage 3	0	(3)
Transfers of financial instruments	7	1
Net remeasurement of ECL on stage transfer	0
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	0
Other	0	(3)
Redemptions and repayments	0
Assets written off	(5)	(3)
Ending balance	17	15		20
Net movement in the year	2	(5)
Financial instruments credit-impaired [member] | Corporate centre [member] | Stage 3 ECL [member] | Subject to Lifetime ECL [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Beginning balance	5	8
Transfers from Stage 1 to Stage 2	0
Transfers from Stage 2 to Stage 1	0
Transfers to Stage 3	0
Transfers from Stage 3	0	(1)
Transfers of financial instruments	0	(1)
Net remeasurement of ECL on stage transfer	2	1
Change in economic scenarios	0
Changes to model	0
New lending and assets purchased	0
Other	1
Redemptions and repayments	0
Assets written off	(2)	(3)
Ending balance	6	5		£ 8
Net movement in the year	1	(3)
Charge/(release) to the Income Statement	3
Less: ECL relating to derecognised income	(1)
Recoveries net of collection costs	0	(3)
Income statement charge/(release) for the year	£ 2	£ (3)
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Credit Risk - Summary of Other

Credit Risk - Summary of Other Segments Exposures by Credit Rating (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 79,125	£ 87,745
Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	76,029	85,942
Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,701	1,490
Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	395	313
Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8,973	9,078
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	14,565	19,041
Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	12,646	16,064
Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,919	2,977
Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	42,587	45,310
Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,060	4,335
Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,400	34,366
Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	857	769
Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,572	4,835
Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	147
Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	698	858
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	21,973	23,394
Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,469	11,908
Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,591	6,743
Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,913	4,743
Internal grade 9 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	36,682	35,803
Internal grade 9 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	36,682	35,803
Internal grade 9 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 9 [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 9 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	664	492
Internal grade 9 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	281	12
Internal grade 9 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	383	480
Internal grade 9 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,787	34,631
Internal grade 9 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	934	1,377
Internal grade 9 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	32,145	30,467
Internal grade 9 [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	542	356
Internal grade 9 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,166	2,431
Internal grade 9 [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 9 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,231	680
Internal grade 9 [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 9 [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 9 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,231	680
Internal grade 8 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	13,371	17,387
Internal grade 8 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	13,371	17,387
Internal grade 8 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 8 [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 8 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,178	4,197
Internal grade 8 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,356	3,187
Internal grade 8 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	822	1,010
Internal grade 8 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,518	9,291
Internal grade 8 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,036	2,839
Internal grade 8 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,255	3,898
Internal grade 8 [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	246	345
Internal grade 8 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	981	2,062
Internal grade 8 [member] | Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk		147
Internal grade 8 [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 8 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,675	3,899
Internal grade 8 [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	25
Internal grade 8 [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 8 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,650	3,899
Internal grade 7 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,467	7,612
Internal grade 7 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,441	7,612
Internal grade 7 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	26
Internal grade 7 [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 7 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,122	6,967
Internal grade 7 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,419	5,535
Internal grade 7 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	703	1,432
Internal grade 7 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	529	441
Internal grade 7 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	90	76
Internal grade 7 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 7 [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	43	47
Internal grade 7 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	396	318
Internal grade 7 [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 7 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	816	204
Internal grade 7 [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	790	66
Internal grade 7 [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 7 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	26	138
Internal grade 6 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7,093	8,755
Internal grade 6 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,901	8,682
Internal grade 6 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	192	73
Internal grade 6 [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 6 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,569	6,416
Internal grade 6 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,558	6,361
Internal grade 6 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11	55
Internal grade 6 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	184	292
Internal grade 6 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	43
Internal grade 6 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	1
Internal grade 6 [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	25	21
Internal grade 6 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	29	24
Internal grade 6 [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	130	203
Internal grade 6 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,340	2,047
Internal grade 6 [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,914	1,745
Internal grade 6 [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	426	302
Internal grade 6 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 5 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8,992	11,236
Internal grade 5 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8,263	10,788
Internal grade 5 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	729	448
Internal grade 5 [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 5 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	842	888
Internal grade 5 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	842	888
Internal grade 5 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 5 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	28	35
Internal grade 5 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 5 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 5 [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1
Internal grade 5 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 5 [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	27	35
Internal grade 5 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8,122	10,313
Internal grade 5 [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,414	5,749
Internal grade 5 [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,708	4,564
Internal grade 5 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 4 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,886	5,414
Internal grade 4 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,586	4,772
Internal grade 4 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,300	635
Internal grade 4 [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	7
Internal grade 4 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	75	3
Internal grade 4 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	75	3
Internal grade 4 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 4 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	98	137
Internal grade 4 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 4 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 4 [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 4 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 4 [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	98	137
Internal grade 4 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,713	5,274
Internal grade 4 [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,348	3,426
Internal grade 4 [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,363	1,846
Internal grade 4 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2	2
Internal grade 3 to 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,299	1,145
Internal grade 3 to 1 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	465	521
Internal grade 3 to 1 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	439	318
Internal grade 3 to 1 [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	395	306
Internal grade 3 to 1 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	115	78
Internal grade 3 to 1 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	115	78
Internal grade 3 to 1 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 3 to 1 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	140	126
Internal grade 3 to 1 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 3 to 1 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 3 to 1 [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 3 to 1 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Internal grade 3 to 1 [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	140	126
Internal grade 3 to 1 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,044	941
Internal grade 3 to 1 [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	946	886
Internal grade 3 to 1 [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	94	31
Internal grade 3 to 1 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4	24
Other [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	335	393
Other [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	320	377
Other [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	15	16
Other [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Other [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Other [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Other [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Other [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	303	357
Other [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Other [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Other [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Other [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Other [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	303	357
Other [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	32	36
Other [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	32	£ 36
Other [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Other [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 0

Credit Risk - Summary of Othe_2

Credit Risk - Summary of Other Segments Exposures by Geographical Distribution (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 79,125	£ 87,745
Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8,973	9,078
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	21,973	23,394
Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,469	11,908
Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,591	6,743
Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,913	4,743
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	14,565	19,041
Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	12,646	16,064
Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,919	2,977
Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	42,587	45,310
Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,060	4,335
Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,400	34,366
Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	857	769
Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,572	4,835
Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	147
Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	698	858
UK [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	21,888	23,319
UK [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,384	11,833
UK [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,591	6,743
UK [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,913	4,743
UK [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,269	13,950
UK [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	10,665	13,080
UK [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	604	870
UK [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,673	34,153
UK [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,060	4,335
UK [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	27,987	26,154
UK [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	329	346
UK [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,710	2,574
UK [member] | Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
UK [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	587	744
Europe [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	84	74
Europe [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	84	74
Europe [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Europe [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Europe [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,763	4,272
Europe [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,922	2,752
Europe [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	841	1,520
Europe [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,695	3,299
Europe [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Europe [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,549	1,802
Europe [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	335	358
Europe [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	811	1,139
Europe [member] | Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Europe [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
US [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
US [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
US [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
US [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
US [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	171	287
US [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2	124
US [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	169	163
US [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,013	1,118
US [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
US [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	856	960
US [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	157	11
US [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
US [member] | Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	147
US [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Rest Of World [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1	1
Rest Of World [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1	1
Rest Of World [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Rest Of World [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Rest Of World [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	362	532
Rest Of World [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	57	108
Rest Of World [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	305	424
Rest Of World [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,206	6,740
Rest Of World [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Rest Of World [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,008	5,450
Rest Of World [member] | Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	36	54
Rest Of World [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	51	1,122
Rest Of World [member] | Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Rest Of World [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 111	£ 114

Credit Risk - Summary of Deta_2

Credit Risk - Summary of Detailed Information about Gross and Net Credit Exposure (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Statement [Line items]
Gross exposure	£ 310,155	£ 305,464
Stage 3 [member]
Statement [Line items]
Gross exposure	2,368	2,571
Stage 3 [member] | Corporate & Commercial Banking [member]
Statement [Line items]
Gross exposure	362	276
Collateral	107	69
Net exposure	255	207
Stage 3 [member] | Corporate & Commercial Banking [member] | SME and Mid Corporate [member]
Statement [Line items]
Gross exposure	279	253
Collateral	51	55
Net exposure	228	198
Stage 3 [member] | Corporate & Commercial Banking [member] | Commercial Real Estate [member]
Statement [Line items]
Gross exposure	83	23
Collateral	56	14
Net exposure	27	9
Stage 3 [member] | Corporate & Investment Banking [member]
Statement [Line items]
Gross exposure	15	26
Collateral	0
Net exposure	15	26
Stage 3 [member] | Corporate & Investment Banking [member] | Large Corporate [member]
Statement [Line items]
Gross exposure	15	26
Collateral	0
Net exposure	15	26
Stage 3 [member] | Corporate Centre [Member]
Statement [Line items]
Gross exposure	17	16
Collateral	11	9
Net exposure	6	6
Stage 3 [member] | Corporate Centre [Member] | Legacy Portfolios in run–off [member]
Statement [Line items]
Gross exposure	17	16
Collateral	11	9
Net exposure	£ 6	£ 6

Credit Risk - Summary of Othe_3

Credit Risk - Summary of Other Segments Exposures by Credit Performance (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 79,125	£ 87,745
Observed impairment loss allowances	272	213
Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8,973	9,078
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	21,973	23,394
Observed impairment loss allowances	210	182
Corporate and commercial banking [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	20,025	21,402
Corporate and commercial banking [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,235	1,336
Corporate and commercial banking [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	351	380
Corporate and commercial banking [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	362	276
Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,469	11,908
Observed impairment loss allowances	164	160
Corporate and commercial banking [member] | SME and Mid Corporate [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	9,864	10,350
Corporate and commercial banking [member] | SME and Mid Corporate [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,056	972
Corporate and commercial banking [member] | SME and Mid Corporate [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	270	333
Corporate and commercial banking [member] | SME and Mid Corporate [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	279	253
Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,591	6,743
Observed impairment loss allowances	46	22
Corporate and commercial banking [member] | Commercial Real Estate [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,338	6,426
Corporate and commercial banking [member] | Commercial Real Estate [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	89	247
Corporate and commercial banking [member] | Commercial Real Estate [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	81	47
Corporate and commercial banking [member] | Commercial Real Estate [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	83	23
Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,913	4,743
Observed impairment loss allowances	0
Corporate and commercial banking [member] | Social Housing [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,823	4,626
Corporate and commercial banking [member] | Social Housing [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	90	117
Corporate and commercial banking [member] | Social Housing [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate and commercial banking [member] | Social Housing [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	14,565	19,041
Observed impairment loss allowances	50	18
Corporate and investment banking [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	13,742	18,281
Corporate and investment banking [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	252	548
Corporate and investment banking [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	556	186
Corporate and investment banking [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	15	26
Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	12,646	16,064
Observed impairment loss allowances	50	18
Corporate and investment banking [member] | Large Corporate [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,833	15,304
Corporate and investment banking [member] | Large Corporate [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	252	548
Corporate and investment banking [member] | Large Corporate [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	546	186
Corporate and investment banking [member] | Large Corporate [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	15	26
Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,919	2,977
Corporate and investment banking [member] | Financial Institutions [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,909	2,977
Corporate and investment banking [member] | Financial Institutions [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	10
Corporate and investment banking [member] | Financial Institutions [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate and investment banking [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Observed impairment loss allowances	0
Corporate and investment banking [member] | Derivative Financial Instruments [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	42,587	45,310
Observed impairment loss allowances	12	13
Corporate centre [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	42,529	45,239
Corporate centre [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	30	48
Corporate centre [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11	7
Corporate centre [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	17	16
Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,060	4,335
Observed impairment loss allowances	0
Corporate centre [member] | Social Housing [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,047	4,313
Corporate centre [member] | Social Housing [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	13	22
Corporate centre [member] | Social Housing [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Social Housing [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,400	34,366
Observed impairment loss allowances	0
Corporate centre [member] | Sovereign And Supranational [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,400	34,366
Corporate centre [member] | Sovereign And Supranational [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Sovereign And Supranational [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Sovereign And Supranational [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	857	769
Observed impairment loss allowances	0
Corporate centre [member] | Financial Institutions [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	854	769
Corporate centre [member] | Financial Institutions [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Financial Institutions [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3
Corporate centre [member] | Financial Institutions [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,572	4,835
Observed impairment loss allowances	0
Corporate centre [member] | Structured Products [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,572	4,835
Corporate centre [member] | Structured Products [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Structured Products [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Structured Products [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	147
Observed impairment loss allowances	0
Corporate centre [member] | Derivative Financial Instruments [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	147
Corporate centre [member] | Derivative Financial Instruments [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Derivative Financial Instruments [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Derivative Financial Instruments [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0
Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	698	858
Observed impairment loss allowances	12	13
Corporate centre [member] | Legacy Portfolios in Run-Off [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	656	809
Corporate centre [member] | Legacy Portfolios in Run-Off [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	17	26
Corporate centre [member] | Legacy Portfolios in Run-Off [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8	7
Corporate centre [member] | Legacy Portfolios in Run-Off [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 17	£ 16

Credit Risk - Summary of Modi_4

Credit Risk - Summary of Modification of Loan Terms (Other Segments Exposures) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Amortised cost before modification	£ 135	£ 104
Net modification loss	8	10
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	34	8
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Amortised cost before modification	0
Net modification loss	0
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	0	7
Corporate centre [member]
Disclosure of credit risk exposure [line items]
Amortised cost before modification	10	2
Net modification loss	1
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	£ 2	£ 4

Credit Risk - Summary of Othe_4

Credit Risk - Summary of Other Segments by Forbearance Applied (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Forbearance [line items]
- Term extension	£ 429	£ 256
- Interest-only	439	502
- Other payment rescheduling	602	587
Loans forbearance	1,481	1,345
Corporate and commercial banking [member]
Disclosure Of Forbearance [line items]
- Term extension	60	67
- Interest-only	110	112
- Other payment rescheduling	192	163
Loans forbearance	£ 362	£ 342
Proportion of portfolio	1.60%	1.50%
Corporate and commercial banking [member] | Stage 1 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	£ 57	£ 43
Corporate and commercial banking [member] | Stage 2 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	75	78
Corporate and commercial banking [member] | Stage 3 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	230	221
Corporate and investment banking [member]
Disclosure Of Forbearance [line items]
- Term extension	42	42
- Interest-only	0
- Other payment rescheduling	15	26
Loans forbearance	£ 57	£ 68
Proportion of portfolio	0.40%	0.40%
Corporate and investment banking [member] | Stage 1 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	£ 42
Corporate and investment banking [member] | Stage 2 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	0	£ 42
Corporate and investment banking [member] | Stage 3 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	15	26
Corporate centre [member]
Disclosure Of Forbearance [line items]
- Term extension	0
- Interest-only	13	8
- Other payment rescheduling	9	10
Loans forbearance	£ 22	£ 18
Proportion of portfolio	3.20%	2.10%
Corporate centre [member] | Stage 1 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	£ 1	£ 3
Corporate centre [member] | Stage 2 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	11	8
Corporate centre [member] | Stage 3 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	£ 10	£ 7

Credit Risk - Summary of Commer

Credit Risk - Summary of Commercial Real Estate by Credit Performance (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Retail Banking Segment [member]
Disclosure of performance obligations [line items]
Consumer loans	£ 241	£ 257
Commercial Real Estate [member]
Disclosure of performance obligations [line items]
Consumer loans	£ 5,109	£ 6,202

Credit Risk - Summary of Comm_2

Credit Risk - Summary of Commercial Real Estate by Credit Performance (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of performance obligations [line items]
Customer loans	£ 207,287	£ 201,289
Commercial Real Estate [member]
Disclosure of performance obligations [line items]
Customer loans	5,350	6,459
NPLs	£ 89	£ 29
NPL ratio	1.55%	0.41%
Gross write-offs	£ 8	£ 23
Impairment loss allowances	£ 49	£ 26

Credit Risk - Summary of Comm_3

Credit Risk - Summary of Commercial Real Estate by Loan to Value (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 207,287	£ 201,289
Commercial Real Estate [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	5,350	6,459
Expected credit loss	49	26
Commercial Real Estate [member] | Development Loans [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	5	61
Expected credit loss	0	1
Commercial Real Estate [member] | Less Than Or Equal To Fifty Percentage [Member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	3,133	3,663
Expected credit loss	17	5
Commercial Real Estate [member] | Greater than fifty percentage to seventy percentage [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	1,557	2,039
Expected credit loss	24	4
Commercial Real Estate [member] | Greater Than 70-100% [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	29	47
Expected credit loss	1	2
Commercial Real Estate [member] | Greater Than 100% [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	9	18
Expected credit loss	1	7
Commercial Real Estate [member] | Standardised Portfolio [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	617	631
Expected credit loss	6	7
Commercial Real Estate [member] | Total With Collateral [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	5,345	6,398
Expected credit loss	49	25
Commercial Real Estate [member] | Stage 3 [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	89	29
Expected credit loss	29	10
Commercial Real Estate [member] | Stage 3 [member] | Development Loans [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	0
Expected credit loss	0
Commercial Real Estate [member] | Stage 3 [member] | Less Than Or Equal To Fifty Percentage [Member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	15	3
Expected credit loss	8
Commercial Real Estate [member] | Stage 3 [member] | Greater than fifty percentage to seventy percentage [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	63	4
Expected credit loss	17
Commercial Real Estate [member] | Stage 3 [member] | Greater Than 70-100% [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	1	1
Expected credit loss	0	1
Commercial Real Estate [member] | Stage 3 [member] | Greater Than 100% [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	3	16
Expected credit loss	1	7
Commercial Real Estate [member] | Stage 3 [member] | Standardised Portfolio [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	7	5
Expected credit loss	3	2
Commercial Real Estate [member] | Stage 3 [member] | Total With Collateral [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	89	29
Expected credit loss	£ 29	£ 10

Credit Risk - Summary of Comm_4

Credit Risk - Summary of Commercial Real Estate by Sector (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 207,287	£ 201,289
Commercial Real Estate [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 5,350	£ 6,459
Percentage of total CRE Portfolio	100.00%	100.00%
Commercial Real Estate [member] | Office [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 1,262	£ 1,556
Percentage of total CRE Portfolio	24.00%	24.00%
Commercial Real Estate [member] | Retail [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 850	£ 1,004
Percentage of total CRE Portfolio	16.00%	16.00%
Commercial Real Estate [member] | Industrial [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 699	£ 888
Percentage of total CRE Portfolio	13.00%	14.00%
Commercial Real Estate [member] | Residential [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 757	£ 927
Percentage of total CRE Portfolio	14.00%	14.00%
Commercial Real Estate [member] | Mixed Use [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 759	£ 932
Percentage of total CRE Portfolio	14.00%	14.00%
Commercial Real Estate [member] | Student Accommodation [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 85	£ 123
Percentage of total CRE Portfolio	2.00%	2.00%
Commercial Real Estate [member] | Hotels and Leisure [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 268	£ 309
Percentage of total CRE Portfolio	5.00%	5.00%
Commercial Real Estate [member] | Other [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 53	£ 89
Percentage of total CRE Portfolio	1.00%	1.00%
Commercial Real Estate [member] | Standardised Portfolio [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 617	£ 631
Percentage of total CRE Portfolio	11.00%	10.00%

Credit Risk - Summary of Social

Credit Risk - Summary of Social Housing Exposure (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Social Housing Exposure [line items]
Drawn	£ 207,287	£ 201,289
Total	79,125	87,745
Loss allowance	785	751
Corporate and commercial banking [member]
Disclosure Of Social Housing Exposure [line items]
Total	21,973	23,394
Corporate centre [member]
Disclosure Of Social Housing Exposure [line items]
Total	42,587	45,310
Social Housing [member]
Disclosure Of Social Housing Exposure [line items]
Drawn	6,379	6,624
Total	8,973	9,078
Loss allowance	0
Social Housing [member] | Corporate and commercial banking [member]
Disclosure Of Social Housing Exposure [line items]
Drawn	2,794	2,844
Total	4,913	4,743
Loss allowance	0
Social Housing [member] | Corporate centre [member]
Disclosure Of Social Housing Exposure [line items]
Drawn	3,585	3,780
Total	4,060	£ 4,335
Loss allowance	£ 0

Market Risk - Summary of NIM an

Market Risk - Summary of NIM and EVE Sensitivity of Interest Rate Risk (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
+50bps [member]
Disclosure Of Sensitivity Limit Of Risk [line items]
NIM sensitivity	£ 99	£ 207
EVE sensitivity (unaudited)	10	162
-50bps [member]
Disclosure Of Sensitivity Limit Of Risk [line items]
NIM sensitivity	56	(23)
EVE sensitivity (unaudited)	£ (88)	£ (124)

Market risk - Disclosure Of Det

Market risk - Disclosure Of Detailed Information About Basis Risk Under EAR Approach Explanatory (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Statement [Line Items]
Basis risk EaR	£ 0.3	£ 0.4
Santander UK plc | EaR Approach
Statement [Line Items]
Basis risk EaR	£ 18	£ 25

Market Risk - Summary of Intern

Market Risk - Summary of Internal VaR for Exposure to Main Classes of Risk (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Market Risk [line items]
Risk exposure	£ 0.3	£ 0.4
Interest Rate Risks [member]
Market Risk [line items]
Risk exposure	0.2	0.5
Equity Risks [member]
Market Risk [line items]
Risk exposure	0
Currency Risk [member]
Market Risk [line items]
Risk exposure	0.4	0.1
Diversification Offsets [member]
Market Risk [line items]
Risk exposure	(0.3)	(0.2)
Weighted average [member]
Market Risk [line items]
Risk exposure	0.3	1.4
Weighted average [member] | Interest Rate Risks [member]
Market Risk [line items]
Risk exposure	0.4	1.4
Weighted average [member] | Equity Risks [member]
Market Risk [line items]
Risk exposure	0	0.2
Weighted average [member] | Currency Risk [member]
Market Risk [line items]
Risk exposure	0.2	0.3
Weighted average [member] | Diversification Offsets [member]
Market Risk [line items]
Risk exposure	(0.3)	(0.5)
Top of Range [member]
Market Risk [line items]
Risk exposure	0.6	3.8
Top of Range [member] | Interest Rate Risks [member]
Market Risk [line items]
Risk exposure	0.6	3.9
Top of Range [member] | Equity Risks [member]
Market Risk [line items]
Risk exposure	0.1	0.6
Top of Range [member] | Currency Risk [member]
Market Risk [line items]
Risk exposure	0.4	0.9
Top of Range [member] | Diversification Offsets [member]
Market Risk [line items]
Risk exposure	(0.5)
Bottom of Range [member]
Market Risk [line items]
Risk exposure	0.2	0.3
Bottom of Range [member] | Interest Rate Risks [member]
Market Risk [line items]
Risk exposure	0.1	£ 0.2
Bottom of Range [member] | Equity Risks [member]
Market Risk [line items]
Risk exposure	0
Bottom of Range [member] | Currency Risk [member]
Market Risk [line items]
Risk exposure	0.1
Bottom of Range [member] | Diversification Offsets [member]
Market Risk [line items]
Risk exposure	£ 0

Liquidity Risk - Summary of Rec

Liquidity Risk - Summary of Reconciliation of Wholesale Funding to Balance Sheet (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Deposits by banks	£ 14,353	£ 17,221
Deposits by customers	181,883	178,090
Repurchase agreements–non trading	18,286	10,910
Financial liabilities at fair value	1,713	6,286
Debt securities in issue	41,129	46,692
Subordinated liabilities	3,528	3,601
Liquidity risk [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	90,300	96,400
Deposits by banks	14,400	17,200
Deposits by customers	9,100	9,700
Repurchase agreements–non trading	18,300	10,900
Financial liabilities at fair value	1,700	6,300
Debt securities in issue	41,100	46,700
Subordinated liabilities	3,500	3,600
Other equity and non-controlling interests	2,200	2,000
Liquidity risk [member] | Repurchase Agreement [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	16,900	10,800
Deposits by banks	0
Deposits by customers	0
Repurchase agreements–non trading	16,900	8,700
Financial liabilities at fair value	0	2,100
Debt securities in issue	0
Subordinated liabilities	0
Other equity and non-controlling interests	0
Liquidity risk [member] | Foreign Exchange And Hedge Accounting [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	2,500	4,200
Deposits by banks	0
Deposits by customers	400	500
Repurchase agreements–non trading	0
Financial liabilities at fair value	0
Debt securities in issue	1,600	3,100
Subordinated liabilities	500	600
Other equity and non-controlling interests	0
Liquidity risk [member] | Other Borrowing [Member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	3,500	8,600
Deposits by banks	3,300	5,400
Deposits by customers	0
Repurchase agreements–non trading	0
Financial liabilities at fair value	200	3,200
Debt securities in issue	0
Subordinated liabilities	0
Other equity and non-controlling interests	0
Liquidity risk [member] | Wholesale Funding [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	67,400	72,800
Deposits by banks	11,100	11,800
Deposits by customers	8,700	9,200
Repurchase agreements–non trading	1,400	2,200
Financial liabilities at fair value	1,500	1,000
Debt securities in issue	39,500	43,600
Subordinated liabilities	3,000	3,000
Other equity and non-controlling interests	2,200	2,000
Liquidity risk [member] | Wholesale Funding [member] | Deposits [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	300	1,000
Deposits by banks	300	1,000
Deposits by customers	0
Repurchase agreements–non trading	0
Financial liabilities at fair value	0
Debt securities in issue	0
Subordinated liabilities	0
Other equity and non-controlling interests	0
Liquidity risk [member] | Wholesale Funding [member] | Certificates of Deposit and Commercial Paper [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	5,800	6,400
Deposits by banks	0
Deposits by customers	0
Repurchase agreements–non trading	0
Financial liabilities at fair value	0
Debt securities in issue	5,800	6,400
Subordinated liabilities	0
Other equity and non-controlling interests	0
Liquidity risk [member] | Wholesale Funding [member] | Senior Unsecured - Public Benchmark [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	18,800	21,200
Deposits by banks	0
Deposits by customers	8,600	8,600
Repurchase agreements–non trading	0
Financial liabilities at fair value	0
Debt securities in issue	10,200	12,600
Subordinated liabilities	0
Other equity and non-controlling interests	0
Liquidity risk [member] | Wholesale Funding [member] | Senior Unsecured - Privately Placed [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	2,700	4,000
Deposits by banks	0
Deposits by customers	100	100
Repurchase agreements–non trading	0
Financial liabilities at fair value	1,000	1,000
Debt securities in issue	1,600	2,900
Subordinated liabilities	0
Other equity and non-controlling interests	0
Liquidity risk [member] | Wholesale Funding [member] | Covered Bonds [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	18,200	16,600
Deposits by banks	0
Deposits by customers	0
Repurchase agreements–non trading	0
Financial liabilities at fair value	0
Debt securities in issue	18,200	16,600
Subordinated liabilities	0
Other equity and non-controlling interests	0
Liquidity risk [member] | Wholesale Funding [member] | Securitisation and Structured Issuance [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	5,600	7,800
Deposits by banks	0
Deposits by customers	0	500
Repurchase agreements–non trading	1,400	2,200
Financial liabilities at fair value	500
Debt securities in issue	3,700	5,100
Subordinated liabilities	0
Other equity and non-controlling interests	0
Liquidity risk [member] | Wholesale Funding [member] | Term Funding Scheme [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	10,800	10,800
Deposits by banks	10,800	10,800
Deposits by customers	0
Repurchase agreements–non trading	0
Financial liabilities at fair value	0
Debt securities in issue	0
Subordinated liabilities	0
Other equity and non-controlling interests	0
Liquidity risk [member] | Wholesale Funding [member] | Subordinated Liabilities and Equity [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	5,200	5,000
Deposits by banks	0
Deposits by customers	0
Repurchase agreements–non trading	0
Financial liabilities at fair value	0
Debt securities in issue	0
Subordinated liabilities	3,000	3,000
Other equity and non-controlling interests	£ 2,200	£ 2,000

Liquidity Risk - Summary of R_2

Liquidity Risk - Summary of Reconciliation of Wholesale Funding to Balance Sheet (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Deposit from customers	£ 181,883	£ 178,090
Other equity and non-controlling interests	2,191	1,991
Liquidity risk [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Deposit from customers	9,100	9,700
Fixed/Floating Rate Non-Cumulative Callable Preference Shares [member] | Liquidity risk [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Other equity and non-controlling interests	0	14
Step-Up Callable Perpetual Reserve Capital Instruments [member] | Liquidity risk [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Other equity and non-controlling interests	235	235
Perpetual Capital Securities [member] | Liquidity risk [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Other equity and non-controlling interests	£ 1,956	£ 1,756

Liquidity Risk - Summary of Sou

Liquidity Risk - Summary of Sources of Wholesale Funding by Maturity (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	£ 14,353	£ 17,221
Subordinated liabilities	3,528	3,601
Wholesale fund amount	67,400	72,800
Of which: - secured	34,600	35,200
Of which: - unsecured	32,800	37,600
Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	8,500
Senior unsecured - privately placed	100
Subordinated liabilities and equity (incl. AT1)	3,000
Wholesale fund amount	11,600
Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	300
Certificates of deposit and commercial paper	5,800
Senior unsecured - public benchmark	10,300
Senior unsecured - privately placed	2,600
Covered bonds	18,200
Subordinated liabilities and equity (incl. AT1)	4,000
Term Funding Scheme	10,800
Subordinated liabilities	2,200
Wholesale fund amount	54,200
Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	1,600
Wholesale fund amount	67,400
Not Later Than One Month [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	1,700	3,100
Of which: - secured	200	800
Of which: - unsecured	1,500	2,300
Not Later Than One Month [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	0
Senior unsecured - privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	0
Not Later Than One Month [member] | Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	100
Certificates of deposit and commercial paper	600
Senior unsecured - public benchmark	800
Senior unsecured - privately placed	0
Covered bonds	0
Subordinated liabilities and equity (incl. AT1)	200
Term Funding Scheme	0
Subordinated liabilities	0
Wholesale fund amount	1,700
Not Later Than One Month [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	0
Wholesale fund amount	1,700
Greater Than 1 and Less Than 3 Months [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	5,500	6,800
Of which: - secured	100	700
Of which: - unsecured	5,400	6,100
Greater Than 1 and Less Than 3 Months [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	0
Senior unsecured - privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	0
Greater Than 1 and Less Than 3 Months [member] | Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	0
Certificates of deposit and commercial paper	3,100
Senior unsecured - public benchmark	1,400
Senior unsecured - privately placed	900
Covered bonds	0
Subordinated liabilities and equity (incl. AT1)	0
Term Funding Scheme	0
Subordinated liabilities	0
Wholesale fund amount	5,400
Greater Than 1 and Less Than 3 Months [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	100
Wholesale fund amount	5,500
Greater Than 3 and Less Than 6 Months [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	4,700	3,000
Of which: - secured	2,700	700
Of which: - unsecured	2,000	2,300
Greater Than 3 and Less Than 6 Months [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	0
Senior unsecured - privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	0
Greater Than 3 and Less Than 6 Months [member] | Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	0
Certificates of deposit and commercial paper	2,000
Senior unsecured - public benchmark	0
Senior unsecured - privately placed	0
Covered bonds	1,800
Subordinated liabilities and equity (incl. AT1)	800
Term Funding Scheme	0
Subordinated liabilities	0
Wholesale fund amount	4,600
Greater Than 3 and Less Than 6 Months [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	100
Wholesale fund amount	4,700
Greater Than 6 and Less Than 9 Months [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	2,100	2,700
Of which: - secured	300	1,700
Of which: - unsecured	1,800	1,000
Greater Than 6 and Less Than 9 Months [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	0
Senior unsecured - privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	0
Greater Than 6 and Less Than 9 Months [member] | Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	200
Certificates of deposit and commercial paper	100
Senior unsecured - public benchmark	600
Senior unsecured - privately placed	900
Covered bonds	0
Subordinated liabilities and equity (incl. AT1)	200
Term Funding Scheme	0
Subordinated liabilities	0
Wholesale fund amount	2,000
Greater Than 6 and Less Than 9 Months [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	100
Wholesale fund amount	2,100
Greater Than 9 and Less Than 12 Months [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	8,500	900
Of which: - secured	5,800	500
Of which: - unsecured	2,700	400
Greater Than 9 and Less Than 12 Months [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	800
Senior unsecured - privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	800
Greater Than 9 and Less Than 12 Months [member] | Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	0
Certificates of deposit and commercial paper	0
Senior unsecured - public benchmark	1,900
Senior unsecured - privately placed	0
Covered bonds	1,000
Subordinated liabilities and equity (incl. AT1)	200
Term Funding Scheme	4,500
Subordinated liabilities	0
Wholesale fund amount	7,600
Greater Than 9 and Less Than 12 Months [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	100
Wholesale fund amount	8,500
Not Later Than 1 Year [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	22,500	16,500
Of which: - secured	9,100	4,400
Of which: - unsecured	13,400	12,100
Not Later Than 1 Year [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	800
Senior unsecured - privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	800
Not Later Than 1 Year [member] | Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	300
Certificates of deposit and commercial paper	5,800
Senior unsecured - public benchmark	4,700
Senior unsecured - privately placed	1,800
Covered bonds	2,800
Subordinated liabilities and equity (incl. AT1)	1,400
Term Funding Scheme	4,500
Subordinated liabilities	0
Wholesale fund amount	21,300
Not Later Than 1 Year [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	400
Wholesale fund amount	22,500
Later Than 1 Year and Not Later Than 2 Years [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	16,600	15,900
Of which: - secured	11,500	8,500
Of which: - unsecured	5,100	7,400
Later Than 1 Year and Not Later Than 2 Years [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	1,800
Senior unsecured - privately placed	0
Subordinated liabilities and equity (incl. AT1)	0
Wholesale fund amount	1,800
Later Than 1 Year and Not Later Than 2 Years [member] | Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	0
Certificates of deposit and commercial paper	0
Senior unsecured - public benchmark	2,900
Senior unsecured - privately placed	400
Covered bonds	5,600
Subordinated liabilities and equity (incl. AT1)	1,300
Term Funding Scheme	4,000
Subordinated liabilities	0
Wholesale fund amount	14,200
Later Than 1 Year and Not Later Than 2 Years [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	600
Wholesale fund amount	16,600
Later Than 2 Year and Not Later Than 5 Years [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	18,500	30,100
Of which: - secured	10,400	18,300
Of which: - unsecured	8,100	11,800
Later Than 2 Year and Not Later Than 5 Years [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	4,200
Senior unsecured - privately placed	0
Subordinated liabilities and equity (incl. AT1)	1,000
Wholesale fund amount	5,200
Later Than 2 Year and Not Later Than 5 Years [member] | Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	0
Certificates of deposit and commercial paper	0
Senior unsecured - public benchmark	1,900
Senior unsecured - privately placed	100
Covered bonds	6,200
Subordinated liabilities and equity (incl. AT1)	1,300
Term Funding Scheme	2,300
Subordinated liabilities	900
Wholesale fund amount	12,700
Later Than 2 Year and Not Later Than 5 Years [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	600
Wholesale fund amount	18,500
Later Than Five Years [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	9,800	10,300
Of which: - secured	3,600	4,000
Of which: - unsecured	6,200	£ 6,300
Later Than Five Years [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	1,700
Senior unsecured - privately placed	100
Subordinated liabilities and equity (incl. AT1)	2,000
Wholesale fund amount	3,800
Later Than Five Years [member] | Other Santander UK plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	0
Certificates of deposit and commercial paper	0
Senior unsecured - public benchmark	800
Senior unsecured - privately placed	300
Covered bonds	3,600
Subordinated liabilities and equity (incl. AT1)	0
Term Funding Scheme	0
Subordinated liabilities	1,300
Wholesale fund amount	6,000
Later Than Five Years [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	0
Wholesale fund amount	£ 9,800

Liquidity Risk - Summary of S_2

Liquidity Risk - Summary of Sources of Wholesale Funding by Maturity (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019
Disclosure of Maturity of Wholesale Funding [Line Items]
Unsecured Debt Issued	94.00%

Liquidity Risk - Summary of Who

Liquidity Risk - Summary of Wholesale Funding by Currency (Detail) - Liquidity risk [member]	Dec. 31, 2019	Dec. 31, 2018
United Kingdom, Pounds [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	25.00%	23.00%
United Kingdom, Pounds [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	11.00%	11.00%
United Kingdom, Pounds [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
United Kingdom, Pounds [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Subordinated Liabilities and Equity [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	67.00%	64.00%
United Kingdom, Pounds [member] | Other Santander UK plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	54.00%	48.00%
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	14.00%	11.00%
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	21.00%	13.00%
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Deposits by banks [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	3.00%	3.00%
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Certificates of Deposit and Commercial Paper [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	45.00%	48.00%
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Covered Bonds [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	54.00%	50.00%
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	72.00%	61.00%
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Term Funding Scheme [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	100.00%	100.00%
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Subordinated liabilities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	49.00%	49.00%
United Kingdom, Pounds [member] | Other Group Entities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	50.00%	46.00%
United Kingdom, Pounds [member] | Other Group Entities [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	95.00%	89.00%
United States of America, Dollars [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	56.00%	57.00%
United States of America, Dollars [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	65.00%	65.00%
United States of America, Dollars [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
United States of America, Dollars [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Subordinated Liabilities and Equity [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	33.00%	36.00%
United States of America, Dollars [member] | Other Santander UK plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	22.00%	25.00%
United States of America, Dollars [member] | Other Santander UK plc [member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	54.00%	56.00%
United States of America, Dollars [member] | Other Santander UK plc [member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	15.00%	12.00%
United States of America, Dollars [member] | Other Santander UK plc [member] | Deposits by banks [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	97.00%	97.00%
United States of America, Dollars [member] | Other Santander UK plc [member] | Certificates of Deposit and Commercial Paper [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	54.00%	52.00%
United States of America, Dollars [member] | Other Santander UK plc [member] | Covered Bonds [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
United States of America, Dollars [member] | Other Santander UK plc [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	28.00%	35.00%
United States of America, Dollars [member] | Other Santander UK plc [member] | Term Funding Scheme [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
United States of America, Dollars [member] | Other Santander UK plc [member] | Subordinated liabilities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	51.00%	51.00%
United States of America, Dollars [member] | Other Group Entities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	27.00%	30.00%
United States of America, Dollars [member] | Other Group Entities [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	5.00%	11.00%
Euro Member Countries, Euro [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	16.00%	17.00%
Euro Member Countries, Euro [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	22.00%	22.00%
Euro Member Countries, Euro [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Euro Member Countries, Euro [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Subordinated Liabilities and Equity [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Euro Member Countries, Euro [member] | Other Santander UK plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	24.00%	26.00%
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	32.00%	33.00%
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	59.00%	72.00%
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Deposits by banks [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Certificates of Deposit and Commercial Paper [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	1.00%
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Covered Bonds [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	45.00%	49.00%
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%	4.00%
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Term Funding Scheme [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Subordinated liabilities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Euro Member Countries, Euro [member] | Other Group Entities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	22.00%	24.00%
Euro Member Countries, Euro [member] | Other Group Entities [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Other [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	3.00%	3.00%
Other [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	2.00%	2.00%
Other [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	100.00%	100.00%
Other [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Subordinated Liabilities and Equity [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Other [member] | Other Santander UK plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%	1.00%
Other [member] | Other Santander UK plc [member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Other [member] | Other Santander UK plc [member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	5.00%	3.00%
Other [member] | Other Santander UK plc [member] | Deposits by banks [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Other [member] | Other Santander UK plc [member] | Certificates of Deposit and Commercial Paper [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Other [member] | Other Santander UK plc [member] | Covered Bonds [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	1.00%	1.00%
Other [member] | Other Santander UK plc [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Other [member] | Other Santander UK plc [member] | Term Funding Scheme [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Other [member] | Other Santander UK plc [member] | Subordinated liabilities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%
Other [member] | Other Group Entities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	1.00%
Other [member] | Other Group Entities [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	0.00%

Liquidity Risk - Summary of Ext

Liquidity Risk - Summary of External Term Issuance (Sterling Equivalent) (Detail) - Liquidity risk [member] - GBP (£) £ in Billions	Dec. 31, 2019	Dec. 31, 2018
Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 0.5	£ 2.7
Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0	2.7
Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Subordinated Liabilities and Equity [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.5	0
Other Santander UK plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	3.8	14
Other Santander UK plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.9	2.9
Other Santander UK plc [member] | Senior Unsecured - Privately Placed [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0	1.6
Other Santander UK plc [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0	2.9
Other Santander UK plc [member] | Covered Bonds [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.9	4.3
Other Santander UK plc [member] | Term Funding Scheme [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0	2.3
Other Group Entities [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	4.5	17.1
Other Group Entities [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.2	£ 0.4
United Kingdom, Pounds [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.5
United Kingdom, Pounds [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United Kingdom, Pounds [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Subordinated Liabilities and Equity [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.5
United Kingdom, Pounds [member] | Other Santander UK plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.1
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.1
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Senior Unsecured - Privately Placed [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Covered Bonds [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2
United Kingdom, Pounds [member] | Other Santander UK plc [member] | Term Funding Scheme [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United Kingdom, Pounds [member] | Other Group Entities [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.8
United Kingdom, Pounds [member] | Other Group Entities [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.2
United States of America, Dollars [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United States of America, Dollars [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United States of America, Dollars [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Subordinated Liabilities and Equity [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United States of America, Dollars [member] | Other Santander UK plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.8
United States of America, Dollars [member] | Other Santander UK plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.8
United States of America, Dollars [member] | Other Santander UK plc [member] | Senior Unsecured - Privately Placed [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United States of America, Dollars [member] | Other Santander UK plc [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United States of America, Dollars [member] | Other Santander UK plc [member] | Covered Bonds [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United States of America, Dollars [member] | Other Santander UK plc [member] | Term Funding Scheme [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
United States of America, Dollars [member] | Other Group Entities [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.8
United States of America, Dollars [member] | Other Group Entities [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro Member Countries, Euro [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro Member Countries, Euro [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro Member Countries, Euro [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Subordinated Liabilities and Equity [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro Member Countries, Euro [member] | Other Santander UK plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.9
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Senior Unsecured - Privately Placed [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Covered Bonds [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.9
Euro Member Countries, Euro [member] | Other Santander UK plc [member] | Term Funding Scheme [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Euro Member Countries, Euro [member] | Other Group Entities [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.9
Euro Member Countries, Euro [member] | Other Group Entities [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Downstreamed from Santander UK Group Holdings plc to Santander UK plc [Member] | Subordinated Liabilities and Equity [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Other Santander UK plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Other Santander UK plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Other Santander UK plc [member] | Senior Unsecured - Privately Placed [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Other Santander UK plc [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Other Santander UK plc [member] | Covered Bonds [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Other Santander UK plc [member] | Term Funding Scheme [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Other Group Entities [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0
Other [member] | Other Group Entities [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 0

Capital Risk - Summary of Regul

Capital Risk - Summary of Regulatory Capital Resources (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	£ 10,419	£ 10,374
AT1 capital	2,443	2,349
Tier 1 capital	12,862	12,723
Tier 2 capital	2,925	3,223
Total regulatory capital	£ 15,787	£ 15,946

Accounting Policies - Additiona

Accounting Policies - Additional information (Detail) - GBP (£) £ in Millions	Jan. 01, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of changes in accounting estimates [line items]
Other assets		£ 2,520	£ 2,280
Other liabilities		2,344	2,448
Provisions		572	509
Expected credit losses allowance		863	807
Amendment to IAS 12 impact on income statement		£ 39	42	£ 46
Bottom of range [member]
Disclosure of changes in accounting estimates [line items]
Hedge effectiveness percentage		80.00%
Top of range [member]
Disclosure of changes in accounting estimates [line items]
Hedge effectiveness percentage		125.00%
Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of changes in accounting estimates [line items]
Expected credit losses allowance		£ 813	789
Corporate and investment banking [member]
Disclosure of changes in accounting estimates [line items]
Expected credit losses allowance		£ 50	18
180 Days [member] | Unsecured Debt [member]
Disclosure of changes in accounting estimates [line items]
Written off period for past due		180 days
House price index [Member]
Disclosure of changes in accounting estimates [line items]
Expected credit losses allowance for residential mortgages		£ 218	£ 237
Stage 2 [member]
Disclosure of changes in accounting estimates [line items]
Probability weight		100.00%
IFRS 16 [member]
Disclosure of changes in accounting estimates [line items]
Increase Property, plant and equipment	£ 210
Other assets	12
Other liabilities	181
Provisions	£ 17

Accounting Policies - Summary o

Accounting Policies - Summary of Detailed Information Of Effect Of New Lease Accounting Standard Explanatory (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure and Detailed Information Of Effect Of New Lease Accounting Standard Explanatory [Line Items]
Rental commitments under non-cancellable operating leases under IAS 17 at 31 December 2018 (see Note 29)	£ 246
Recognition exemption for short-term leases	(72)
Effect from discounting at the incremental borrowing rate at 1 January 2019	7
Additional liabilities recognised based on the initial application of IFRS 16 at 1 January 2019	£ 181

Accounting Policies - Summary_2

Accounting Policies - Summary of Useful Lives or Depreciation Rates Used for Property, Plant and Equipment (Detail)	12 Months Ended
	Dec. 31, 2019
Right-of-use assets [member]
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	Shorter of the lease term or the useful life of the underlying asset
Bottom of Range [member] | Office Fixtures and Equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	3 years
Bottom of Range [member] | Computer Software [member]
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	3 years
Top of Range [member] | Owner-occupied properties [member]
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	50 years
Top of Range [member] | Office Fixtures and Equipment [member]
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	15 years
Top of Range [member] | Computer Software [member]
Disclosure of detailed information about property, plant and equipment [line items]
Useful lives or depreciation rates, property, plant and equipment	7 years

Accounting Policies - Summary_3

Accounting Policies - Summary of Probability Weights Applied for Each Scenario of Expected Credit Losses Allowance (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 207,287	£ 201,289
ECL	863	807
Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
ECL	50	18
Weighted | Retail Banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	206,479	195,805
Exposure - of which: mortgages	178,788	169,170
ECL	591	594
ECL - of which: mortgages	£ 218	£ 237
Proportion of assets in Stage 2	4.70%	5.40%
Proportion of assets in Stage 2 - of which: mortgages	4.60%	5.60%
Weighted | Corporate and commercial banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 21,855	£ 22,835
ECL	£ 210	£ 182
Proportion of assets in Stage 2	10.00%	5.50%
Weighted | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 13,456	£ 17,618
ECL	£ 50	£ 18
Proportion of assets in Stage 2	2.90%	0.80%
Weighted | Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 74,532	£ 74,690
ECL	£ 12	£ 13
Proportion of assets in Stage 2	0.20%	0.20%
Upside 2 [member] | Retail Banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 206,479	£ 195,805
Exposure - of which: mortgages	178,788	169,170
ECL	456	431
ECL - of which: mortgages	£ 122	£ 121
Proportion of assets in Stage 2	3.20%	3.40%
Proportion of assets in Stage 2 - of which: mortgages	3.10%	3.40%
Upside 2 [member] | Corporate and commercial banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 21,855	£ 22,835
ECL	£ 156	£ 115
Proportion of assets in Stage 2	7.40%	3.00%
Upside 2 [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 13,456	£ 17,618
ECL	£ 19	£ 8
Proportion of assets in Stage 2	1.50%	0.40%
Upside 2 [member] | Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 74,532	£ 74,690
ECL	£ 9	£ 8
Proportion of assets in Stage 2	0.10%	0.10%
Upside 1 [member] | Retail Banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 206,479	£ 195,805
Exposure - of which: mortgages	178,788	169,170
ECL	467	452
ECL - of which: mortgages	£ 127	£ 131
Proportion of assets in Stage 2	3.30%	3.50%
Proportion of assets in Stage 2 - of which: mortgages	3.10%	3.60%
Upside 1 [member] | Corporate and commercial banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 21,855	£ 22,835
ECL	£ 169	£ 135
Proportion of assets in Stage 2	7.40%	3.00%
Upside 1 [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 13,456	£ 17,618
ECL	£ 34	£ 12
Proportion of assets in Stage 2	1.50%	0.40%
Upside 1 [member] | Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 74,532	£ 74,690
ECL	£ 10	£ 9
Proportion of assets in Stage 2	0.10%	0.10%
Base case [member] | Retail Banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 206,479	£ 195,805
Exposure - of which: mortgages	178,788	169,170
ECL	485	480
ECL - of which: mortgages	£ 137	£ 137
Proportion of assets in Stage 2	3.30%	3.70%
Proportion of assets in Stage 2 - of which: mortgages	3.10%	3.70%
Base case [member] | Corporate and commercial banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 21,855	£ 22,835
ECL	£ 183	£ 157
Proportion of assets in Stage 2	7.40%	3.10%
Base case [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 13,456	£ 17,618
ECL	£ 48	£ 17
Proportion of assets in Stage 2	1.50%	0.40%
Base case [member] | Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 74,532	£ 74,690
ECL	£ 10	£ 11
Proportion of assets in Stage 2	0.10%	0.10%
Downside 1 [member] | Retail Banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 206,479	£ 195,805
Exposure - of which: mortgages	178,788	169,170
ECL	570	637
ECL - of which: mortgages	£ 196	£ 273
Proportion of assets in Stage 2	3.70%	4.70%
Proportion of assets in Stage 2 - of which: mortgages	3.60%	4.90%
Downside 1 [member] | Corporate and commercial banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 21,855	£ 22,835
ECL	£ 219	£ 192
Proportion of assets in Stage 2	8.50%	4.30%
Downside 1 [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 13,456	£ 17,618
ECL	£ 53	£ 22
Proportion of assets in Stage 2	1.50%	0.40%
Downside 1 [member] | Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 74,532	£ 74,690
ECL	£ 13	£ 13
Proportion of assets in Stage 2	0.20%	0.20%
Downside 2 [member] | Retail Banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 206,479	£ 195,805
Exposure - of which: mortgages	178,788	169,170
ECL	1,148	1,607
ECL - of which: mortgages	£ 660	£ 1,105
Proportion of assets in Stage 2	8.30%	15.10%
Proportion of assets in Stage 2 - of which: mortgages	8.70%	16.50%
Downside 2 [member] | Corporate and commercial banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 21,855	£ 22,835
ECL	£ 317	£ 302
Proportion of assets in Stage 2	16.30%	10.70%
Downside 2 [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 13,456	£ 17,618
ECL	£ 58	£ 27
Proportion of assets in Stage 2	1.50%	0.40%
Downside 2 [member] | Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
Exposure	£ 74,532	£ 74,690
ECL	£ 18	£ 21
Proportion of assets in Stage 2	0.30%	0.40%

Accounting Policies - Summary_4

Accounting Policies - Summary of Increase (Decrease in Profit Before Tax (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure - Accounting Policies - Summary of Increase (Decrease in Profit Before Tax [Abstract]
Increase in profit before tax due to 20 percentage increase in HPI rate	£ 16	£ 20
Increase in profit before tax due to 10 percentage increase in HPI rate	10	12
Decrease in profit before tax due to 10 percentage decrease in HPI rate	(16)	(20)
Decrease in profit before tax due to 20 percentage decrease in HPI rate	£ (43)	£ (52)

Segments - Additional Informati

Segments - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)
Retail banking [member]
Disclosure of operating segments [line items]
Turnover from Small business customers	£ 6.5
Corporate and commercial banking [member] | Bottom of Range [member]
Disclosure of operating segments [line items]
Annual turnover of business	6.5
Corporate and commercial banking [member] | Top of Range [member]
Disclosure of operating segments [line items]
Annual turnover of business	500
Corporate and investment banking [member]
Disclosure of operating segments [line items]
Annual turnover of business	£ 500

Segments - Summary of Results b

Segments - Summary of Results by Segment (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)Employee	Dec. 31, 2018GBP (£)Employee		Dec. 31, 2017GBP (£)Employee
Disclosure of operating segments [line items]
Net interest income/(expense)	£ 3,292	£ 3,603	[1]	£ 3,803	[1]
Non-interest income/(expense)	881	931		1,109
Total operating income/(expense)	4,173	4,534		4,912
Operating expenses before credit impairment losses, provisions and charges	(2,499)	(2,579)	[1]	(2,499)	[1]
Credit impairment (losses)/releases	(221)	(153)	[1]	(203)	[1]
Provisions for other liabilities and charges	(441)	(257)	[1]	(393)	[1]
Total operating credit impairment losses, provisions and (charges)/releases	(662)	(410)	[1]	(596)	[1]
Profit before tax	1,012	1,545	[1]	1,817	[1]
Revenue from external customers	4,173	4,534		4,912
Inter-segment revenue	4,173	4,534	[1]	4,912	[1]
Total operating income/(expense)	4,173	4,534		4,912
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	758	753		791
Insurance, protection and investments	77	105		100
Credit cards	86	85		92
Non-banking and other fees	191	227		239
Total fee and commission income	1,112	1,170	[1]	1,222	[1]
Fee and commission expense	(426)	(421)	[1]	(415)	[1]
Net fee and commission income	686	749		807
Customer loans	205,008	199,586		200,324
Total assets	281,702	283,372		314,765
Customer deposits	171,716	167,315		175,921
Total liabilities	£ 265,685	£ 267,463		£ 298,560
Average number of staff | Employee	23,570	24,205		19,559
Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ 0
Retail banking [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	2,876	3,126		3,270
Non-interest income/(expense)	698	638		615
Total operating income/(expense)	3,574	3,764		3,885
Operating expenses before credit impairment losses, provisions and charges	(1,994)	(1,929)		(1,856)
Credit impairment (losses)/releases	(160)	(124)		(36)
Provisions for other liabilities and charges	(292)	(230)		(342)
Total operating credit impairment losses, provisions and (charges)/releases	(452)	(354)		(378)
Profit before tax	1,128	1,481		1,651
Revenue from external customers	4,311	4,421		4,534
Total operating income/(expense)	3,574	3,764		3,885
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	702	697		737
Insurance, protection and investments	76	105		100
Credit cards	86	85		92
Non-banking and other fees	61	75		45
Total fee and commission income	925	962		974
Fee and commission expense	(373)	(382)		(367)
Net fee and commission income	552	580		607
Customer loans	180,398	172,747		168,729
Total assets	187,556	179,572		174,524
Customer deposits	145,050	142,065		143,834
Total liabilities	£ 145,917	£ 142,839		£ 150,847
Average number of staff | Employee	20,832	21,215		17,194
Retail banking [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ (737)	£ (657)		£ (649)
Corporate and commercial banking [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	359	403		391
Non-interest income/(expense)	78	82		74
Total operating income/(expense)	437	485		465
Operating expenses before credit impairment losses, provisions and charges	(264)	(258)		(223)
Credit impairment (losses)/releases	(37)	(23)		(13)
Provisions for other liabilities and charges	(20)	(14)		(55)
Total operating credit impairment losses, provisions and (charges)/releases	(57)	(37)		(68)
Profit before tax	116	190		174
Revenue from external customers	530	638		639
Total operating income/(expense)	437	485		465
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	27	27		27
Insurance, protection and investments	0
Credit cards	0
Non-banking and other fees	56	62		63
Total fee and commission income	83	89		90
Fee and commission expense	(23)	(25)		(31)
Net fee and commission income	60	64		59
Customer loans	16,297	17,702		19,391
Total assets	16,297	17,702		19,391
Customer deposits	18,234	17,606		17,760
Total liabilities	£ 18,260	£ 17,634		£ 18,697
Average number of staff | Employee	1,796	1,732		1,240
Corporate and commercial banking [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ (93)	£ (153)		£ (174)
Corporate and investment banking [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	63	69		67
Non-interest income/(expense)	112	183		261
Total operating income/(expense)	175	252		328
Operating expenses before credit impairment losses, provisions and charges	(171)	(250)		(292)
Credit impairment (losses)/releases	(22)	(14)		(174)
Provisions for other liabilities and charges	(17)	(8)		(11)
Total operating credit impairment losses, provisions and (charges)/releases	(39)	(22)		(185)
Profit before tax	(35)	(20)		(149)
Revenue from external customers	181	297		396
Total operating income/(expense)	175	252		328
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	29	29		27
Insurance, protection and investments	0
Credit cards	0
Non-banking and other fees	71	87		123
Total fee and commission income	100	116		150
Fee and commission expense	(17)	(14)		(17)
Net fee and commission income	83	102		133
Customer loans	4,114	4,613		6,037
Total assets	4,727	8,607		25,368
Customer deposits	6,101	4,853		4,546
Total liabilities	£ 6,500	£ 8,885		£ 24,388
Average number of staff | Employee	901	1,083		1,006
Corporate and investment banking [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ (6)	£ (45)		£ (68)
Corporate centre [member]
Disclosure of operating segments [line items]
Net interest income/(expense)	(6)	5		75
Non-interest income/(expense)	(7)	28		159
Total operating income/(expense)	(13)	33		234
Operating expenses before credit impairment losses, provisions and charges	(70)	(142)		(128)
Credit impairment (losses)/releases	(2)	8		20
Provisions for other liabilities and charges	(112)	(5)		15
Total operating credit impairment losses, provisions and (charges)/releases	(114)	3		35
Profit before tax	(197)	(106)		141
Revenue from external customers	(849)	(822)		(657)
Total operating income/(expense)	(13)	33		234
Revenue from external customers includes the following fee and commission income disaggregated by income type:
Current account and debit card fees	0
Insurance, protection and investments	1
Credit cards	0
Non-banking and other fees	3	3		8
Total fee and commission income	4	3		8
Fee and commission expense	(13)
Net fee and commission income	(9)	3		8
Customer loans	4,199	4,524		6,167
Total assets	73,122	77,491		95,482
Customer deposits	2,331	2,791		9,781
Total liabilities	£ 95,008	£ 98,105		£ 104,628
Average number of staff | Employee	41	175		119
Corporate centre [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ 836	£ 855		£ 891
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Segments - Summary of Results_2

Segments - Summary of Results by Segment (Parenthetical) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Corporate centre [member]
Disclosure of operating segments [line items]
Profit Before tax re-segmentation of short term markets business in Corporate Centre rather than Corporate & Investment Banking	£ 77	£ 98

Net Interest Income - Summary o

Net Interest Income - Summary of Net Interest Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Interest and similar income:
Loans and advances to customers	£ 5,230	£ 5,458		£ 5,494
Loans and advances to banks	137	202		164
Reverse repurchase agreements – non trading	244	124		20
Other	306	282		227
Total interest and similar income	5,917	6,066	[1]	5,905	[1]
Interest expense and similar charges:
Deposits by customers	(1,540)	(1,433)		(1,330)
Deposits by banks	(134)	(117)		(35)
Repurchase agreements – non trading	(126)	(42)		(5)
Debt securities in issue	(678)	(721)		(590)
Subordinated liabilities	(137)	(142)		(134)
Other	(10)	(8)		(8)
Total interest expense and similar charges	(2,625)	(2,463)	[1]	(2,102)	[1]
Net interest income	£ 3,292	£ 3,603	[1]	£ 3,803	[1]
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Net Interest Income - Summary_2

Net Interest Income - Summary of Net Interest Income (Parenthetical) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Analysis of income and expense [abstract]
Interest income on financial assets at fair value through other comprehensive income	£ 203	£ 209
Interest expense on financial assets at fair value through other comprehensive income	£ 310	£ 298

Net Fee and Commission Income -

Net Fee and Commission Income - Summary of Net Fee and Commission Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Net Fee And Commission Income [Line Items]
Fee and commission income	£ 1,112	£ 1,170	[1]	£ 1,222	[1]
Fee and commission expense	(426)	(421)	[1]	(415)	[1]
Net fee and commission income	686	749	[1]	807	[1]
Current account and debit card fees [member]
Net Fee And Commission Income [Line Items]
Fee and commission income	758	753		791
Insurance, protection and investments [member]
Net Fee And Commission Income [Line Items]
Fee and commission income	77	105		100
Credit cards [member]
Net Fee And Commission Income [Line Items]
Fee and commission income	86	85		92
Non-banking and other fees [member]
Net Fee And Commission Income [Line Items]
Fee and commission income	£ 191	£ 227		£ 239
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Net Trading and Other Income -

Net Trading and Other Income - Summary of Net Trading and Other Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Net Trading And Other Income [abstract]
Net trading and funding of other items by the trading book	£ 6	£ 245		£ 205
Net gains/(losses) on other financial assets at fair value through profit or loss	19	(6)		80
Net losses on other financial liabilities at fair value through profit or loss	(83)	(44)		(97)
Net gains/(losses) on derivatives managed with assets/liabilities held at fair value through profit or loss	69	(128)		(17)
Hedge ineffectiveness	8	34		5
Net profit on sale of available-for-sale assets				54
Net profit on sale of financial assets at fair value through other comprehensive income	15	19
Income from operating lease assets	124	86		44
Other	37	(24)		28
Net trading and other income	£ 195	£ 182	[1]	£ 302	[1]
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Net Trading and Other Income _2

Net Trading and Other Income - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Disclosure of subordinated liabilities [line items]
Fair value gains/(losses) on net trading and funding of other items by trading book	£ (42)	£ 22		£ (27)
(Losses)/gains on equity derivatives trading desk	43	(21)		28
Net gain on equity index-linked deposits and the related economic hedges	1	1		1
Exchange rate differences recognised	1,102	(689)		(109)
Principally offset from cash flow hedge reserve	(1,013)	£ 752	[1]	94	[1]
Residual value risk [member]
Disclosure of subordinated liabilities [line items]
Increase decrease in provisions	(24)
Accelarated depreciation expense	7.5
Residual value risk [member] | Reversal of Expenses in The Prior Period [Member]
Disclosure of subordinated liabilities [line items]
Increase decrease in provisions	(22)
Accelarated depreciation expense	2.3
Vocalink Holdings Limited [member]
Disclosure of subordinated liabilities [line items]
Gain on sale of shares	£ 15			£ 48
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Operating Expenses Before Cre_3

Operating Expenses Before Credit Impairment Losses, Provisions and Charges - Summary of Operating Expenses Before Credit Impairment Losses, Provisions and Charges (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Staff costs:
Wages and salaries	£ 852	£ 898		£ 743
Performance-related payments	159	159		157
Social security costs	111	111		93
Pensions costs – defined contribution plans	66	67		54
Pensions costs - defined benefit plans	35	79		32
Other share-based payments	0	3		10
Other personnel costs	40	52		45
Staff costs	1,263	1,369		1,134
Other administration expenses	693	835		1,011
Depreciation, amortisation and impairment	543	375		354
Total operating expenses before impairment losses, provisions and charges	£ 2,499	£ 2,579	[1]	£ 2,499	[1]
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Operating Expenses Before Cre_4

Operating Expenses Before Credit Impairment Losses, Provisions and Charges - Summary of Deferred Performance Awards (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of deferred performance awards [line Items]
Cash	£ 27	£ 32
Shares	24	30
Expenses charged in the year [member]
Disclosure of deferred performance awards [line Items]
Cash	10	12
Shares	9	13
Deferred performance awards	19
Expenses charged in the year [member] | Arising From Awards in Current Year [member]
Disclosure of deferred performance awards [line Items]
Cash	3
Shares	3
Deferred performance awards	6
Expenses charged in the year [member] | Arising From Awards in Prior Year [member]
Disclosure of deferred performance awards [line Items]
Cash	7
Shares	6
Deferred performance awards	13
Expenses deferred to future periods [member]
Disclosure of deferred performance awards [line Items]
Cash	17	20
Shares	15	£ 17
Deferred performance awards	32
Expenses deferred to future periods [member] | Arising From Awards in Current Year [member]
Disclosure of deferred performance awards [line Items]
Cash	7
Shares	6
Deferred performance awards	13
Expenses deferred to future periods [member] | Arising From Awards in Prior Year [member]
Disclosure of deferred performance awards [line Items]
Cash	10
Shares	9
Deferred performance awards	£ 19

Operating Expenses Before Cre_5

Operating Expenses Before Credit Impairment Losses, Provisions and Charges - Summary of Amount of Bonus Awarded to Employees (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of amount of bonus awarded to employees [line items]
Cash award - not deferred	£ 130	£ 123
- deferred	27	32
Share awards - not deferred	10	11
- deferred	24	30
Total discretionary bonus	191	196
Expenses charged in the year [member]
Disclosure of amount of bonus awarded to employees [line items]
Cash award - not deferred	130	123
- deferred	10	12
Share awards - not deferred	10	11
- deferred	9	13
Total discretionary bonus	159	159
Expenses deferred to future periods [member]
Disclosure of amount of bonus awarded to employees [line items]
Cash award - not deferred	0
- deferred	17	20
Share awards - not deferred	0
- deferred	15	17
Total discretionary bonus	£ 32	£ 37

Operating Expenses Before Cre_6

Operating Expenses Before Credit Impairment Losses, Provisions and Charges - Additional Information (Detail) £ in Millions	Oct. 26, 2018GBP (£)	Dec. 31, 2019GBP (£)Employee	Dec. 31, 2018GBP (£)Employee	Dec. 31, 2017Employee
Operating Expenses Before Credit Impairment Losses Provision And Charges [Line Items]
Allowance included in the scheme liabilities value		£ 45	£ 40
Increase in liabilities	£ 40	£ 5
Average number of full-time equivalent staff | Employee		23,570	24,205	19,559
Property, plant and equipment		£ 1,967	£ 1,832
Property, plant and equipment subject to operating leases [member]
Operating Expenses Before Credit Impairment Losses Provision And Charges [Line Items]
Depreciation, property, plant and equipment		103	63
Property, plant and equipment		574	£ 470
Santander UK Government And HMRC [Member] | IFRS 16
Operating Expenses Before Credit Impairment Losses Provision And Charges [Line Items]
Depreciation for lease assets		60
Operating lease assets		£ 152

Audit and Other Services - Summ

Audit and Other Services - Summary of Audit and Other Services (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Audit fees:
Fees payable to the Company's auditor and its associates for the audit of the Santander UK group's annual accounts	£ 8	£ 7.2	£ 7.4
- Audit of the Santander UK group's subsidiaries	1.3	1.1	1.4
Total audit fees	9.3	8.3	8.8
Non-audit fees:
Audit-related assurance services	0.8	0.7	0.7
Other assurance services	0.2	0.1	0.1
Other non-audit services	0.2	1	0.4
Total non-audit fees	£ 1.2	£ 1.8	£ 1.2

Audit and Other Services - Su_2

Audit and Other Services - Summary of Audit and Other Services (Parenthetical) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of audit fees and non audit fees [Line Items]
Audit-related assurance services	£ 0.8	£ 0.7	£ 0.7
Prior year audit services [member]
Disclosure of audit fees and non audit fees [Line Items]
Auditors fee	0.1	0
Audit-related assurance services	£ 0.1	£ 0.1

Audit and Other Services - Addi

Audit and Other Services - Additional Information (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of audit fees and non audit fees [Line Items]
Audit fees payable for statutory audit	£ 9,300,000	£ 8,300,000	£ 8,800,000
Non -audit fees - Audit fees per US Securities and Exchange Commission guidance	600,000	100,000	100,000
Non- audit fees -Audit Related Fees" per US Securities and Exchange Commission guidance	400,000	600,000	600,000
Non- audit fees- All Other Fees" per US Securities and Exchange Commission guidance'	200,000	1,100,000	500,000
Corporate and Other Borrowers [member]
Disclosure of audit fees and non audit fees [Line Items]
Audit fees payable for statutory audit	£ 0	£ 150,000	£ 45,000

Credit Impairment Losses and _3

Credit Impairment Losses and Provisions - Summary of Impairment Losses and Provisions (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Disclosure of credit impairment loss and provisions [abstract]
Loans and advances to customers	£ 239	£ 189		£ 257
Recoveries of loans and advances, net of collection costs	(40)	(42)		(54)
Off-balance sheet exposures (See Note 27)	22	6
Impairment loss on financial assets	221	153	[1]	203	[1]
Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 27)	435	257		385
Provisions for RV and voluntary termination	6	0		8
Provisions for other liabilities and charges	441	257	[1]	393	[1]
Total operating impairment losses, provisions and charges	£ 662	£ 410	[1]	£ 596	[1]
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Credit Impairment Losses and _4

Credit Impairment Losses and Provisions - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)
Disclosure of credit impairment loss and provisions [abstract]
Impairment losses on loans and advances to banks	£ 0
Impairment losses on Non-trading reverse repurchase agreements	0
Impairment losses on other financial assets at amortised cost	0
Impairment losses on financial assets at FVOCI	£ 0

Taxation - Disclosure of Tax on

Taxation - Disclosure of Tax on Profit (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Current tax:
UK corporation tax on profit for the year	£ 265	£ 408		£ 510
Adjustments in respect of prior years	(25)	(20)		(27)
Total current tax	240	388		483
Deferred tax:
Charge for the year	46	16		23
Adjustments in respect of prior years	(7)	(5)		9
Total deferred tax	39	11		32
Tax on profit	£ 279	£ 399	[1]	£ 515	[1]
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Taxation - Additional Informati

Taxation - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Expense Benefits [line items]
Applicable tax rate	19.00%	19.00%	19.25%
Bank corporation tax surcharge		8.00%		8.00%
Effective tax rate	27.60%	25.80%	28.30%
Unrecognised capital losses carried forward	£ 0	£ 0
Increase decrease in deferred tax liability	£ 12
Banking Entities [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	27.00%	27.00%	27.25%
Non-banking Entities [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	19.00%	19.00%	19.25%
Deferred Tax Assets That Rely on Future Profitability Excluding Timing Differences [member]
Income Tax Expense Benefits [line items]
Recognised capital losses carried forward	£ 11	£ 17
Finance (No.2) Act 2016 [member] | Bottom of Range [member] | Corporation Tax Rate in 2020 [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	17.00%	17.00%

Taxation - Schedule of Tax on P

Taxation - Schedule of Tax on Profit Before Tax Differs from Theoretical Amount that Arise Using Basic Corporation Tax Rate (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Reconciliation of accounting profit multiplied by applicable tax rates [abstract]
Profit before tax	£ 1,012	£ 1,545	[1]	£ 1,817	[1]
Tax calculated at a tax rate of 19% (2018: 19%, 2017: 19.25%)	192	294		350
Bank surcharge on profits	65	109		132
Non-deductible preference dividends paid	8	8		9
Non-deductible UK Bank Levy	24	20		25
Non-deductible conduct remediation, fines and penalties	44	6		35
Other non-deductible costs and non-taxable income	31	30		30
Effect of change in tax rate on deferred tax provision	(14)	(1)		(2)
Tax relief on dividends in respect of other equity instruments	(39)	(42)		(46)
Adjustment to prior year provisions	(32)	(25)		(18)
Tax charge	£ 279	£ 399	[1]	£ 515	[1]
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Taxation - Schedule of Tax on_2

Taxation - Schedule of Tax on Profit Before Tax Differs from Theoretical Amount that Arise Using Basic Corporation Tax Rate (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Reconciliation of accounting profit multiplied by applicable tax rates [abstract]
Standard tax rate	19.00%	19.00%	19.25%

Taxation - Disclosure of Moveme

Taxation - Disclosure of Movements in Current Tax Assets and Liabilities (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Current Tax Assets and Liabilities [abstract]
Assets	£ 153
Liabilities	0	£ (3)
Beginning Balance	153	(3)
Income statement charge	(240)	(388)		£ (483)
Other comprehensive income (charge)/credit	(4)	34
Corporate income tax paid	292	391	[1]	484	[1]
Other movements	(1)	119
Ending Balance	200	153		(3)
Assets	200	153
Liabilities	£ 0	£ 0		£ (3)
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Taxation - Disclosure of Deferr

Taxation - Disclosure of Deferred Tax Assets and Liabilities Including Movement in Deferred Tax Account (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	£ (223)	£ (88)
Adoption of IFRS 9 (see Note 1)		68
Beginning Balance, After adoption of IFRS 9		(20)
Income statement (charge)/credit	(39)	(11)
Transfers/reclassifications	0	(20)
Credited/(charged) to other comprehensive income	113	(172)
Ending Balance	(149)	(223)
Fair Value of Financial Instruments [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(51)	(41)
Beginning Balance, After adoption of IFRS 9		(41)
Income statement (charge)/credit	(1)	(10)
Transfers/reclassifications	0
Credited/(charged) to other comprehensive income	0
Ending Balance	(52)	(51)
Pension Remeasurement [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(183)	(41)
Beginning Balance, After adoption of IFRS 9		(41)
Income statement (charge)/credit	(44)	(24)
Transfers/reclassifications	0
Credited/(charged) to other comprehensive income	131	(118)
Ending Balance	(96)	(183)
Cash Flow Hedges [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(43)	3
Beginning Balance, After adoption of IFRS 9		3
Income statement (charge)/credit	0
Transfers/reclassifications	22
Credited/(charged) to other comprehensive income	(37)	(46)
Ending Balance	(58)	(43)
Available-for-Sale [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance		(26)
Adoption of IFRS 9 (see Note 1)		26
Fair value reserve [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(13)
Adoption of IFRS 9 (see Note 1)		(26)
Beginning Balance, After adoption of IFRS 9		(26)
Income statement (charge)/credit	0
Transfers/reclassifications	5
Credited/(charged) to other comprehensive income	0	13
Ending Balance	(8)	(13)
Tax Losses Carried Forward [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	20	25
Beginning Balance, After adoption of IFRS 9		25
Income statement (charge)/credit	(7)	(5)
Transfers/reclassifications	0
Credited/(charged) to other comprehensive income	0
Ending Balance	13	20
Accelerated Tax Depreciation [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(6)	(4)
Beginning Balance, After adoption of IFRS 9		(4)
Income statement (charge)/credit	23
Transfers/reclassifications	0	(2)
Credited/(charged) to other comprehensive income	0
Ending Balance	17	(6)
Other temporary differences [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	53	(4)
Adoption of IFRS 9 (see Note 1)		68
Beginning Balance, After adoption of IFRS 9		64
Income statement (charge)/credit	(10)	28
Transfers/reclassifications	(27)	(18)
Credited/(charged) to other comprehensive income	19	(21)
Ending Balance	£ 35	£ 53

Dividends on Ordinary Shares -

Dividends on Ordinary Shares - Disclosure of Dividends on Ordinary Shares Declared and Paid (Detail) - GBP (£) £ / shares in Units, £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Dividends on Ordinary Shares [Line Items]
Dividend per share	£ 1.02	£ 3.67	£ 1.78
Dividends	£ 315	£ 1,139	£ 553
First Interim [member]
Disclosure of Dividends on Ordinary Shares [Line Items]
Dividend per share	£ 0.53	£ 0.81	£ 1.04
Dividends	£ 164	£ 250	£ 323
Second Interim [member]
Disclosure of Dividends on Ordinary Shares [Line Items]
Dividend per share	£ 0.49	£ 2.15	£ 0.74
Dividends	£ 151	£ 668	£ 230
Third Interim [member]
Disclosure of Dividends on Ordinary Shares [Line Items]
Dividend per share	£ 0	£ 0.71
Dividends	£ 0	£ 221

Dividends on Ordinary - Additio

Dividends on Ordinary - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of Dividends on Ordinary Shares [line items]
Dividends declared and paid	£ 668
Percentage of dividend on recurring earnings	50.00%
First dividend paid [member]
Disclosure of Dividends on Ordinary Shares [line items]
Dividends declared and paid	£ 250
Second dividend paid [member]
Disclosure of Dividends on Ordinary Shares [line items]
Dividends declared and paid	£ 221

Derivative Financial Instrume_3

Derivative Financial Instruments - Notional Amounts and Fair Values of Derivatives (Detail) - GBP (£) £ in Millions		Dec. 31, 2019	Dec. 31, 2018
Disclosure of detailed information about hedges [line items]
Notional amount		£ 205,172	£ 237,771
Fair value assets		3,316	5,259
Fair value liabilities		1,448	1,369
Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount		63,187	95,630
Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount		141,985	142,141
Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount		96,032	89,432
Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount		45,953	52,709
Exchange Rate Contracts [member]
Disclosure of detailed information about hedges [line items]
Notional amount		44,133	50,741
Exchange Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount		14,149	13,830
Exchange Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount		1,482	3,010
Exchange Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount		28,502	33,901
Interest Rate Contracts [member]
Disclosure of detailed information about hedges [line items]
Notional amount		158,565	184,268
Interest Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount		46,564	79,038
Interest Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount		94,550	86,422
Interest Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount		17,451	18,808
Equity and Credit Contracts [member]
Disclosure of detailed information about hedges [line items]
Notional amount		2,474	2,762
Equity and Credit Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Notional amount		2,474	2,762
Equity and Credit Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Notional amount		0
Fair Value [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		3,316	5,259
Fair value liabilities		1,448	1,369
Fair Value [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		1,135	2,126
Fair value liabilities		675	1,624
Fair Value [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		3,395	5,005
Fair value liabilities		1,987	1,617
Fair Value [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		1,188	1,422
Fair value liabilities		1,490	1,315
Fair Value [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		2,207	3,583
Fair value liabilities		497	302
Fair Value [member] | Exchange Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		134	454
Fair value liabilities		200	351
Fair Value [member] | Exchange Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		166	357
Fair value liabilities		2
Fair Value [member] | Exchange Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		2,023	3,537
Fair value liabilities		462	200
Fair Value [member] | Interest Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		718	1,421
Fair value liabilities		315	1,105
Fair Value [member] | Interest Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		1,022	1,065
Fair value liabilities		1,488	1,315
Fair Value [member] | Interest Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		184	46
Fair value liabilities		35	102
Fair Value [member] | Equity and Credit Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		283	251
Fair value liabilities		160	168
Fair Value [member] | Equity and Credit Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		0
Fair value liabilities		0
Fair Value [member] | Netting adjustments [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	[1]	(1,214)	(1,872)
Fair value liabilities	[1]	£ (1,214)	£ (1,872)
[1]	Derivative netting excludes the effect of cash collateral, which is offset against the gross derivative position. The amount of cash collateral received that had been offset against the gross derivative assets was £222m (2018: £9m) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was £629m (2018: £354m).

Derivative Financial Instrume_4

Derivative Financial Instruments - Notional Amounts and Fair Values of Derivatives (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of detailed information about hedges [line items]
Financial collateral, Assets	£ 25,014	£ 22,811
Financial collateral, Liabilities	18,823	11,104
Derivative Assets [member]
Disclosure of detailed information about hedges [line items]
Financial collateral, Assets	222	9
Derivative Liabilities [member]
Disclosure of detailed information about hedges [line items]
Financial collateral, Liabilities	£ 629	£ 354

Derivative Financial Instrume_5

Derivative Financial Instruments - Analysis of the Notional and Fair Values of Derivatives by Trading and Settlement Method (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	£ 205,172	£ 237,771
Exchange Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	44,133	50,741
Interest Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	158,565	184,268
Equity and Credit Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	2,474	2,762
Traded on Recognised Exchanges [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	0
Assets traded over the counter	0
Liabilities traded over the counter	0
Traded on Recognised Exchanges [member] | Exchange Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	0
Assets traded over the counter	0
Liabilities traded over the counter	0
Traded on Recognised Exchanges [member] | Interest Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	0
Assets traded over the counter	0
Liabilities traded over the counter	0
Traded on Recognised Exchanges [member] | Equity and Credit Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	0
Assets traded over the counter	0
Liabilities traded over the counter	0
Settled by Central Counterparties [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	131,538	154,106
Settled by Central Counterparties [member] | Exchange Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	0
Settled by Central Counterparties [member] | Interest Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	131,538	154,106
Settled by Central Counterparties [member] | Equity and Credit Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	0
Not Settled by Central Counterparties [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	73,634	83,665
Not Settled by Central Counterparties [member] | Exchange Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	44,133	50,741
Not Settled by Central Counterparties [member] | Interest Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	27,027	30,162
Not Settled by Central Counterparties [member] | Equity and Credit Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	2,474	2,762
Traded Over the Counter [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Assets traded over the counter	3,316	5,259
Liabilities traded over the counter	1,448	1,369
Traded Over the Counter [member] | Exchange Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Assets traded over the counter	2,324	4,349
Liabilities traded over the counter	663	551
Traded Over the Counter [member] | Interest Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Assets traded over the counter	709	659
Liabilities traded over the counter	625	650
Traded Over the Counter [member] | Equity and Credit Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Assets traded over the counter	283	251
Liabilities traded over the counter	£ 160	£ 168

Derivative Financial Instrume_6

Derivative Financial Instruments - Summary of Nominal Value in Hedging Instruments (Detail) Unit_pure in Millions	Dec. 31, 2019
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	90,898
GBP LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	76,640
USD LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	13,071
Other [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	1,187
Maturing after transition date [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	33,509
Maturing after transition date [member] | GBP LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	28,228
Maturing after transition date [member] | USD LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	4,541
Maturing after transition date [member] | Other [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	740
Cash flow hedges [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	31,397
Cash flow hedges [member] | GBP LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	23,396
Cash flow hedges [member] | USD LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	8,001
Cash flow hedges [member] | Other [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	0
Cash flow hedges [member] | Maturing after transition date [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	14,417
Cash flow hedges [member] | Maturing after transition date [member] | GBP LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	11,773
Cash flow hedges [member] | Maturing after transition date [member] | USD LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	2,644
Cash flow hedges [member] | Maturing after transition date [member] | Other [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	0
Fair value hedges [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	59,501
Fair value hedges [member] | GBP LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	53,244
Fair value hedges [member] | USD LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	5,070
Fair value hedges [member] | Other [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	1,187
Fair value hedges [member] | Maturing after transition date [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	19,092
Fair value hedges [member] | Maturing after transition date [member] | GBP LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	16,455
Fair value hedges [member] | Maturing after transition date [member] | USD LIBOR [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	1,897
Fair value hedges [member] | Maturing after transition date [member] | Other [member]
Disclosure of detailed information about hedged items [line items]
notional value of hedging instruments	740

Derivative Financial Instrume_7

Derivative Financial Instruments - Summary of Maturity Profile and Average Price/Rate of Hedging Instruments Used in Hedging Strategies (Detail) £ in Millions	Dec. 31, 2019GBP (£)	Dec. 31, 2018GBP (£)
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 205,172	£ 237,771
Interest Rate Contracts [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	158,565	184,268
Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	94,314	84,344
Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	6,576	6,806
Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	236	2,078
Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	10,120	11,217
Interest Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	755	785
Exchange Rate Contracts [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	44,133	50,741
Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	1,482	3,010
Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	16,221	18,876
Exchange Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	12,281	15,025
Less Than One Month [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 4,354	£ 6,162
Less Than One Month [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0077	0.0063
Less Than One Month [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | Euro Member Countries, Euro [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	(0.0041)	(0.0022)
Less Than One Month [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United States of America, Dollars [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate		0.0151
Less Than One Month [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0
Less Than One Month [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 392
Average GBP - EUR exchange rate	0
Average GBP - USD exchange rate	0	1.5800
Less Than One Month [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member] | United States of America, Dollars [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate		0.0362
Less Than One Month [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0
Average GBP - EUR exchange rate	1.2742
Average GBP - USD exchange rate	0
Less Than One Month [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0249
Less Than One Month [member] | Interest Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0
Average GBP - JPY exchange rate	0
Average GBP - EUR exchange rate	0
Average GBP - USD exchange rate	1.2856	1.3035
Less Than One Month [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 392
Less Than One Month [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	812
Less Than One Month [member] | Exchange Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	1,187	3,916
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 5,804	£ 8,411
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0090	0.0079
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | Euro Member Countries, Euro [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0029	0.0067
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United States of America, Dollars [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0154	0.0131
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 339	£ 1,715
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0076	0.0073
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0	£ 1,295
Average GBP - EUR exchange rate	0
Average GBP - USD exchange rate	1.5110	1.3325
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member] | United States of America, Dollars [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0238	0.0250
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0
Average GBP - EUR exchange rate	0
Average GBP - USD exchange rate	0
Greater Than 1 and Less Than 3 Months [member] | Interest Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0
Average GBP - JPY exchange rate	145.9275	147.2149
Average GBP - EUR exchange rate	1.1444
Average GBP - USD exchange rate	1.2624	1.3067
Greater Than 1 and Less Than 3 Months [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 755	£ 1,295
Greater Than 1 and Less Than 3 Months [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	0
Greater Than 1 and Less Than 3 Months [member] | Exchange Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	2,119	2,552
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 27,405	£ 14,611
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0088	0.0106
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | Euro Member Countries, Euro [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0221	0.0091
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United States of America, Dollars [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0199	0.0134
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 1,066	£ 1,991
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0082	0.0073
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0
Average GBP - EUR exchange rate	0
Average GBP - USD exchange rate	0
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 3,121	£ 784
Average GBP - EUR exchange rate	1.1689	1.2523
Average GBP - USD exchange rate	1.5357	1.6333
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0216	0.0234
Later Than Three Months and Not Later Than One Year [member] | Interest Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0
Average GBP - JPY exchange rate	143.0857	146.3718
Average GBP - EUR exchange rate	1.1167	1.2803
Average GBP - USD exchange rate	1.2925	1.3099
Later Than Three Months and Not Later Than One Year [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0
Later Than Three Months and Not Later Than One Year [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	3,367	£ 1,773
Later Than Three Months and Not Later Than One Year [member] | Exchange Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	3,758	2,961
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 43,652	£ 39,508
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0133	0.0159
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | Euro Member Countries, Euro [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0136	0.0109
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United States of America, Dollars [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0269	0.0268
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 4,671	£ 3,100
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0146	0.0133
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 18	£ 90
Average GBP - EUR exchange rate	1.1781	1.1827
Average GBP - USD exchange rate	0	1.5110
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member] | Euro Member Countries, Euro [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0352	0.0389
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member] | United States of America, Dollars [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate		0.0238
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 4,829	£ 7,562
Average GBP - EUR exchange rate	1.3114	1.2707
Average GBP - USD exchange rate	1.5811	1.5447
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0287	0.0266
Later Than One Year and Not Later Than Five Years [member] | Interest Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 755	£ 785
Average GBP - JPY exchange rate	140.8152	145.3191
Average GBP - EUR exchange rate	1.1526	1.1349
Average GBP - USD exchange rate	1.2991	1.3049
Later Than One Year and Not Later Than Five Years [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 317	£ 1,101
Later Than One Year and Not Later Than Five Years [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	8,009	11,481
Later Than One Year and Not Later Than Five Years [member] | Exchange Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	5,217	5,596
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 13,099	£ 15,652
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0300	0.0285
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | Euro Member Countries, Euro [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0236	0.0126
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Fair Value Hedges [member] | United States of America, Dollars [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0456	0.0218
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 500
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate Risks [member] | Cash Flow Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.004
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 218	£ 301
Average GBP - EUR exchange rate	1.1603	1.1682
Average GBP - USD exchange rate	0
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member] | Euro Member Countries, Euro [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0212	0.0392
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member] | United States of America, Dollars [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate		0.0795
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 2,170	£ 2,871
Average GBP - EUR exchange rate	1.2090	1.2167
Average GBP - USD exchange rate	1.4499	1.5109
Later Than Five Years [member] | Interest Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member] | United Kingdom, Pounds [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average fixed interest rate	0.0296	0.0290
Later Than Five Years [member] | Interest Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0
Average GBP - JPY exchange rate	0
Average GBP - EUR exchange rate	0
Average GBP - USD exchange rate	0
Later Than Five Years [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 410	£ 222
Later Than Five Years [member] | Exchange Rate Contracts [member] | Interest Rate And Foreign Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	4,033	£ 5,622
Later Than Five Years [member] | Exchange Rate Contracts [member] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Notional amount	£ 0

Derivative Financial Instrume_8

Derivative Financial Instruments - Summary of Net Gains Or Losses Arising from Fair Value and Cash Flow Hedges Included in Net Trading and Other Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about hedges [line items]
Hedge ineffectiveness	£ 8	£ 34	£ 5
Fair Value and Cash Flow Hedges [member]
Disclosure of detailed information about hedges [line items]
(Losses)/gains on hedging instruments	(360)	4	56
Gains/(losses) on hedged items attributable to hedged risks	414	75	(2)
Fair value hedging ineffectiveness	54	79	54
Cash flow hedging ineffectiveness	(46)	(45)	(49)
Hedge ineffectiveness	£ 8	£ 34	£ 5

Derivative Financial Instrume_9

Derivative Financial Instruments - Summary of Information About Hedging Ineffectiveness by Risk Category (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value Hedges [member]
Disclosure of detailed information about hedges [line items]
Changes in FV of hedging instruments to calculate hedge ineffectiveness	£ (360)	£ 4
Change in FV of hedged items	414	75
Hedge ineffectiveness recognised in income statement	54	79
Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Changes in FV of hedging instruments to calculate hedge ineffectiveness	(264)	26
Change in FV of hedged items	284	15
Hedge ineffectiveness recognised in income statement	20	41
Fair Value Hedges [member] | Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Changes in FV of hedging instruments to calculate hedge ineffectiveness	(96)	(22)
Change in FV of hedged items	130	60
Hedge ineffectiveness recognised in income statement	34	38
Cash Flow Hedges [member]
Disclosure of detailed information about hedges [line items]
Changes in FV of hedging instruments to calculate hedge ineffectiveness	(903)	748
Changes in value of hedging instrument recognised in OCI	857	(793)
Hedge ineffectiveness recognised in income statement	(46)	(45)
Amount reclassified from cash flow hedging reserve to income statement	£ (1,012)	752
Cash Flow Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Income statement line item affected by the reclassification	Net interest income
Changes in FV of hedging instruments to calculate hedge ineffectiveness	£ 34	20
Changes in value of hedging instrument recognised in OCI	(33)	(14)
Hedge ineffectiveness recognised in income statement	1	6
Amount reclassified from cash flow hedging reserve to income statement	£ 13	26
Cash Flow Hedges [member] | Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Income statement line item affected by the reclassification	Net interest income/net trading and other income
Changes in FV of hedging instruments to calculate hedge ineffectiveness	£ (604)	722
Changes in value of hedging instrument recognised in OCI	561	(771)
Hedge ineffectiveness recognised in income statement	(43)	(49)
Amount reclassified from cash flow hedging reserve to income statement	£ (709)	726
Cash Flow Hedges [member] | Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Income statement line item affected by the reclassification	Net interest income/net trading and other income
Changes in FV of hedging instruments to calculate hedge ineffectiveness	£ (333)	18
Changes in value of hedging instrument recognised in OCI	329	(20)
Hedge ineffectiveness recognised in income statement	(4)	(2)
Amount reclassified from cash flow hedging reserve to income statement	£ (316)	9
Cash Flow Hedges [member] | Equity Risks [member]
Disclosure of detailed information about hedges [line items]
Income statement line item affected by the reclassification	Operating expenses
Changes in FV of hedging instruments to calculate hedge ineffectiveness	£ 0	(12)
Changes in value of hedging instrument recognised in OCI	0	12
Hedge ineffectiveness recognised in income statement	0
Amount reclassified from cash flow hedging reserve to income statement	£ 0	£ (9)

Derivative Financial Instrum_10

Derivative Financial Instruments - Additional Information (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Derivative Financial Instruments [abstract]
Ceased cash flow hedge accounting	£ 4	£ 12

Derivative Financial Instrum_11

Derivative Financial Instruments - Summary of Reconciliation by Risk Category of Components of Equity and Analysis of Other Comprehensive Income Items Resulting from Hedge Accounting (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of detailed information about hedges [line items]
Beginning Balance	£ 326	£ 285
Effective portion of changes in fair value	(857)	793
Income statement transfers	1,012	(752)
Ending Balance	481	326
Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Effective portion of changes in fair value	33	14
Income statement transfers	(13)	(26)
Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Effective portion of changes in fair value	(329)	20
Income statement transfers	316	(9)
Equity Risks [member]
Disclosure of detailed information about hedges [line items]
Effective portion of changes in fair value	0	(12)
Income statement transfers	0	9
Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Effective portion of changes in fair value	(561)	771
Income statement transfers	£ 709	£ (726)

Derivative Financial Instrum_12

Derivative Financial Instruments - Summary of Details of Hedged Exposures by Hedging Strategies (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about hedges [line items]
Cash flow hedge reserve	£ 481	£ 326	£ 285
Fair Value Hedges [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	414	75
Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	284	15
Fair Value Hedges [member] | Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	130	60
Santander UK Group [member] | Fair Value Hedges [member]
Disclosure of detailed information about hedges [line items]
Carrying value of assets	52,375	50,101
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	(608)	(526)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	800	455
Change in value used for calculating hedge ineffectiveness	414	75
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	186	67
Santander UK Group [member] | Cash Flow Hedges [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	857	(793)
Cash flow hedge reserve	481	326
Balances on cash flow hedge reserve where hedge accounting is no longer applied	8	51
Santander UK Group [member] | Loans and Advances to Customers [member] | Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Carrying value of assets	43,098	42,075
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	0
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	870	638
Change in value used for calculating hedge ineffectiveness	258	(149)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	630	729
Santander UK Group [member] | Loans and Advances to Customers [member] | Cash Flow Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	(34)	(19)
Cash flow hedge reserve	21	(4)
Balances on cash flow hedge reserve where hedge accounting is no longer applied	(11)	(2)
Santander UK Group [member] | Other financial assets at amortised cost [member] | Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Carrying value of assets	6,627	6,640
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	0
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	142	59
Change in value used for calculating hedge ineffectiveness	83	59
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	121
Santander UK Group [member] | Reverse repo agreement non trading [member] | Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Carrying value of assets	17,121	10,954
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	0
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	(2)
Change in value used for calculating hedge ineffectiveness	(2)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	0
Santander UK Group [member] | Other financial assets at fair value through other comprehensive income [member] | Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Carrying value of assets	5,944	7,429
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	102	10
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	0
Change in value used for calculating hedge ineffectiveness	125	(46)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	82	123
Santander UK Group [member] | Other financial assets at fair value through other comprehensive income [member] | Fair Value Hedges [member] | Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Carrying value of assets	241	18
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	3
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	0
Change in value used for calculating hedge ineffectiveness	(4)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	0
Santander UK Group [member] | Deposits by customers [member] | Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Carrying value of liabilities	(9,944)	(702)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	(85)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	4	1
Change in value used for calculating hedge ineffectiveness	(110)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(11)
Santander UK Group [member] | Deposits by customers [member] | Cash Flow Hedges [member] | Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	3
Cash flow hedge reserve	0
Balances on cash flow hedge reserve where hedge accounting is no longer applied	0
Santander UK Group [member] | Deposits by banks [member] | Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Carrying value of liabilities	(517)	(516)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	(16)	(15)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	0
Change in value used for calculating hedge ineffectiveness	(1)	9
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(17)	(23)
Santander UK Group [member] | Deposits by banks [member] | Cash Flow Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	3	6
Cash flow hedge reserve	(2)	(1)
Balances on cash flow hedge reserve where hedge accounting is no longer applied	0
Santander UK Group [member] | Deposits by banks [member] | Cash Flow Hedges [member] | Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	4
Cash flow hedge reserve	0
Balances on cash flow hedge reserve where hedge accounting is no longer applied	0
Santander UK Group [member] | Debt Securities [member] | Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Carrying value of liabilities	(8,099)	(11,920)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	(303)	(199)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	(166)	(191)
Change in value used for calculating hedge ineffectiveness	(50)	121
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(300)	(369)
Santander UK Group [member] | Debt Securities [member] | Fair Value Hedges [member] | Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Carrying value of liabilities	(1,396)	(3,192)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	(135)	(170)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	0
Change in value used for calculating hedge ineffectiveness	136	37
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(122)	(179)
Santander UK Group [member] | Debt Securities [member] | Cash Flow Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	0	(1)
Cash flow hedge reserve	0
Balances on cash flow hedge reserve where hedge accounting is no longer applied	0
Santander UK Group [member] | Debt Securities [member] | Cash Flow Hedges [member] | Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	177	(218)
Cash flow hedge reserve	(3)	22
Balances on cash flow hedge reserve where hedge accounting is no longer applied	0	3
Santander UK Group [member] | Subordinated liabilities [member] | Fair Value Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Carrying value of liabilities	(707)	(694)
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	(181)	(161)
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	(48)	(52)
Change in value used for calculating hedge ineffectiveness	(19)	21
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(204)	(223)
Santander UK Group [member] | Subordinated liabilities [member] | Fair Value Hedges [member] | Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Carrying value of assets	7	9
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	7	9
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	0
Change in value used for calculating hedge ineffectiveness	(2)	23
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	7	9
Santander UK Group [member] | Loans and advances to banks [member] | Cash Flow Hedges [member] | Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	(2)
Cash flow hedge reserve	0	(2)
Balances on cash flow hedge reserve where hedge accounting is no longer applied	0
Santander UK Group [member] | Other financial assets measured at fair value through other comprehensive income [member] | Cash Flow Hedges [member] | Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	(122)	199
Cash flow hedge reserve	3	(1)
Balances on cash flow hedge reserve where hedge accounting is no longer applied	0
Santander UK Group [member] | Highly probable forecast transactions [member] | Cash Flow Hedges [member] | Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	267	(1)
Cash flow hedge reserve	2
Balances on cash flow hedge reserve where hedge accounting is no longer applied	0
Santander UK Group [member] | Other Liabilities [member] | Cash Flow Hedges [member] | Equity Risks [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	0	12
Cash flow hedge reserve	0
Balances on cash flow hedge reserve where hedge accounting is no longer applied	(1)
Santander UK Group [member] | Debt securities in issue and loans and advances to customers [member] | Cash Flow Hedges [member] | Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	630	(564)
Cash flow hedge reserve	280	233
Balances on cash flow hedge reserve where hedge accounting is no longer applied	20	50
Santander UK Group [member] | Subordinated Liabilities and loans and advances to customers [member] | Cash Flow Hedges [member] | Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	(69)	(207)
Cash flow hedge reserve	180	£ 79
Balances on cash flow hedge reserve where hedge accounting is no longer applied	£ 0

Other Financial Assets at Fai_3

Other Financial Assets at Fair Value Through Profit or Loss - Summary of Other Financial Assets at Fair Value Through Profit or Loss (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	£ 386	£ 5,617
Loans and Advances to Customers [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	92	94
Loans and Advances to Customers [member] | Loans to Housing Associations [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	12	13
Loans and Advances to Customers [member] | Other Loans [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	80	81
Debt Securities [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	294	3,251
Equity Securities [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	0
Reverse repurchase agreements - non-trading [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	£ 0	£ 2,272

Other Financial Assets at Fai_4

Other Financial Assets at Fair Value Through Profit or Loss - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Financial assets mandatorily at FVTPL	£ 374	£ 4,522
Net (loss)/gain attributable to changes in credit risk for loans and advances at fair value through profit or loss	0	(1)	£ 49
Cumulative net loss attributable to changes in credit risk for loans and advances at fair value through profit or loss	2	2
Financial assets designated at FVTPL	12	£ 1,095
Debt Securities [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Senior tranches of credit linked notes netted against senior cash deposits	1,500
Senior credit linked notes presented on a net basis	£ 2,100

Loans and Advances to Custome_3

Loans and Advances to Customers - Summary of Net Loans and Advances to Customers (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Net Loans and Advances to Customers [abstract]
Loans secured on residential properties	£ 165,356	£ 157,957
Corporate loans	27,043	27,763
Finance leases	6,264	6,821
Secured Advances	0
Other unsecured loans	7,096	7,554
Amounts due from fellow Banco Santander subsidiaries and joint ventures	2,366	1,997
Amounts due from Santander UK Group Holdings plc	8	17
Amounts due from subsidiaries	0
Loans and advances to customers	208,133	202,109
Credit impairment loss allowances on loans and advances to customers	(785)	(751)
RV and voluntary termination provisions on finance leases	(61)	(69)
Net loans and advances to customers	£ 207,287	£ 201,289

Loans and Advances to Custome_4

Loans and Advances to Customers - Summary of Finance Lease and Hire Purchase Contract Receivables (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	£ 7,156	£ 7,355
Unearned finance income	(892)	(534)
Net investment	6,264	6,821
Not later than one year [member]
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	2,650	3,730
Unearned finance income	(371)	(210)
Net investment	2,279	3,520
Later than one year and not later than two years [member]
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	1,829	1,839
Unearned finance income	(207)	(148)
Net investment	1,622	1,691
Later than two years and not later than three years [member]
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	1,047	1,056
Unearned finance income	(119)	(87)
Net investment	928	969
Later than three years and not later than four years [member]
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	473	488
Unearned finance income	(54)	(39)
Net investment	419	449
Later than four years and not later than five years [member]
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	41	32
Unearned finance income	(4)	(4)
Net investment	37	28
Later than five years [member]
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	1,116	210
Unearned finance income	(137)	(46)
Net investment	£ 979	£ 164

Loans and Advances To Custome_5

Loans and Advances To Customers - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of finance lease and hire purchase contract receivables [abstract]
Unguaranteed residual value of leases	£ 1,219	£ 1,034
Contingent rent income	0	0	£ 5
Finance income on the net investment in finance leases	299	346	£ 201
Contractual amount outstanding on financial assets, written off	£ 72	£ 76

Securitisations and Covered B_3

Securitisations and Covered Bonds - Analysis of Securitisations and Covered Bonds (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of securitisations and covered bonds [line items]
Gross assets	£ 36,391	£ 36,195
External notes in issue	22,783	23,984
Notes issued to Santander UK plc/subsidiaries as collateral	4,786	3,541
Total securitisation and covered bond programmes (see Note 28)	22,783	23,445
Securitisation Programmes [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	13,068	14,617
External notes in issue	3,779	5,331
Notes issued to Santander UK plc/subsidiaries as collateral	4,786	3,541
Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	11,046	12,094
External notes in issue	2,226	3,381
Notes issued to Santander UK plc/subsidiaries as collateral	4,221	2,851
Securitisation Programmes [member] | Other Securitisation Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	2,022	2,523
External notes in issue	1,553	1,950
Notes issued to Santander UK plc/subsidiaries as collateral	565	690
Holmes [member] | Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	4,262	4,414
External notes in issue	1,931	3,182
Notes issued to Santander UK plc/subsidiaries as collateral	463	463
Fosse [member] | Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	3,708	4,646
External notes in issue	295	199
Notes issued to Santander UK plc/subsidiaries as collateral	1,404	34
Langton [member] | Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	3,076	3,034
External notes in issue	0
Notes issued to Santander UK plc/subsidiaries as collateral	2,354	2,354
Auto ABS UK Loans [member] | Securitisation Programmes [member] | Other Securitisation Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	1,532	1,468
External notes in issue	1,229	1,212
Notes issued to Santander UK plc/subsidiaries as collateral	368	316
Euro 35bn Global Covered Bond Programme [member] | Covered Bond Programme [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	23,323	21,578
External notes in issue	19,004	18,653
Notes issued to Santander UK plc/subsidiaries as collateral	0
held by the Santander UK group	0	(539)
Motor [member] | Securitisation Programmes [member] | Other Securitisation Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	490	1,055
External notes in issue	324	738
Notes issued to Santander UK plc/subsidiaries as collateral	£ 197	£ 374

Securitisations and Covered B_4

Securitisations and Covered Bonds - Summary of Issuances and Redemptions of Securitisation and Covered Bond Programme (Detail) - GBP (£) £ in Billions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Internal [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	£ 1.5	£ 0.1
Internal and external redemptions	0.8	0.6
Internal [member] | Master Trust Structures [member] | Holmes [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	0.1
Internal and external redemptions	0
Internal [member] | Master Trust Structures [member] | Fosse [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	1.4
Internal and external redemptions	0
Internal [member] | Other Securitisation Structures [member] | Motor [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0
Internal and external redemptions	0.2	0.1
Internal [member] | Other Securitisation Structures [member] | Auto ABS UK Loans [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0.1
Internal and external redemptions	0.1
Internal [member] | Covered Bond Programme [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0
Internal and external redemptions	0.5	0.5
External [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	3.2	6.5
Internal and external redemptions	3.2	2.9
External [member] | Master Trust Structures [member] | Holmes [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0	1.8
Internal and external redemptions	1.1	0.1
External [member] | Master Trust Structures [member] | Fosse [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0.1
Internal and external redemptions	0	0.4
External [member] | Other Securitisation Structures [member] | Motor [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0
Internal and external redemptions	0.4	0.1
External [member] | Other Securitisation Structures [member] | Auto ABS UK Loans [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0.2	0.4
Internal and external redemptions	0.2	0.4
External [member] | Covered Bond Programme [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	2.9	4.3
Internal and external redemptions	£ 1.5	£ 1.9

Securitisations and Covered B_5

Securitisations and Covered Bonds - Additional Information (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Holmes [member]
Disclosure of gross asset securitised [line items]
Beneficial interest in residential mortgage loans	£ 2,100	£ 3,200
Cash deposits	283	218
Fosse [member]
Disclosure of gross asset securitised [line items]
Beneficial interest in residential mortgage loans	1,700	200
Cash deposits	0	0
Langton [member]
Disclosure of gross asset securitised [line items]
Beneficial interest in residential mortgage loans	£ 2,400	£ 2,300

Transfers of Financial Assets_3

Transfers of Financial Assets Not Qualifying for Derecognition - Carrying Amount of Financial Assets that Did Not Qualify for Derecognition and their Associated Financial Liabilities (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	£ 17,779	£ 19,369
Carrying amount of associated financial liabilities	(10,661)	(12,639)
Sale and Repurchase Agreements [member]
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	7,592	7,642
Carrying amount of associated financial liabilities	(6,739)	(7,188)
Securities lending agreements [member]
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	195	144
Carrying amount of associated financial liabilities	(143)	(120)
Securitisations [member]
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	9,992	11,583
Carrying amount of associated financial liabilities	£ (3,779)	£ (5,331)

Reverse Repurchase Agreements_3

Reverse Repurchase Agreements - Non Trading - Summary of Reverse Repurchase Agreements - Non Trading (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of reserve repurchase agreements non-trading [line items]
Reverse repurchase agreements-non trading	£ 23,636	£ 21,127
Agreements with banks [member]
Disclosure of reserve repurchase agreements non-trading [line items]
Reverse repurchase agreements-non trading	2,161	3,254
Agreements with customers [member]
Disclosure of reserve repurchase agreements non-trading [line items]
Reverse repurchase agreements-non trading	£ 21,475	£ 17,873

Other Financial Assets At Amo_3

Other Financial Assets At Amortised Cost - Summary of Other Financial Assets at Amortised Cost (Detail) - Other Financial Assets [member] - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financial assets at amortised cost [line items]
Financial assets at amortised cost	£ 7,056	£ 7,229
Asset backed securities [member]
Financial assets at amortised cost [line items]
Financial assets at amortised cost	532	720
Debt Securities [member]
Financial assets at amortised cost [line items]
Financial assets at amortised cost	£ 6,524	£ 6,509

Financial Assets At Fair Valu_3

Financial Assets At Fair Value Through Other Comprehensive Income - Summary of Financial Assets at Fair Value Through Other Comprehensive Income (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of financial assets at fair value through other comprehensive income [line items]
Financial assets at fair value through other comprehensive income	£ 9,747	£ 13,302
Debt securities [member]
Disclosure of financial assets at fair value through other comprehensive income [line items]
Debt securities	9,691	13,229
Loans and advances to customers [Member]
Disclosure of financial assets at fair value through other comprehensive income [line items]
Loans and advances to customers	£ 56	£ 73

Interests in Other Entities - S

Interests in Other Entities - Schedule of Interests in Other Entities (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of interest in other entities [abstract]
Subsidiaries	£ 0
Joint ventures	117	£ 88
Total	£ 117	£ 88

Interests In Other Entities - A

Interests In Other Entities - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of subsidiaries [line items]
Percentage of ownership in subsidiaries	100.00%
Subsidiaries with material non-controlling interests [member]
Disclosure of subsidiaries [line items]
Percentage of ownership in subsidiaries	50.00%	50.00%

Interests in Other Entities -_2

Interests in Other Entities - Schedule of Subsidiaries With Significant Non-Controlling Interests (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Disclosure of subsidiaries [line items]
Profit attributable to non-controlling interests	£ 19	£ 22	[1]	£ 21	[1]
Accumulated non-controlling interests of the subsidiary	160	151
Total assets	281,702	283,372		314,765
Total liabilities	265,685	267,463		298,560
Profit for the year	733	1,146	[1]	1,302	[1]
Total comprehensive income for the year	395	1,549	[1]	£ 980	[1]
Subsidiaries with material non-controlling interests [member]
Disclosure of subsidiaries [line items]
Profit attributable to non-controlling interests	19	22
Accumulated non-controlling interests of the subsidiary	160	151
Dividends paid to non-controlling interests	12	22
Total assets	3,228	3,289
Total liabilities	2,905	2,987
Profit for the year	40	43
Total comprehensive income for the year	£ 40	£ 43
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Interests In Other Entities - I

Interests In Other Entities - Interests in Joint Ventures - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of joint ventures [line items]
Carrying value of interest in joint venture	£ 117	£ 88
Joint ventures [member]
Disclosure of joint ventures [line items]
Profit after tax	30	15
Carrying value of interest in joint venture	117	88
Commitments and contingent liabilities	£ 0	£ 0

Interests In Other Entities -_3

Interests In Other Entities - Interests in Unconsolidated Structured Entities - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)	Dec. 31, 2018GBP (£)
Disclosure of information about unconsolidated subsidiaries [line items]
Number of credit protection vehicles	4	3
Credit Linked Notes issued	£ 110	£ 3,053
Senior Credit Linked Notes issued	3,766	3,053
Junior Credit Linked Notes issued	825	408
Santander (UK) Common Investment Fund [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Defined benefit assets and obligations	£ 12,446	£ 11,433
Name of subsidiary	The Santander (UK) Common Investment Fund

Intangible Assets - Schedule of

Intangible Assets - Schedule of Goodwill (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of goodwill [line items]
Carrying amount	£ 1,203	£ 1,203
Cost [member]
Disclosure of goodwill [line items]
Carrying amount	1,269
Accumulated Impairment [member]
Disclosure of goodwill [line items]
Carrying amount	£ (66)

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of detailed information about intangible assets [abstract]
Goodwill impairment recognised	£ 0	£ 0
Increase/(decrease) in discount rate percentage	(0.70%)
Discount rate percentage	9.80%	10.50%

Intangible Assets - Schedule _2

Intangible Assets - Schedule of Goodwill for Cash Generating Units (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of information for cash-generating units [line items]
Goodwill	£ 1,203	£ 1,203
Discount rate	9.80%	10.50%
Personal Financial Services [member]
Disclosure of information for cash-generating units [line items]
Goodwill	£ 1,169	£ 1,169
Discount rate	9.80%	10.50%
Growth rate	3.00%	2.00%
Private Banking [member]
Disclosure of information for cash-generating units [line items]
Goodwill	£ 30	£ 30
Discount rate	9.80%	10.50%
Growth rate	4.00%	2.00%
Other [member]
Disclosure of information for cash-generating units [line items]
Goodwill	£ 4	£ 4
Discount rate	9.80%	10.50%
Growth rate	3.00%	2.00%

Intangible Assets - Schedule _3

Intangible Assets - Schedule of Goodwill for Cash Generating Units (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of information for cash-generating units [abstract]
Terminal growth rate	1.60%	1.60%

Intangible Assets - Schedule _4

Intangible Assets - Schedule of Other Intangibles (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of detailed information about intangible assets [line items]
Beginning balance	£ 605	£ 539
Additions	173	204
Disposals	(14)
Charge	(191)	(138)
Impairment	(10)
Ending balance	563	605
Cost [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	1,090	962
Additions	173	204
Write offs		(76)
Disposals	(14)
Charge	0
Impairment	0
Ending balance	1,249	1,090
Accumulated amortisation / impairment [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	(485)	(423)
Additions	0
Write offs		76
Disposals	0
Charge	(191)	(138)
Impairment	(10)
Ending balance	£ (686)	£ (485)

Other Financial Liabilities a_3

Other Financial Liabilities at Fair Value Through Profit or Loss - Summary of Other Financial Liabilities at Fair Value Through Profit or Loss (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	£ 1,713	£ 6,286
US$30bn Euro Medium Term Note Programme [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	159	165
Structured Notes Programmes [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	809	696
Eurobonds [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	137	129
Structured Deposits [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	435	133
Collateral and associated financial guarantees [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	173	3,053
Repurchase agreements - non trading [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	£ 0	£ 2,110

Other Financial Liabilities a_4

Other Financial Liabilities at Fair Value Through Profit or Loss - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Other Financial Liabilities At Fair Value Through Profit Or Loss [line items]
Net gain (loss) on financial liabilities designated at fair value, attributable to changes in credit risk	£ (77)	£ 84	£ (29)
Accumulated gain (loss) on financial liabilities designated at fair value, attributable to changes in credit risk	0	77
Difference between carrying amount of financial liability and amount contractually required to pay at maturity to holder of obligation	£ 4	£ 128
Statement describing other financial liabilities at fair value through profit or loss	For the Santander UK group, all (2018: all) of the other financial liabilities at fair value through profit or loss were designated as such.
Collateral and associated financial guarantees [member]
Disclosure Of Other Financial Liabilities At Fair Value Through Profit Or Loss [line items]
Cash deposits netted against senior credit linked notes	£ 1,500
Cash deposits presented on a net basis	£ 2,100

Deposits by Customers - Schedul

Deposits by Customers - Schedule of Deposits by Customers (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of deposits from customers [line items]
Deposits from customers	£ 181,883	£ 178,090
Current and Demand Accounts - [member]
Disclosure of deposits from customers [line items]
Deposits from customers	89,221	86,207
Savings Accounts [member]
Disclosure of deposits from customers [line items]
Deposits from customers	65,835	66,039
Time Deposits [member]
Disclosure of deposits from customers [line items]
Deposits from customers	16,680	15,485
Amounts due to other Santander UK Group Holdings plc subsidiaries [member]
Disclosure of deposits from customers [line items]
Deposits from customers	44	83
Amounts due to Santander UK Group Holdings plc [member]
Disclosure of deposits from customers [line items]
Deposits from customers	8,869	9,206
Amounts Due to Fellow Banco Santander Subsidiaries and Joint Ventures - [member]
Disclosure of deposits from customers [line items]
Deposits from customers	£ 1,234	£ 1,070

Deposits by Customers - Sched_2

Deposits by Customers - Schedule of Deposits by Customers (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of deposits from customers [line items]
Deposits from customers	£ 181,883	£ 178,090
Equity Index Linked Deposits [member]
Disclosure of deposits from customers [line items]
Deposits from customers	1,139	1,176
Capital amount guaranteed or protected	1,139	1,176
Capital amount of return guaranteed	£ 18	£ 28

Deposits by Banks - Schedule of

Deposits by Banks - Schedule of Deposits by Banks (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of deposits from banks [line items]
Deposits from banks	£ 14,353	£ 17,221
Items in Course of Transmission [member]
Disclosure of deposits from banks [line items]
Deposits from banks	337	262
Deposits Held as Collateral [member]
Disclosure of deposits from banks [line items]
Deposits from banks	2,169	4,048
Other Deposits [member]
Disclosure of deposits from banks [line items]
Deposits from banks	11,847	12,891
Amounts due to Santander UK subsidiaries [member]
Disclosure of deposits from banks [line items]
Deposits from banks	£ 0	£ 20

Deposits by Banks - Schedule _2

Deposits by Banks - Schedule of Deposits by Banks (Parenthetical) (Detail) - GBP (£) £ in Billions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of deposits from banks [abstract]
Drawdown from TFS	£ 10.8	£ 10.8

Repurchase Agreements - Non T_3

Repurchase Agreements - Non Trading - Summary of Repurchase Agreements Non Trading (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements–non trading	£ 18,286	£ 10,910
Agreements with banks [member]
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements–non trading	10,227	5,865
Agreements with customers [member]
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements–non trading	£ 8,059	£ 5,045

Debt Securities In Issue - Summ

Debt Securities In Issue - Summary of Debt Securities in Issue (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt securities in issue [line items]
Debt Securities	£ 41,129	£ 46,692
Credit Linked Notes	110	3,053
Medium Term Notes [member]
Debt securities in issue [line items]
Debt Securities	15,480	19,984
Medium Term Notes [member] | US$30bn Euro Medium Term Note Programme [member]
Debt securities in issue [line items]
Debt Securities	4,679	7,229
Medium Term Notes [member] | Euro 30bn Euro Medium Term Note Programme [member]
Debt securities in issue [line items]
Debt Securities	1,896	1,975
Medium Term Notes [member] | US SEC - Registered - Santander UK Plc [member]
Debt securities in issue [line items]
Debt Securities	5,891	7,649
Medium Term Notes [member] | US$20bn Commercial Paper Programmes [member]
Debt securities in issue [line items]
Debt Securities	3,014	3,131
Euro 35bn Global Covered Bond Programme [member]
Debt securities in issue [line items]
Debt Securities	19,004	18,114
Certificates of Deposit [member]
Debt securities in issue [line items]
Debt Securities	2,806	3,221
Credit Linked Note [member]
Debt securities in issue [line items]
Credit Linked Notes	60	42
Securitisation Programmes [member]
Debt securities in issue [line items]
Debt Securities	£ 3,779	£ 5,331

Subordinated Liabilities - Sche

Subordinated Liabilities - Schedule of Subordinated Liabilities (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of Subordinated Liabilities [abstract]
£325m Sterling Preference Shares	£ 344	£ 344
Undated subordinated liabilities	581	574
Dated subordinated liabilities	2,603	2,683
Subordinated liabilities	£ 3,528	£ 3,601

Subordinated Liabilities - Sc_2

Subordinated Liabilities - Schedule of Subordinated Liabilities (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of Subordinated Liabilities [abstract]
325m Sterling Preference Shares, Notional amount	£ 325	£ 325

Subordinated Liabilities - Addi

Subordinated Liabilities - Additional Information (Detail) - GBP (£)	Dec. 31, 2019	Dec. 31, 2018
Disclosure of subordinated liabilities [line items]
Defaults of principal, interest or other breaches with respect to subordinated liabilities	£ 0	£ 0
7.375% 20 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Interest rate	7.375%	7.375%
7.375% 20 Year Step-up Perpetual Callable Subordinated Notes [member] | Santander UK Plc [member]
Disclosure of subordinated liabilities [line items]
Interest rate	7.375%
7.125% 30 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Interest rate	7.125%	7.125%
7.125% 30 Year Step-up Perpetual Callable Subordinated Notes [member] | Santander UK Plc [member]
Disclosure of subordinated liabilities [line items]
Interest rate	7.125%
10.0625% Exchangeable Capital Securities [member]
Disclosure of subordinated liabilities [line items]
Interest rate	10.0625%	10.0625%
10.0625% Exchangeable Capital Securities [member] | Santander UK Plc [member]
Disclosure of subordinated liabilities [line items]
Interest rate	10.0625%
10.375% exchangeable subordinated capital securities [member]
Disclosure of subordinated liabilities [line items]
Interest rate	10.375%
Par value per share		£ 1
10.375% non-cumulative non-redeemable sterling preference shares [member]
Disclosure of subordinated liabilities [line items]
Par value per share	£ 1

Subordinated Liabilities - Summ

Subordinated Liabilities - Summary of Undated Subordinated Liabilities (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of subordinated liabilities [line items]
Undated subordinated liabilities	£ 581	£ 574
10.0625% Exchangeable Capital Securities [member]
Disclosure of subordinated liabilities [line items]
Undated subordinated liabilities	£ 205	£ 205
First call date	n/a	n/a
7.375% 20 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Undated subordinated liabilities	£ 15	£ 16
First call date	2020	2020
7.125% 30 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Undated subordinated liabilities	£ 361	£ 353
First call date	2030	2030

Subordinated Liabilities - Su_2

Subordinated Liabilities - Summary of Undated Subordinated Liabilities (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
10.0625% Exchangeable Capital Securities [member]
Disclosure of subordinated liabilities [line items]
Interest rate	10.0625%	10.0625%
First call date	n/a	n/a
7.375% 20 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Interest rate	7.375%	7.375%
Notes maturity, year	20 years	20 years
First call date	2020	2020
7.125% 30 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Interest rate	7.125%	7.125%
Notes maturity, year	30 years	30 years
First call date	2030	2030

Subordinated Liabilities - Su_3

Subordinated Liabilities - Summary of Dated Subordinated Liabilities (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 2,603	£ 2,683
5% Subordinated Notes 2023 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 1,132	£ 1,173
Maturity period	2023	2023
4.75% Subordinated Notes 2025 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 763	£ 791
Maturity period	2025	2025
7.95% Subordinated Notes 2029 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 280	£ 278
Maturity period	2029	2029
6.50% Subordinated Notes 2030 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 40	£ 38
Maturity period	2030	2030
5.875% Subordinated Notes 2031 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 9	£ 9
Maturity period	2031	2031
5.625% Subordinated Notes 2045 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 379	£ 394
Maturity period	2045	2045

Subordinated Liabilities - Su_4

Subordinated Liabilities - Summary of Dated Subordinated Liabilities (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
5% Subordinated Notes 2023 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	5.00%	5.00%
Notional amount	$ 1,500	$ 1,500
4.75% Subordinated Notes 2025 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	4.75%	4.75%
Notional amount	$ 1,000	$ 1,000
7.95% Subordinated Notes 2029 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	7.95%	7.95%
Notional amount	$ 1,000	$ 1,000
6.50% Subordinated Notes 2030 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	6.50%	6.50%
5.875% Subordinated Notes 2031 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	5.875%	5.875%
5.625% Subordinated Notes 2045 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	5.625%	5.625%
Notional amount	$ 500	$ 500

Provisions - Summary of Provisi

Provisions - Summary of Provisions Reconciliation (Detail) - GBP (£) £ in Millions	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2019
Disclosure of other provisions [line items]
Beginning balance	£ 509	£ 509	£ 509
Adoption of IFRS 16 (see Note 1)			17
Balance on January 1 2019			526
Additional provisions (see Note 8)			487
Provisions released (see Note 8)			(30)
Utilisation and other			(421)
Recharge			10
Ending balance			572
To be settled:
Ending balance			572
Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Ending balance			545
To be settled:
Ending balance			545
More than One Year [member]
Disclosure of other provisions [line items]
Ending balance			27
To be settled:
Ending balance			27
PPI [member]
Disclosure of other provisions [line items]
Beginning balance	246	246	246
Balance on January 1 2019			246
Additional provisions (see Note 8)	70	99	169
Provisions released (see Note 8)			0
Utilisation and other			(226)
Recharge			0
Ending balance			189
To be settled:
Ending balance			189
PPI [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Ending balance			189
To be settled:
Ending balance			189
PPI [member] | More than One Year [member]
Disclosure of other provisions [line items]
Ending balance			0
To be settled:
Ending balance			0
Other products [member]
Disclosure of other provisions [line items]
Beginning balance	30	30	30
Balance on January 1 2019			30
Additional provisions (see Note 8)			0
Provisions released (see Note 8)			0
Utilisation and other			(5)
Recharge			0
Ending balance			25
To be settled:
Ending balance			25
Other products [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Ending balance			18
To be settled:
Ending balance			18
Other products [member] | More than One Year [member]
Disclosure of other provisions [line items]
Ending balance			7
To be settled:
Ending balance			7
FSCS And Bank Levy [member]
Disclosure of other provisions [line items]
Beginning balance	45	45	45
Balance on January 1 2019			45
Additional provisions (see Note 8)			86
Provisions released (see Note 8)			(5)
Utilisation and other			(90)
Recharge			10
Ending balance			46
To be settled:
Ending balance			46
FSCS And Bank Levy [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Ending balance			46
To be settled:
Ending balance			46
FSCS And Bank Levy [member] | More than One Year [member]
Disclosure of other provisions [line items]
Ending balance			0
To be settled:
Ending balance			0
Vacant Property [member]
Disclosure of other provisions [line items]
Beginning balance	37	37	37
Adoption of IFRS 16 (see Note 1)			17
Balance on January 1 2019			54
Additional provisions (see Note 8)			44
Provisions released (see Note 8)			(21)
Utilisation and other			(18)
Recharge			0
Ending balance			59
To be settled:
Ending balance			59
Vacant Property [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Ending balance			43
To be settled:
Ending balance			43
Vacant Property [member] | More than One Year [member]
Disclosure of other provisions [line items]
Ending balance			16
To be settled:
Ending balance			16
Off- balance sheet ECL [member]
Disclosure of other provisions [line items]
Beginning balance	56	56	56
Balance on January 1 2019			56
Additional provisions (see Note 8)			22
Provisions released (see Note 8)			0
Utilisation and other			0
Recharge			0
Ending balance			78
To be settled:
Ending balance			78
Off- balance sheet ECL [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Ending balance			78
To be settled:
Ending balance			78
Off- balance sheet ECL [member] | More than One Year [member]
Disclosure of other provisions [line items]
Ending balance			0
To be settled:
Ending balance			0
Regulatory and other [member]
Disclosure of other provisions [line items]
Beginning balance	£ 95	£ 95	95
Balance on January 1 2019			95
Additional provisions (see Note 8)			166
Provisions released (see Note 8)			(4)
Utilisation and other			(82)
Recharge			0
Ending balance			175
To be settled:
Ending balance			175
Regulatory and other [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Ending balance			171
To be settled:
Ending balance			171
Regulatory and other [member] | More than One Year [member]
Disclosure of other provisions [line items]
Ending balance			4
To be settled:
Ending balance			£ 4

Provisions - Additional Informa

Provisions - Additional Information (Detail) £ in Millions	6 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2019GBP (£)	Sep. 30, 2019GBP (£)	Dec. 31, 2019GBP (£)Complaints	Dec. 31, 2018GBP (£)	Dec. 31, 2017GBP (£)
Future expected provision number
Provisions			£ 572	£ 509
Provisions released			30
Additional provision charge			487
PPI [member]
Future expected provision number
Provisions			189	246
Provisions released			£ 0
Cumulative to 31 December 2019 | Complaints			3,500,000
Complaints reviewing | Complaints			327,000
Future expected | Complaints			49,000
Additional inbound PPI complaints | Complaints			10,000
Additional provision charge	£ 70	£ 99	£ 169
PPI [member] | For Every 10000 PPI [Member]
Future expected provision number
additional PPI provions charge			4
Other products [member]
Future expected provision number
Provisions			25	30
Provisions released			0
Additional provision charge			0
Regulatory Related Uk Bank Levy [member]
Future expected provision number
Provisions			£ 46	£ 40
Bank levy rate			0.15%	0.16%
Cost of UK Bank Levy Incurred			£ 86	£ 69	£ 92
Amount paid as UK Bank Levy			£ 90	86
Regulatory Related Uk Bank Levy [member] | Top of Range [member]
Future expected provision number
UK Bank Levy			0.21%
Regulatory Related Uk Bank Levy [member] | Bottom of Range [member]
Future expected provision number
UK Bank Levy			0.10%
Compliance with Consumer Credit Act [member]
Future expected provision number
Additional operational risk losses and restructuring provision			£ 68	58
Regulatory Other Provisions [Member]
Future expected provision number
Transformation charge			65
Charge related to operational risk and provisions			68
Property [Member]
Future expected provision number
Transformation charge			40
FSCS [Member]
Future expected provision number
Provisions			0	4
Provisions released			£ 4	£ 4
Additional provision charge					£ 1

Retirement Benefit Plans - Summ

Retirement Benefit Plans - Summary of Retirement Benefit Plans (Detail) - Santander UK Group [member] - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets/(liabilities)
Total net assets	£ 389	£ 728
Unfunded Pension And Post Retirement Medical Benefits [Member]
Assets/(liabilities)
Surplus (deficit) in plan	(41)	(39)
Surplus [member] | Funded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	669	842
Deficit [member] | Funded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	£ (239)	£ (75)

Retirement Benefit Plans - Su_2

Retirement Benefit Plans - Summary of Remeasurement Losses/(Gains) Recognised In Other Comprehensive Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Disclosure of net defined benefit liability (asset) [abstract]
Pension remeasurement	£ 522	£ (470)	[1]	£ 103	[1]
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Retirement Benefit Plans - Addi

Retirement Benefit Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019GBP (£)Directors	Dec. 31, 2018GBP (£)Directors	Dec. 31, 2017GBP (£)	Aug. 31, 2019GBP (£)	Mar. 01, 2015
Disclosure of defined benefit plans [line items]
Defined contribution expense	£ 66,000,000	£ 67,000,000	£ 54,000,000
Key management personnel expense	None	None	None
Percentage of employee covered defined benefit pension schemes	11.00%	13.00%
Number of directors selected | Directors	5	6
Number of directors nominated | Directors	5	6
Actuarial valuation deficit				£ 1,136,000,000
Equity securities hold	£ 0	£ 0
Property occupied	0	0
Other assets occupied	0	0
Contribution to scheme based on agreement	£ 203,000,000	£ 176,000,000
Improvements to life expectancy of female employees	1.25%
Improvements to life expectancy of male employees	1.25%
Average duration of defined benefit obligation	18.8 years	19.1 years
Percentage of pension pay increase	2.90%	2.90%	2.90%		1.00%
Increase decrease in allowance	£ 5,000,000
GMP allowance included in scheme liabilities	£ 45,000,000	£ 40,000,000
Forward curve term	30 years
Percentage improvements in membership profile retirement benefits plan	0.15%
Bottom of Range [member]
Disclosure of defined benefit plans [line items]
Period over which the forward rate is used for computing retirement benefits	15 years
Top of Range [member]
Disclosure of defined benefit plans [line items]
Period over which the forward rate is used for computing retirement benefits	30 years
Actuarial assumption of mortality rates [member]
Disclosure of defined benefit plans [line items]
Negative impact on accounting surplus	£ 44,000,000
Santander CF Trustee Limited [member]
Disclosure of defined benefit plans [line items]
Number of trustee directors | Directors	5
Santander (UK) Group Pension Scheme Trustees Limited [member]
Disclosure of defined benefit plans [line items]
Number of trustee directors | Directors	2
Equity collar [member]
Disclosure of defined benefit plans [line items]
Gross notional value	£ 1,560,000,000	1,795,000,000
Currency futures [member]
Disclosure of defined benefit plans [line items]
Gross notional value	2,079,000,000	2,112,000,000
Present value of defined benefit obligations [member]
Disclosure of defined benefit plans [line items]
Estimated increase in liabilities in relation to judgment on GMP equalisation	£ 0	(40,000,000)
Santander UK Plc [member]
Disclosure of defined benefit plans [line items]
Number of trustee directors | Directors	3
Deficit Repair Contributions [member]
Disclosure of defined benefit plans [line items]
Contribution to scheme based on agreement	£ 153,000,000	123,000,000
Deficit Group Section Contributions Plan [member] | Santander UK Group [member]
Disclosure of defined benefit plans [line items]
Contributions to defined benefit plans		£ 187,000,000
Maturity date for contribution	31 March 2026

Retirement Benefit Plans - Tota

Retirement Benefit Plans - Total Defined Benefit Plan Amount Charged to Income Statement (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of net defined benefit liability (asset) [abstract]
Net interest income	£ (23)	£ (7)	£ (5)
Current service cost	34	41	31
Past service and GMP costs	1	41	1
Administration costs	8	8	8
Total	£ 20	£ 83	£ 35

Retirement Benefit Plans - Su_3

Retirement Benefit Plans - Summary of Amounts Recognised in Other Comprehensive Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Disclosure of net defined benefit liability (asset) [abstract]
Return on plan assets (excluding amounts included in net interest expense)	£ (855)	£ 246		£ (435)
Actuarial losses/(gains) arising from changes in demographic assumptions	42	(56)		(151)
Actuarial (gains)/losses arising from experience adjustments	(42)	15		(11)
Actuarial losses/(gains) arising from changes in financial assumptions	1,377	(675)		700
Pension remeasurement	£ 522	£ (470)	[1]	£ 103	[1]
[1]	Adjusted to reflect the amendment to IAS 12, as described in Note 1.

Retirement Benefit Plans - Disc

Retirement Benefit Plans - Disclosure of Movements in Present Value of Defined Benefit Obligations (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of net defined benefit liability (asset) [line items]
Current service cost paid by Santander UK plc	£ 34	£ 41	£ 31
Interest cost	(23)	(7)	(5)
Past service cost	1	41	1
Remeasurement due to actuarial movements arising from:
- Changes in demographic assumptions	42	(56)	(151)
- Experience adjustments	(42)	15	(11)
- Changes in financial assumptions	1,377	(675)	700
Present value of defined benefit obligations [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	(10,804)	(11,583)
Current service cost paid by Santander UK plc	(22)	(27)
Current service cost paid by other subsidiaries	(12)	(14)
Current service cost paid by fellow Banco Santander subsidiaries	0
Interest cost	(308)	(282)
Employer salary sacrifice contributions	(9)	(6)
Past service cost	(1)	(1)
GMP equalisation cost	0	(40)
Remeasurement due to actuarial movements arising from:
- Changes in demographic assumptions	(42)	56
- Experience adjustments	42	(15)
- Changes in financial assumptions	(1,377)	675
Benefits paid	375	433
Ending balance	£ (12,158)	£ (10,804)	£ (11,583)

Retirement Benefit Plans - Di_2

Retirement Benefit Plans - Disclosure of Movements in Fair Value of Scheme Assets (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of net defined benefit liability (asset) [line items]
Interest income	£ (23)	£ (7)	£ (5)
Return on plan assets (excluding amounts included in net interest expense)	(855)	246	(435)
Fair value of scheme assets [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	11,532	11,746
Interest income	331	289
Contributions paid by employer and scheme members	212	184
Contributions paid by fellow Banco Santander subsidiaries	0
Administration costs paid	(8)	(8)
Return on plan assets (excluding amounts included in net interest expense)	855	(246)
Benefits paid	(375)	(433)
Ending balance	£ 12,547	£ 11,532	£ 11,746

Retirement Benefit Plans - Su_4

Retirement Benefit Plans - Summary of Composition and Fair Value of Plan Assets (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of net defined benefit liability (asset) [line items]
UK equities	1.00%	1.00%
Overseas equities	21.00%	24.00%
Corporate bonds	15.00%	16.00%
Government fixed interest bonds	22.00%	23.00%
Government index-linked bonds	35.00%	37.00%
Property	11.00%	10.00%
Derivatives	1.00%
Cash	8.00%	6.00%
Repurchase agreements	(26.00%)	(26.00%)
Other	12.00%	9.00%
Total	100.00%	100.00%
UK equities	£ 128	£ 159
Overseas equities	2,675	2,732
Corporate bonds	1,777	1,847
Government fixed interest bonds	2,710	2,636
Government index-linked bonds	4,543	4,248
Property	1,332	1,143
Derivatives	94	65
Cash	984	662
Repurchase agreements	(3,263)	(2,981)
Other	1,567	1,021
Total	£ 12,547	£ 11,532
Quoted Prices in Active Markets [member]
Disclosure of net defined benefit liability (asset) [line items]
UK equities	1.00%	1.00%
Overseas equities	14.00%	16.00%
Corporate bonds	11.00%	13.00%
Government fixed interest bonds	22.00%	23.00%
Government index-linked bonds	35.00%	37.00%
Property	0.00%
Derivatives	0.00%
Cash	0.00%
Repurchase agreements	0.00%
Other	0.00%
Total	83.00%	90.00%
UK equities	£ 128	£ 159
Overseas equities	1,742	1,854
Corporate bonds	1,333	1,536
Government fixed interest bonds	2,710	2,636
Government index-linked bonds	4,543	4,248
Property	0
Derivatives	0
Cash	0
Repurchase agreements	0
Other	0
Total	£ 10,456	£ 10,433
Prices Not Quoted in Active Markets [member]
Disclosure of net defined benefit liability (asset) [line items]
UK equities	0.00%
Overseas equities	7.00%	8.00%
Corporate bonds	4.00%	3.00%
Government fixed interest bonds	0.00%
Government index-linked bonds	0.00%
Property	11.00%	10.00%
Derivatives	1.00%
Cash	8.00%	6.00%
Repurchase agreements	(26.00%)	(26.00%)
Other	12.00%	9.00%
Total	17.00%	10.00%
UK equities	£ 0
Overseas equities	933	£ 878
Corporate bonds	444	311
Government fixed interest bonds	0
Government index-linked bonds	0
Property	1,332	1,143
Derivatives	94	65
Cash	984	662
Repurchase agreements	(3,263)	(2,981)
Other	1,567	1,021
Total	£ 2,091	£ 1,099

Retirement Benefit Plans - Su_5

Retirement Benefit Plans - Summary of Principal Actuarial Assumptions Used for Defined Benefit Schemes (Detail)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 01, 2015
Disclosure of sensitivity analysis for actuarial assumptions [abstract]
- Discount rate for scheme liabilities	2.10%	2.90%	2.50%
- General price inflation	3.00%	3.20%	3.20%
- General salary increase	1.00%	1.00%	1.00%
- Expected rate of pension increase	2.90%	2.90%	2.90%	1.00%
Longevity at 60 for current pensioners, on the valuation date:
- Males	27 years 3 months 18 days	27 years 3 months 18 days	27 years 4 months 24 days
- Females	29 years 9 months 18 days	30 years 1 month 6 days	30 years 1 month 6 days
Longevity at 60 for future pensioners currently aged 40, on the valuation date:
- Males	28 years 10 months 24 days	28 years 8 months 12 days	28 years 10 months 24 days
- Females	31 years 3 months 18 days	31 years 7 months 6 days	31 years 8 months 12 days

Retirement Benefit Plans - Su_6

Retirement Benefit Plans - Summary of Actuarial Assumption Sensitivities (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Actuarial Assumption of Discount Rates [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase decrease in defined benefit obligation	£ (564)	£ (483)
Description of changes in methods and assumptions	25 bps increase
Actuarial Assumption of Expected Rates of Inflation [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase decrease in defined benefit obligation	£ 407	350
Description of changes in methods and assumptions	25 bps increase
Actuarial Assumption of Expected Rates of Mortality [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase decrease in defined benefit obligation	£ 419	£ 335
Description of changes in methods and assumptions	Each additional year of longevity assumed

Retirement Benefit Plans - Di_3

Retirement Benefit Plans - Disclosure of Benefits Expected To Be Paid (Detail) £ in Millions	Dec. 31, 2019GBP (£)
Not Later Than 1 Year [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	£ 332
Later Than 1 Year and Not Later Than 2 Years [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	308
2 - 3 years [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	330
3 - 4 years [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	343
4 - 5 years [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	364
Five Years Ending 2029 [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	£ 2,083

Contingent Liabilities and Co_3

Contingent Liabilities and Commitments - Summary of Contingent Liabilities and Commitments (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of contingent liabilities and commitments [line items]
Guarantees and formal standby facilities, credit lines and other commitments	£ 41,595	£ 41,721
Contingent Liability for Guarantees [Member]
Disclosure of contingent liabilities and commitments [line items]
Guarantees given to third parties	1,198	1,610
Loan commitments [member] | Not Later Than 1 Year [member]
Disclosure of contingent liabilities and commitments [line items]
Formal standby facilities, credit lines and other commitments	18,248	8,550
Loan commitments [member] | More than One Year [member]
Disclosure of contingent liabilities and commitments [line items]
Formal standby facilities, credit lines and other commitments	£ 22,149	£ 31,561

Contingent Liabilities and Co_4

Contingent Liabilities and Commitments - Additional Information (Detail) £ in Millions, $ in Millions	Nov. 02, 2015	Dec. 31, 2019GBP (£)	Dec. 31, 2019EUR (€)	Dec. 31, 2018GBP (£)	Dec. 31, 2017GBP (£)	Feb. 27, 2020USD ($)
Disclosure of contingent liabilities and commitments [line items]
Amount of preferred stock upon indemnity more than one billion | €			€ 0
Description of material leasing arrangements by lessee classified as operating lease		The majority of leases are subject to a third party outsourcing contract which expires in December 2020 and the remainder are held directly by the Santander UK group with third party landlords. Where leases subject to the outsourcing contract expire on or after the expiry of the outsourcing contract in December 2020 and occupation is still required, negotiations will be held directly with the landlords of these properties, to agree renewal terms.	The majority of leases are subject to a third party outsourcing contract which expires in December 2020 and the remainder are held directly by the Santander UK group with third party landlords. Where leases subject to the outsourcing contract expire on or after the expiry of the outsourcing contract in December 2020 and occupation is still required, negotiations will be held directly with the landlords of these properties, to agree renewal terms.	The majority of leases are subject to a third party outsourcing contract which expires in December 2020 and the remainder are held directly by the Santander UK group with third party landlords. Where leases subject to the outsourcing contract expire on or after the expiry of the outsourcing contract in December 2020 and occupation is still required, negotiations will be held directly with the landlords of these properties, to agree renewal terms.
Minimum lease extension period		3 years	3 years
Terms of notice period		12 months	12 months
Rental expense				£ 61	£ 61
Minimum rentals				63	61
Sub-lease rental income				2	£ 0
Contingent rent expense		£ 0
Compliance with Consumer Credit Act [member]
Disclosure of contingent liabilities and commitments [line items]
Additional operational risk losses and restructuring provision		£ 68		58
Bottom of Range [member]
Disclosure of contingent liabilities and commitments [line items]
Losses on litigation settlements | €			€ 1,000,000,000
Visa Europe Ltd [member]
Disclosure of contingent liabilities and commitments [line items]
Sale of share capital	100.00%
Genworth Financial International Holdings Inc [Member]
Disclosure of contingent liabilities and commitments [line items]
Percentage of litigation on settlement		90.00%
Litigation claim		£ 350		£ 265
Genworth Financial International Holdings Inc [Member] | Commencement of major litigation [member]
Disclosure of contingent liabilities and commitments [line items]
Litigation claim | $						$ 560
Santander UK Group [member]
Disclosure of contingent liabilities and commitments [line items]
Liability arising through disallowance of tax allowance		£ 146

Contingent Liabilities and Co_5

Contingent Liabilities and Commitments - Operating Lease Commitments (Detail) £ in Millions	Dec. 31, 2018GBP (£)
Disclosure of finance lease and operating lease by lessee [line items]
Lease payments	£ 246
Not Later Than 1 Year [member]
Disclosure of finance lease and operating lease by lessee [line items]
Lease payments	72
Later Than One Year and Not Later Than Five Years [member]
Disclosure of finance lease and operating lease by lessee [line items]
Lease payments	114
Later Than Five Years [member]
Disclosure of finance lease and operating lease by lessee [line items]
Lease payments	£ 60

Share Capital - Schedule of Sha

Share Capital - Schedule of Share Capital Issued and Fully Paid (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018
Disclosure of classes of share capital [line items]
Issued and fully paid share capital	£ 3,105	£ 3,119	£ 3,119	£ 3,119
Redemption of preference shares, amount	£ (14)
Ordinary Share Capital [member]
Disclosure of classes of share capital [line items]
Number of shares issued and fully paid	31,051,768,866	31,051,768,866	31,051,768,866	31,051,768,866
Issued and fully paid share capital	£ 3,105	£ 3,105	£ 3,105	£ 3,105
Number of redemption of preference shares	0
Redemption of preference shares, amount	£ 0
Three Hundred Million Preference Shares [Member]
Disclosure of classes of share capital [line items]
Number of shares issued and fully paid	0	13,780	13,780	13,780
Issued and fully paid share capital	£ 0	£ 14	£ 14	£ 14
Number of redemption of preference shares	(13,780)
Redemption of preference shares, amount	£ (14)

Share Capital - Schedule of S_2

Share Capital - Schedule of Share Capital Issued and Fully Paid (Parenthetical) (Detail) - GBP (£) £ / shares in Units, £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of classes of share capital [line items]
Notional amount	£ 205,172	£ 237,771
Ordinary Share Capital [member]
Disclosure of classes of share capital [line items]
Price per share	£ 0.10
Three Hundred Million Preference Shares [Member]
Disclosure of classes of share capital [line items]
Price per share	£ 1,000
Notional amount	£ 300

Share Capital - Summary of Shar

Share Capital - Summary of Share Premium (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of classes of share capital [abstract]
Share premium	£ 5,620	£ 5,620

Share Capital - Additional Info

Share Capital - Additional Information (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of classes of share capital [line items]
Sterling preference shares, Notional amount	£ 325	£ 325

Other Equity Instruments - Summ

Other Equity Instruments - Summary of Other Equity Instruments (Detail) - GBP (£) £ in Millions	Aug. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Disclosure of other equity instruments [line items]
Other equity instruments		£ 2,191	£ 1,991
300m Step-up Callable Perpetual Reserve Capital Instruments [member]
Disclosure of other equity instruments [line items]
Next call date		2026-02
Interest rate		7.037%
Other equity instruments		£ 235	235
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Next call date		2024-06
Interest rate	6.30%	6.75%
Other equity instruments		£ 496	496
750m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Next call date		2022-06
Interest rate		7.375%
Other equity instruments		£ 750	750
300m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Interest rate		7.60%
Other equity instruments		£ 0	300
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Next call date		2020-03
Interest rate		5.18%
Other equity instruments		£ 210	£ 210
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Next call date		2025-03
Interest rate		6.30%
Other equity instruments		£ 500

Other Equity Instruments - Su_2

Other Equity Instruments - Summary of Other Equity Instruments (Parenthetical) (Detail) - GBP (£) £ in Millions	Aug. 31, 2019	Dec. 31, 2019
300m Step-up Callable Perpetual Reserve Capital Instruments [member]
Disclosure of other equity instruments [line items]
Capital securities		£ 300
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities	£ 500	500
750m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities		750
300m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities		300
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities		500
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities		£ 500

Other Equity Instruments - Addi

Other Equity Instruments - Additional Information (Detail) - GBP (£) £ in Millions	Aug. 31, 2019	Feb. 14, 2016	Dec. 31, 2019
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Common equity tier 1 capital ratio minimum			7.00%
Distribution rate resets, period			5 years
Perpetual Capital Securities issued	£ 500		£ 500
Interest rate	6.30%		6.75%
300m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Reserve Capital Instruments bear interest rate reset period		5 years
Reserve Capital Instruments benchmark gilt rate period		5 years
Interest rate	7.60%
Perpetual capital securities purchased and redeemed	£ 300
750m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Perpetual Capital Securities issued			£ 750
Interest rate			7.375%
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Perpetual Capital Securities issued			£ 500
Interest rate			6.30%
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Perpetual Capital Securities issued			£ 500
Interest rate			5.18%

Non-Controlling Interests - Sch

Non-Controlling Interests - Schedule of Amounts Attributable to Non-Controlling Interests (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of noncontrolling interests [line items]
Non-controlling interests	£ 160	£ 151
PSA Finance UK Limited [member]
Disclosure of noncontrolling interests [line items]
Non-controlling interests	£ 160	£ 151

Changes in Liabilities Arisin_3

Changes in Liabilities Arising From Financing Activities - Summary of Changes in Liabilities Arising from Financing Activities (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	£ 52,284	£ 48,707
Cash flows from financing activities	(4,112)	2,730
Cash flows from operating activities	(529)	(2,453)
- Unrealised foreign exchange	(1,370)	1,520
- Other changes	575	1,780
Ending Balance	46,848	52,284
Debt Securities [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	46,692	42,633
Cash flows from financing activities	(3,839)	4,615
Cash flows from operating activities	(529)	(2,522)
- Unrealised foreign exchange	(1,320)	1,371
- Other changes	125	595
Ending Balance	41,129	46,692
Subordinated liabilities [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	3,601	3,793
Cash flows from financing activities	0	(277)
Cash flows from operating activities	0	69
- Unrealised foreign exchange	(50)	149
- Other changes	(23)	(133)
Ending Balance	3,528	3,601
Other Equity Instruments [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	1,991	2,281
Cash flows from financing activities	196	(290)
Cash flows from operating activities	0
- Unrealised foreign exchange	0
- Other changes	4
Ending Balance	2,191	1,991
Dividends Paid [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	0
Cash flows from financing activities	(469)	(1,318)
Cash flows from operating activities	0
- Unrealised foreign exchange	0
- Other changes	469	1,318
Ending Balance	£ 0	£ 0

Assets Charged as Security fo_3

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets - Financial Assets Charged as Security Under On-Balance Sheet and Off-Balance (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	£ 4,786	£ 3,541
On-Balance Sheet [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	63,025	61,755
On-Balance Sheet [member] | Cash and Balances at Central Banks [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	1,080	1,080
On-Balance Sheet [member] | Loans and advances to banks [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	403	218
On-Balance Sheet [member] | Loans and Advances to Customers [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	36,225	35,694
On-Balance Sheet [member] | Loans and Advances to Customers [member] | Other [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	16,282	15,175
On-Balance Sheet [member] | Other financial assets at amortised cost [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	3,026	3,763
On-Balance Sheet [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	6,009	5,825
Off-Balance Sheet [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	£ 15,098	£ 15,220

Assets Charged as Security fo_4

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets - Additional Information (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	£ 4,786	£ 3,541
Gross assets charged as security for liabilities	36,391	36,195
Notes issued under securitisation and covered bond programmes retained internally	22,783	23,984
Securities Lending [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	21,563	24,714
Collateral accepted as security for assets	4,676	7,508
Internally Retained [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Notes issued under securitisation and covered bond programmes retained internally	4,728	4,039
Third Party Bilateral Secured Funding Transactions [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	1,581	1,834
Cash [member] | Derivative Financial Instruments [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	1,716	1,465
Collateral accepted as security for assets	2,169	4,048
Purchase and resale agreements [member]
Disclosure of assets pledged as security [line items]
Collateral accepted as security for assets	20,444	15,728
Fellow Subsidiaries [member] | Sale and Repurchase Agreements [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	20,686	17,485
Fellow Subsidiaries [member] | Loans and advances to customers- securitisations and covered bonds [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	2,067	2,383
Santander UK Plc [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Gross assets charged as security for liabilities	36,391	36,195
Santander UK Plc [member] | Internally Retained [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Internally retained securitisation and covered bond issuances available for creating collateral	£ 166	£ 501

Assets Charged as Security fo_5

Assets Charged as Security for Liabilities and Collateral Accepted as Security for Assets - Schedule of Collateral Held as Security for Assets (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
On-Balance Sheet [member]
Disclosure of assets pledged as security [line items]
Total on-balance sheet/ off-balance sheet	£ 2,169	£ 4,048
On-Balance Sheet [member] | Deposits by banks [member]
Disclosure of assets pledged as security [line items]
Total on-balance sheet/ off-balance sheet	2,169	4,048
Off-Balance Sheet [member]
Disclosure of assets pledged as security [line items]
Total on-balance sheet/ off-balance sheet	£ 25,120	£ 23,236

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2019GBP (£)awardScheme£ / sharesshares	Dec. 31, 2018GBP (£)Scheme£ / sharesshares
Disclosure of terms and conditions of share-based payment arrangement [line items]
Liabilities arising from share-based payment transactions		£ 2,400,000	£ 7,700,000
Liabilities arising from share-based payment transactions, vested liabilities		£ 1,400,000	£ 700,000
Number of sharesave schemes launched | Scheme		11	11
Discount percent on share price under share based compensation plan		10.00%
Weighted average share price | £ / shares		£ 3.18	£ 3.79
Weighted average grant-date fair value		£ 0.49	£ 0.53
Number of shares outstanding | shares		2,396,909	2,346,108
Employees [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Deferred shares description		Any deferred awards are dependent on continued employment or subject to Santander's discretion for leavers. For 2018 and 2019 bonus awards, deferral of the award is over a three, five or seven-year period from the anniversary of the initial award. Deferred bonus awards in shares are subject to an additional one-year retention period from the point of delivery.
Cash [member] | Employees [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Annual bonus percentage		50.00%
Shares [member] | Employees [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Annual bonus percentage		50.00%
Long-Term Incentive Plan (LTIP) [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
LTIP awarded | award		0
Percent of other equity instruments vested	65.78%
Share Incentive Plans [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Maximum investment value per tax year		£ 1,800
Percentage of maximum salary that can be invested		10.00%
Vesting requirements for sharebased payment arrangement		no vesting conditions attached to these shares, and no restrictions as to when the shares can be removed from the trust. However, if a participant chooses to sell the shares before the end of five years, they will be liable for the taxable benefit received when the shares are taken out of the trust. The shares can be released from trust after five years free of income tax and national insurance contributions. 2,396,909 shares were outstanding at 31 December 2019 (2018: 2,346,108 shares).
Bottom of Range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Year of grant of share-based payment arrangement		2008
Employee saving on share based compensation		£ 5
Terms of options		3 years
Top of Range [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Year of grant of share-based payment arrangement		2018
Employee saving on share based compensation		£ 500
Terms of options		5 years
Variable Pay of Less Than 500,000 [member] | Employees [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Percentage of defer annual bonus		40.00%
Variable Pay at or Above 500,000 [member] | Employees [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Percentage of defer annual bonus		60.00%

Share-Based Compensation - Summ

Share-Based Compensation - Summary of Movement in Share Options (Detail) - Sharesave Schemes [member] Unit_pure in Thousands	12 Months Ended
	Dec. 31, 2019£ / shares	Dec. 31, 2018£ / shares
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options outstanding beginning balance	26,838	27,201
Number of options granted	9,594	6,210
Number of options exercised	(7,978)	(3,340)
Number of options forfeited/expired	(5,081)	(3,233)
Number of options outstanding ending balance	23,373	26,838
Number of options exercisable	2,519	10,370
Weighted average exercise price outstanding beginning balance	£ 3.12	£ 3.12
Weighted average exercise price granted	2.83	3.46
Weighted average exercise price exercised	2.83	3.16
Weighted average exercise price forfeited/expired	3.42	3.76
Weighted average exercise price outstanding ending balance	3.03	3.12
Weighted average exercise price exercisable ending balance	£ 3.62	£ 2.81

Share-Based Compensation - Su_2

Share-Based Compensation - Summary of Range of Exercise Prices and Weighted Average Remaining Contractual Life of the Options Outstanding (Detail) - Sharesave Schemes [member] - £ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Option outstanding, Weighted average exercise price	£ 3.03	£ 3.12	£ 3.12
2 to 3 [member]
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Options outstanding , Weighted average remaining contractual life years	3 years	2 years
Option outstanding, Weighted average exercise price	£ 2.80	£ 2.75
3 to 4 [member]
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Options outstanding , Weighted average remaining contractual life years	2 years	3 years
Option outstanding, Weighted average exercise price	£ 3.38	£ 3.36
4 to 5 [member]
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Options outstanding , Weighted average remaining contractual life years	2 years	3 years
Option outstanding, Weighted average exercise price	£ 4.13	£ 4.11

Share-Based Compensation - Su_3

Share-Based Compensation - Summary of Range of Exercise Prices and Weighted Average Remaining Contractual Life of the Options Outstanding (Parenthetical) (Detail) - Sharesave Schemes [member]	Dec. 31, 2019£ / shares
2 to 3 [member] | Bottom of Range [member]
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	£ 2
2 to 3 [member] | Top of Range [member]
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	3
3 to 4 [member] | Bottom of Range [member]
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	3
3 to 4 [member] | Top of Range [member]
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	4
4 to 5 [member] | Bottom of Range [member]
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	4
4 to 5 [member] | Top of Range [member]
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Range of exercise prices	£ 5

Share-Based Compensation - Su_4

Share-Based Compensation - Summary of Movement in Value of Conditional Awards in LTIPs (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
2015 LTIP [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Conditional awards at the beginning of the year	£ 6,374	£ 6,503
Conditional award payments made	(4,578)
Conditional awards forfeited or cancelled	(1,796)	(129)
Conditional awards outstanding at the end of the year	0	6,374
2014 LTIP [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Conditional awards at the beginning of the year	0	1,910
Conditional award payments made	0
Conditional awards forfeited or cancelled	0	(1,910)
Conditional awards outstanding at the end of the year	£ 0	£ 0

Transactions With Directors a_3

Transactions With Directors and Other Key Management Personnel - Summary of Remuneration of the Directors and Other Key Management Personnel (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Remuneration Of Directors And Other Key Management Personnel [abstract]
Salaries and fees	£ 5,025,665	£ 5,028,434	£ 4,406,908
Performance-related payments	3,864,965	5,194,317	3,685,464
Other fixed remuneration (pension and other allowances & non-cash benefits)	1,367,069	1,467,011	1,580,321
Expenses	42,526	25,198	96,358
Total remuneration	10,300,225	11,714,960	9,769,051
Short-term employee benefits	21,925,975	24,445,189	24,642,085
Post-employment benefits	3,590,466	2,399,261	2,292,857
Total compensation	£ 25,516,441	£ 26,844,450	£ 26,934,942

Transactions With Directors a_4

Transactions With Directors and Other Key Management Personnel - Summary of Remuneration of the Directors and Other Key Management Personnel (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2019GBP (£)IndividualsDirectors	Dec. 31, 2018GBP (£)IndividualsDirectorsshares	Dec. 31, 2017GBP (£)Individualsshares
Disclosure of directors and key management remuneration [line items]
Payments made as buy-outs of deferred performance-related payment | £		£ 266,667	£ 52,100
Number of previously employed individuals for buy-out of deferred performance related payment | Individuals	0	1	1
Termination payment | £	£ 1,076,435	£ 847,388
Number key management persons who receives termination benefit | Directors	1	2
Banco Santander SA London Branch [member]
Disclosure of directors and key management remuneration [line items]
Number of shares made as buy-outs of deferred performance-related payment | shares		189,381	603,614
Number of previously employed individuals for grants of shares as buy-out of deferred performance related payment | Individuals		5	5

Transactions With Directors a_5

Transactions With Directors and Other Key Management Personnel - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019GBP (£)DirectorSecurityLoan	Dec. 31, 2018GBP (£)DirectorSecurityLoan	Dec. 31, 2017GBP (£)
Disclosure of transactions between related parties [line items]
Remuneration excluding pension contribution	£ 3,725,993	£ 4,635,497
Remuneration excluding pension contribution performance related	1,989,900	2,317,000
Deferred pension benefit accruing under a defined benefit scheme	20,973	20,402
Ex gratia pensions paid to former Directors	335,202	87,300	£ 2,482
Sharedealing transactions through the Santander UK group's	£ 0	£ 0
Number of Directors undertook sharedealing transactions | Director	0	0
Loans made to directors	£ 1,767,066	£ 65,232
Number of loan made to directors | SecurityLoan	9	8
Directors who held any interest in the shares | Director	0	0
Directors who exercised or were granted any rights to subscribe for shares | Director	0	0
Other key management personnel [member]
Disclosure of transactions between related parties [line items]
Loans made to key management personnel	£ 3,153,343	£ 2,969,462
Number of loan made to key management personnel | SecurityLoan	9	8

Transactions With Directors a_6

Transactions With Directors and Other Key Management Personnel - Summary of Transactions with Directors, Other Key Management Personnel (Detail) - Key management personnel of entity or parent [member] £ in Thousands	12 Months Ended
	Dec. 31, 2019GBP (£)LoansDeposits	Dec. 31, 2018GBP (£)LoansDeposits
Disclosure of directors and key management remuneration [line items]
Number of secured loans, unsecured loans and overdrafts, beginning balance | Loans	16	7
Number of secured loans, unsecured loans and overdrafts, net movements | Loans	2	9
Number of secured loans, unsecured loans and overdrafts, ending balance | Loans	18	16
Beginning balance	£ 3,035	£ 1,216
Net movements	1,885	1,819
Ending balance	£ 4,920	£ 3,035
Number of deposit, bank and instant access accounts and investments, beginning balance | Deposits	30	25
Number of deposit, bank and instant access accounts and investments, net movements | Deposits	2	5
Number of deposit, bank and instant access accounts and investments, ending balance | Deposits	32	30
Beginning balance	£ 10,963	£ 13,184
Net movements	1,012	(2,221)
Ending balance	£ 11,975	£ 10,963

Related Party Disclosures - Sum

Related Party Disclosures - Summary of Transactions With Related Parties (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	£ (232)	£ (189)	£ (159)
Interest, fees and other expenses paid	756	670	1,019
Amounts owed by related parties	3,966	4,534
Amounts owed to related parties	(13,629)	(15,393)
Ultimate parent [member]
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(130)	(72)	(60)
Interest, fees and other expenses paid	266	217	321
Amounts owed by related parties	1,560	2,491
Amounts owed to related parties	(2,143)	(3,594)
Immediate parent [member]
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(7)	(3)	(3)
Interest, fees and other expenses paid	317	275	207
Amounts owed by related parties	8
Amounts owed to related parties	(10,012)	(10,392)
Fellow Subsidiaries [member]
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(66)	(86)	(76)
Interest, fees and other expenses paid	173	178	491
Amounts owed by related parties	204	57
Amounts owed to related parties	(544)	(689)
Associates and joint ventures [member]
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(29)	(28)	£ (20)
Interest, fees and other expenses paid	0
Amounts owed by related parties	2,194	1,986
Amounts owed to related parties	£ (930)	£ (718)

Related Party Disclosures - Add

Related Party Disclosures - Additional Information (Detail) - GBP (£) £ in Millions	1 Months Ended
	Jul. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of transactions between related parties [line items]
Other assets		£ 2,520	£ 2,280
Liabilities		£ 265,685	£ 267,463	£ 298,560
Decrease in RWAs due to transfers	£ 5,500
Dividend paid	668
Banco Santander London Branch [member]
Disclosure of transactions between related parties [line items]
Customer loans	1,400
Other assets	21,500
Liabilities	20,700
Banco Santander London Branch [member] | Derivative Financial Instruments [member]
Disclosure of transactions between related parties [line items]
Other assets	19,700
Liabilities	£ 18,800
Santander UK Group Holdings Plc [Member]
Disclosure of transactions between related parties [line items]
Sale Of Share Capital Issued Percentage	100.00%
Consideration paid (received)	£ 337

Financial Instruments - Analysi

Financial Instruments - Analysis of Fair Value of Financial Instruments Carried at Amortised (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	£ 207,287	£ 201,289
Loans and advances to banks	1,855	2,799
Reverse repurchase agreements - non trading	23,636	21,127
Deposits by customers	181,883	178,090
Deposits by banks	14,353	17,221
Repurchase agreements–non trading	18,286	10,910
Debt securities in issue	41,129	46,692
Subordinated liabilities	3,528	3,601
Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial assets	244,395	235,101
Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial liabilities	261,582	258,000
Deposits by customers [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by customers	182,013	178,181
Deposits by banks [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by banks	14,363	17,232
Repurchase agreements - non trading [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Repurchase agreements–non trading	18,292	10,923
Debt Securities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Debt securities in issue	42,694	47,787
Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Subordinated liabilities	4,220	3,877
Loans and Advances to Customers [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	211,796	204,061
Loans and advances to banks [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to banks	1,855	2,799
Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Reverse repurchase agreements - non trading	23,634	21,130
Other financial assets at amortised cost [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Other financial assets at amortised cost	7,110	7,111
Level 1 [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial assets	6,575	6,390
Level 1 [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial liabilities	0
Level 1 [member] | Deposits by customers [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by customers	0
Level 1 [member] | Deposits by banks [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by banks	0
Level 1 [member] | Repurchase agreements - non trading [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Repurchase agreements–non trading	0
Level 1 [member] | Debt Securities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Debt securities in issue	0
Level 1 [member] | Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Subordinated liabilities	0
Level 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	0
Level 1 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to banks	0
Level 1 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Reverse repurchase agreements - non trading	0
Level 1 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Other financial assets at amortised cost	6,575	6,390
Level 2 [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial assets	25,908	24,590
Level 2 [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial liabilities	79,257	78,851
Level 2 [member] | Deposits by customers [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by customers	95	21
Level 2 [member] | Deposits by banks [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by banks	13,956	16,243
Level 2 [member] | Repurchase agreements - non trading [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Repurchase agreements–non trading	18,292	10,923
Level 2 [member] | Debt Securities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Debt securities in issue	42,694	47,787
Level 2 [member] | Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Subordinated liabilities	4,220	3,877
Level 2 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	0
Level 2 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to banks	1,739	2,739
Level 2 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Reverse repurchase agreements - non trading	23,634	21,130
Level 2 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Other financial assets at amortised cost	535	721
Level 3 [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial assets	211,912	204,121
Level 3 [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial liabilities	182,325	179,149
Level 3 [member] | Deposits by customers [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by customers	181,918	178,160
Level 3 [member] | Deposits by banks [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by banks	407	989
Level 3 [member] | Repurchase agreements - non trading [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Repurchase agreements–non trading	0
Level 3 [member] | Debt Securities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Debt securities in issue	0
Level 3 [member] | Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Subordinated liabilities	0
Level 3 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	211,796	204,061
Level 3 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to banks	116	60
Level 3 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Reverse repurchase agreements - non trading	0
Level 3 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Other financial assets at amortised cost	0
Fair Value [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial assets	239,834	232,444
Fair Value [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial liabilities	259,179	256,514
Fair Value [member] | Deposits by customers [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by customers	181,883	178,090
Fair Value [member] | Deposits by banks [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by banks	14,353	17,221
Fair Value [member] | Repurchase agreements - non trading [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Repurchase agreements–non trading	18,286	10,910
Fair Value [member] | Debt Securities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Debt securities in issue	41,129	46,692
Fair Value [member] | Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Subordinated liabilities	3,528	3,601
Fair Value [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to customers	207,287	201,289
Fair Value [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Loans and advances to banks	1,855	2,799
Fair Value [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Reverse repurchase agreements - non trading	23,636	21,127
Fair Value [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Other financial assets at amortised cost	£ 7,056	£ 7,229

Financial Instruments - Fair Va

Financial Instruments - Fair Values of Financial Instruments Measured at Fair Value on a Recurring Basis (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 13,449	£ 24,178
Liabilities at fair value	3,161	7,655
Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,713	6,286
derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,448	1,369
derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	3,316	5,259
Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	386	5,617
Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	9,747	13,302
Level 1 [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	9,209	12,505
Liabilities at fair value	0
Level 1 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0
Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0
Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Level 1 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	18
Level 1 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	9,209	12,487
Level 2 [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	3,723	10,530
Liabilities at fair value	3,068	7,540
Level 2 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,652	6,237
Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,416	1,303
Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	3,241	5,165
Level 2 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	4,623
Level 2 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	482	742
Level 3 [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	517	1,143
Liabilities at fair value	93	115
Level 3 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	61	49
Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	32	66
Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	75	94
Level 3 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	386	976
Level 3 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 56	73
Exchange Rate Contracts [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 664	551
Exchange Rate Contracts [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 2,323	4,348
Valuation technique	A
Exchange Rate Contracts [member] | Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 0
Exchange Rate Contracts [member] | Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Exchange Rate Contracts [member] | Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	660	528
Exchange Rate Contracts [member] | Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	2,317	4,323
Exchange Rate Contracts [member] | Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	4	23
Exchange Rate Contracts [member] | Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 6	25
Interest Rate Contracts [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A & C
Liabilities at fair value	£ 1,838	2,522
Interest Rate Contracts [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 1,924	2,532
Valuation technique	A & C
Interest Rate Contracts [member] | Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 0
Interest Rate Contracts [member] | Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Interest Rate Contracts [member] | Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,836	2,515
Interest Rate Contracts [member] | Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	1,915	2,526
Interest Rate Contracts [member] | Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	2	7
Interest Rate Contracts [member] | Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	9	6
Equity and Credit Contracts [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 52	54
Equity and Credit Contracts [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	B & D
Liabilities at fair value	£ 160	168
Equity and Credit Contracts [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 283	251
Valuation technique	B & D
Equity and Credit Contracts [member] | Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 0
Equity and Credit Contracts [member] | Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Equity and Credit Contracts [member] | Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	134	132
Equity and Credit Contracts [member] | Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	223	188
Equity and Credit Contracts [member] | Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	26	36
Equity and Credit Contracts [member] | Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	60	63
Netting [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	(1,214)	(1,872)
Netting [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	(1,214)	(1,872)
Netting [member] | Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0
Netting [member] | Level 1 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Netting [member] | Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	(1,214)	(1,872)
Netting [member] | Level 2 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	(1,214)	(1,872)
Netting [member] | Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0
Netting [member] | Level 3 [member] | derivative financial instruments [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Debt Securities [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 294	3,251
Valuation technique	A, B & D
Debt Securities [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 9,691	13,229
Valuation technique	D
Debt Securities [member] | Level 1 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 0	18
Debt Securities [member] | Level 1 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	9,209	12,487
Debt Securities [member] | Level 2 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	2,339
Debt Securities [member] | Level 2 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	482	742
Debt Securities [member] | Level 3 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	294	894
Debt Securities [member] | Level 3 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Equity securities [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 0
Valuation technique	B
Equity securities [member] | Level 1 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 0
Equity securities [member] | Level 2 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Equity securities [member] | Level 3 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Loans and Advances to Customers [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 92	94
Valuation technique	A
Loans and Advances to Customers [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 56	73
Valuation technique	D
Loans and Advances to Customers [member] | Level 1 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 0
Loans and Advances to Customers [member] | Level 1 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Loans and Advances to Customers [member] | Level 2 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	12
Loans and Advances to Customers [member] | Level 2 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Loans and Advances to Customers [member] | Level 3 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	92	82
Loans and Advances to Customers [member] | Level 3 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 56	73
Debt Securities [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 1,105	990
Debt Securities [member] | Level 1 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0
Debt Securities [member] | Level 2 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	1,099	983
Debt Securities [member] | Level 3 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 6	7
Reverse repurchase agreements - non-trading [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 0	2,110
Reverse repurchase agreements - non-trading [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 0	2,272
Valuation technique	A
Reverse repurchase agreements - non-trading [member] | Level 1 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 0
Reverse repurchase agreements - non-trading [member] | Level 1 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0
Reverse repurchase agreements - non-trading [member] | Level 2 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0	2,110
Reverse repurchase agreements - non-trading [member] | Level 2 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	0	2,272
Reverse repurchase agreements - non-trading [member] | Level 3 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0
Reverse repurchase agreements - non-trading [member] | Level 3 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Assets at fair value	£ 0
Structured Deposits [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 435	133
Structured Deposits [member] | Level 1 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0
Structured Deposits [member] | Level 2 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	406	104
Structured Deposits [member] | Level 3 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 29	29
Collateral and associated financial guarantees [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Valuation technique	D
Liabilities at fair value	£ 173	3,053
Collateral and associated financial guarantees [member] | Level 1 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	0
Collateral and associated financial guarantees [member] | Level 2 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	147	3,040
Collateral and associated financial guarantees [member] | Level 3 [member] | Other Financial Liabilities at fair value through profit or loss, category [member]
Disclosure of fair value measurements of assets and liabilities [line items]
Liabilities at fair value	£ 26	£ 13

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of financial assets [abstract]
Fair value of financial instruments transferred from Level 1 to Level 2	£ 0
Fair value of financial instruments transferred from Level 2 to Level 1	0
Fair value of financial instruments transferred from Level 2 to Level 3	0	£ 35
Fair value of financial instruments transferred from Level 3 to Level 2	0	0
Exposure to wrong-way risk
Disclosure of financial liabilities [abstract]
Fair value of financial instruments transferred from Level 2 to Level 3		31
Fair value of financial instruments transferred from Level 3 to Level 2	£ 0	£ 0

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value Adjustment (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of financial assets [line items]
Fair value adjustments	£ 17	£ 67
Bid-Offer and Trade Specific Adjustments [Member]
Disclosure of financial assets [line items]
Fair value adjustments	(12)	13
Uncertainty [Member]
Disclosure of financial assets [line items]
Fair value adjustments	17	36
Credit Risk Adjustment [Member]
Disclosure of financial assets [line items]
Fair value adjustments	6	9
Funding Fair Value Adjustment [Member]
Disclosure of financial assets [line items]
Fair value adjustments	6	4
Risk Related Adjustments [Member]
Disclosure of financial assets [line items]
Fair value adjustments	17	62
Model-Related [Member]
Disclosure of financial assets [line items]
Fair value adjustments	£ 0	£ 5

Financial Instruments - Analy_2

Financial Instruments - Analysis of Financial Instruments Valued Using Internal Models Based on Information Other Than Market Data (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of financial assets and liabilities [line items]
FVTPL	£ 386	£ 5,617
FVOCI	9,747	13,302
Total net assets	424	1,028	£ 0
Total (expense)/ income	(5)	6	(34)
Other Level 3 [member] | Level 3 [member]
Disclosure of financial assets and liabilities [line items]
Other Level 3 assets	23	40
Other Level 3 liabilities	(41)	(67)
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	16	(2)	(26)
Derivative liabilities and other Level 3 liabilities, fair value movements recognised in profit/(loss)	(5)	1	19
Level 3 [member]
Disclosure of financial assets and liabilities [line items]
Financial assets and liabilities	442	1,055
Financial asset liabilities	(16)	7	(27)
Reversionary property securities [member] | Equity and Credit Contracts [member]
Disclosure of financial assets and liabilities [line items]
Derivative assets	52	54
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	2	30	(6)
Reversionary property securities [member] | Debt Securities [member]
Disclosure of financial assets and liabilities [line items]
FVTPL	120	142
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	(17)	(28)	(18)
Loans and Advances to Customers [member] | Roll-up Mortgage Portfolio [member]
Disclosure of financial assets and liabilities [line items]
FVTPL	51	53
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	0	8	2
Loans and Advances to Customers [member] | Other Loans [member]
Disclosure of financial assets and liabilities [line items]
FVTPL	41	29
FVOCI	56	73
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	1	2
Loans and Advances to Customers [member] | Other Loans [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of financial assets and liabilities [line items]
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	(2)	(5)
Credit Linked Note [member] | Debt Securities [member]
Disclosure of financial assets and liabilities [line items]
FVTPL	174	752
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	7	13
Property Related Options and Forwards [Member] | Equity Securities [member]
Disclosure of financial assets and liabilities [line items]
Derivative liabilities	(26)	(35)
Derivative liabilities and other Level 3 liabilities, fair value movements recognised in profit/(loss)	0		£ (5)
Credit Protection Guarantees [member] | Financial Guarantees [member]
Disclosure of financial assets and liabilities [line items]
FVTPL	(26)	(13)
Derivative liabilities and other Level 3 liabilities, fair value movements recognised in profit/(loss)	£ (7)	£ (13)

Financial Instruments - Liabili

Financial Instruments - Liabilities Reconciliation of Fair Value Measurements in Level 3 of the Fair Value Hierarchy (Detail) - GBP (£) £ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Disclosure of fair value measurement of liabilities [line items]
Beginning balance		£ (267,463)	£ (298,560)
Transfers in			(31)
Ending Balance		(265,685)	(267,463)
Level 3 [member] | Fair Value Through P&L [member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance		(49)
At 1 January 2018			(6)
Total gains/(losses) recognised in profit or loss, fair value movements		(6)	(13)
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements		(6)	(1)
Transfers in		0	(29)
Netting	[1]	0
Additions		(3)
Sales		0
Settlements		3
Ending Balance		(61)	(49)
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		(12)	(14)
Level 3 [member] | Financial Liabilities at Fair Value, Class [member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance		(115)
At 1 January 2018			(69)
Total gains/(losses) recognised in profit or loss, fair value movements		(12)	(12)
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements		(6)	4
Transfers in		0	(60)
Netting	[1]	0
Additions		(3)
Sales		0
Settlements		43	22
Ending Balance		(93)	(115)
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		(18)	(8)
Level 3 [member] | Derivative Liabilities [Member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance		(66)
At 1 January 2018			(63)
Total gains/(losses) recognised in profit or loss, fair value movements		(6)	1
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements		0	5
Transfers in		0	(31)
Netting	[1]	0
Additions		0
Sales		0
Settlements		40	22
Ending Balance		(32)	(66)
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		£ (6)	£ 6
[1]	This 19. relates to the effect of netting on the fair value of the credit linked notes due to a legal right of set-off between the principal amounts of the senior notes and the associated cash deposits. For more, see ‘ii) Credit protection entities’ in Note

Financial Instruments - Assets

Financial Instruments - Assets Reconciliation of Fair Value Measurements in Level 3 of the Fair Value Hierarchy (Detail) - GBP (£) £ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018
Disclosure of fair value measurement of assets [line items]
Beginning balance		£ 283,372	£ 314,765
Transfers in		0	35
Ending Balance		281,702	283,372
Level 3 [member] | Fair Value Through P&L [Member]
Disclosure of fair value measurement of assets [line items]
Beginning balance		976
At 1 January 2018			838
Total gains/(losses) recognised in profit or loss, fair value movements		(9)	(5)
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements		6
Transfers in		11	18
Netting	[1]	(430)
Additions		188	280
Sales		0	(95)
Settlements		(356)	(60)
Ending Balance		386	976
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		(3)	(5)
Level 3 [member] | Financial assets at FVOCI [member]
Disclosure of fair value measurement of assets [line items]
Beginning balance		73
At 1 January 2018			199
Total gains/(losses) recognised in profit or loss, fair value movements		(2)	(5)
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements		0
Transfers in		0
Netting	[1]	0
Additions		0	17
Sales		0
Settlements		(15)	(138)
Ending Balance		56	73
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		(2)	(5)
Level 3 [member] | Financial assets at Fair Value Class [member]
Disclosure of fair value measurement of assets [line items]
Beginning balance		1,143
At 1 January 2018			1,101
Total gains/(losses) recognised in profit or loss, fair value movements		7	18
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements		6	(5)
Transfers in		11	53
Netting	[1]	(430)
Additions		190	297
Sales		0	(95)
Settlements		(410)	(226)
Ending Balance		517	1,143
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		13	13
Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets [line items]
Beginning balance		94
At 1 January 2018			64
Total gains/(losses) recognised in profit or loss, fair value movements		18	28
Total gains/(losses) recognised in profit or loss, foreign exchange and other movements		0	(5)
Transfers in		0	35
Netting	[1]	0
Additions		2
Sales		0
Settlements		(39)	(28)
Ending Balance		75	94
Gains/(losses) recognised in profit or loss relating to assets and liabilities held at the end of the year		£ 18	£ 23
[1]	This 19. relates to the effect of netting on the fair value of the credit linked notes due to a legal right of set-off between the principal amounts of the senior notes and the associated cash deposits. For more, see ‘ii) Credit protection entities’ in Note

Financial Instruments - Effects

Financial Instruments - Effects of Changes in Significant Unobservable Assumptions to Reasonably Possible Alternatives (Level 3) (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2019GBP (£)Index	Dec. 31, 2018GBP (£)Index
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ (3,161)	£ (7,655)
Fair value	13,449	24,178
Equity and Credit Contracts [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ 52	£ 54
Assumption description	HPI Forward growth rate HPI Spot rate	HPI Forward growth rate HPI Spot rate
Shift	1.00%	1.00%
Favourable changes	£ 8	£ 8
Unfavourable changes	£ (8)	£ (8)
Equity and Credit Contracts [member] | Reversionary property derivatives [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Shift	10.00%	10.00%
Favourable changes	£ 7	£ 7
Unfavourable changes	£ (7)	£ (7)
HPI spot rate index level | Index	802	783
Equity Contracts [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ (26)	£ (35)
Assumption description	HPI Forward growth rate HPI Spot rate	HPI Forward growth rate HPI Spot rate
Shift	1.00%	1.00%
Favourable changes	£ 2	£ 2
Unfavourable changes	£ (2)	£ (2)
Equity Contracts [Member] | Property Related Options and Forwards [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Shift	10.00%	10.00%
Favourable changes	£ 3	£ 3
Unfavourable changes	£ (3)	£ (4)
HPI spot rate index level | Index	758	722
Bottom of Range [member] | Equity and Credit Contracts [member] | Reversionary property derivatives [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	0.00%	0.00%
Bottom of Range [member] | Equity Contracts [Member] | Property Related Options and Forwards [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	0.00%	0.00%
Top of Range [member] | Equity and Credit Contracts [member] | Reversionary property derivatives [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	5.00%	5.00%
Top of Range [member] | Equity Contracts [Member] | Property Related Options and Forwards [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	5.00%	5.00%
Weighted average [member] | Equity and Credit Contracts [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	2.57%	2.68%
Weighted average [member] | Equity Contracts [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	2.44%	2.59%
Fair Value Through P&L [Member] | Debt Securities [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ 120	£ 142
Assumption description	HPI Forward growth rate HPI Spot rate	HPI Forward growth rate HPI Spot rate
Shift	1.00%	1.00%
Favourable changes	£ 0	£ 6
Unfavourable changes	£ 0	£ (6)
Fair Value Through P&L [Member] | Debt Securities [member] | Reversionary property securities [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Shift	10.00%	10.00%
Favourable changes	£ 6	£ 10
Unfavourable changes	£ (6)	£ (10)
HPI spot rate index level | Index	802	783
Fair Value Through P&L [Member] | Loans and Advances to Customers [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption description	Credit spreads
Fair Value Through P&L [Member] | Loans and Advances to Customers [member] | Roll-up Mortgage Portfolio [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ 51	£ 53
Assumption description	HPI Forward growth rate	HPI Forward growth rate
Shift	1.00%	1.00%
Favourable changes	£ 2	£ 2
Unfavourable changes	(2)	(2)
Fair Value Through P&L [Member] | Loans and Advances to Customers [member] | Other Loans [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ 41	£ 29
Assumption description		Credit spreads
Shift	20.00%	20.00%
Favourable changes	£ 0
Unfavourable changes	£ 0
Fair Value Through P&L [Member] | Bottom of Range [member] | Debt Securities [member] | Reversionary property securities [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	0.00%	0.00%
Fair Value Through P&L [Member] | Bottom of Range [member] | Loans and Advances to Customers [member] | Roll-up Mortgage Portfolio [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	0.00%	0.00%
Fair Value Through P&L [Member] | Bottom of Range [member] | Loans and Advances to Customers [member] | Other Loans [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	0.00%	0.00%
Fair Value Through P&L [Member] | Top of Range [member] | Debt Securities [member] | Reversionary property securities [Member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	5.00%	5.00%
Fair Value Through P&L [Member] | Top of Range [member] | Loans and Advances to Customers [member] | Roll-up Mortgage Portfolio [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	5.00%	5.00%
Fair Value Through P&L [Member] | Top of Range [member] | Loans and Advances to Customers [member] | Other Loans [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	1.00%	1.00%
Fair Value Through P&L [Member] | Weighted average [member] | Debt Securities [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	2.57%	2.68%
Fair Value Through P&L [Member] | Weighted average [member] | Loans and Advances to Customers [member] | Roll-up Mortgage Portfolio [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	2.69%	2.77%
Fair Value Through P&L [Member] | Weighted average [member] | Loans and Advances to Customers [member] | Other Loans [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	0.35%	0.52%
Financial assets at fair value through other comprehensive income [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ 9,747	£ 13,302
Financial assets at fair value through other comprehensive income [member] | Loans and Advances to Customers [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	56	73
Financial assets at fair value through other comprehensive income [member] | Loans and Advances to Customers [member] | Other Loans [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ 56	£ 73
Assumption description	Credit spreads	Credit spreads
Shift	20.00%	20.00%
Favourable changes	£ 0
Unfavourable changes	£ 0
Financial assets at fair value through other comprehensive income [member] | Bottom of Range [member] | Loans and Advances to Customers [member] | Other Loans [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	0.00%	0.00%
Financial assets at fair value through other comprehensive income [member] | Top of Range [member] | Loans and Advances to Customers [member] | Other Loans [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	1.00%	2.00%
Financial assets at fair value through other comprehensive income [member] | Weighted average [member] | Loans and Advances to Customers [member] | Other Loans [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	0.51%	0.80%

Financial Instruments - Maturit

Financial Instruments - Maturities of Undiscounted Cash Flows for Financial Liabilities and Off Balance Sheet Commitments (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Other financial liabilities at fair value through profit or loss	£ 1,713	£ 6,286
Deposits by customers	181,883	178,090
Deposits by banks	14,353	17,221
Repurchase agreements–non trading	18,286	10,910
Debt securities in issue	41,129	46,692
Subordinated liabilities	3,528	3,601
Undiscounted Cash Flow [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Derivative financial instruments	1,495	1,532
Other financial liabilities at fair value through profit or loss	1,796	6,496
Deposits by customers	182,655	178,443
Deposits by banks	14,519	17,438
Repurchase agreements–non trading	18,308	11,441
Debt securities in issue	42,828	48,649
Subordinated liabilities	5,870	6,377
Financial liabilities	267,471	270,376
Off-balance sheet commitments given	40,344	40,019
Undiscounted Cash Flow [member] | On Demand [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Derivative financial instruments	9
Other financial liabilities at fair value through profit or loss	1	11
Deposits by customers	160,833	159,009
Deposits by banks	2,711	5,096
Repurchase agreements–non trading	6	2
Debt securities in issue	0
Subordinated liabilities	0
Financial liabilities	163,560	164,118
Off-balance sheet commitments given	18,907	18,667
Undiscounted Cash Flow [member] | Not Later Than Three Months [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Derivative financial instruments	243	431
Other financial liabilities at fair value through profit or loss	6	2,146
Deposits by customers	2,531	3,422
Deposits by banks	486	1,100
Repurchase agreements–non trading	15,878	9,101
Debt securities in issue	7,129	9,157
Subordinated liabilities	239	255
Financial liabilities	26,512	25,612
Off-balance sheet commitments given	7,829	5,843
Undiscounted Cash Flow [member] | Later Than Three Months and Not Later Than One Year [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Derivative financial instruments	293	57
Other financial liabilities at fair value through profit or loss	203	76
Deposits by customers	6,476	9,491
Deposits by banks	4,764	90
Repurchase agreements–non trading	1,578	972
Debt securities in issue	8,702	5,520
Subordinated liabilities	131	134
Financial liabilities	22,147	16,340
Off-balance sheet commitments given	840	670
Undiscounted Cash Flow [member] | Later Than One Year and Not Later Than Five Years [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Derivative financial instruments	418	41
Other financial liabilities at fair value through profit or loss	617	408
Deposits by customers	9,770	5,216
Deposits by banks	6,338	11,100
Repurchase agreements–non trading	846	849
Debt securities in issue	18,100	23,051
Subordinated liabilities	1,539	709
Financial liabilities	37,628	41,374
Off-balance sheet commitments given	11,490	13,413
Undiscounted Cash Flow [member] | Later Than Five Years [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Derivative financial instruments	532	1,003
Other financial liabilities at fair value through profit or loss	969	3,855
Deposits by customers	3,045	1,305
Deposits by banks	220	52
Repurchase agreements–non trading	0	517
Debt securities in issue	8,897	10,921
Subordinated liabilities	3,961	5,279
Financial liabilities	17,624	22,932
Off-balance sheet commitments given	£ 1,278	£ 1,426

Offsetting Financial Assets a_3

Offsetting Financial Assets and Liabilities - Summary of Information about Impact of Offsetting of Financial Assets and Liabilities (Detail) - GBP (£) £ in Millions	Dec. 31, 2019	Dec. 31, 2018
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	£ 35,005	£ 40,052
Amounts offset, Assets	(4,138)	(6,771)
Net amounts reported on the balance sheet, Assets	30,867	33,281
Financial instruments, Assets	(1,305)	(3,654)
Financial collateral, Assets	(25,014)	(22,811)
Net amount, Assets	4,548	6,816
Assets not subject to enforceable netting arrangements, Assets	205,227	199,465
Balance sheet total, Assets	236,094	232,746
Gross amounts, Liabilities	33,973	31,987
Amounts offset, Liabilities	(4,138)	(6,771)
Net amounts reported on the balance sheet, Liabilities	29,835	25,216
Financial instruments, Liabilities	(1,305)	(3,654)
Financial collateral, Liabilities	(18,823)	(11,104)
Net amount, Liabilities	9,707	10,458
Assets not subject to enforceable netting arrangements, Liabilities	186,135	184,484
Balance sheet total, Liabilities	215,970	209,700
Derivative Financial Liabilities [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Liabilities	2,616	3,187
Amounts offset, Liabilities	(1,214)	(1,872)
Net amounts reported on the balance sheet, Liabilities	1,402	1,315
Financial instruments, Liabilities	(768)	(933)
Financial collateral, Liabilities	(572)	(303)
Net amount, Liabilities	62	79
Assets not subject to enforceable netting arrangements, Liabilities	46	54
Balance sheet total, Liabilities	1,448	1,369
Amortised cost [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	25,312	24,733
Amounts offset, Assets	(1,676)	(3,606)
Net amounts reported on the balance sheet, Assets	23,636	21,127
Financial instruments, Assets	(537)	(2,721)
Financial collateral, Assets	(23,099)	(18,406)
Net amount, Assets	0
Assets not subject to enforceable netting arrangements, Assets	0
Balance sheet total, Assets	23,636	21,127
Gross amounts, Liabilities	19,962	14,516
Amounts offset, Liabilities	(1,676)	(3,606)
Net amounts reported on the balance sheet, Liabilities	18,286	10,910
Financial instruments, Liabilities	(537)	(2,721)
Financial collateral, Liabilities	(17,749)	(8,189)
Net amount, Liabilities	0
Assets not subject to enforceable netting arrangements, Liabilities	0
Balance sheet total, Liabilities	18,286	10,910
Fair Value [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	0	2,272
Amounts offset, Assets	0
Net amounts reported on the balance sheet, Assets	0	2,272
Financial instruments, Assets	0
Financial collateral, Assets	0	(2,272)
Net amount, Assets	0
Assets not subject to enforceable netting arrangements, Assets	0
Balance sheet total, Assets	0	2,272
Gross amounts, Liabilities	0	2,110
Amounts offset, Liabilities	0
Net amounts reported on the balance sheet, Liabilities	0	2,110
Financial instruments, Liabilities	0
Financial collateral, Liabilities	0	(2,110)
Net amount, Liabilities	0
Assets not subject to enforceable netting arrangements, Liabilities	0
Balance sheet total, Liabilities	0	2,110
Deposits by customers and banks [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Liabilities	11,395	12,174
Amounts offset, Liabilities	(1,248)	(1,293)
Net amounts reported on the balance sheet, Liabilities	10,147	10,881
Financial instruments, Liabilities	0
Financial collateral, Liabilities	(502)	(502)
Net amount, Liabilities	9,645	10,379
Assets not subject to enforceable netting arrangements, Liabilities	186,089	184,430
Balance sheet total, Liabilities	196,236	195,311
Derivative Financial Instruments [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	4,446	7,026
Amounts offset, Assets	(1,214)	(1,872)
Net amounts reported on the balance sheet, Assets	3,232	5,154
Financial instruments, Assets	(768)	(933)
Financial collateral, Assets	(1,915)	(2,133)
Net amount, Assets	549	2,088
Assets not subject to enforceable netting arrangements, Assets	84	105
Balance sheet total, Assets	3,316	5,259
Loans and Advances to Customers [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	5,247	6,021
Amounts offset, Assets	(1,248)	(1,293)
Net amounts reported on the balance sheet, Assets	3,999	4,728
Financial instruments, Assets	0
Financial collateral, Assets	0
Net amount, Assets	3,999	4,728
Assets not subject to enforceable netting arrangements, Assets	205,143	199,360
Balance sheet total, Assets	£ 209,142	£ 204,088

Events After the Balance Shee_2

Events After the Balance Sheet Date - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2019
Disclosure of non-adjusting events after reporting period [abstract]
Description of nature of Non adjusting event after reporting period	Since the balance sheet date there has been a global pandemic arising from an outbreak of respiratory illness known as COVID-19. This is causing disruption to financial markets and business activity in the UK. While it is too early to accurately estimate the financial and business impact of the COVID-19 outbreak, we expect a negative impact on our 2020 financial results.