Santander Uk 20-F 8 Mar 19 2018 FY Annual report (foreign) Financial data

Document and Entity Information

Document and Entity Information	12 Months Ended
	Dec. 31, 2018shares
Document and entity information [abstract]
Document Type	20-F
Amendment Flag	false
Document Period End Date	Dec. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	FY
Trading Symbol	CK0001649373
Entity Registrant Name	SANTANDER UK GROUP HOLDINGS PLC
Entity Central Index Key	1,649,373
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	7,060,000,000

Consolidated Income Statement

Consolidated Income Statement - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Profit (loss) [abstract]
Interest and similar income	£ 6,072	£ 5,905	£ 6,467
Interest expense and similar charges	(2,466)	(2,102)	(2,885)
Net interest income	3,606	3,803	3,582
Fee and commission income	1,170	1,222	1,188
Fee and commission expense	(421)	(415)	(418)
Net fee and commission income	749	807	770
Net trading and other income	188	302	443
Total operating income	4,543	4,912	4,795
Operating expenses before credit impairment losses, provisions and charges	(2,563)	(2,502)	(2,417)
Credit impairment losses	(153)	(203)	(67)
Provisions for other liabilities and charges	(260)	(393)	(397)
Total operating credit impairment losses, provisions and charges	(413)	(596)	(464)
Profit before tax	1,567	1,814	1,914
Tax on profit	(446)	(560)	(597)
Profit after tax	1,121	1,254	1,317
Attributable to:
Equity holders of the parent	1,082	1,215	1,272
Non-controlling interests	39	39	45
Profit after tax	£ 1,121	£ 1,254	£ 1,317

Consolidated Statement of Compr

Consolidated Statement of Comprehensive Income - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of comprehensive income [abstract]
Profit after tax	£ 1,121	£ 1,254	£ 1,317
Available-for-sale securities:
- Change in fair value		80	127
- Income statement transfers		(54)	(115)
- Taxation		(6)	(16)
Other comprehensive income available-for-sale securities, total		20	(4)
Movement in fair value reserve (debt instruments):
- Change in fair value	(74)
- Income statement transfers	21
- Taxation	14
Other comprehensive income fair value reserve (debt instruments)	(39)
Cash flow hedges:
- Effective portion of changes in fair value	788	(238)	4,365
- Income statement transfers	(751)	(94)	(4,076)
- Taxation	(14)	89	(72)
Other comprehensive income cash flow hedges, total	23	(243)	217
Currency translation on foreign operations			(3)
Net other comprehensive income that may be reclassified to profit or loss subsequently	(16)	(223)	210
Pension remeasurement:
- Change in fair value	469	(103)	(528)
- Taxation	(117)	26	133
Pension remeasurement, total	352	(77)	(395)
Own credit adjustment:
- Change in fair value	84	(29)
- Taxation	(21)	7
Own credit adjustment, total	63	(22)
Net other comprehensive income that will not be reclassified to profit or loss subsequently	415	(99)	(395)
Total other comprehensive income net of tax	399	(322)	(185)
Total comprehensive income	1,520	932	1,132
Attributable to:
Equity holders of the parent	1,481	893	1,087
Non-controlling interests	39	39	45
Total comprehensive income	£ 1,520	£ 932	£ 1,132

Consolidated Balance Sheet

Consolidated Balance Sheet - GBP (£) £ in Millions		Dec. 31, 2018	Dec. 31, 2017
Assets
Cash and balances at central banks		£ 24,180	£ 32,771
Financial assets at fair value through profit or loss:
- Trading assets			30,555
- Derivative financial instruments		5,321	19,942
- Other financial assets at fair value through profit or loss		6,137	2,096
Financial assets at amortised cost
- Loans and advances to customers		201,619	199,332
- Loans and advances to banks		3,515	3,466
- Reverse repurchase agreements - non trading		21,127	2,614
- Other financial assets at amortised cost		7,228
Financial assets at fair value through other comprehensive income		13,302
Financial investments			17,611
Interests in other entities		88	73
Intangible assets		1,814	1,742
Property, plant and equipment		1,835	1,598
Current tax assets		106
Retirement benefit assets		842	449
Other assets		2,267	2,511
Total assets		289,381	314,760
Financial liabilities at fair value through profit or loss:
- Trading liabilities			31,109
- Derivative financial instruments		1,594	17,613
- Other financial liabilities at fair value through profit or loss		6,286	2,315
Financial liabilities at amortised cost
- Deposits by customers		173,692	177,421
- Deposits by banks		17,824	12,708
- Repurchase agreements - non trading		10,910	1,076
- Debt securities in issue		55,906	48,860
- Subordinated liabilities		3,601	3,793
Other liabilities		2,507	2,728
Provisions		515	558
Current tax liabilities			3
Deferred tax liabilities		211	88
Retirement benefit obligations		115	286
Total liabilities		273,161	298,558
Equity
Share capital		7,060	7,060
Other equity instruments		2,041	2,041
Retained earnings		6,439	6,399
Other reserves		280	301
Total shareholders' equity		15,820	15,801
Non-controlling interests		400	401
Total equity		16,220	16,202
Total liabilities and equity		289,381	314,760
Santander UK Group Holdings plc [member]
Financial assets at amortised cost
- Loans and advances to banks		9,214	6,260
Other financial assets at amortised cost	[1]	1,185
Financial investments	[1]		1,116
Interests in other entities		13,400	13,313
Current tax assets		1
Other assets		2	1
Total assets		23,802	20,690
Financial liabilities at amortised cost
- Deposits by banks			8
- Debt securities in issue		9,295	6,256
- Subordinated liabilities		1,185	1,116
Total liabilities		10,480	7,380
Equity
Share capital		7,060	7,060
Other equity instruments		2,041	2,041
Retained earnings		4,221	4,209
Total shareholders' equity		13,322	13,310
Total equity		13,322	13,310
Total liabilities and equity		£ 23,802	£ 20,690
[1]	On adoption of IFRS 9, the 'financial investments' balance sheet line item was split. This resulted in the inclusion of the 'other financial assets at amortised cost' balance sheet line. This approach aligns the balance sheet line items to the IFRS 9 accounting classifications and provides a clearer understanding of our financial position.

Consolidated Cash Flow Statemen

Consolidated Cash Flow Statement - GBP (£) £ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash flows from operating activities
Profit after tax		£ 1,121	£ 1,254	£ 1,317
Non-cash items included in profit:
- Depreciation and amortisation		378	354	322
- Provisions for other liabilities and charges		260	393	397
- Impairment losses		189	257	132
- Corporation tax charge		446	560	597
- Other non-cash items		(68)	(218)	(599)
- Pension charge for defined benefit pension schemes		81	32	26
Adjustments to reconcile profit (loss)		1,286	1,378	875
Net change in operating assets and liabilities:
- Cash and balances at central banks		(161)	(25)	(30)
- Trading assets		24,528	(941)	(2,049)
- Derivative assets		14,621	5,529	(4,560)
- Other financial assets at fair value through profit or loss		(3,467)	25	257
- Loans and advances to banks and customers		(8,221)	(1,829)	(2,262)
- Other assets		203	(246)	(121)
- Deposits by banks and customers		1,845	8,805	11,201
- Derivative liabilities		(16,018)	(5,490)	1,595
- Trading liabilities		(31,101)	15,017	2,837
- Other financial liabilities at fair value through profit or loss		4,480	717	336
- Debt securities in issue		(2,760)	132	399
- Other liabilities		(824)	(1,388)	1,604
Net change in operating assets and liabilities		(16,875)	20,306	9,207
Corporation tax paid		(445)	(484)	(507)
Effects of exchange rate differences		1,731	(574)	3,885
Net cash flows from operating activities		(13,182)	21,880	14,777
Cash flows from investing activities
Investments in other entities		(66)
Proceeds from disposal of subsidiaries	[1]			149
Purchase of property, plant and equipment and intangible assets		(699)	(542)	(374)
Proceeds from sale of property, plant and equipment and intangible assets		26	52	65
Purchase of financial investments		(7,002)	(726)	(9,539)
Proceeds from sale and redemption of financial investments		3,816	2,032	2,359
Net cash flows from investing activities		(3,925)	816	(7,340)
Cash flows from financing activities
Issue of AT1 Capital Securities			500
Issuance costs of AT1 Capital Securities			(4)
Issue of debt securities and subordinated notes		13,329	8,748	8,788
Issuance costs of debt securities and subordinated notes		(31)	(23)	(28)
Repayment of debt securities		(6,303)	(13,763)	(11,352)
Repurchase of non-controlling interests				(7)
Dividends paid on ordinary shares		(1,123)	(829)	(419)
Dividends paid on other equity instruments		(145)	(135)	(111)
Dividends paid on non-controlling interests		(40)	(37)	(30)
Net cash flows from financing activities		5,687	(5,543)	(3,159)
Change in cash and cash equivalents		(11,420)	17,153	4,278
Cash and cash equivalents at beginning of the year		42,228	25,709	20,354
Effects of exchange rate changes on cash and cash equivalents		161	(634)	1,077
Cash and cash equivalents at the end of the year		30,969	42,228	25,709
Cash and cash equivalents consist of:
Cash and balances at central banks		24,180	32,771	17,107
Less: regulatory minimum cash balances		(636)	(395)	(370)
Cash and bank balances at central banks less regulatory minimum cash balances		23,544	32,376	16,737
Net trading other cash equivalents			5,953	6,537
Net non-trading other cash equivalents		7,425	3,899	2,435
Cash and cash equivalents at the end of the year		30,969	42,228	25,709
Santander UK Group Holdings plc [member]
Cash flows from operating activities
Profit after tax		1,253	659
Non-cash items included in profit:
Adjustments to reconcile profit (loss)		(48)	50
Net change in operating assets and liabilities:
Net change in operating assets and liabilities		(2,604)	(1,412)
Corporation tax paid		(28)
Effects of exchange rate differences		419	(429)
Net cash flows from operating activities		(1,008)	(1,132)
Cash flows from investing activities
Investments in other entities		(377)	(495)
Net cash flows from investing activities		(377)	(495)
Cash flows from financing activities
Issue of AT1 Capital Securities			500
Issuance costs of AT1 Capital Securities			(4)
Issue of debt securities and subordinated notes		2,679	2,103
Issuance costs of debt securities and subordinated notes			(9)
Repayment of debt securities		(21)
Dividends paid on ordinary shares		(1,123)	(829)
Dividends paid on other equity instruments		(145)	(135)
Net cash flows from financing activities		1,390	1,626
Change in cash and cash equivalents		5	(1)
Cash and cash equivalents at beginning of the year		3	4
Cash and cash equivalents at the end of the year		8	3	4
Cash and cash equivalents consist of:
Cash and cash equivalents at the end of the year		£ 8	£ 3	£ 4
[1]	In 2016, the Santander UK group sold a number of subsidiaries for a cash consideration of £149m. The carrying value of the net assets disposed of was £149m.

Consolidated Cash Flow Statem_2

Consolidated Cash Flow Statement (Parenthetical) £ in Millions	12 Months Ended
	Dec. 31, 2016GBP (£)
Statement of cash flows [abstract]
Cash consideration received on sale of subsidiaries	£ 149	[1]
Carrying value of assets and liabilities	£ 149
[1]	In 2016, the Santander UK group sold a number of subsidiaries for a cash consideration of £149m. The carrying value of the net assets disposed of was £149m.

Consolidated Statement of Chang

Consolidated Statement of Changes in Equity - GBP (£) £ in Millions	Total	Share Capital [member]	Other Equity Instruments [member]	Retained Earnings [member]	Other Reserves Available-For-Sale [member]	[1]	Other Reserves Fair Value Reserves [member]	[1]	Other Reserves Cash Flow Hedging [member]	Other Reserves Currency Translation [member]	Total [member]	Non-Controlling Interests [member]	Santander UK Group Holdings plc [member]	Santander UK Group Holdings plc [member]Share Capital [member]	Santander UK Group Holdings plc [member]Other Equity Instruments [member]	Santander UK Group Holdings plc [member]Retained Earnings [member]
Beginning balance at Dec. 31, 2015	£ 15,031	£ 7,060	£ 1,545	£ 5,721	£ 52				£ 254	£ 8	£ 14,640	£ 391
- Profit after tax	1,317			1,272							1,272	45
Other comprehensive income, net of tax:
- Available-for-sale securities	(4)				(4)						(4)
- Cash flow hedges	217								217		217
- Pension remeasurement	(395)			(395)							(395)
- Currency translation on foreign operations	(3)									(3)	(3)
Total comprehensive income	1,132			877	(4)				217	(3)	1,087	45
Repurchase of non-controlling interests	(7)											(7)
Dividends on ordinary shares	(593)			(593)							(593)
Dividends on other equity instruments	(111)			(111)							(111)
Dividends on non-controlling interests	(30)											(30)
Tax on non-controlling interests and other equity instruments	31			31							31
Ending balance at Dec. 31, 2016	15,453	7,060	1,545	5,925	48				471	5	15,054	399	£ 12,817	£ 7,060	£ 1,545	£ 4,212
- Profit after tax	1,254			1,215							1,215	39	659			659
Other comprehensive income, net of tax:
- Available-for-sale securities	20				20						20
- Cash flow hedges	(243)								(243)		(243)
- Pension remeasurement	(77)			(77)							(77)
- Own credit adjustment	(22)			(22)							(22)
Total comprehensive income	932			1,116	20				(243)		893	39
Issue of AT1 capital securities	496		496								496		496		496
Dividends on ordinary shares	(553)			(553)							(553)		(553)			(553)
Dividends on other equity instruments	(135)			(135)							(135)		(135)			(135)
Dividends on non-controlling interests	(37)											(37)
Tax on non-controlling interests and other equity instruments	46			46							46		26			26
Ending balance at Dec. 31, 2017	16,202	7,060	2,041	6,399	68				228	5	15,801	401	13,310	7,060	2,041	4,209
Adoption of IFRS 9 (see Note 1)	(192)			(187)	(68)		£ 63				(192)
Ending balance at Jan. 01, 2018	16,010	7,060	2,041	6,212			63		228	5	15,609	401
Beginning balance at Dec. 31, 2017	16,202	7,060	2,041	6,399	£ 68				228	5	15,801	401	13,310	7,060	2,041	4,209
- Profit after tax	1,121			1,082							1,082	39	1,253			1,253
Other comprehensive income, net of tax:
- Fair value reserve (debt instruments)	(39)						(39)				(39)
- Cash flow hedges	23								23		23
- Pension remeasurement	352			352							352
- Own credit adjustment	63			63							63
Total comprehensive income	1,520			1,497			(39)		23		1,481	39
Other	(45)			(45)							(45)
Dividends on ordinary shares	(1,123)			(1,123)							(1,123)		(1,123)			(1,123)
Dividends on other equity instruments	(145)			(145)							(145)		(145)			(145)
Dividends on non-controlling interests	(40)											(40)
Tax on non-controlling interests and other equity instruments	43			43							43		27			27
Ending balance at Dec. 31, 2018	£ 16,220	£ 7,060	£ 2,041	£ 6,439			£ 24		£ 251	£ 5	£ 15,820	£ 400	£ 13,322	£ 7,060	£ 2,041	£ 4,221
[1]	Following the adoption of IFRS 9, a fair value reserve was introduced to replace the available-for-sale reserve, as described in Note 1.

Risk Framework

Risk Framework	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Risk Framework	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 with risk management responsibilities: • Risk organisational structure: Committees The Board Level Committee responsibilities for risk are: Board Level Committee Main risk responsibilities The Board (including the Santander UK plc 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 risks relating to conduct, compliance, competition, financial crime and 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 reputation and how this impacts our brand and market positioning. Board Audit Committee •  Monitors and reviews the integrity of the financial statements, and any formal announcements relating to financial performance •  Reviews the adequacy and effectiveness of the internal financial controls and whistleblowing arrangements •  Monitors and reviews the effectiveness of Santander UK’s internal audit function. The Executive Level Committee responsibilities for risk are: Executive Level Committee Main risk responsibilities Executive Committee •  Reviews and approves business plans in line with our Risk Framework and Risk Appetite before they are recommended to the Board for approval •  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. Executive Credit Approval Committee •  Approves corporate and wholesale credit transactions which exceed levels delegated to lower level approval forums or individuals. Executive Investment Approval Committee •  Approves equity type investment transactions which exceed levels delegated to lower level approval forums or individuals. Key senior management roles with risk management responsibilities Chief Executive Officer The Board delegates responsibility for our business activities and managing risk on a day-to-day Chief Risk Officer As the leader of the Risk Division, the CRO oversees and challenges risk activities, and ensures new lending decisions are made within our Risk Appetite. The CRO is accountable for the control and oversight of credit, market, liquidity, capital, pension, strategic, operational and model risk. Chief Legal and Regulatory Officer The CLRO is 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 The CFO is responsible for the development of strategy, leadership and management of the CFO Division. In supporting Santander UK’s corporate goals within the constraints of risk appetite, the CFO is responsible for the management of interest rate, liquidity, pension and capital risks. Chief Internal Auditor The 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 The Money Laundering Reporting Officer (MLRO) is 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, 2018
Text block [abstract]
Credit risk	Credit risk 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 also discuss our ECL methodology and the key inputs to our ECL model. We then analyse our key metrics, as well as credit performance and forbearance. 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 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, treasury products, and treasury markets activities. •  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, as well as sovereigns and other international organisations. •  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 Jersey and Isle of Man branches in Corporate Centre rather than in Retail Banking as in previous years, as a result of their transfer from Santander UK plc to ANTS in 2018. 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 across the lifecycle 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 corporate clients) and Corporate Centre (for our 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 analysts who specialise in this type of risk. •  We manage risk through expert analysis. We support this with decision-making tools based on internal risk assessment models. The adoption of IFRS 9 LOGO On 1 January 2018, IFRS 9 replaced IAS 39, and introduced new rules on how to classify and measure financial assets, as well as new concepts, principles and measures for credit impairment charges. Throughout 2018, we enhanced and refined our accounting processes and procedures, internal controls and governance framework to embed the new requirements of IFRS 9 into our business. IFRS 9 was a significant challenge to our Risk and Finance divisions as they had to analyse large volumes of data from various systems, as well as enhance their skills and expertise. As IFRS 9 affects the timing of when we recognise credit impairment charges, but not the amount of credit write-offs, its adoption did not materially change our credit risk policies. Our Retail collections and recoveries procedures were unchanged, and we reviewed our risk-adjusted hurdle rates for Corporate lending, but this didn’t lead to a significant change in our credit policy. Our credit risk appetite in terms of target markets, market share and the credit quality of customers we want to lend to, were also not directly impacted. The main impacts were on how we monitor credit risk. As part of this, we began to monitor IFRS 9 metrics. These mainly centre on ECL and classification of exposures as Stages 1, 2 and 3. We expect to develop our metrics further in 2019 as how we embed IFRS 9 in our business continues to evolve. We also continued to monitor NPLs in 2018 as the NPL ratio is one of our Key Performance Indicators for 2016-2018. Our disclosures reflect recommendations made by DECL where it is practical to do so, and we expect to enhance them further in future. 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 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, business goals, and financial and technical resources with our attitude to risk (our Risk Appetite). To do this, we focus particularly on economic and market conditions and forecasts, regulations, conduct considerations, 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 undertake 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 anything that mitigates it, such as netting or collateral • Our risk policy, limits and appetite • Whether we can balance the amount of risk we face with the returns we expect. We also use stress testing, for example to estimate how a customer might be able to cope if interest rates increase. 3. Monitoring We measure and monitor changes in our credit risk profile on a regular and systematic basis against 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 a formal structure of governance and forums/committees across our business segments. 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 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 Banco Santander wants to offer in that country. For more geographical information, see ‘Country risk exposures’. Industry concentrations We also set exposure limits by industry sector. These limits are set 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 they may fall into payment arrears or breach 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 financially. This helps us put in place the right strategy to manage their debt • Work with them to get their account back to normal 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 prove ineffective. If this happens, we have to end our relationship 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 financial 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 separately as forborne. For retail accounts, if an account is in Stage 1 when we agree forbearance, we transfer it to Stage 2. For all accounts, if an account is already in Stage 2 when we agree forbearance, we keep it in Stage 2 unless the forbearance arrangement involves the forgiveness of fees and interest which would put the case into Stage 3. If an account is already in Stage 3 when we agree forbearance, we keep it in Stage 3. We monitor the performance of all forborne loans. A loan moves from a lifetime ECL (Stages 2 or 3) to a 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 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 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 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. 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. Non-Performing We use NPLs to monitor how our portfolios behave. We classify loans as NPLs when customers do not make a payment for three months or more, or if we have data to make us doubt they can keep up with their payments. There are differences between NPL and Stage 3, which we set out in the ‘Definition of default used for NPL’ section below. Although we adopted IFRS 9 from 1 January 2018, we continued to monitor NPLs as a key metric in 2018 as the NPL ratio was one of Santander UK’s Key Performance Indicators for 2016-2018. We also assess risks from other perspectives, such as geography, business area, product and process. We do this 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 leverage the existing Basel advanced IRB risk components, we need to make several significant 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 Probability of Default (PD) Probability of default in the next 12 months Includes forward-looking economic information 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 Removal of 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 the 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 risk since the origination date. The ECL approach estimate takes into account forward-looking data, including a range of possible outcomes, which should be unbiased and probability-weighted in order to reflect the likelihood of a loss being incurred even when it is considered unlikely. Multiple economic scenarios and probability weights For all our portfolios, except CIB, 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. For example, the Downside 2 scenario reflects the possibility of a recession occurring. We believe that our five scenarios, in particular Downside 1 and Downside 2, reflect the range of outcomes that Brexit may take, including a deal with a transition period or a no-deal Base case • Our base case assumes that the UK will negotiate an orderly exit with the EU that avoids a so-called • GDP forecast for 2018 was lowered in August to reflect disappointing Q1 results, which results in slower growth in the following years until reverting to the long run annual growth of 1.6% in 2024. • Unemployment continues its current trend over the forecast period, tightening labour markets further and pushing up average earnings growth. This growth along with the expected fall in inflation result in positive real earnings growth for 2019 onwards. • The UK’s net trade position is expected to fall back as sterling rallies against the dollar reducing the competitiveness of UK exports. Even though the Brexit negotiations are likely to result in some increased trade costs between the EU and UK, these are not projected to significantly impact the downwards trend in the share of UK exports going to the EU. • For Bank Rate, the base case currently assumes one bank rate rise in 2019 and another in 2020. • In the medium term, the forecast projections assume that current demographic and productivity trends will continue, causing a reduction in the UK’s growth potential which is reflected in an average annual growth expectation of less than 2%. • In summary, the base case assumes that activity will continue to run at this relatively sluggish pace. With CPI inflation likely to slow as we move through 2019, and a positive increase in wage growth predicted, this will provide a boost to household spending power. However, the effect of this will be softened by the continued impact of the UK Government’s welfare reforms and the projected slowing of employment growth. In addition, with the household savings ratio at low levels and with credit conditions starting to tighten these two areas are unlikely to be able to compensate for any downside effects to growth. Our methodology to derive the scenarios relies on a set of parameters embodied 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 the long-run Once the GDP paths have been forecast, we run them through the Oxford Global Economic Model (OGEM) to derive the other macroeconomic variables, such as unemployment and house prices, and then impose the Bank Rate for each scenario. The forecasting period for GDP is 5 years and then we revert back to the average trend growth over 3 years based on the OBR’s long-run The annual growth rates over the 5 year forecast for each of our scenarios are: Upside 2 Upside 1 Base case Downside 1 Downside 2 Assumption % % % % % House price index (1) 3.40 2.30 2.00 (2.00 ) (9.50 ) GDP (1) 2.50 2.10 1.60 0.70 0.30 Unemployment rate 2.80 3.80 4.30 6.90 8.60 Interest rate 1.00 1.25 1.50 2.50 2.25 (1) Compound annual growth rate To determine our initial scenario probability weightings, we give the highest weight to the base case, whilst the extreme scenarios typically attract lower weights than the more moderate ones. In addition, due to the current economic position and policy concerns evidenced by the PRA and Financial Policy Committee (FPC), and due to political concerns we have applied a higher weighting to the downside scenarios. We consider this appropriate in light of the consensus view of future performance of the UK economy, including projections for GDP growth. The probability weights we applied to the scenarios are: Scenario type Probability % Upside 2 5 Upside 1 15 Base case 40 Downside 1 30 Downside 2 10 As part of our review of the scenarios and weights that we use, we performed statistical analysis to assess whether the scenarios and weights we use capture the non-linearity of losses implied by the results. The outcome of this analysis, which modelled a number of different scenarios, demonstrated that there is a non-linear For our CIB portfolio, our approach was developed centrally by Banco Santander to ensure consistent treatment of these large and/or international counterparties across the organisation. For CIB, we use three scenarios (base, upside and downside). Similar to the UK scenarios, the base case uses the base scenario that has been developed and is used in other work that Banco Santander undertakes 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 half way 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. The average annual growth rates over a 4 year forecast for each of the scenarios for our CIB portfolio are: Upside Base case Downside Assumption % % % GDP 4.2 3.6 2.7 The probability weights we applied to the scenarios for our CIB portfolio are: Scenario type Probability % Upside 20 Base case 60 Downside 20 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 available data and OBR fan charts, which are then reviewed and approved by ALCO. Probability weights are reassessed by ALCO at least quarterly. We aim to avoid embedding new economic scenarios into our models on a quarter-end quarter-end 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 maturity of the loan, or behavioural term for revolving facilities. Loans which have not experienced a SICR are subject to 12 month ECL. We assess each facility’s credit risk profile 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 approves 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 quantitative 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 are: Retail Banking (1) Consumer (auto) Other unsecured Corporate & Corporate & Mortgages finance (2) Personal loans (2) Credit cards Overdrafts Commercial Banking (2) Investment Banking 30bps 300bps 400bps 340bps 260bps 400bps Internal rating method (1) In Business banking, for larger customers we apply the same criteria that we use for Corporate & Commercial Banking. (2) Consumer (auto) finance, Personal loans and Corporate & Commercial Banking use the comparison of lifetime PDs to determine Stage allocation, unlike other products which first turn the lifetime PD into an average yearly PD (annualised) and then do the comparison. We also apply a relative threshold of 100% (doubling the PD) across all portfolios except CIB. 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 qualitative criteria are: Retail Banking (1) Consumer (auto) Other unsecured Corporate & Corporate & Mortgages finance Personal loans Credit cards Overdrafts Commercial Banking Investment Banking In forbearance Default in last 24m In forbearance Deceased or Insolvent In Collections Default in last 12m In Fees In Watchlist – >30 Days past due (DPD) in last 12m Court ‘Return of goods’ order or Police watchlist NPL in last 12m In Debit NPL in last Bankrupt Agreement terminated Default at £100+ arrears Payment holiday £50+ arrears £100+ Any Cash Collection Behaviour (1) In Business banking, for larger customers we apply the same criteria that we use for Corporate & Commercial Banking. Backstop criteria As a backstop, we classify all exposures more than 30 or 90 DPD in at least Stage 2 or in Stage 3, respectively. This means that we do not rebut the backstop presumptions in IFRS 9 (i.e. credit risk has significantly increased if contractual payments are more than 30 days past due) relating to either a SICR or default. Improvement in credit risk or cure In some cases, instruments with a lifetime ECL (in Stage 2 or 3) may be transferred back to 12 month ECL (Stage 1). Financial assets in Stage 3 can only be transferred to Stage 2 or Stage 1 when they are no longer considered to be credit impaired, as defined in the next section. Financial assets in Stage 2 can only be transferred to Stage 1 when they are no longer considered to have experienced a SICR. Where we identified a SICR using quantitative criteria, the instruments automatically transfer back to Stage 1 when the original PD-based Definition of default (Credit impaired) We define a financial instrument as in default (i.e. credit impaired) for purposes of calculating ECL if it is more than three months past due, or if we have data to make us doubt they can keep up with their payments i.e. they are unlikely to pay. The data we have on customers varies across our business segments. It typically includes where: Retail Banking • They have been reported bankrupt or insolvent • Their loan term has ended, but they still owe us money more than three months later • They have had forbearance while in default, but have not caught up with the payments they had missed before that, or they have had multiple forbearance • We have suspended their fees and interest because they are in financial difficulties • We have repossessed the property. Other business segments: Corporate & Commercial Banking, Corporate & Investment Banking and Corporate Centre • They have had a winding up notice issued, or something happens that is likely to trigger insolvency – such as, another lender calls in a loan • Something happens that makes them less likely to be able to pay us – such as they lose an important client or contract • They have regularly missed or delayed payments, even though they have not gone over the three-month limit for default • Their loan is unlikely to be refinanced or repaid in full on maturity • Their loan has an excessive LTV that is unlikely to be resolved, such as by a change in planning policy, pay-downs, Where we use the advanced internal ratings-based basis for a portfolio in our capital calculations, we use the same default definitions for ECL purposes. We review and approve the definition of default each quarter. The Board Audit Committee reviews and approves the definition each year, or more often if we change it. Definition of default used for NPL The definition of default we use to identify NPLs is not significantly different to the definition of default we use to identify Stage 3 exposures. The only difference relates to mortgages. For NPL, we classify a mortgage customer as bankrupt for at least two years after first being declared bankrupt before we reassess their position. For Stage 3, the equivalent period is at least seven years before we reassess their position. Measuring ECL For accounts not in default at the reporting date, we estimate a monthly ECL for each exposure and for each month over the forecast period. The lifetime ECL is the sum of the monthly ECLs over the forecast period, while the 12-month Factor Description Survival rate (SR) The probability that the exposure has not closed or defaulted since the reporting date. PD The likelihood of a borrower defaulting in the following month, assuming it has not closed or defaulted since the reporting date. For each month in the forecast period, we estimate the monthly PD from a range of factors. These include the current risk grade for the exposure, which becomes less relevant further into the forecast period, as well as the expected evolution of the account risk with maturity and factors for changing economics. We support this with historical data analysis. EAD The amount we expect to be owed if a default event was to occur. We determine EAD for each month of the forecast period by the expected payment profile, which varies by product type. For amortising products, we base it on the borrower’s contractual repayments over the forecast period. We adjust this for any expected overpayments on Stage 1 accounts that the borrower may make and for any arrears we expect if the account was to default. For revolving products, or amortising products with an off-balance LGD Our expected loss if a default event were to occur. We express it as a percentage and calculate it as the expected loss divided by EAD for each month of the forecast period. We base LGD on factors that impact the likelihood and value of any subsequent write-offs, which vary according to whether the product is secured or unsecured. If the product is secured, we take into account collateral values as well as the historical discounts to market/book values due to forced sales type. We use the original effective interest rate as the discount rate. For accounts in default, we use the EAD as the reporting date balance. We also calculate an LGD to reflect the default status of the account, considering the current DPD and loan to value. PD and SR are not required for accounts in default. Forecast period We base the forecast period for amortising facilities on the remaining contractual term. For revolving facilities, we use an analytical approach based on the behavioural, rather than contractual, characteristics of the facility type. In some cases, we shorten the period to simplify the calculation. If we do this, we apply a post model adjustment to reflect our view of the full lifetime ECL. Forward-looking information Our assessments of a SICR and the calculation of ECL both incorporate forward-looking information. We perform historical analysis and identify the key economic variables that impact credit risk and ECL for each portfolio. These can include GDP, house prices and unemployment. Where applicable, we incorporate these economic variables and their associated impacts into our models. Grouping of instruments for losses measured on a collective basis We measure ECL at the individual financial instrument level. However, we typically group instruments and assess them for impairment collectively where they share risk characteristics (as described in Retail Banking – credit risk management) 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 instru

Market risk

Market risk	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Market risk	Market risk Overview Key metrics 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 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 explain how the implementation of our ring-fencing plans in 2018 changed our exposure to trading market risk. Net Interest Margin (NIM) sensitivity to +50bps decreased to £207m and to -50bps decreased to £(23)m (2017: £212m and £(125)m) Economic Value of Equity (EVE) sensitivity to +50bps increased to £162m and to -50bps decreased to £(124)m (2017: £95m and £(213)m) BALANCE SHEET ALLOCATION BY MARKET RISK CLASSIFICATION We analyse our assets and liabilities exposed to market risk between banking and trading market risk as follows: 2018 2017 Banking Trading Total Banking Trading Total £m £m £m £m £m £m Key risk factors Assets subject to market risk Cash and balances at central banks 24,180 — 24,180 32,771 — 32,771 FX, Interest rate Financial assets at FVTPL: – Trading assets — — — — 30,555 30,555 Equity, FX, interest rate – Derivative financial instruments 4,621 700 5, 321 5,198 14,744 19,942 Equity, FX, interest rate – Other financial assets at FVTPL 6,137 — 6,137 2,096 — 2,096 Interest rate, credit spread Financial assets at amortised cost: – Loans and advances to customers (1) 201, — 201,619 199, — 199, Interest rate – Loans and advances to banks (1) 3,515 — 3,515 3,466 — 3,466 FX, interest rate – Reverse repurchase agreements – non trading (1) 21,127 — 21,127 2,614 — 2,614 FX, Interest rate – Other financial assets at amortised cost 7,228 — 7,228 FX, interest rate, inflation, credit spread Financial assets at FVOCI 13,302 — 13,302 FX, interest rate, inflation, credit spread Financial investments 17,611 — 17,611 FX, interest rate, inflation, credit spread Macro hedge of interest rate risk (2) 697 — 697 833 — 833 Interest rate Retirement benefit assets 842 — 842 449 — 449 Equity, FX, interest rate, inflation, credit spread Total assets 283,268 700 283,968 264,370 45,299 309,669 Liabilities subject to market risk Financial liabilities at FVTPL: – Trading liabilities — — — — 31,109 31,109 Equity, FX, interest rate – Derivative financial instruments 875 719 1,594 722 16,891 17,613 Equity, FX, interest rate – Other financial liabilities at FVTPL 6,286 — 6,286 703 1,612 2,315 Interest rate, credit spread Financial Liabilities at amortised cost: – Deposits by customers 173,692 — 173,692 177,421 — 177,421 Interest rate – Deposits by banks (1) 17,824 — 17,824 12,708 — 12,708 FX, interest rate – Repurchase agreements – non trading (1) 10,910 — 10,910 1,076 — 1,076 FX, Interest rate – Debt securities in issue 55,906 — 55,906 48,860 — 48,860 FX, interest rate – Subordinated liabilities 3,601 — 3,601 3,793 — 3,793 FX, interest rate Macro hedge of interest rate risk (3) 242 — 242 — — — Interest rate Retirement benefit obligations 115 — 115 286 — 286 Equity, FX, interest rate, inflation, credit spread Total liabilities 269,451 719 270,170 245,569 49,612 295,181 (1) From 1 January 2018, the non-trading non-trading (2) This is included in Other assets of £2,267m (2017: £2,511m). (3) This is included in Other liabilities of £2,507m (2017: £2,728m). We classify assets or liabilities as trading market risk (in total or just in part) as follows: Balance sheet classification Market risk classification Trading assets and liabilities We classify all our trading portfolios as trading market risk. Following the implementation of our ring-fencing plans in 2018, the level of trading activity significantly reduced. Since then, we only classify exposures from product sales or other activities with anticipated short holding periods, as well as any related hedging, as trading market risk. For more, see Notes 11 and 23 to the Consolidated Financial Statements. Other financial assets and liabilities at fair value through profit or loss We classify all our financial assets designated at fair value as banking market risk. We classify our warrant programmes and structured customer deposits as trading market risk. This is because we manage them on a fair value basis. We classify all our other financial liabilities designated at fair value as banking market risk. For more, see Notes 13 and 24 to the Consolidated Financial Statements. Derivative financial instruments For accounting purposes, we classify derivatives as held for trading unless they are designated as being in a hedging relationship. We treat derivatives that we do not manage on a trading intent basis as banking market risk. For more, see Note 12 to the Consolidated Financial Statements. 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 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 the risk measures we explain in the ‘Trading market risk management’ section that follows. 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 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 it generally needs to be combined with other risk measures to cover all aspects of a risk profile, such as projected changes over time. Other metrics we can use include VaR and Earnings at Risk (EaR). VaR can be useful because it captures changes in economic values, as we describe in the Trading market risk section below. However, VaR will not reflect the actual impact of most of our banking book assets and liabilities on our Income Statement. This is because we account for them at amortised cost rather than fair value. EaR is similar to VaR but captures changes in income rather than value. We use this approach mainly to generate a one-year Stress testing We use stress testing of market risk factors to complement the risk measurement we get from standard sensitivities. 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 measures because of data or model limitations. We can also use stress tests to estimate losses in extreme market events beyond the confidence level used in VaR models. 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 We can produce stress tests using either income or value measures. They cover one or more categories of exposures accounted for on an accruals basis or at fair value. We use expert judgement to define appropriate hypothetical stress tests and any adjusting assumptions based on the balance sheet, management actions and customer behaviour. 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 limits and triggers. For more, see ‘Our funding strategy and structure’ 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 2018 compared to 2017 (unaudited) The reduction in NIM sensitivities in 2018 was largely driven by higher levels of the yield curve over the year and the base rate rise in August 2018. The NIM sensitivities also reflect balance sheet management activities undertaken to manage the net structural position of the business. Each year, we 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. These changes in our underlying assumptions for risk measurement purposes also contributed to the movements in 2018. The movement in EVE sensitivities in 2018 was mainly due to the balance sheet management activities, changes in our underlying modelling assumptions for risk measurement purposes, and the yield curve movements mentioned above. The basis risk EaR in 2018 remained broadly stable. 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 2018 and 2017. 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 2018 2017 +50bps -50bps +50bps -50bps NIM sensitivity 207 (23 ) 212 (125 ) EVE sensitivity (unaudited) 162 (124 ) 95 (213 ) Basis risk We report basis risk using the EaR approach. 2018 2017 Basis risk EaR 25 24 Interest rate repricing gap The table below shows the interest rate repricing gap of our balance sheet by repricing buckets. 2018 3 months 1 year 3 years 5 years >5 years Not sensitive Total £m 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 ) — 2017 Assets 142,195 34,661 59,253 18,746 15,453 16,782 287,090 Liabilities 178,179 18,003 25,487 17,746 25,559 24,801 289,775 Off-balance (10,383 ) (3,025 ) 4,364 5,636 6,093 — 2,685 Net gap (46,367 ) 13,633 38,130 6,636 (4,013 ) (8,019 ) — Spread risks The table below shows the risk metrics covering the portfolios of securities held for liquidity and investment purposes. 2018 2017 VaR 4 3 Worst three month stressed loss 190 193 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’. The impact of ring-fencing As part of our ring-fencing plans, activities that can no longer be served by a ring-fenced bank were migrated to the Banco Santander London Branch in 2018. This resulted in most of our market-making activity and the associated trading market risk being transferred outside of the Santander UK group. In addition, some market risk positions have been in run-off The ring-fenced bank has two trading desks, the Link Desk and Retailed Structured Products (RSP) Desk. The Link Desk is a multi-asset trading desk facilitating the trading of ring-fenced bank permissible products (vanilla products) for those clients served by our CIB division. The aim of the desk is to provide a platform for CIB activity within the ring-fenced bank. The desk operates under an appropriate governance framework to ensure all activity adheres to ring-fencing legislation. The Link Desk will enter into hedging transactions with Relevant Financial Institutions, in accordance with ring-fencing legislation. The RSP desk provides a channel to sell CIB hedged investments (such as ISAs and other notes) to retail investors, through our UK branches and elsewhere. Notes are issued by Santander UK plc and hedged with Relevant Financial Institutions, in accordance with ring-fencing legislation. This RSP activity raises funding for the Santander UK group. There is low trading market risk associated with the trading activity as notes are hedged and a price is made before any client transaction which reflects the live execution prices of all hedge and funding unwinds. Following the implementation of our ring-fencing plans, the majority of trading market risk is now from hedging activity and back-to-back As a result of ring-fencing, and in response to the significant reduction in trading market risk in Santander UK and the corresponding reduction in market risk-related capital, we applied for and received approval from the ECB and PRA to decommission our Internal Model from 1 January 2019. The permission for an internal model was for certain trading book activity that has now been closed. For more on our Internal Model, see the ‘Capital requirement measures’ section below. 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 sets the controls, risk limits and key risk metrics for trading market risk. The key risk metrics include a stress economic loss limit and risk-factor stress scenarios. We report these key metrics to the BRC and the ERCC each month. Risk measurement We have a range of ways of measuring trading market risk, but one of the most important is a statistical measure based on a historical simulation of events called ‘Value at Risk’ (VaR). VaR VaR • VaR shows the losses that we might suffer because of unfavourable changes in the markets under normal non-stressed • To calculate VaR we run a historical simulation, at a given confidence level, over a specified time period. We use one or two years of daily price history, with each day given equal weighting. • This means we include most market risk factors that could make a difference, and it gives us a consistent way of assessing risk for all these factors in all our portfolios. • We work with three main types of VaR, which all use the same calculation models. They are Internal VaR, Regulatory VaR and Stressed VaR. We have governance and controls for all forms of VaR, and we regularly review and assess them. Internal VaR • We use this to calculate the total VaR in our trading book. It covers all the risk asset classes: interest rate, equity, credit (spread) and foreign exchange. We use two years of data for this simulation. • Like the rest of Banco Santander, we use a time horizon of one day and a confidence level of 99%. For any given day’s trading position, we would 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. • For Internal VaR, we also calculate a time-weighted VaR using Banco Santander’s method. This gives more weight to the most recent days in the last two years, which means VaR changes more quickly in line with current market volatility. That gives us a better indication of how the market’s behaviour is changing, mitigating some limitations of VaR. • We measure Internal VaR every day, comparing the equally-weighted result with the time-weighted result and report the higher against the Santander UK and business unit level limits. The Santander UK limits were previously approved by the ERCC. Following the completion of the ring-fencing transfer scheme and the significant reduction in trading book activity, the Santander UK limits are now approved by the Market and Structural Risk Control Forum rather than ERCC. We also report our equally weighted VaR against asset class and individual desk level limits. Whenever we find a limit has been exceeded, we report it, following the market risk framework. The main classes of risk that we measure Internal VaR on are interest rate, equity and credit spread risks. Regulatory VaR and Stressed VaR • We use these VaR models to calculate how much capital we need to hold for trading market risk. For these calculations, we only look at the factors for which we hold approval from the ECB and PRA (as we operate under their joint supervision). For credit and foreign exchange – factors which are not approved by the PRA for our VaR capital models – we use the standardised approach to calculate how much capital to hold. We also use the standardised approach for the ring-fenced bank. For more on this, see the ‘Capital requirement measures’ section. • For Regulatory VaR, we use a time horizon of ten days and a confidence level of 99%. To calculate the ten-day one-day The limitations of VaR Whilst VaR is a useful and important market standard measure of risk it does however have some limitations, these include: • VaR assumes what happened in the past is a reliable way to predict what will happen in the future, which 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 gives no guide to 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 or whose structures are more complex. Back-testing – comparing VaR estimates with reality In order to check that the way we estimate VaR is reasonable, we back-test our one day 99% Internal and Regulatory VaR each day by comparing them against both actual and hypothetical profits and losses, using a one-day Back-testing allows us to identify exceptions – times when the predictions were out of line with what happened. We can then look for trends in these exceptions, which can help us decide whether we need to recalibrate our VaR model. The CRR sets out criteria for how many exceptions are acceptable in the Regulatory VaR model. The PRA’s Supervisory Statements clarify the requirements further. If there are five or more exceptions in 250 days, then points are added to our capital requirement multiplier. It is not normally possible to back-test Stressed VaR, because it is not intended to tell us anything about our performance in normal conditions. 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. Stress testing scenarios The scenarios we use for stress testing are outlined in our trading market risk appetite and are central to the monthly Board Risk Appetite reporting. The scenarios are also part of our daily processes for setting and monitoring risk management limits. We calculate the impact of over 100 scenarios on our CIB trading books each day. Over half of these are reported against limits, and we escalate any breaches. This could lead to our front office being asked to reduce risk. The others are not calibrated to the same severity – for instance to a much longer holding period or for a completely artificial scenario—and so are not in the same limit structure. The scenarios we create are partly inspired by past events, like the global financial crisis. They also include plausible ways that unusual market conditions could occur in the future that impact interest rates, equity prices, exchange rates and credit spreads. Stress testing helps us to see how different amounts of liquidity in the markets would affect us in a stress event, such as an equity crash. It is important to make sure that the stress result we report is as realistic as possible. For more on how we design our scenarios for stress testing see ‘Stress Testing’ in the Risk Governance section. How we use stress testing We use limits to manage how much risk we take. They are expressed as how much we could lose in a stress event. We need to make sure the effects of potential poor market conditions do not exceed the Risk Appetite set by the Board. We regularly inform senior managers, including the ERCC, and the BRC about the results of our stress calculations, based on our current positions. Capital requirement measures Whenever we make changes to our models, we assess their effect on our capital requirements. Sometimes that means we need to tell the PRA and ECB and get their approval before we can make the change. Method Description The Internal Models Approach (IMA) The PRA has given us permission to use the IMA, in line with CRR, and every three months the PRA reviews what we are doing. The IMA means we can use Regulatory and Stressed VaR and RNIV to calculate the trading market risk capital requirement for the risk factors and businesses that we have ECB and PRA approval for. Following the implementation of the Ring-Fence Transfer Scheme and the run-off The standardised approach For risk factors and businesses not included in the IMA, we use the standardised approach set out by the CRR and PRA Supervisory Statements. At 31 December 2018, this amounted to 34% (2017: 11%) of our total market risk capital requirement. This increase is due to the lower level of total market risk capital from the IMA reduction at the year end. 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 take action 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 document and maintain a complete set of written policies, procedures and processes to help identify, assess, manage and report trading market risk. TRADING MARKET RISK REVIEW 2018 compared to 2017 (unaudited) 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. As noted earlier, as part of our ring-fencing plans, activities that can no longer be served by a ring-fenced bank were migrated to the Banco Santander London Branch in 2018. This resulted in most of our market-making activity and the associated trading market risk being transferred outside of the Santander UK group. In addition, some market risk positions have been in run-off There were no total VaR limit breaches in 2018. Following the completion of ring-fencing we saw an increase in the number of regulatory back-testing exceptions. This was due to the profit and losses on the residual activity in the trading book being driven more by non-market 2-3 CRR-required run-off, VaR This table and graph shows our Internal VaR for exposure to each of the main classes of risk for 2018 and 2017. Year-end exposure Average exposure Highest exposure Lowest exposure Trading instruments 2018 2017 2018 2017 2018 2017 2018 2017 Interest rate risks 0.5 2.6 1.4 2.5 3.9 3.5 0.2 1.8 Equity risks — 0.3 0.2 0.6 0.6 2.0 — 0.2 Foreign exchange risks 0.1 0.3 0.3 0.4 0.9 1.6 — — Diversification offsets (1) (0.2 ) (0.7 ) (0.5 ) (0.8 ) — — — — Total correlated one-day 0.4 2.5 1.4 2.7 3.8 3.7 0.3 2.0 (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

Liquidity risk

Liquidity risk	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Liquidity risk	Liquidity risk Overview 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 LCR and our eligible liquidity pool. We then explain our funding strategy and structure and we analyse our loan to deposit ratio (LDR) and our wholesale funding. Finally, we analyse how we have encumbered some of our assets to support our funding activities. Key metrics LCR increased to 164% (2017: 120%) Wholesale funding with maturity <1 year up to £16.8bn (2017: £14.9bn) LCR eligible liquidity pool increased to £54.1bn (2017: £48.5bn) Loan-to-deposit 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 15, 28 and 29 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. 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 In 2018 we managed 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. Under this model, and the PRA’s liquidity rules, Santander UK plc and its subsidiaries ANTS and Cater Allen Limited form the Domestic Liquidity Sub-group With effect from 1 January 2019, and in accordance with our ring-fence structure, Santander UK plc was granted a new DoLSub permission, withdrawing ANTS from the existing UK DoLSub. As a result, from 1 January 2019 we monitor and manage liquidity risk for the Santander UK plc group and ANTS plc separately. We transfer liquidity risks from the products Santander UK Group Holdings plc issues, or the contracts it executes, into our subsidiaries largely through back-to-back Risk appetite Our LRA statement is based on the principles of liquidity management we use to manage our balance sheet. It also supports our need to meet or exceed the rules of our regulators. In line with our liquidity management principles, we avoid an over-reliance on funding from a single product, customer or counterparty. We also maintain enough unencumbered customer assets to support current and future funding and collateral requirements, and maintain enough capacity to monetise liquid assets and other counterbalancing capacity within an appropriate timeframe. Our LRA is proposed to the Risk division and the Board, which is then approved under advice from the Board Risk Committee. Our LRA, in the context of our overall Risk Appetite, is reviewed and approved by the Board each year, or more often if needed. From 1 January 2019, separate LRAs for Santander UK plc and for ANTS plc have been approved. These are appropriate to their individual business models and consistent with the strategy of Santander UK Group Holdings plc. Risk measurement We use a number of metrics to manage liquidity risk. These include metrics that show the difference between cash and collateral inflows and outflows in different periods. They also include structural metrics, such as our LDR ratio and our level of encumbered assets. Ongoing business management Within our framework of prudent funding and liquidity management, we manage our activities to minimise our liquidity risk. We have clear responsibilities for short-term funding, medium-term funding, encumbrance, collateral and liquid asset management. This ensures we manage liquidity risks as part of our daily operations, strategy and planning. Our liquidity management framework is split between short-term and strategic activities. Our short-term activities focus on intra-day We regularly test the liquidity of our eligible liquidity pool, in line with PRA and Basel rules. We do this by realising some of the assets through repurchase or outright sale to the market. We make sure that over any 12-month 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 test 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 stand 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. The 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 Plan 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) 2018 compared to 2017 • Throughout 2018 we maintained robust risk management controls to monitor and manage the levels of our eligible liquidity pool and encumbrance. The LCR increased to 164% at 31 December 2018 (2017: 120%), This increase reflects prudent planning and some pre-funding • Our LCR eligible liquidity pool significantly exceeded our wholesale funding of less than one year, with a coverage ratio of 322% at 31 December 2018 (2017: 326%). The coverage ratio was broadly flat year on year, but continues to be volatile due to the management of normal short-term business commitments. • The LRA increased 29%, reflecting prudent planning and some pre-funding Liquidity Coverage Ratio This table shows our LCR and LRA at 31 December 2018 and 2017. It reflects the stress testing methodology in place at that time. LCR LRA (1) 2018 2017 2018 2017 £bn £bn £bn £bn Eligible liquidity pool (liquidity value) 53.0 47.4 52.2 45.7 Net stress outflows (32.4 ) (39.7 ) (32.1 ) (34.7 ) Surplus 20.6 7.7 20.1 11.0 Eligible liquidity pool as a percentage of anticipated net cash flows 164 % 120 % 163 % 132 % (1) The LRA 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 2018 and 2017. It also shows the weighted average carrying value in the year. Carrying value Liquidity value (1) Weighted average carrying 2018 2017 2018 2017 2018 2017 £bn £bn £bn £bn £bn £bn Cash and balances at central banks 22.4 30.9 22.4 30.9 24.4 23.6 Government bonds 26.1 12.5 25.7 12.3 16.8 19.6 Supranational bonds and multilateral development banks 1.1 1.0 1.1 1.0 1.1 1.1 Covered bonds 2.7 2.7 2.5 2.3 2.6 2.7 Asset-backed securities 1.7 0.6 1.3 0.5 1.4 0.8 Equities 0.1 0.8 — 0.4 2.1 1.1 54.1 48.5 53.0 47.4 48.4 48.9 54.1 48.5 53.0 47.4 48.4 48.9 (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 2018 and 2017, the composition of the pool is consistent with the currency profile of our net liquidity outflows. US Dollar Euro Sterling Other Total 2018 5.3 3.9 42.2 2.7 54.1 2017 9.2 1.8 36.7 0.8 48.5 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 2018 and 2017. 2018 2017 LCR eligible liquidity pool Of which LCR eligible liquidity pool Of which Level 1 Level 2A Level 2B Total LRA Level 1 Level 2A Level 2B Total LRA Cash and balances at central banks 22.4 — — 22.4 21.8 30.9 — — 30.9 30.3 Government bonds: - AAA to AA- 23.6 — — 23.6 23.3 11.0 — — 11.0 11.0 - A+ to A — 2.5 — 2.5 2.5 — 1.5 — 1.5 1.5 Supranational bonds and multilateral development banks: - AAA to AA- 1.1 — — 1.1 1.1 1.0 — — 1.0 1.0 Covered bonds: - AAA to AA- 1.6 1.1 — 2.7 2.7 1.5 1.2 — 2.7 2.7 Asset-backed securities: - AAA to AA- — — 1.7 1.7 1.7 — — 0.6 0.6 0.6 Equities — — 0.1 0.1 0.1 — — 0.8 0.8 0.8 48.7 3.6 1.8 54.1 53.2 44.4 2.7 1.4 48.5 47.9 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 need 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. This is reflected in our LDR ratio which we monitor against budget each month. At the same time, it makes sure we do not concentrate our sources of funding too much on any one product. 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. Around 90% 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 onto 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 needs resolving. 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 and offers no guarantee to them. This structure is a Bank of England recommended configuration which aims to resolve banks without disrupting the activities of their operating companies, 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. Santander UK Group Holdings plc is the issuer of capital and MREL/Total Loss Absorbing Capacity (TLAC) eligible senior unsecured debt. We also access the wholesale markets through securitisations of certain assets of the Santander UK group’s 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 sufficient collateral is placed and available at the Discount Window. FUNDING RISK REVIEW 2018 compared to 2017 (unaudited) • 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. 2018 presented a challenging market environment for issuance, debt capital markets experienced pockets of volatility throughout the year. However, despite the continuing backdrop of global geo-political • In 2018, our total term funding was £17.1bn (2017: £11.8bn), of which £14.8bn (2017: £7.3bn) was medium-term issuance and £2.3bn (2017: £4.0bn) was from the UK Government’s Term Funding Scheme (TFS). • The £14.8bn medium-term funding included £2.7bn of senior unsecured notes from the Company, £4.5bn of senior unsecured notes, £4.3bn of covered bonds and £3.3bn of securitisations from our operating company Santander UK plc. • Maturities in 2018 were £6.9bn (2017: £13.1bn). At 31 December 2018, 77% (2017: 75%) of wholesale funding had a maturity of greater than one year, with an overall residual duration of 37 months (2017: 43 months). The total drawdown outstanding from the TFS was £10.8bn (2017: £8.5bn) and the total drawdowns of UK Treasury Bills under the FLS were at £1.0bn (2017: £3.2bn). • Customer deposits decreased £3.8bn, with lower corporate deposits and management pricing actions contributing to a reduction in retail savings products. This was partially offset by a £0.9bn increase in personal current account balances. • Our level of encumbrance from external and internal issuance of securitisations and covered bonds remained broadly static in 2018, as planned. Reconciliation of wholesale funding to the balance sheet This table reconciles our wholesale funding to our balance sheet at 31 December 2018 and 2017. Balance sheet line item 2018 Funding Deposits by banks £bn Defined by customers (1) £bn Repurchase (2) Trading Financial Debt securities in issue £bn Subordinated £bn Other equity (3) £bn Deposits 1.0 1.0 — — — — — — — Certificates of deposit and commercial paper 6.4 — — — — — 6.4 — — Senior unsecured – public benchmark 21.3 — — — — — 21.3 — — Senior unsecured – privately placed 4.0 — — — — 1.0 3.0 — — 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 5.3 — — — — — — 3.0 2.3 Total wholesale funding 73.2 11.8 0.5 2.2 — 1.0 52.4 3.0 2.3 Repos 10.8 — — 8.7 — 2.1 — — — Foreign exchange and hedge accounting 4.1 — — — — — 3.5 0.6 — Other 9.2 6.0 (4) — — — 3.2 — — — Balance sheet total 97.3 17.8 0.5 10.9 — 6.3 55.9 3.6 2.3 2017 Deposits by banks 0.3 0.2 — — — 0.1 — — — Certificates of deposit and commercial paper 8.0 — — — — 0.4 7.6 — — Senior unsecured – public benchmark 17.8 — — — — — 17.8 — — Senior unsecured – privately placed 3.1 — — — — 1.1 2.0 — — Covered bonds 14.2 — — — — — 14.2 — — Securitisation and structured issuance 5.5 — 0.5 1.0 — — 4.0 — — Term Funding Scheme 8.5 8.5 — — — — — — — Subordinated liabilities and equity 5.5 — — — — — — 3.2 2.3 Total wholesale funding 62.9 8.7 0.5 1.0 — 1.6 45.6 3.2 2.3 Repos 25.6 — — 0.1 25.5 — — — — Foreign exchange and hedge accounting 3.9 — — — — — 3.3 0.6 — Other 10.3 4.0 (4) — — 5.6 (5) 0.7 — — — Balance sheet total 102.7 12.7 0.5 1.1 31.1 2.3 48.9 3.8 2.3 (1) This is included in our balance sheet total of £173,692m (2017: £177,421m). (2) From 1 January 2018, the non-trading re-presented (3) Consists of £14m (2017: £14m) fixed/floating rate non-cumulative Step-up (4) Other consists of items in the course of transmission and other deposits, excluding the TFS. See Note 26 to the Consolidated Financial Statements. (5) Short positions in securities and unsettled trades, cash collateral and short-term deposits. 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 financing repurchase 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 and >6 and >9 and Sub-total >1 and >2 and month £ 3 months £ 6 months £ 9 months £ 12 months £ 1 year £ 2 years £ 5 years >5 years Total 2018 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Santander UK Group Holdings plc (1) Senior unsecured – public benchmark — — — — — — 0.8 6.2 1.7 8.7 Senior unsecured – privately placed — — — — — — — — 0.1 0.1 Subordinated liabilities and equity (incl. AT1) — — 0.5 — 0.3 0.8 — 0.8 1.5 3.1 — — 0.5 — 0.3 0.8 0.8 7.0 3.3 11.9 Santander UK plc Deposits by banks — 1.0 — — — 1.0 — — — 1.0 Certificates of deposit and commercial paper 1.5 3.6 1.1 0.1 0.1 6.4 — — — 6.4 Senior unsecured – public benchmark 0.8 1.5 — 0.6 — 2.9 4.8 3.5 1.4 12.6 Senior unsecured – privately placed — — 1.0 0.3 — 1.3 1.8 0.4 0.4 3.9 Covered bonds — — — 1.4 — 1.4 2.8 8.4 4.0 16.6 Securitisation and structured issuance (2) 0.8 0.6 0.6 0.2 0.4 2.6 0.8 2.5 — 5.9 Term Funding Scheme — — — — — — 4.5 6.3 — 10.8 Subordinated liabilities — — — — — — — 0.9 1.3 2.2 3.1 6.7 2.7 2.6 0.5 15.6 14.7 22.0 7.1 59.4 Other group entities Securitisation and structured issuance (3) — 0.1 0.1 0.1 0.1 0.4 0.4 1.1 — 1.9 Total at 31 December 2018 3.1 6.8 3.3 2.7 0.9 16.8 15.9 30.1 10.4 73.2 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 2.6 1.0 0.4 12.4 7.4 11.8 6.4 38.0 3.1 6.8 3.3 2.7 0.9 16.8 15.9 30.1 10.4 73.2 Total at 31 December 2017 4.8 3.9 3.3 1.4 1.5 14.9 7.9 28.9 11.2 62.9 Of which: – Secured 0.9 — 1.4 — 1.3 3.6 2.9 18.3 3.4 28.2 – Unsecured 3.9 3.9 1.9 1.4 0.2 11.3 5.0 10.6 7.8 34.7 4.8 3.9 3.3 1.4 1.5 14.9 7.9 28.9 11.2 62.9 (1) 95% 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 2018 and 2017. 2018 2017 Sterling US Dollar Euro Other Sterling US Dollar Euro Other % % % % % % % % Santander UK Group Holdings plc Senior unsecured – public benchmark 11 65 22 2 9 67 22 2 Senior unsecured – privately placed — — — 100 — — — 100 Subordinated liabilities and equity (incl. AT1) 68 32 — — 68 32 — — 26 56 16 2 28 54 14 4 Santander UK plc Deposits by banks 3 97 — — 27 73 — — Certificates of deposit and commercial paper 48 52 — — 89 10 — 1 Senior unsecured – public benchmark 11 56 33 — 9 49 42 — Senior unsecured – privately placed 13 12 72 3 7 19 70 4 Covered bonds 50 — 49 1 47 — 52 1 Securitisation and structured issuance 61 35 4 — 80 20 — — Term Funding Scheme 100 — — — 100 — — — Subordinated liabilities 49 51 — — 52 48 — — 48 25 26 1 49 19 32 — Other group entities Deposits by banks — — — — — 100 — — Certificates of deposit and commercial paper — — — — 34 65 1 — Securitisation and structured issuance 89 11 — — 91 — 9 — 89 11 — — 47 50 3 — Total 46 30 24 — 45 28 25 2 Term issuance In 2018, our external term issuance (sterling equivalent) was: Sterling US Dollar Euro Other Total 2018 Total 2017 £bn £bn £bn £bn £bn £bn Santander UK Group Holdings plc Senior unsecured – public benchmark 0.5 1.5 0.7 — 2.7 2.0 Senior unsecured – privately placed — — — — — 0.1 Subordinated debt and equity (incl. AT1) — — — — — 0.5 0.5 1.5 0.7 — 2.7 2.6 Santander UK plc Securitisations and other secured funding 1.4 1.5 — — 2.9 0.5 Covered bonds 2.5 — 1.8 — 4.3 2.3 Senior unsecured – public benchmark 0.4 2.5 — — 2.9 1.1 Senior unsecured – privately placed 0.3 — 1.3 — 1.6 0.1 Term Funding Scheme 2.3 — — — 2.3 4.0 6.9 4.0 3.1 — 14.0 8.0 Other group entities Securitisations 0.4 — — — 0.4 1.2 Total gross issuances 7.8 5.5 3.8 — 17.1 11.8 Loan-to-deposit This table shows our customer loans, deposits and LDR at 31 December 2018 and 2017. The business segments data excludes fair value loans, impairment loss allowances, accrued interest and other. The total data includes them but excludes repurchase agreements. 2018 2017 Customer Customer loans deposits LDR LDR £bn £bn % % Retail Banking 172.8 142.1 122 113 Corporate & Commercial Banking 17.7 17.6 101 104 Corporate & Investment Banking 4.6 4.8 96 133 Corporate Centre 4.8 7.6 63 174 Total customer loans and deposits (2) 199.9 172.1 116 113 Adjust for: fair value loans, impairment loss allowances, accrued interest and other 1.7 1.6 Statutory loans and advances to customers/deposits by customers (1) 201.6 173.7 Total 201.6 173.7 (1) The customer loans and customer deposits numbers are the amounts disclosed in the Consolidated Balance Sheet. (2) We calculate the total LDR as loans and advances to customers divided by deposits by customers. Encumbrance We have encumbered an asset if we have pledged 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 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 these programmes, see Notes 15 and 37 to the Consolidated Financial Statements. On-balance Encumbered with counterparties other Assets Unencumbered assets not pre-positioned with positioned Other Covered Securitis- at central Readily available Cannot be Total bonds ations Other Total banks (4) available assets encumbered Total assets 2018 £m £m £m £m £m £m £m £m £m £m Cash and balances at central — — 1,080 1,080 636 22,464 — — 23,100 24,180 banks (1)(2) Financial assets at FVTPL: – Derivative financial instruments — — — — — — — 5,321 5,321 5,321 – Other financial assets at FVTPL — — — — — — — 6,137 6,137 6,137 Financial assets at amortised cost: – Loans and advances to customers 21,240 14,454 256 35,950 52,497 71,942 20,943 20,287 165,669 201,619 – Loans and advances to banks — — 402 402 — — — 3,113 3,113 3,515 – Repurchase agreements- non — — — — — — — 21,127 21,127 21,127 trading (3) – Other financial assets at — — 3,763 3,763 — 3,465 — — 3,465 7,228 amortised cost Financial assets at FVOCI — — 5,825 5,825 — 7,477 — — 7,477 13,302 Interests in other entities — — — — — — — 88 88 88 Intangible assets — — — — — — — 1,814 1,814 1,814 Property, plant and equipment — — — — — — 1,835 — 1,835 1,835 Current tax assets — — — — — — — 106 106 106 Retirement benefit assets — — — — — — — 842 842 842 Other assets — — — — — — — 2,267 2,267 2,267 Total assets 21,240 14,454 11,326 47,020 53,133 105,348 22,778 61,102 242,361 289,381 2017 (5) Cash and balances at central — — 1,010 1,010 395 31,366 — — 31,761 32,771 banks (1)(2) Trading assets — — 17,092 17,092 — 903 — 12,560 13,463 30,555 Derivative financial instruments — — — — — — — 19,942 19,942 19,942 Other financial assets at FVTPL — — — — — 1,405 691 — 2,096 2,096 Loans and advances to banks (3) — — 105 105 — — — 3,361 3,361 3,466 Loans and advances to customers (3) 18,891 16,530 31 35,452 57,644 64,412 20,459 21,365 163,880 199,332 Repurchase agreements- non — — — — — — — 2,614 2,614 2,614 trading (3) Financial investments — — 6,755 6,755 — 10,856 — — 10,856 17,611 Interests in other entities — — — — — — — 73 73 73 Intangible assets — — — — — — — 1,742 1,742 1,742 Property, plant and equipment — — — — — — 1,598 — 1,598 1,598 Retirement benefit assets — — — — — — — 449 449 449 Other assets — — — — — — — 2,511 2,511 2,511 Total assets 18,891 16,530 24,993 60,414 58,039 108,942 22,748 64,617 254,346 314,760 (1) Encumbered cash and ba

Capital risk

Capital risk	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Capital risk	Capital risk Overview 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 also give details of the impact of IFRS 9 on regulatory capital, and the results of the Bank of England’s 2018 stress testing exercise. 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 CET1 capital ratio of 13.2% (2017: 12.2%) Total capital resources decreased to £15.0bn (2017: £15.5bn) UK leverage ratio of 4.5% (2017: 4.4%) 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 a member 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 immediate and ultimate parent Banco Santander SA and we operate as an autonomous subsidiary. As we are part of the UK sub-group sub-group CAPITAL RISK MANAGEMENT The Board is responsible for capital management strategy and policy and ensuring that our capital resources are monitored and controlled 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 commercial 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 for 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 economic 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. As a result, Santander UK Group Holdings 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 CRD IV end-point 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 macroeconomic 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 internally assigned 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. For details on our Recovery framework in the event of a capital stress, see the risk mitigation section in the ‘Liquidity risk’ section. 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. Every 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 2018 compared to 2017 Our CET1 capital ratio increased 100bps to 13.2% at 31 December 2018 (2017: 12.2%), with ongoing capital accretion and risk management initiatives leaving us strongly capitalised in the current environment. CET1 capital was broadly in line with the prior year at £10.4bn, with dividend payments largely offset by ongoing capital accretion through retained profits. Our total capital ratio increased to 19.1% at 31 December 2018 (2017: 17.8%). RWAs decreased £8.2bn, largely as a result of ring-fence transfers (£5.5bn), risk management initiatives (£3.0bn) and the widening of scope of our large corporate risk model earlier in the year. This was partially offset by higher RWAs in the Corporate Centre. • Retail Banking RWAs increased in line with customer loan growth. • Corporate & Commercial Banking RWAs decreased 12%, largely as a result of ring-fence implementation and risk management initiatives, including SRT securitisations. These actions have positioned the bank prudently, though they will have an economic impact in 2019. • Corporate & Investment Banking RWAs decreased 56% to £7.2bn largely as a result of ring-fence transfers and risk management initiatives. Other assets and liabilities of £21.5bn and £20.7bn, primarily relating to derivative contracts, were transferred to Banco Santander London Branch in July 2018. RWAs attributable to customer loans were £5.2bn (2017: £7.2bn). These actions will result in significantly lower future profits for this segment. • Corporate Centre RWAs were higher at £8.4bn, due to increases in counterparty risk with more concentrated exposures to Banco Santander London Branch, following derivative business transfers as part of ring-fence implementation. RWAs attributable to non-core Impact of IFRS 9 on regulatory capital The implementation of IFRS 9 on 1 January 2018 resulted in an initial reduction in our CET1 capital ratio by 8 basis points to 12.13% which, following the application of EU transitional arrangements for the capital impact of IFRS 9, reduced to 12.16%. As a result, the adoption of IFRS 9 did not have a material impact on our capital position. As our ECL methodology takes account of forward-looking data covering a range of possible economic outcomes, ECL-based pro-cyclicality ECL-based We reflect projections of ECL-based Bank of England stress testing The results of the latest round of PRA stress tests were released in November 2018. With a stressed CET1 ratio of 10.9% after allowed management actions, on an IFRS 9 transitional basis, we significantly exceeded the PRA threshold requirement of 7.5%. Additionally, with a stressed leverage ratio of 3.9% we exceeded the PRA threshold requirement of 3.26%. Since the introduction of IFRS 9 on 1 January 2018, the stress test results are published on an IFRS 9 transitional and non-transitional end-point non-transitional end-point non-transitional For the third year in a row, we had the lowest stressed CET1 ratio impact of all participating firms, demonstrating our resilient balance sheet and prudent approach to risk. The Bank of England’s CET1 hurdle rate comprises the CRR Pillar 1 minimum of 4.5% together with a Pillar 2A CET1 requirement, an estimate of the applicable Systemic Risk Buffer and an adjustment to offset the pro-cyclical On an IFRS 9 transitional basis, our lowest post-stress end-point non-transitional end-point non-transitional Meeting evolving capital requirements We target a CET1 management buffer that is of sufficient size to absorb market volatility and changes in the regulatory minimum requirement, such as application of any dynamic countercyclical capital buffer (CCyB). At 31 December 2018, our 7% AT1 permanent write down (PWD) securities benefitted from a £4.9bn (6.2% RWA) CET1 buffer above the 7% trigger. The current CET1 buffer to restrictions on distributions (maximum distributable amount) is £9.0bn (10.6% RWA). In June 2018 the Bank of England confirmed Santander UK’s non-binding Key capital ratios Santander UK Group Holdings plc Santander UK plc 2018 % 2017 2018 % 2017 CET1 capital ratio 13.2 12.2 13.2 12.2 AT1 2.6 2.3 2.2 2.4 Grandfathered Tier 1 0.4 0.5 0.8 0.8 Tier 2 2.9 2.8 4.1 3.8 Total capital ratio 19.1 17.8 20.3 19.2 The total capital difference between Santander UK Group Holdings plc and Santander UK plc was due to the recognition of minority interests. The total subordination available to Santander UK plc bondholders was 20.3% (2017: 19.7%) of RWAs. Regulatory capital resources This table shows our regulatory capital. 2018 £m 2017 CET1 capital instruments and reserves: - Capital instruments 7,060 7,060 - Retained earnings 6,439 6,399 - Accumulated other reserves and non-controlling 431 453 CET1 capital before regulatory adjustments 13,930 13,912 CET1 regulatory adjustments: - Additional value adjustments (42 ) (70 ) - Goodwill (net of tax) (1,161 ) (1,165 ) - Other intangibles (610 ) (539 ) - Fair value reserves related to gains or losses on cash flow hedges (251 ) (228 ) - Negative amounts resulting from the calculation of regulatory expected loss amounts (599 ) (748 ) - Gains or losses on liabilities valued at fair value resulting from changes in own credit standing (67 ) (13 ) - Deferred tax assets that rely on future profitability excluding timing differences (20 ) (25 ) - Defined benefit pension fund assets (631 ) (333 ) - Dividend accrual (18 ) (19 ) - IFRS 9 Transitional Adjustment 21 — - Deduction for non-controlling (151 ) (152 ) CET1 capital 10,401 10,620 AT1 capital instruments: - Capital instruments 2,041 2,041 - Amount of qualifying items subject to phase out from AT1 593 707 - Regulatory deductions for instruments issued by subsidiary undertakings (268 ) (301 ) AT1 capital 2,366 2,447 Tier 1 capital 12,767 13,067 Tier 2 capital instruments: - Capital instruments 2,888 2,749 - Amount of qualifying items subject to phase out from Tier 2 369 587 - Regulatory deductions for instruments issued by subsidiary undertakings or subject to CRDIV amortisation (986 ) (915 ) Tier 2 capital 2,271 2,421 Total regulatory capital (1) 15,038 15,488 (1) Capital resources include a transitional IFRS 9 benefit at 31 December 2018 of £21m (1 January 2018: £18m).

Accounting Policies

Accounting Policies	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Accounting Policies	1. ACCOUNTING POLICIES These financial statements are prepared for Santander UK Group Holdings plc (the Company) and the Santander UK Group Holdings plc group (the Santander UK group) under the UK Companies Act 2006. The principal activity of the Santander UK group is the provision of an extensive range of personal financial services, and a wide range of banking and financial services to personal, business and corporate customers. Santander UK Group Holdings 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. 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. The Company financial statements have been prepared in accordance with IFRSs as adopted by the European Union and as applied in accordance with the provision of the UK Companies Act 2006. 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 On 1 January 2018, the Santander UK group adopted IFRS 9 ‘Financial Instruments’ (IFRS 9) and IFRS 15 ‘Revenue from Contracts with Customers’ (IFRS 15). The new or revised accounting policies are set out below. The impact of applying IFRS 9 is disclosed in Note 44. The accounting policy changes for IFRS 9, set out below, have been applied from 1 January 2018. Comparatives have not been restated. As a result of the change from IAS 39 to IFRS 9, some disclosures presented in respect of certain financial assets are not comparable because their classification may have changed between the two standards. This means that some IFRS 9 disclosures are not directly comparable and some disclosures that relate to information presented on an IAS 39 basis are no longer relevant in the current period. As explained in Note 44, the classification and measurement changes to financial assets that arose on adoption of IFRS 9 have been aligned to the presentation in the balance sheet. The Santander UK group decided to continue adopting IAS 39 hedge accounting and consequently there have been no changes to the hedge accounting policies and practices following the adoption of IFRS 9. However, additional hedge accounting disclosure requirements of IFRS 7 ‘Financial Instruments: Disclosures’ (IFRS 7) have been included in these financial statements. In addition, non-trading non-trading non-trading non-trading re-presented re-presentation The application of IFRS 15 had no material impact on the Santander UK group as there were no significant changes in the recognition of in-scope Future accounting developments At 31 December 2018, the Santander UK group has not yet adopted the following significant new or revised standards and interpretations, and amendments thereto, which have been issued but which are not yet effective for the Santander UK group: • IFRS 16 ‘Leases’ (IFRS 16) – In January 2016, the IASB issued IFRS 16. The standard is effective for annual periods beginning on or after 1 January 2019. IFRS 16 sets out the principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. For lessee accounting, IFRS 16 introduces a single lessee accounting model and requires a lessee to recognise a right-of-use The Santander UK group has elected to apply the modified retrospective approach whereby the ROU asset at the date of initial application is measured at an amount equal to the lease liability. The ROU asset is adjusted for any prepaid lease payments and incentives relating to the relevant leases that were recognised on the balance sheet at 31 December 2018. It includes the estimated costs of restoring the underlying assets to the condition required by the lease terms and conditions. For the Santander UK group, the application of IFRS 16 at 1 January 2019 is expected to increase property, plant and equipment by £211m (being the net increase in ROU assets referred to above), reduce other assets by £12m, increase other liabilities by £182m from recognising lease liabilities, and increase provisions by £17m. There is expected to be no impact on shareholders’ equity. In arriving at the estimated impact, as well as excluding leases whose terms end within 12 months, the Santander UK group applies a single discount rate to a portfolio of leases with similar remaining lease terms. 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 • Amendment to IAS 12 ‘Income Taxes’ (part of ‘Annual Improvements to IFRS Standards 2015-2017 Cycle’) – In December 2017, as part of its annual improvements project, the IASB issued an amendment to IAS 12 to clarify 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 is applied retrospectively and is effective for annual reporting periods beginning on or after 1 January 2019, is awaiting EU endorsement at the time of approving these Consolidated Financial Statements. The effects of the amendment are expected to lead to a reduction in the effective tax rate where the tax relief on coupons in respect of AT1 capital securities would be recognised in the income statement rather than in equity. 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 has (i) 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 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. Interests in subsidiaries in the Company unconsolidated financial statements are held at cost subject to impairment. 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 (including foreign branch operations) 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 non-monetary available-for-sale), 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) 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 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. Share-based payments The Santander UK group engages in cash-settled and equity-settled share-based payment transactions in respect of services received from certain of its employees. Shares of the Santander UK group’s parent, Banco Santander SA are purchased in the open market by the Santander UK group (for the Employee Sharesave scheme) or are purchased by Banco Santander SA or another Banco Santander company (for awards granted under the Long-Term Incentive Plan and the Deferred Shares Bonus Plan) to satisfy share options or awards as they vest. 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 payment transactions. 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 payments. A liability equal to the amount to be reimbursed to Banco Santander SA is recognised at the fair value determined at the grant date for equity-settled share-based payments. 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 non-market 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 at each balance sheet date, 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 basis over their useful life of three to seven years, unless the software is an integral part of the related computer hardware, in which case it is treated as property, plant and equipment as described below. Capitalisation of costs ceases when the software is capable of operating as intended. Costs of maintaining software are expensed as incurred. 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 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 Depreciation is not charged on freehold land and assets under construction. 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 fair value through profit or loss 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 From 1 January 2018, the Santander UK group has applied IFRS 9 Financial Instruments and 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 li
Santander UK Group Holdings plc [member]
Statement [LineItems]
Accounting Policies	1. ACCOUNTING POLICIES These financial statements are prepared for Santander UK Group Holdings plc (the Company) under the Companies Act 2006. The principal activity of the Company is a financial services holding company. Santander UK Group Holdings plc is a public limited company incorporated in England and Wales having a registered office in England. Basis of preparation This basis of preparation differs from that applied in the Consolidated Financial Statements. See Note 1 to the Consolidated Financial Statements for details of the periods for which the Consolidated Financial Statements have been prepared. The accounting policies of the Company are the same as those of the Santander UK Group Holdings plc group which are set out in Note 1 to the Consolidated Financial Statements, to the extent that the Company has similar transactions to the Santander UK Group Holdings plc group. The financial statements have been prepared on the going concern basis using the historical cost convention. An assessment of the appropriateness of the adoption of the going concern basis of accounting is disclosed in the Directors’ statement of going concern set out in the Directors’ Report. Compliance with International Financial Reporting Standards The Company’s financial statements have been prepared in accordance with International Financial Reporting Standards as issued by the IASB, including interpretations issued by the IFRS Interpretations Committee (IFRIC) of the IASB (together IFRS). The Company has also complied with IFRS as adopted by the European Union as there are no applicable differences between the two frameworks for the period presented. Recent accounting developments See Note 1 to Consolidated Financial Statements. The adoption of IFRS 9 did not have any significant impact on the Company.

Segments

Segments	12 Months Ended
	Dec. 31, 2018
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 re-branded • Corporate & Investment Banking • Corporate Centre non-core non-core run-down 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 in this Annual Report has been changed, and prior periods restated, to report our Jersey and Isle of Man branches in Corporate Centre rather than in Retail Banking as in previous years, as a result of their transfer from Santander UK plc to ANTS in December 2018. Prior periods have not been restated for the changes in our statutory perimeter in the third quarter of 2018, following the ring-fence transfers to Banco Santander London Branch, as described in Note 43. Results by segment Corporate & Corporate & Retail Commercial investment Corporate Banking Banking Banking Centre Total 2018 £m £m £m £m £m Net interest income 3,126 403 69 8 3,606 Non-interest 638 82 272 (55 ) 937 Total operating income/(expense) 3,764 485 341 (47 ) 4,543 Operating expenses before credit impairment losses, provisions and charges (1,929 ) (258 ) (262 ) (114 ) (2,563 ) Credit impairment (losses)/releases (124 ) (23 ) (14 ) 8 (153 ) Provisions for other liabilities and charges (230 ) (14 ) (8 ) (8 ) (260 ) Total operating credit impairment losses, provisions and (charges)/releases (1) (354 ) (37 ) (22 ) — (413 ) Profit/(loss) before tax 1,481 190 57 (161 ) 1,567 Revenue from external customers 4,421 638 386 (902 ) 4,543 Inter-segment revenue (657 ) (153 ) (45 ) 855 — Total operating income/(expense) 3,764 485 341 (47 ) 4,543 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 4,807 199,869 Total assets (4) 201,261 17,702 33,657 36,761 289,381 Customer deposits 142,065 17,606 4,853 7,607 172,131 Total liabilities 142,839 17,634 14,222 98,466 273,161 Average number of staff 20,694 1,732 1,108 114 23,648 (1) Credit impairment losses for 2018 are calculated on an IFRS 9 basis and for 2017 and earlier on an IAS 39 basis. For more on this methodology change, see the IFRS 9 accounting policy changes in Note 1 and the IFRS 9 transition disclosures in Note 44. (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 (4) Includes customer loans, net of credit impairment loss allowances. Corporate & Corporate & Retail Commercial Investment Corporate Banking (5) Banking Banking Centre (5) Total 2017 £m £m £m £m £m Net interest income 3,270 391 74 68 3,803 Non-interest 615 74 364 56 1,109 Total operating income 3,885 465 438 124 4,912 Operating expenses before credit impairment losses, provisions and charges (1,856 ) (223 ) (304 ) (119 ) (2,502 ) 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 (51 ) 40 1,814 Revenue from external customers 4,534 639 506 (767 ) 4,912 Inter-segment revenue (649 ) (174 ) (68 ) 891 — Total operating income 3,885 465 438 124 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 51,078 69,767 314,760 Customer deposits 143,834 17,760 4,546 9,781 175,921 Total liabilities 150,847 18,697 45,603 83,411 298,558 Average number of staff 17,194 1,240 1,006 119 19,559 2016 Net interest income 3,117 380 73 12 3,582 Non-interest 559 76 312 266 1,213 Total operating income 3,676 456 385 278 4,795 Operating expenses before credit impairment losses, provisions and charges (1,785 ) (215 ) (281 ) (136 ) (2,417 ) Credit impairment (losses)/releases (1) (21 ) (29 ) (21 ) 4 (67 ) Provisions for other liabilities and charges (338 ) (26 ) (11 ) (22 ) (397 ) Total operating credit impairment losses, provisions and charges (359 ) (55 ) (32 ) (18 ) (464 ) Profit before tax 1,532 186 72 124 1,914 Revenue from external customers 4,387 651 474 (717 ) 4,795 Inter-segment revenue (711 ) (195 ) (89 ) 995 — Total operating income 3,676 456 385 278 4,795 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) – Current account and debit card fees 697 27 23 — 747 – Insurance, protection and investments 94 — — — 94 – Credit cards 95 — — — 95 – Non-banking (3) 53 57 132 10 252 Total fee and commission income 939 84 155 10 1,188 Fee and commission expense (369 ) (31 ) (17 ) (1 ) (418 ) Net fee and commission income 570 53 138 9 770 Customer loans 168,389 19,382 5,659 6,726 200,156 Total assets (4) 175,100 19,381 39,777 68,252 302,510 Customer deposits 143,996 16,082 4,054 8,219 172,351 Total liabilities 149,793 17,203 36,506 83,555 287,057 Average number of staff 17,424 1,435 916 88 19,863 (1) Credit impairment losses for 2018 are calculated on an IFRS 9 basis and for 2017 and earlier on an IAS 39 basis. For more on this methodology change, see the IFRS 9 accounting policy changes in Note 1 and the IFRS 9 transition disclosures in Note 44. (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 (4) Includes customer loans, net of credit impairment loss allowances. (5) The re-segmentation re-presented

Net Interest Income

Net Interest Income	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Net Interest Income	3. NET INTEREST INCOME 2018 2017 2016 £m £m £m Interest and similar income: Loans and advances to customers 5,459 5,494 6,198 Loans and advances to banks 207 164 112 Reverse repurchase agreements – non trading 124 20 15 Other 282 227 142 Total interest and similar income (1) 6,072 5,905 6,467 Interest expense and similar charges: Deposits by customers (1,224 ) (1,183 ) (1,809 ) Deposits by banks (120 ) (35 ) (18 ) Repurchase agreements – non trading (37 ) (5 ) (38 ) Debt securities in issue (936 ) (737 ) (853 ) Subordinated liabilities (141 ) (134 ) (143 ) Other (8 ) (8 ) (24 ) Total interest expense and similar charges (2) (2,466 ) (2,102 ) (2,885 ) Net interest income 3,606 3,803 3,582 (1) This includes £209m of interest income on financial assets at fair value through other comprehensive income. (2) This includes £298m of interest expense on financial assets at fair value through other comprehensive income. In 2017, interest and similar income included £66m (2016: £79m) on impaired loans.

Net Fee and Commission Income

Net Fee and Commission Income	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Net Fee and Commission Income	4. NET FEE AND COMMISSION INCOME 2018 2017 2016 £m £m £m Fee and commission income: Current account and debit card fees 753 791 747 Insurance, protection and investments 105 100 94 Credit cards 85 92 95 Non-banking (1) 227 239 252 Total fee and commission income 1,170 1,222 1,188 Total fee and commission expense (421 ) (415 ) (418 ) Net fee and commission income 749 807 770 (1) Non-banking

Net Trading and Other Income

Net Trading and Other Income	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Net Trading and Other Income	5. NET TRADING AND OTHER INCOME 2018 2017 2016 £m £m £m Net trading and funding of other items by the trading book 263 205 75 Net (losses)/gains on other financial assets at fair value through profit or loss (18 ) 80 253 Net (losses)/gains on other financial liabilities at fair value through profit or loss (44 ) (97 ) 28 Net losses on derivatives managed with assets/liabilities held at fair value through profit or loss (128 ) (17 ) (135 ) Hedge ineffectiveness 34 5 28 Net profit on sale of available-for-sale 54 115 Net profit on sale of financial assets at fair value through other comprehensive income 19 Net income from operating lease assets 86 44 35 Other (24 ) 28 44 188 302 443 ‘Net trading and funding of other items by the trading book’ includes fair value gains of £22m (2017: losses of £27m, 2016: losses of £50m) 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 losses of £21m (2017: gains of £28m, 2016: gains of £51m). 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 (2017: £1m, 2016: £1m). In 2017, ‘Net profit on sale of available-for-sale available-for-sale In November 2018, pursuant to a Partnership Special Redemption Event, the Abbey National Capital Trust I 8.963% Non-cumulative Step-up Exchange rate differences recognised in the Consolidated Income Statement on items not at fair value through profit or loss were £689m expense (2017: £109m expense, 2016: £4,051m 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 £751m income (2017: £94m income, 2016: £4,076m 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.

Operating Expenses Before Credi

Operating Expenses Before Credit Impairment Losses, Provisions and Charges	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Operating Expenses Before Credit Impairment Losses, Provisions and Charges	6. OPERATING EXPENSES BEFORE CREDIT IMPAIRMENT LOSSES, PROVISIONS AND CHARGES 2018 2017 2016 Staff costs: Wages and salaries 905 746 731 Performance-related payments 160 157 157 Social security costs 111 93 94 Pensions costs – defined contribution plans 66 54 52 – defined benefit plans 81 32 26 Other share-based payments 3 10 3 Other personnel costs 50 45 62 1,376 1,137 1,125 Other administration expenses 809 1,011 970 Depreciation, amortisation and impairment 378 354 322 2,563 2,502 2,417 Staff costs ‘Performance-related payments’ include bonuses paid in the form of cash and share awards granted under the Long-Term Incentive Plan, as described in Note 38. Included in this are the Santander UK group’s equity-settled share-based payments, none of which related to option-based schemes. These are disclosed in the table below as ‘Share awards’. Performance-related payments above include amounts related to deferred performance awards as follows: Costs recognised in 2018 Costs expected to be recognised in 2019 or later Arising from Arising from Total Arising from Arising from Total Cash 4 9 13 10 10 20 Shares 3 10 13 8 9 17 7 19 26 18 19 37 The following table shows the amount of bonus awarded to employees for the performance year 2018. 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 2018 £m 2017 2018 £m 2017 2018 2017 Cash award – not deferred 123 116 — — 123 116 – deferred 13 13 20 17 33 30 Share awards – not deferred 11 12 — — 11 12 – deferred 13 16 17 18 30 34 Total discretionary bonus 160 157 37 35 197 192 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 guaranteed minimum pension (GMP), and concluded on the methods that were appropriate. The estimated increase in liabilities at the date of the judgement was £40m and is based on a number of assumptions and the actual impact may be different. This has been reflected in ‘Pensions costs – defined benefit plans’ and in the closing net accounting surplus of the Santander (UK) Group Pension Scheme. ‘Other share-based payments’ consist of options granted under the Employee Sharesave scheme which comprise the Santander UK group’s cash-settled share-based payments. For more, see Note 38. The average number of full-time equivalent staff was 23,648 (2017: 19,559, 2016: 19,863). The increase in staff numbers in 2018 reflected Santander UK plc’s acquisition of Santander Services on 1 January 2018. Following the acquisition, the costs relating to the staff associated with these businesses are now recognised as staff costs. In 2017 and earlier years, the equivalent costs were included in other administrative expenses. For more details, see Note 21. Depreciation, amortisation and impairment No impairments were charged in 2018. In 2017, an impairment charge of £32m was recognised that primarily related to capitalised software costs for a credit risk management system, part of which was no longer in use.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Operating Expenses Before Credit Impairment Losses, Provisions and Charges	2. OPERATING EXPENSES BEFORE CREDIT IMPAIRMENT LOSSES, PROVISIONS AND CHARGES These comprise wages and salaries of £3m (2017: £3m) recharged by the operating company, Santander UK plc. In 2018 and 2017, the Company had no full-time staff as they are all employed by Santander UK plc.

Audit and Other Services

Audit and Other Services	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Audit and Other Services	7. AUDIT AND OTHER SERVICES 2018 2017 2016 Audit fees: Fees payable to the Company’s auditor and its associates for the audit of the Santander UK group’s annual accounts 7.7 7.8 4.9 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 1.6 1.4 1.1 Total audit fees (1) 9.3 9.2 6.0 Non-audit Audit-related assurance services (2) 2.2 1.6 1.3 Taxation compliance services — — 0.1 Other assurance services 0.1 0.1 — Other non-audit 1.0 0.4 1.9 Total non-audit 3.3 2.1 3.3 (1) 2018 audit fees included £nil (2017: £0.6m) which related to the prior year. (2) 2018 audit-related assurance services included £0.1m (2017: £0.1m) which related to the prior year. Audit fees payable for the statutory audit of Santander UK Group Holdings plc were £0.5m (2017: £0.4m, 2016: £0.3m). Audit-related assurance services relate to services performed in connection with the statutory and regulatory filings of the Company and its associates. Of this category, £1.1m (2017: £0.8m, 2016: £0.6m) accords with the definition of ‘Audit fees’ per US Securities and Exchange Commission (SEC) guidance. The remaining £1.1m (2017: £0.8m, 2016: £0.7m) accords with the definition of ‘Audit-related fees’ per that guidance and relates to services performed in connection with securitisation, debt issuance and related work and reporting to prudential and conduct regulators. Taxation compliance services accord with the SEC definition of ‘Tax fees’ and relate to compliance services performed in respect of US tax returns and other similar tax compliance services. Other assurance services and other non-audit In 2018, the Company’s auditors also earned fees of £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, 2018
Text block [abstract]
Credit Impairment Losses and Provisions	8. CREDIT IMPAIRMENT LOSSES AND PROVISIONS 2018 2017 2016 Credit impairment losses: Loans and advances to customers (See Note 14) 189 257 132 Recoveries of loans and advances, net of collection costs (See Note 14) (42 ) (54 ) (65 ) Off-balance 6 153 203 67 Provisions for other liabilities and charges (excluding off-balance 260 385 397 Provisions for RV and voluntary termination (See Note 14) — 8 — 260 393 397 413 596 464 The credit impairment loss allowance requirements introduced by IFRS 9 mandated a change from recognising impairment losses on an incurred loss basis (as reflected in 2017) to an expected credit loss (ECL) basis (as reflected in 2018). For more on this change in methodology, see the IFRS 9 accounting policy changes in Note 1 and the IFRS 9 transition disclosures in Note 44. There were no material credit impairment losses on loans and advances to banks, non-trading

Taxation

Taxation	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Taxation	9. TAXATION 2018 2017 2016 Current tax: UK corporation tax on profit for the year 456 555 610 Adjustments in respect of prior years (22 ) (27 ) (13 ) Total current tax 434 528 597 Deferred tax: Charge/(credit) for the year 11 23 (11 ) Adjustments in respect of prior years 1 9 11 Total deferred tax 12 32 — Tax on profit 446 560 597 The standard rate of UK corporation tax was 27% for banking entities and 19% for non-banking non-banking The Santander UK group’s effective tax rate for 2018, based on profit before tax, was 28.5% (2017: 30.9%, 2016: 31.2%). 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: 2018 2017 2016 Profit before tax 1,567 1,814 1,914 Tax calculated at a tax rate of 19% (2017: 19.25%, 2016: 20.00%) 298 349 383 Bank surcharge on profits 111 132 134 Non-deductible 8 9 8 Non-deductible 20 25 30 Non-deductible 6 35 39 Other non-deductible non-taxable 26 30 7 Effect of change in tax rate on deferred tax provision (2 ) (2 ) (2 ) Adjustment to prior year provisions (21 ) (18 ) (2 ) Tax charge 446 560 597 The decrease in effective tax rate from 2017 to 2018 was largely due to the reduction in the statutory tax rate, reductions in the bank levy, the reduced impact of non-deductible non-deductible Current tax assets and liabilities Movements in current tax assets and liabilities during the year were as follows: 2018 2017 Assets — — Liabilities (3 ) (53 ) At 1 January (3 ) (53 ) Income statement charge (434 ) (528 ) Other comprehensive income credit/(charge) 75 44 Corporate income tax paid 445 484 Other movements 23 50 106 (3 ) Assets 106 — Liabilities — (3 ) At 31 December 106 (3 ) 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. 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 and Company has the legal right to offset and intends to settle on a net basis. Fair value Pension Cash flow Available- for-sale Fair Tax Accelerated Other Total At 31 December 2017 (41 ) (41 ) 3 (26 ) 25 (4 ) (4 ) (88 ) Adoption of IFRS 9 (see Note 1) — — — 26 (26 ) — — 68 68 At 1 January 2018 (41 ) (41 ) 3 (26 ) 25 (4 ) 64 (20 ) Income statement (charge)/credit (10 ) (24 ) — — (5 ) — 27 (12 ) Transfers/reclassifications — — — — — — (9 ) (9 ) Credited/(charged) to other comprehensive income — (117 ) (46 ) 14 — — (21 ) (170 ) At 31 December 2018 (51 ) (182 ) (43 ) (12 ) 20 (4 ) 61 (211 ) At 1 January 2017 (31 ) (35 ) (50 ) (27 ) 5 (5 ) 15 (128 ) Income statement (charge)/credit (10 ) (32 ) — — 20 1 (11 ) (32 ) Transfers/reclassifications — — — 7 — — (7 ) — Credited/(charged) to other comprehensive income — 26 53 (6 ) — — (1 ) 72 At 31 December 2017 (41 ) (41 ) 3 (26 ) 25 (4 ) (4 ) (88 ) 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 22) would not cause a reduction in the deferred tax assets recognised. At 31 December 2018, the Santander UK group had a recognised deferred tax asset in respect of UK capital losses carried forward of £17m (2017: £21m) included within tax losses carried forward. There are no unrecognised deferred tax assets on capital losses carried forward (2017: £nil). In the November 2018 budget, the UK government proposed changes that could restrict the use of capital losses. Based on the changes indicated, the Santander UK group does not believe that such changes would have a material impact on the recognition of deferred tax assets on such capital losses once enacted. In addition, the Santander UK group had net operating losses carried forward in the US of $nil (2017: $76m) as such losses expired on the closure of the ANTS US Branch. A deferred tax asset was not previously recognised on these losses as the Santander UK group did not anticipate being able to offset the losses against future profits or gains in order to realise any economic benefit in the foreseeable future.

Dividends on Ordinary Shares

Dividends on Ordinary Shares	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Dividends on Ordinary Shares	10. DIVIDENDS ON ORDINARY SHARES Dividends on ordinary shares declared and paid during the year were as follows: 2018 2017 2016 2018 2017 2016 In respect of current year – first interim 3.54 4.58 4.49 250 323 317 – second interim 9.46 3.26 3.91 668 230 276 – third interim 2.90 — — 205 — — 15.90 7.84 8.40 1,123 553 593 In 2018, and in addition to the dividends of £250m and £205m 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. For more on our ring-fencing implementation, see Note 43.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Dividends on Ordinary Shares	3. DIVIDENDS ON ORDINARY SHARES Dividends on ordinary shares declared and paid during the year are set out in Note 10 to the Consolidated Financial Statements.

Trading Assets

Trading Assets	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Trading Assets	11. TRADING ASSETS 2018 2017 Securities purchased under resale agreements — 8,870 Debt securities — 5,156 Equity securities — 9,662 Cash collateral associated with trading balances — 6,156 Short-term loans — 711 — 30,555 In 2018, as part of our ring-fencing plans, the trading business in the Santander UK group was run down as the prohibited elements moved to the Banco Santander London Branch. For more on our ring-fence implementation, see Note 43. In 2017, a significant portion of the debt and equity securities were held in our eligible liquidity pool. They consisted mainly of government bonds and quoted stocks. Detailed disclosures can be found in the ‘Liquidity risk’ section of the Risk review.

Derivative Financial Instrument

Derivative Financial Instruments	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Derivative Financial Instruments	12. 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. In 2018, as part of our ring-fencing implementation, we transferred the majority of our derivatives held for trading to the Banco Santander London Branch as these constituted transactions that Santander UK plc would not be able to retain as a ring-fenced bank. For more on our ring-fence implementation, see Note 43. 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. b) Analysis of derivatives The notional amounts in the tables below indicate the nominal value of transactions outstanding at the balance sheet date; they do not represent actual exposures. 2018 2017 Fair value Fair value Notional amount Assets Liabilities Notional amount Assets Liabilities £m £m £m £m £m £m Derivatives held for trading Exchange rate contracts 14,165 455 351 144,160 2,559 4,130 Interest rate contracts 79,522 1,455 1,326 863,151 22,091 21,619 Equity and credit contracts 2,854 278 168 19,814 888 693 Total derivatives held for trading 96,541 2,188 1,845 1,027,125 25,538 26,442 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 3,010 357 — 2,641 312 6 Interest rate contracts 86,422 1,065 1,315 59,610 1,272 1,470 Equity derivative contracts — — — 16 — 4 89,432 1,422 1,315 62,267 1,584 1,480 Designated as cash flow hedges: Exchange rate contracts 33,901 3,537 200 23,117 3,206 55 Interest rate contracts 18,808 46 102 12,884 84 115 Equity derivative contracts 69 — 4 26 9 — 52,778 3,583 306 36,027 3,299 170 Total derivatives held for hedging 142,210 5,005 1,621 98,294 4,883 1,650 Derivative netting (1) (1,872 ) (1,872 ) (10,479 ) (10,479 ) Total derivatives 238,751 5,321 1,594 1,125,419 19,942 17,613 (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 £9m (2017: £333m) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was £354m (2017: £706m). For information about the impact of netting arrangements on derivative assets and liabilities in the table above, see Note 42. The table below analyses the notional and fair values of derivatives by trading and settlement method. Notional Traded over the counter Asset Liability 2018 Traded on Settled by Not settled by Total £m Traded on Traded Traded on Traded Exchange rate contracts — — 51,076 51,076 — 4,349 — 551 Interest rate contracts — 154,106 30,646 184,752 — 694 — 871 Equity and credit contracts — — 2,923 2,923 — 278 — 172 — 154,106 84,645 238,751 — 5,321 — 1,594 2017 Exchange rate contracts — — 169,918 169,918 — 6,077 — 4,191 Interest rate contracts 71,618 626,600 237,427 935,645 — 12,968 — 12,725 Equity and credit contracts 30 — 19,826 19,856 — 897 1 696 71,648 626,600 427,171 1,125,419 — 19,942 1 17,612 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. 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 following table shows the fixed rate instruments hedged, their underlying currency and the respective hedged benchmark rates: Instrument Currency Designated benchmark instrument rate Fixed rate mortgages GBP 3-month Fixed rate loans GBP, EUR 3-month Reverse repurchase agreements GBP, USD SONIA, USD Fed Funds Investment assets GBP, EUR, USD SONIA, 3-month Fixed rate savings GBP, USD 3-month 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. Equity risk on cash settled share-based transactions Santander Equity Investments Limited (SEIL) offers employees the chance to buy shares in Banco Santander SA at a discount under Sharesave schemes. This exposes Santander UK to equity price risk. The equity risk is managed by purchasing share options which allow Santander UK to buy shares at a fixed price. These instruments are entered into to match the amount of employee share options expected to be exercised. The equity price risk is the change in cash flows arising from the change in share price over time. Santander UK established the hedge ratio by matching the notional of the derivative with the notional of the employee share options being hedged. Effectiveness is assessed by comparing the changes in fair value of the share options with changes in the fair value of the employee share options by using a hypothetical derivative method. Possible sources of hedge ineffectiveness Possible sources of hedge ineffectiveness for each type of hedge relationship are set out below: Fair value hedges Cash flow hedges Possible sources of ineffectiveness Portfolio hedges Micro hedges of Micro hedges Micro hedges Equity risk on Hedging derivatives with a non-zero • • • • • Differences in discounting between hedged item and hedging instrument as cash collateralised swaps discount using Overnight Indexed Swaps (OIS) discount curves, not applied to underlying hedged item • • Counterparty credit risk impacts fair value of derivative but not hedged item • • Differences in expected and actual volume of prepayments • Differences in discounting between hedged item and hedging instrument as cash collateralised cross currency swaps discount using OIS discount curves, not applied to underlying hedged item • Differences in timing of cash flows between hedged item and hedging instrument • • • Differences in basis of cash flows between hedged items and hedging instruments • Changes in the expected number of Sharesave options to be exercised • 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: 2018 Hedging Instruments Less than one Later than one Later than Later than Later than Total Fair value hedges: Interest rate risk Interest rate contracts: – Nominal 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/foreign currency (FX) risk Exchange rate contracts: – Nominal amount (£m) 392 1,295 — 1,101 222 3,010 Interest rate contracts: – Nominal 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: – Nominal 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: – Nominal amount (£m) 3,916 2,552 2,961 5,596 — 15,025 Interest rate contracts: – Nominal 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 — Equity risk Equity derivative contracts – Nominal amount (£m) — — 37 32 — 69 Interest rate/FX risk Exchange rate contracts: – Nominal amount (£m) — — 1,773 11,481 5,622 18,876 Interest rate contracts: – Nominal 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 2018 2017 2016 Fair value hedging: Gains/(losses) on hedging instruments 4 56 (274 ) (Losses)/gains on hedged items attributable to hedged risks 75 (2 ) 335 Fair value hedging ineffectiveness 79 54 61 Cash flow hedging ineffectiveness (45 ) (49 ) (33 ) 34 5 28 Hedge ineffectiveness can be analysed by risk category as follows: 2018 Changes in FV of hedging Changes in FV of hedged Hedge Fair value hedges: Interest rate risk 26 15 41 Interest rate/FX risk (22 ) 60 38 4 75 79 2018 Income statement line item affected Changes in FV of hedging instruments to calculate hedge ineffectiveness Changes in value of Hedge ineffectiveness Amount reclassified from Cash flow hedges: Interest rate risk Net interest income 20 (14) 6 26 FX risk Net interest income/net trading and other income 17 (19) (2) 9 Equity risk Operating expenses (16) 16 — (10) Interest rate/FX risk Net interest income/net trading and other income 722 (771) (49) 726 743 (788) (45) 751 In 2018, cash flow hedge accounting of £12m (2017: £nil) 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. Cash flow 2018 £m Balance at 1 January 2018 285 Effective portion of changes in fair value: – Interest rate risk 14 – Foreign currency risk 19 – Equity risk (16 ) – Interest rate/foreign currency risk 771 788 Income statement transfers – Interest rate risk (26 ) – Foreign currency risk (9 ) – Equity risk 10 – Interest rate/foreign currency risk (726 ) (751 ) Balance at 31 December 2018 322 Hedged exposures Santander UK hedges its exposures to various risks, including interest rate risk and foreign currency risk, in connection with certain mortgage assets, covered bond issuances, subordinated debt and senior debt securities in issue. The following table sets out the exposures covered by the Santander UK group’s hedging strategies: Carrying value Accumulated amount of FV Accumulated amount of FV interest rate Change in Accumulated 2018 Hedged item balance sheet line item Assets Liabilities Assets £m Liabilities Assets £m Liabilities calculating -ness £m balance sheet £m Fair value hedges: Interest rate risk: Loans and advances to customers 42,075 — — — 638 — (149) 729 Other financial assets at amortised cost 6,640 — — — 59 — 59 — Reverse repo agreements – non trading 10,954 — — — — — — — Other financial assets at FVOCI 7,447 — 10 — — — (46) 123 Deposits by customers — 702 — — — (1) — — Deposits by banks — 516 — 15 — — 9 (23) Interest rate/FX risk: Debt securities in issue — 15,112 — 369 — 191 158 (548) Subordinated liabilities — 685 — 152 — 52 44 (214) 67,116 17,015 10 536 697 242 75 67 2018 Hedged item balance sheet line item Change in value used for Cash flow Balances on cash flow Cash flow hedges: Interest rate risk: Loans and advances to customers (19 ) (4 ) (2 ) Loans and advances to banks — (2 ) — Deposits by banks 6 (1 ) — Debt securities in issue (1 ) — — FX risk: Other financial assets at FVOCI 199 (1 ) — Not applicable – highly probable forecast transactions (1 ) — — Debt securities in issue (217 ) 21 3 Equity risk: Other liabilities 16 (3 ) (2 ) Interest rate/FX risk: Debt securities in issue/loans and advances to customers (564 ) 233 50 Subordinated liabilities/loans and advances to customers (207 ) 79 — (788 ) 322 49

Other Financial Assets At Fair

Other Financial Assets At Fair Value Through Profit Or Loss	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Other Financial Assets At Fair Value Through Profit Or Loss	13. OTHER FINANCIAL ASSETS AT FAIR VALUE THROUGH PROFIT OR LOSS 2018 2017 Loans and advances to customers: Loans to housing associations 13 1,034 Other loans 496 515 509 1,549 Debt securities 3,263 547 Equity securities 93 — Reverse repurchase agreements – non trading 2,272 — 6,137 (1) 2,096 (1) For the Santander UK group, this comprises £1,521m of financial assets designated at FVTPL and £4,616m of financial assets mandatorily at FVTPL. Loans and advances to customers principally represented other loans, being a portfolio of roll-up As part of the establishment of credit protection vehicles sponsored by Santander UK, we retained £3,053m of senior tranches of credit linked notes, classified as debt securities in the table above. These vehicles provide credit protection on reference portfolios of Santander UK group loans with junior notes sold to external investors. As these notes do not have SPPI characteristics they are mandatorily held at fair value. These credit linked notes are valued using the same parameters as the related collateral and financial guarantees described in Note 24, such that changes in their respective valuations are offset exactly, and there is no charge or credit to the income statement. For more, see ‘Credit protection entities’ in Note 21. 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 £(1m) (2017: £49m, 2016: £40m). The cumulative net loss attributable to changes in credit risk for loans and advances at fair value through profit or loss at 31 December 2018 was £2m (2017: £120m).

Loans and Advances to Customers

Loans and Advances to Customers	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Loans and Advances to Customers	14. LOANS AND ADVANCES TO CUSTOMERS 2018 £m 2017 £m Loans secured on residential properties 158,248 155,355 Corporate loans 27,819 30,856 Finance leases 6,821 6,710 Secured advances — — Other unsecured loans 7,554 6,230 Amounts due from fellow Banco Santander subsidiaries and joint ventures 1,997 1,199 Loans and advances to customers 202,439 200,350 Credit impairment loss allowances on loans and advances to customers (751 ) (940 ) RV and voluntary termination provisions on finance leases (69 ) (78 ) Net loans and advances to customers 201,619 199,332 Movement in credit impairment loss allowances: Loans secured Other on residential Corporate Finance unsecured properties loans leases loans Total £m £m £m £m £m At 31 December 2017 225 490 46 179 940 Adoption of IFRS 9 (see Note 1) (1) 47 99 11 54 211 Re-allocation off-balance (1) (3 ) (25 ) — (22 ) (50 ) At 1 January 2018 269 564 57 211 1,101 (Release)/charge to the income statement (see Note 8) (18 ) 17 51 139 189 Write-offs and other items (2) (3) (17 ) (355 ) (23 ) (144 ) (539 ) At 31 December 2018 234 226 85 206 751 Recoveries, net of collection costs (see Note 8) 2 1 6 33 42 At 1 January 2017 279 382 45 215 921 (Release)/charge to the income statement (see Note 8) (37 ) 172 20 102 257 Write-offs and other items (2) (17 ) (64 ) (19 ) (138 ) (238 ) At 31 December 2017 225 490 46 179 940 Of which: – Observed 105 433 12 59 609 – Incurred but not yet observed 120 57 34 120 331 225 490 46 179 940 Recoveries, net of collection costs (see Note 8) 3 1 6 44 54 At 1 January 2016 424 395 20 269 1,108 (Release)/charge to the income statement (see Note 8) (116 ) 59 47 142 132 Write-offs and other items (2) (29 ) (72 ) (22 ) (196 ) (319 ) At 31 December 2016 279 382 45 215 921 Of which: – Observed 130 287 13 73 503 – Incurred but not yet observed 149 95 32 142 418 279 382 45 215 921 Recoveries, net of collection costs (see Note 8) 4 3 2 56 65 (1) The adjustment for the adoption of IFRS 9 related to the re-measurement re-allocation off-balance (2) Mortgage write-offs exclude the effect of the unwind over time of the discounting in estimating losses, as described in the accounting policy ‘Financial instruments’ in Note 1. Mortgage write-offs including this effect were £18m (2017: £22m, 2016: £33m) (3) The contractual amount outstanding on financial assets that were written off in the year, and are still subject to enforcement activity was £76m. Finance lease and hire purchase contract receivables may be analysed as follows: 2018 2017 Gross Unearned Net Gross Unearned Net Not later than one year 3,730 (210 ) 3,520 3,633 (177 ) 3,456 Later than one year and not later than five years 3,415 (278 ) 3,137 3,316 (226 ) 3,090 Later than five years 210 (46 ) 164 214 (50 ) 164 7,355 (534 ) 6,821 7,163 (453 ) 6,710 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 £1,034m (2017: £886m) of unguaranteed RV at the end of the current lease terms, which is expected to be recovered through re-payment, re-financing 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 15.

Securitisations and Covered Bon

Securitisations and Covered Bonds	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Securitisations and Covered Bonds	15. SECURITISATIONS AND COVERED BONDS 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 securities, other asset-backed securities and covered bonds mainly in order to obtain diverse, low cost funding, but also to use as collateral for raising funds via third party bilateral secured funding transactions or for liquidity purposes in the future. The Santander UK group has successfully used bilateral secured transactions as an additional form of medium-term funding; this has allowed the Santander UK group to further diversify its medium-term funding investor base. 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 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 the liquidity coverage requirements for credit institutions. 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 and the carrying value of the notes in issue at 31 December 2018 and 2017 are listed below. Gross assets External notes in issue Notes issued to Santander UK 2018 2017 2018 2017 2018 £m 2017 Mortgage-backed master trust structures: – Holmes 4,414 4,299 3,182 1,400 463 389 – Fosse 4,646 5,732 199 616 34 34 – Langton 3,034 3,893 — — 2,354 2,355 12,094 13,924 3,381 2,016 2,851 2,778 Other asset-backed securitisation structures: – Motor 1,055 1,318 738 852 374 514 – Auto ABS UK Loans 1,468 1,498 1,212 1,240 316 306 2,523 2,816 1,950 2,092 690 820 Total securitisation programmes 14,617 16,740 5,331 4,108 3,541 3,598 Covered bond programme: – Euro 35bn Global Covered Bond Programme 21,578 19,772 18,653 16,866 — — Total securitisation and covered bond programmes 36,195 36,512 23,984 20,974 3,541 3,598 Less: held by the Santander UK group: – Euro 35bn Global Covered Bond Programme (539 ) (1,067 ) Total securitisation and covered bond programmes (see Note 28) 23,445 19,907 The following table sets out the internal and external issuances and redemptions in 2018 and 2017 for each securitisation and covered bond programme. Internal issuances External issuances Internal External 2018 2017 2018 2017 2018 2017 2018 2017 £bn £bn £bn £bn £bn £bn £bn £bn Mortgage-backed master trust structures: – Holmes 0.1 — 1.8 0.5 — 0.2 0.1 1.8 – Fosse — — — — — 0.1 0.4 1.8 Other asset-backed securitisation structures: – Motor — 0.1 — 0.5 0.1 0.1 0.1 0.3 – Auto ABS UK Loans — 0.2 0.4 0.7 — — 0.4 0.7 Covered bond programme — — 4.3 2.3 0.5 0.3 1.9 3.2 0.1 0.3 6.5 4.0 0.6 0.7 2.9 7.8 Holmes Funding Ltd has a beneficial interest of £3.2bn (2017: £1.7bn) 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 £0.2bn (2017: £0.6bn) 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 £2.3bn (2017: £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 £218m (2017: £nil), 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 (2017: £24m), 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, 2018
Text block [abstract]
Transfers of Financial Assets Not Qualifying for Derecognition	16. 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 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: 2018 2017 Assets Liabilities Assets Liabilities Nature of transaction £m £m £m £m Sale and repurchase agreements 7,642 (7,188 ) 10,808 (7,734 ) Securities lending agreements 144 (120 ) 302 (235 ) Securitisations (See Notes 15 and 28) 11,583 (5,331 ) 12,847 (4,108 ) 19,369 (12,639 ) 23,957 (12,077 )

Reverse Repurchase Agreements -

Reverse Repurchase Agreements - Non Trading	12 Months Ended
	Dec. 31, 2018
Reverse repurchase agreements - non-trading [member]
Statement [LineItems]
Reverse Repurchase Agreements - Non Trading	17. REVERSE REPURCHASE AGREEMENTS – NON TRADING 2018 2017 Agreements with banks 3,254 2,464 Agreements with customers 17,873 150 21,127 2,614 In 2018, as part of our ring-fencing implementation, Santander UK plc revised the classification of the majority of our permitted non trading reverse repurchase agreements at amortised cost, in line with our ring-fenced business model for managing these assets as part of our overall funding and liquidity plans. For more on our ring-fence implementation, see Note 43.

Other Financial Assets At Amort

Other Financial Assets At Amortised Cost	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Other Financial Assets At Amortised Cost	18. OTHER FINANCIAL ASSETS AT AMORTISED COST 2018 2017 Asset backed securities (1) 719 Debt securities (2) 6,509 7,228 (1) These securities were previously classified as ‘Financial investments’ under IAS 39. See Note 44. (2) These debt securities were previously classified as held-to-maturity On adoption of IFRS 9, the Santander UK group split the ‘financial investments’ balance sheet line item (Note 20) between ‘other financial assets at amortised cost’ and ‘financial assets at fair value through other comprehensive income’. This aligned the balance sheet line items to the IFRS 9 accounting classifications and provides a clearer understanding of our financial position. In addition, certain available-for-sale 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.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Other Financial Assets At Amortised Cost	5. OTHER FINANCIAL ASSETS AT AMORTISED COST These consisted of investments in subordinated notes and have a maturity greater than 10 years. On adoption of IFRS 9, the ‘financial investments’ balance sheet line item was split. This resulted in the inclusion of the ‘other financial assets at amortised cost’ balance sheet line. This approach aligns the balance sheet line items to the IFRS 9 accounting classifications and provides a clearer understanding of our financial position.

Financial Assets At Fair Value

Financial Assets At Fair Value Through Other Comprehensive Income	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Financial Assets At Fair Value Through Other Comprehensive Income	19. FINANCIAL ASSETS AT FAIR VALUE THROUGH OTHER COMPREHENSIVE INCOME 2018 2017 Debt securities (1) 13,229 Loans and advances to customers (2) 73 13,302 (1) These debt securities were previously classified as available-for-sale (2) These comprise other loans and receivables mainly held within hold to collect and sell business models that were moved from trading assets and loans and advances to customers at amortised cost, to ‘Financial assets at FVOCI’, due to their reclassification to FVOCI on adoption of IFRS 9. See Note 44. On adoption of IFRS 9, the Santander UK group split the ‘financial investments’ balance sheet line item (Note 20) between ‘other financial assets at amortised cost’ and ‘financial assets at fair value through other comprehensive income’. For more information, see Note 44. 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 Investments

Financial Investments	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Financial Investments	20. FINANCIAL INVESTMENTS 2018 2017 Asset backed securities (1) 2,180 Debt securities: – Available-for-sale (2) 8,772 – Held-to-maturity (3) 6,578 Available-for-sale (4) 81 17,611 (1) These were reclassified to ‘Other financial assets at amortised cost’ and ‘Other financial assets at fair value through profit or loss’ on adoption of IFRS 9. See Note 44. (2) These were reclassified to ‘Financial assets at FVOCI’ and ‘Other financial assets at fair value through profit or loss’ on adoption of IFRS 9. See Note 44. (3) These were reclassified to ‘Other financial assets at amortised cost’ on adoption of IFRS 9. See Note 44. (4) These were reclassified to ‘Other financial assets at fair value through profit or loss’ on adoption of IFRS 9. See Note 44. On adoption of IFRS 9, the Santander UK group split the ‘financial investments’ balance sheet line item between ‘other financial assets at amortised cost’ and ‘financial assets at FVOCI’. For more information, see Note 44. A significant portion of the debt securities were 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.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Financial Investments	6. FINANCIAL INVESTMENTS These consisted of investments in subordinated notes and have a maturity greater than 10 years. On adoption of IFRS 9, the ‘financial investments’ balance sheet line item was split. This resulted in the inclusion of the ‘other financial assets at amortised cost’ balance sheet line. This approach aligns the balance sheet line items to the IFRS 9 accounting classifications and provides a clearer understanding of our financial position.

Interests in Other Entities

Interests in Other Entities	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Interests in Other Entities	21. INTERESTS IN OTHER ENTITIES 2018 2017 Joint ventures 88 73 88 73 The Santander UK group consists of a parent company, Santander UK Group Holdings 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. ANTS has branch offices in Jersey and the Isle of Man, and had a branch office in the US which closed in 2018. On 1 January 2018, Santander UK plc acquired 100% of the share capital 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), for a final cash consideration of £66m. Immediately prior to this, the UK business of Produban Servicios Informaticos Generales SL was acquired by Santander UK Technology Ltd for a final cash consideration of £13m. These businesses are referred to as Santander Services. Subsidiaries with significant non-controlling The only subsidiary with significant non-controlling non-controlling 2018 2017 Profit attributable to non-controlling 22 21 Accumulated non-controlling 151 152 Dividends paid to non-controlling 22 19 Summarised financial information: – Total assets 3,289 3,215 – Total liabilities 2,987 2,909 – Profit for the year 43 43 – Total comprehensive income for the year 43 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 15 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 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, closed-ended, protected cell company. The objective of each cell is to achieve capital growth for retail investors. In order to achieve the investment objective, GIP, on behalf of the respective cells, has entered into transactions with Santander UK plc. Santander Guarantee Company, a Santander UK group company, also guarantees the shareholders of cells a fixed return on their investment and/or the investment amount. GIP has no third party assets. Although the share capital is owned by the retail investors, Santander UK continues to have exposure to variable risks and returns through Santander Guarantee Company’s guarantee and has therefore consolidated this entity. ii) Santander UK Foundation Limited Santander UK Foundation Limited supports disadvantaged people throughout the UK through the charitable priorities of education and financial capability. The entity was set up by Santander UK plc, although its control was transferred to Santander UK Group Holdings plc in June 2018. All of its revenue since that date arises through donations from Santander UK Group Holdings plc. Its third party assets of £15m (2017: £16m) are not material to the results of the Santander UK group. This entity has been consolidated as Santander UK Group Holdings plc directs its activities. 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 2018, Santander UK’s share in the profit after tax of its joint ventures was £15m (2017: £12m) before elimination of transactions between Santander UK and the joint ventures. At 31 December 2018, the carrying amount of Santander UK’s interest was £88m (2017: £73m). At 31 December 2018 and 2017, 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 £11,433m (2017: £11,626m) 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 31. 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) Trust preferred entities The trust preferred entities, Abbey National Capital Trust I and Abbey National Capital LP I, were 100% owned finance subsidiaries (as defined in Regulation S-X Non-cumulative In 2018, following a Partnership Special Redemption Event, the outstanding US$104m Abbey National Capital Trust I 8.963% Non-cumulative iii) Credit protection entities Santander UK has established three (2017: two) credit protection entities which are private limited companies 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 £3,053m (2017: £830m), are issued to, and held by, Santander UK. These notes are included within ‘Other financial assets at fair value through profit or loss’ on the balance sheet (see Note 13). Junior credit linked notes, which amounted to £408m (2017: £187m), 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. Deposits and associated guarantees in respect of the senior credit linked notes are included within ‘Other financial liabilities at fair value through profit or loss’ (see Note 24), and in respect of the junior credit linked notes are included within ‘Deposits by customers’ (see Note 25). 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. Because 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 largely relate to the legacy treasury asset portfolio and 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 18. 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.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Interests in Other Entities	7. INTERESTS IN OTHER ENTITIES 2018 2017 Interests in ordinary shares of subsidiaries 11,645 11,268 £500m Fixed Rate Reset Perpetual AT1 Capital Securities 495 495 £750m Fixed Rate Reset Perpetual AT1 Capital Securities 750 750 £300m Perpetual Capital Securities 300 300 £500m Perpetual Capital Securities 210 500 13,400 13,313 Interests in subsidiaries are held at cost subject to impairment. During 2018 and 2017, no impairment was recognised. The Company has no associates. The movement in the Company’s interests in subsidiaries was as follows: Cost £m Impairment Net book At 1 January 2017, 31 December 2017 and 1 January 2018 11,268 — 11,268 Additions 377 — 377 At 31 December 2018 11,645 — 11,645 Interests in ordinary shares of subsidiaries include the Company’s investment in 100% of the ordinary share capital of Santander UK plc, Abbey National Treasury Services plc (ANTS) and Santander Equity Investments Limited (SEIL). During the year the following restructures were carried out as part of the Santander UK group’s ring-fencing plans: • Santander UK Group Holdings plc acquired 100% of the share capital of SEIL from ANTS, for a consideration of £40m, which was equivalent to the book value of the associated assets and liabilities. • Santander UK Group Holdings plc acquired 100% of the share capital of ANTS from Santander UK plc, for a consideration of £337m, which was equivalent to the book value of the associated assets and liabilities. For more on our ring-fencing plans, see Note 43 to the Consolidated Financial Statements. Details of subsidiary undertakings and joint ventures are set out in the Shareholder information section. For information on AT1 and Perpetual Capital Securities, see Note 34 to the Consolidated Financial Statements.

Intangible Assets

Intangible Assets	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Intangible Assets	22. INTANGIBLE ASSETS a) Goodwill Cost Accumulated Net book value £m £m £m At 31 December 2017, 1 January 2018 and 31 December 2018 1,285 (82 ) 1,203 Impairment of goodwill In 2018 and 2017, 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 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 (all within Retail Banking) 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 (1) 2018 2017 2018 2017 2018 2017 CGU £m £m % % % % Personal financial services 1,169 1,169 10.5 10.8 2 1 Private banking 30 30 10.5 10.8 2 1 Other 4 4 10.5 10.8 2 1 1,203 1,203 (1) Average growth rate based on the five-year plan for the first five years and a growth rate of 2.0 % (2017: 1.5%) applied thereafter. In 2018, the discount rate decreased by 0.3 percentage points to 10.5% (2017: 10.8%). The decrease reflected changes in current market and economic conditions. In 2018, the change in growth rates reflected Santander UK’s updated strategic priorities in the context of forecast economic conditions. b) Other intangibles Cost Accumulated Net book value At 1 January 2018 962 (423 ) 539 Additions 213 — 213 Write offs (76 ) 76 — Charge — (141 ) (141 ) Sales — — — At 31 December 2018 1,099 (488 ) 611 At 1 January 2017 760 (278 ) 482 Additions 205 — 205 Disposals (3 ) 3 — Charge — (116 ) (116 ) Impairment — (32 ) (32 ) At 31 December 2017 962 (423 ) 539 Other intangibles consist of computer software. In 2017, impairments primarily related to capitalised software costs for a credit risk management system, part of which was no longer in use.

Trading Liabilities

Trading Liabilities	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Trading Liabilities	23. TRADING LIABILITIES 2018 2017 Securities sold under repurchase agreements — 25,504 Short positions in securities and unsettled trades — 3,694 Cash collateral — 1,911 — 31,109 In 2018, as part of our ring-fence plans, the trading business in the Santander UK group was run down, and the gilt-edged market making business was transferred to Banco Santander London Branch. For more on our ring-fencing transition, see Note 43.

Other Financial Liabilities at

Other Financial Liabilities at Fair Value Through Profit or Loss	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Other Financial Liabilities at Fair Value Through Profit or Loss	24. OTHER FINANCIAL LIABILITIES AT FAIR VALUE THROUGH PROFIT OR LOSS 2018 2017 US$10bn Euro Commercial Paper Programme — 387 US$30bn Euro Medium Term Note Programme 165 169 Structured Notes Programmes 696 932 Eurobonds 129 147 Structured deposits 133 680 Collateral and associated financial guarantees 3,053 — Repurchase agreements – non trading 2,110 — 6,286 (1) 2,315 (1) For the Santander UK group, this comprises £6,286m of financial liabilities designated at fair value through profit or loss and £nil of financial liabilities mandatorily at fair value through profit or loss. The collateral and associated financial guarantees relates to collateral received, together with associated credit protection guarantees, relating to the proceeds of the retained senior tranches of credit linked notes described in Note 13, and have been designated at fair value through profit or loss. 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. For more, see ‘Credit protection entities’ in Note 21, and ‘Internal models based on information other than market data (Level 3)’ in Note 41. 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 gain during the year attributable to changes in the Santander UK group’s own credit risk on the above securities was £84m (2017: £29m loss, 2016: £6m gain). The cumulative net gain attributable to changes in the Santander UK group’s own credit risk on the above securities at 31 December 2018 was £77m (2017: £7m loss). At 31 December 2018, the amount that would be required to be contractually paid at maturity of the securities above was £128m lower (2017: £4m lower) than the carrying value.

Deposits by Customers

Deposits by Customers	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Deposits by Customers	25. DEPOSITS BY CUSTOMERS 2018 £m 2017 Current and demand accounts 87,316 85,780 Savings accounts (1) 69,102 70,461 Time deposits 16,204 20,453 Amounts due to fellow Banco Santander subsidiaries and joint ventures 1,070 727 173,692 177,421 (1) Includes equity index-linked deposits of £1,176m (2017: £1,301m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,176m and £28m (2017: £1,301m and £67m) respectively.

Deposits by Banks

Deposits by Banks	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Deposits by Banks	26. DEPOSITS BY BANKS 2018 2017 Items in the course of transmission 262 303 Deposits held as collateral 4,058 1,760 Other deposits (1) 13,504 10,645 17,824 12,708 (1) Includes drawdown from the TFS of £10.8bn (2017: £8.5bn).
Santander UK Group Holdings plc [member]
Statement [LineItems]
Deposits by Banks	8. DEPOSITS BY BANKS These consist of amounts due to subsidiaries and are repayable on demand.

Repurchase Agreements - Non Tra

Repurchase Agreements - Non Trading	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Repurchase Agreements - Non Trading	27. REPURCHASE AGREEMENTS – NON TRADING 2018 2017 Agreements with banks 5,865 1,076 Agreements with customers 5,045 — 10,910 1,076 In 2018, as part of our ring-fencing implementation, Santander UK plc revised the classification of the majority of our permitted non trading repurchase agreements at amortised cost, in line with our ring-fenced business model for managing these liabilities as part of our overall funding and liquidity plans. For more on our ring-fence implementation, see Note 43.

Debt Securities in Issue

Debt Securities in Issue	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Debt Securities in Issue	28. DEBT SECURITIES IN ISSUE 2018 2017 Medium-term notes: – US$30bn Euro Medium Term Note Programme 7,229 8,816 – Euro 30bn Euro Medium Term Note Programme 5,348 2,177 – US SEC-registered 5,841 4,050 – US SEC-registered 7,649 6,280 – US$20bn Commercial Paper Programmes 3,131 2,906 29,198 24,229 Euro 35bn Global Covered Bond Programme (See Note 15) 18,114 15,799 Certificates of deposit 3,221 4,681 Credit linked notes 42 43 Securitisation programmes (See Note 15) 5,331 4,108 55,906 48,860 The funding from the Euro 30bn Euro Medium Term Note Programme and the US SEC-registered The credit linked notes were issued by PSA Finance UK Limited and reference a pool of auto loans and leases originated by PSA Finance UK Limited that, in return for a fee, provides credit protection on the first 7.6% of losses in the reference portfolio.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Debt Securities in Issue	9. DEBT SECURITIES IN ISSUE The Company issues notes in the US from time to time pursuant to a shelf registration statement on Form F-3 filed with the SEC in 2018.

Subordinated Liabilities

Subordinated Liabilities	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Subordinated Liabilities	29. SUBORDINATED LIABILITIES 2018 2017 £325m Sterling Preference Shares 344 344 £175m Fixed/Floating Rate Tier One Preferred Income Capital Securities — 2 Undated subordinated liabilities 574 584 Dated subordinated liabilities 2,683 2,863 3,601 3,793 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 of specific subordinated liabilities is determined in respect of the issuer. The claims of holders of preference shares are generally junior to those of the holders of undated subordinated liabilities, which in turn are generally junior to the claims of holders of the dated subordinated liabilities. The subordination of the preference shares ranks equally with that of the £300m fixed/floating rate non-cumulative Step-up non-controlling In 2018 and 2017, 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. In 2017, Santander UK exercised its option to call the £175m Fixed/Floating Rate Tier One Preferred Income Capital Securities. These were fully redeemed on 9 February 2018. Undated subordinated liabilities First call date 2018 2017 10.0625% Exchangeable capital securities n/a 205 205 7.375% 20 Year Step-up 2020 16 17 7.125% 30 Year Step-up 2030 353 362 574 584 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 Maturity 2018 2017 10.125% Subordinated guaranteed bonds 2023 — 78 9.625% Subordinated notes 2023 — 129 5% Subordinated notes (US$1,500m) 2023 1,173 1,103 4.75% Subordinated notes (US$1,000m) 2025 791 745 7.95% Subordinated notes (US$1,000m) 2029 278 275 6.50% Subordinated notes 2030 38 40 8.963% Subordinated notes (US$1,000m) 2045 — 113 5.875% Subordinated notes 2031 9 9 5.625% Subordinated notes (US$500m) 2045 394 371 2,683 2,863 The dated subordinated liabilities are redeemable in whole at the option of Santander UK plc at any time and, in the case of the 7.95% Subordinated notes, on any interest payment date, 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. Each of the subordinated liabilities issued by Santander UK Group Holdings plc has been downstreamed to Santander UK plc by means of Santander UK plc issuing equivalent subordinated liabilities to Santander UK Group Holdings plc. In 2018, Santander UK plc exercised its option to call the 9.625% Subordinated notes and 8.963% Subordinated notes. These were fully redeemed on 30 October 2018 and 15 November 2018 respectively. In 2017, Santander UK plc exercised its option to call the 10.125% Subordinated guaranteed bonds. These were fully redeemed on 4 January 2018.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Subordinated Liabilities	10. SUBORDINATED LIABILITIES Dated subordinated liabilities Maturity 2018 2017 4.75% Subordinated notes (US$1,000m) 2025 791 745 5.625% Subordinated notes (US$500m) 2045 394 371 1,185 1,116

Provisions

Provisions	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Provisions	30. PROVISIONS Conduct remediation PPI Other FSCS and Vacant Off-balance Regulatory Total At 31 December 2017 356 47 57 39 59 558 Reallocation of ECL on off-balance (1) — — — — 50 — 50 At 1 January 2018 356 47 57 39 50 59 608 Additional provisions (see Note 8) — — 69 15 6 208 298 Provisions released (see Note 8) — (14 ) (4 ) — — (14 ) (32 ) Utilisation (110 ) (3 ) (92 ) (14 ) — (154 ) (373 ) Other — — 14 (2) — — — 14 At 31 December 2018 246 30 44 40 56 99 515 To be settled: – Within 12 months 246 22 44 25 56 99 492 – In more than 12 months — 8 — 15 — — 23 246 30 44 40 56 99 515 At 1 January 2017 457 36 96 47 64 700 Additional provisions 109 35 93 4 144 385 Utilisation (210 ) (34 ) (132 ) (12 ) (149 ) (537 ) Transfers — 10 — — — 10 At 31 December 2017 356 47 57 39 59 558 To be settled: – Within 12 months 167 38 57 23 59 344 – In more than 12 months 189 9 — 16 — 214 356 47 57 39 59 558 (1) ECL on off-balance (2) Santander UK plc recharged £14m (2017: £nil) 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) In November 2015, the FCA issued a Consultation Paper 15/39 (Rules and guidance on payment protection insurance complaints) which introduced the concept of unfair commission in relation to Plevin decision for customer redress plus a deadline by which customers would need to make their PPI complaints. On 2 August 2016, the FCA issued Consultation Paper 16/20 (Rules and Guidance on payment protection insurance complaints: Feedback on CP 15/39 and further consultation). The paper outlined the FCA’s proposed approach to PPI in light of the 2014 decision of the Supreme Court in Plevin v Paragon Personal Finance Ltd (Plevin) and also recommended a two-year non-disclosure non-disclosure PPI assumptions A provision for conduct remediation has been recognised in respect of the misselling of PPI policies. The provision is calculated based on a number of key assumptions. These are: • Claim volumes — the estimated number of customer complaints received • Plevin in scope rates — the number of rejected misselling claims that will be in scope for Plevin redress • The determination of liability with respect to a specific portfolio of claims. The assumptions have been based on the following: • Analysis completed of the causes of complaints, uphold rates, industry factors, FCA activity/guidance and how these are likely to vary in the future • Actual claims activity registered to date • The level of redress paid to customers, together with a forecast of how this is likely to change over time • The impact on complaints levels of proactive customer contact • The effect media coverage and the August 2019 time bar are expected to have on the complaints inflows • Commission and profit share earned from Insurance providers over the lifetime of the products and related legal and regulatory guidance • In relation to a specific PPI portfolio of complaints, an analysis of the relevant facts and circumstances including legal and regulatory responsibilities, informed by external legal advice. The key assumptions are kept under review, and are regularly reassessed and validated against actual customer data. The provision represents management’s best estimate of Santander UK’s future liability in respect of misselling of PPI policies. The most critical factors in determining the level of provision are the volume of claims for future inflow levels, and the determination of liability with respect to a specific portfolio of PPI claims. 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. In setting the provision, management estimated the total claims that were likely to be received until August 2019 i.e. the date on which the time bar for claims takes effect. The table below sets out the key drivers of the provision balance and forecast assumptions used in calculating the provision, as well as the sensitivity of the provision to changes in the assumptions. It reflects a blended view across all our retail products and portfolios and includes redress for Plevin-related claims. The PPI misselling redress element of the provision linked to future claims levels and any associated Plevin redress is £101m. Expected future complaints through to the August 2019 time bar are estimated to be at a level consistent with the highest individual monthly inflow level in 2018. Were this level to be 20% higher or lower, the impact on the PPI misselling element of the provision of £101m would be an increase or decrease of £16m. The remainder of the provision relates to portfolios of complaints which were on hold pending further regulatory clarification in respect of which utilisation will begin in 2019, and to our best estimate of liability in respect of a legal dispute regarding allocation of responsibility for a specific portfolio further described in Note 32. No further information regarding the best estimate has been provided on the basis it would be seriously prejudicial. Cumulative to Future expected Sensitivity analysis Inbound complaints (1) 2,141 415 25 = £7.4m Outbound contact (‘000) 488 217 25 = £5.4m Response rate to outbound contact 54 % 64 % 1% = £0.8m Average uphold rate per claim (2) 37 % 76 % 1% = £2.7m Average redress per claim (3) £ 1,474 £ 545 £ 50 = £16.4m (1) Includes all claims, including the specific portfolio of complaints referred to above, regardless of the likelihood of the Santander UK group incurring a liability. Excludes claims where the complainant has not held a PPI policy. (2) Claims include inbound and responses to outbound contact. (3) The average redress per claim reduced from the cumulative average value at 31 December 2018 of £1,474 to a future average value of £545 due to the inclusion of Plevin cases in the provision, as well as a shift in the complaint mix to a greater proportion of storecards, which typically held lower average balances. The Santander UK overturn rate at the Financial Ombudsman Service was 16% in the first half of 2018, and 12% in the second half of 2018, reflecting reducing inflows over the same period. 2018 compared to 2017 The remaining provision for PPI redress and related costs was £246m (2017: £356m). We made no additional PPI charges in the year, based on our recent claims experience and having considered the FCA Consultation paper CP18/33 issued on 7 November 2018. We will continue to monitor our provision levels, and take account of the impact of any further claims received and FCA guidance. 2017 compared to 2016 The remaining provision for PPI redress and related costs amounted to £356m. The total charge for the year was £109m (2016: £144m) and was driven by an increase in estimated future claims driven by the start of the FCA advertising campaign for PPI, offset by an expected decline relating to a specific PPI portfolio review. In 2016, a provision of £114m was made when we applied the principles published in the August 2016 FCA papers, and a further £32m was made in relation to a past business review. Monthly utilisation increased from the 2016 average following the confirmation of a deadline for customer complaints, broadly in line with our assumptions. (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 £30m (2017: £47m), which primarily related to the sale of interest rate derivatives, following an ongoing review of the regulatory classification of certain customers potentially eligible for redress. Following further analysis, management assessed the provision requirements resulting in a release of £11m in the second quarter of 2018. b) FSCS and Bank Levy (I) Financial Services Compensation Scheme (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. On 25 April 2017, following the sale of certain Bradford & Bingley mortgage assets, the amount that the FSCS owed to HM Treasury reduced to £4.7bn, from £15.7bn. The interest payable on the loan, and the Santander UK group’s share of that interest, fell accordingly. Based on the latest estimates from the FSCS the balance outstanding will be repaid earlier mostly through recoveries from asset sales, surplus cash flow or other recoveries in relation to the assets of the firms that defaulted. According to the new estimates, the amount to be provided by the Santander UK group for the interest payable on the loan was lower than initially expected. As a result, there was a release of £4m (2017: £1m charge, 2016: £34m charge) to bring the provision down to the amount now expected to be charged for the remaining interest. The Santander UK group provided for a liability for the FSCS of £4m at 31 December 2018 (2017: £13m). (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 0.16% applies for 2018 (2017: 0.17%). The cost of the UK Bank Levy for 2018 was £69m (2017: £92m, 2016: £107m). The Santander UK group paid £86m in 2018 (2017: £109m) and provided for a liability of £40m at 31 December 2018 (2017: £44m). c) Vacant property Vacant property provisions are made by reference to an estimate of any expected sub-let d) Off-balance Following the adoption of IFRS 9 on 1 January 2018, 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 comprise 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 periodically. Regulatory and other provisions charged in 2018 included the following items: • In the fourth quarter of 2018, we were fined £33m by the FCA in relation to an investigation into our historical probate and bereavement practices. We acknowledged the findings of the FCA and apologised to the families and beneficiaries of deceased customers affected by these failings. This amount was charged and paid in the year. • An amount of £58m (2017: £nil) that was charged in 2018 and arose from a systems related historical issue identified by Santander UK, relating to compliance with certain requirements of the Consumer Credit Act (CCA). 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 2018 of potential costs in respect of the identified issue. However, as detailed in Note 32, these reviews and the related analysis are not yet complete, such that the approach and timing to any remediation has not yet been finalised, although it is expected to commence in 2019.

Retirement Benefit Plans

Retirement Benefit Plans	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Retirement Benefit Plans	31. RETIREMENT BENEFIT PLANS The amounts recognised in the balance sheet were as follows: 2018 2017 £m £m Assets/(liabilities) Funded defined benefit pension scheme – surplus 842 449 Funded defined benefit pension scheme – deficit (76 ) (245 ) Unfunded defined benefit pension scheme (39 ) (41 ) Total net assets 727 163 Remeasurement (gains)/losses recognised in other comprehensive income during the year were as follows: 2018 2017 2016 £m £m £m Pension remeasurement (469 ) 103 528 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. In December 2017, the Santander UK group ceased to contribute to the Santander Retirement Plan, an occupational defined contribution plan, and future contributions are paid into a defined contribution Master Trust, LifeSight. This Master Trust is the plan into which eligible employees are enrolled automatically. During the year the Santander Retirement Plan was wound up and all assets were transferred to LifeSight. The assets of the LifeSight Master Trust are held in separate trustee-administered funds. An expense of £66m (2017: £54m, 2016: £52m) 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 2018, 2017 and 2016. 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 under the terms of a merger of former schemes operated by Santander UK plc agreed in 2012. The Scheme covers 13% (2017: 17%) of the Santander UK group’s 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. During 2017, the Trustee was a wholly-owned subsidiary of Santander UK plc, but was transferred as part of the ring-fencing implementation. The principal duty of the Trustee is to act in the best interests of the members of the Scheme. The Trustee board comprises six Directors selected by Santander UK plc, plus 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 2016 was finalised in March 2017, with a deficit to be funded of £1,739m. The next triennial funding valuation will be at 31 March 2019. 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: 2018 2017 2016 £m £m £m Net interest income (7 ) (5 ) (18 ) Current service cost 41 31 33 Past service and GMP costs 41 1 1 Administration costs 8 8 8 83 35 24 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 is based on a number of assumptions and the actual impact may be different. This has been reflected in the income statement and in the closing net accounting surplus of the Scheme. The amounts recognised in other comprehensive income were as follows: 2018 2017 2016 £m £m £m Return on plan assets (excluding amounts included in net interest expense) 246 (435 ) (1,447 ) Actuarial (gains)/losses arising from changes in demographic assumptions (56 ) (151 ) 30 Actuarial gains arising from experience adjustments 15 (11 ) (80 ) Actuarial (gains)/losses arising from changes in financial assumptions (674 ) 700 2,025 Pension remeasurement (469 ) 103 528 Movements in the present value of defined benefit scheme obligations were as follows: 2018 2017 £m £m At 1 January (11,583 ) (11,082 ) Current service cost paid by Santander UK plc (27 ) (30 ) Current service cost paid by other subsidiaries (14 ) (1 ) Current service cost paid by fellow Banco Santander subsidiaries — (12 ) Interest cost (282 ) (305 ) Employer salary sacrifice contributions (6 ) (6 ) Past service cost (1 ) (1 ) GMP equalisation cost (40 ) — Remeasurement due to actuarial movements arising from: – Changes in demographic assumptions 56 151 – Experience adjustments (15 ) 11 – Changes in financial assumptions 674 (700 ) Benefits paid 433 392 At 31 December (10,805 ) (11,583 ) Movements in the fair value of the schemes’ assets were as follows: 2018 2017 £m £m At 1 January 11,746 11,218 Interest income 289 310 Contributions paid by employer and scheme members 184 171 Contributions paid by fellow Banco Santander subsidiaries — 12 Administration costs paid (8 ) (8 ) Return on plan assets (excluding amounts included in net interest expense) (246 ) 435 Benefits paid (433 ) (392 ) At 31 December 11,532 11,746 The composition and fair value of the schemes’ assets by category was: Quoted prices in Prices not quoted in Total 2018 £m % £m % £m % 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 — — (2,981 ) (26 ) (2,981 ) (26 ) Other — — 1,021 9 1,021 9 10,433 90 1,099 10 11,532 100 2017 UK equities 187 1 — — 187 1 Overseas equities 2,204 19 706 6 2,910 25 Corporate bonds 1,665 14 209 2 1,874 16 Government fixed interest bonds 255 2 — — 255 2 Government index-linked bonds 3,506 30 — — 3,506 30 Property — — 1,547 13 1,547 13 Derivatives — — 512 4 512 4 Cash — — 206 2 206 2 Other — — 749 7 749 7 7,817 66 3,929 34 11,746 100 Scheme assets are stated at fair value based upon quoted prices in active markets with the exception of property funds, derivatives and those classified under ‘Other’. The ‘Other’ category consists of asset-backed securities, annuities and funds (including private equity 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. In addition, the Scheme entered into an equity collar in 2017 which was extended and resized in 2018. At 31 December 2018, the equity collar had a notional value of £1,795m (2017: £2,000m). In addition, 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. At 31 December 2018, repurchase agreements were entered into by the Scheme over an equivalent value of Government fixed interest and index-linked bonds and have therefore been included in the table above. A strategy is also in place to manage currency risk. 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 2018 and 2017. 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 March 2017, 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 2016 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 £176m in 2018 (2017: £163m) to the Scheme, of which £123m (2017: £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 £119m each year from 1 April 2017 increasing by 5% to 31 March 2026 plus contributions of £28m per annum increasing at 5% from 1 April 2021 to 31 March 2023 followed by £66m per annum increasing at 5% per annum from 1 April 2023 to 31 March 2026. In addition, the Santander UK group has agreed to pay further contingent contributions should investment performance be worse than expected, or should the funding position have fallen behind plan at the next formal actuarial valuation. Actuarial assumptions The principal actuarial assumptions used for the defined benefit schemes were: 2018 2017 2016 To determine benefit obligations: – Discount rate for scheme liabilities 2.9 2.5 2.8 – General price inflation 3.2 3.2 3.1 – 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 27.4 27.8 – Females 30.1 30.1 30.3 Longevity at 60 for future pensioners currently aged 40, on the valuation date: – Males 28.7 28.9 30.0 – Females 31.6 31.7 32.2 Discount rate for scheme liabilities The rate used to discount the retirement benefit obligation 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. We consider a number of different data sources and methods of projecting forward the corporate bond curve. 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. During 2018 we reduced the level of management adjustment to the discount rate, noting the expanded range of different models used by UK companies, and the relatively higher discount rates being adopted. At 31 December 2018 this increased the discount rate applied and had a positive impact of £104m on the accounting surplus. 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. During the year, the assumptions for setting the inflation risk premium were updated to reflect management’s current views of long term inflation. At 31 December 2018, this had a negative impact of £65m on the accounting surplus. Expected rate of pension increase During the year, the methodology for setting the expected rate of pension increases was changed to better represent the current expectations for inflation volatility and the impact of caps and collars on pension increases. The revised 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 provides an improvement in estimate because it allows for the likelihood that high or low inflation in one year feeds into inflation remaining high or low in the next year. At 31 December 2018 this had a negative impact of £85m on the accounting surplus. Mortality assumptions The mortality assumptions are based on an independent analysis of the Santander (UK) Group Pension Scheme’s actual mortality experience, carried out as part of the triennial actuarial valuations, together with recent evidence from the Continuous Mortality Investigation Table ‘S2 Light’ mortality tables. An allowance is then made for expected future improvements to life expectancy based on the Continuous Mortality Investigation Tables. During 2018 we adopted the CMI 2017 projection model for future improvements in life expectancy with a long-term rate of future improvements to life expectancy of 1.25% for male and female members. This model incorporates the latest available data on trends in life expectancy. At 31 December 2018, this had a positive impact of £57m 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. Increase/(decrease) Assumption Change in pension obligation at year-end from 2018 2017 Discount rate 25 bps increase (483 ) (550 ) General price inflation 25 bps increase 350 365 General salary increase 25 bps increase n/a n/a Mortality Each additional year of longevity assumed 335 367 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 2019 266 2020 269 2021 287 2022 309 2023 325 Five years ending 2028 1,903 The average duration of the defined benefit obligation at 31 December 2018 was 19.1 years (2017: 20.1 years).

Contingent Liabilities And Comm

Contingent Liabilities And Commitments	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Contingent Liabilities And Commitments	32. CONTINGENT LIABILITIES AND COMMITMENTS 2018 (1) 2017 Guarantees given to third parties 1,611 1,557 Formal standby facilities, credit lines and other commitments with original term to maturity of: – One year or less 8,560 10,664 – Later than one year 31,566 31,278 41,737 43,499 (1) For segmental and credit risk staging analysis relating to off-balance At 31 December 2018, the Santander UK group had credit impairment loss provisions relating to guarantees given to third parties and undrawn loan commitments. See Note 30 for further details. Where the items set out below can be reliably estimated, they are disclosed in the table above. Domestic Liquidity Sub-group As a firm subject to the liquidity obligations in the Capital Requirements Regulation (CRR), Santander UK plc applied for, and was granted, a CRR Article 8 DoLSub CRR permission (DoLSub Article 8 permission). At 31 December 2018, the UK DoLSub comprised the entities Santander UK plc, ANTS plc and Cater Allen Limited. With effect from 1 January 2019, and in accordance with our ring-fenced structure, Santander UK plc was granted a new DolSub permission, withdrawing ANTS plc from the UK DoLSub. The DoLSub waiver replaces the requirement for liquidity adequacy and reporting on an individual basis. 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 30, the Santander UK group participates in the UK’s national resolution scheme, the FSCS, and is thus subject to levies to fund the FSCS. In the event that 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 15, 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 transaction included in Note 15, 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 securitisation and covered bond transactions 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 15, 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 portfolio, 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, 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 Note 30 details our provisions including those in relation to PPI. In relation to a specific PPI portfolio of complaints, a legal dispute regarding allocation of liability is in its early stages. There are factual issues to be resolved which may have legal consequences including in relation to liability. These issues create uncertainties which mean that it is difficult to reliably predict the resolution of the matter including timing or the significance of the possible impact. The PPI provision 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. German dividend tax arbitrage transactions Santander UK plc, ANTS and Cater Allen International Limited (all subsidiaries of Santander UK Group Holdings plc) are currently under investigation by the Cologne Criminal Prosecution Office and the German Federal Tax Office in relation to historical involvement in German dividend tax arbitrage transactions (known as cum/ex transactions). We are cooperating with the German authorities and are conducting our own internal investigation into the matters in question. There are factual issues to be resolved which may have legal consequences including potentially material financial penalties. These issues create uncertainties which mean that it is difficult to predict with reasonable certainty the resolution of the matter including timing or the significance of the possible impact. 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 potential breaches of these requirements 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 30, other provisions includes an amount of £58m 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, but these reviews are not yet complete, such that the approach and timing to any remediation has not yet been finalised. As a result, the actual cost of customer compensation could differ materially from the amount provided, and it is not currently practicable to provide a reliable estimate of the amount or timing of any additional financial effects. Taxation The Santander UK group engages in discussion, and co-operates, 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. Additional deferred cash consideration is also payable following the third anniversary of closing. 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, 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 37. 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 Rental commitments under non-cancellable 2018 2017 Not later than one year 73 73 Later than one year and not later than five years 114 160 Later than five years 60 70 247 303 The majority of leases are subject to a third party outsourcing contract whereby the Santander UK group has the right to extend the occupation of properties by a minimum of three years subject to 12 months’ notice and a lease renewal being available from external landlords. Where leases expire after the expiry of the outsourcing contract in 2020 and occupation is still required, negotiations will be held with the landlords to agree renewal terms. In 2018, rental expense amounted to £61m (2017: £61m, 2016: £61m), including minimum rentals of £63m (2017: £61m, 2016: £61m), offset by sub-lease
Santander UK Group Holdings plc [member]
Statement [LineItems]
Contingent Liabilities And Commitments	12. CONTINGENT LIABILITIES AND COMMITMENTS Capital Support Deed At 31 December 2018, Santander UK plc, Abbey National Treasury Services plc and Cater Allen Limited, which are the three PRA-regulated non-regulated non-regulated The core UK group permission as supported by the Capital Support Deed 2015 expired on 31 December 2018. With effect from 1 January 2019, and in accordance with our ring-fenced structure, ANTS, Santander UK Group Holdings plc and Santander Equity Investments Limited have entered into a Capital Support Deed dated 13 November 2018 (the NRFB Sub-Group Sub-Group Sub-Group

Share Capital

Share Capital	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Share Capital	33. SHARE CAPITAL Ordinary shares of £1 each Issued and fully paid share capital No. £m At 31 December 2017, 1 January 2018 and 31 December 2018 7,060,000,000 7,060
Santander UK Group Holdings plc [member]
Statement [LineItems]
Share Capital	13. SHARE CAPITAL Details of the Company’s share capital are set out in Note 33 to the Consolidated Financial Statements.

Other Equity Instruments

Other Equity Instruments	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Other Equity Instruments	34. OTHER EQUITY INSTRUMENTS Initial interest rate First call date 2018 2017 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 745 745 – £300m Perpetual Capital Securities 7.60 December 2019 300 300 – £500m Perpetual Capital Securities 6.625 June 2019 500 500 2,041 2,041 AT1 securities The AT1 securities issued by the Company meet the CRD IV AT1 rules and are fully recognised as AT1 capital. 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, The £300m and £500m Perpetual Capital Securities and £100m of the £750m Fixed Rate Reset Perpetual AT1 Capital Securities were subscribed by the Company’s immediate parent company, Banco Santander SA.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Other Equity Instruments	14. OTHER EQUITY INSTRUMENTS Details of the Company’s other equity instruments are set out in Note 34 to the Consolidated Financial Statements.

Non-Controlling Interests

Non-Controlling Interests	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Non-Controlling Interests	35. NON-CONTROLLING Initial interest rate First call date 2018 2017 Santander UK plc issued: – £300m Fixed/Floating Rate Non-Cumulative 6.222 May 2019 14 14 – £300m Step-up 7.037 February 2026 235 235 PSA Finance UK Limited 151 152 400 401 Fixed/Floating Rate Non-Cumulative These shares entitle the holders to a fixed non-cumulative 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. PSA Finance UK Limited 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, 2018
Statement [LineItems]
Changes in Liabilities Arising from Financing Activities	36. CHANGES IN LIABILITIES ARISING FROM FINANCING ACTIVITIES The table below shows the changes in liabilities arising from financing activities. 2018 2017 Balance sheet line item Balance sheet line item Debt Subordinated £m Other instruments Dividends Total Debt Subordinated Other Dividends Total At 1 January 48,860 3,793 2,041 — 54,694 54,792 4,303 1,545 — 60,640 Cash flows from financing activities 7,272 (277 ) — (1,308 ) 5,687 (4,986 ) (52 ) 496 (1,001 ) (5,543 ) Cash flows from operating activities (2,760 ) (2 ) — — (2,762 ) 112 254 — — 366 Non-cash – Unrealised foreign exchange (2,085 ) 149 — — (1,936 ) (685 ) (235 ) — — (920 ) – Other changes 4,619 (62 ) — 1,308 5,865 (373 ) (477 ) — 1,001 151 At 31 December 55,906 3,601 2,041 — 61,548 48,860 3,793 2,041 — 54,694
Santander UK Group Holdings plc [member]
Statement [LineItems]
Changes in Liabilities Arising from Financing Activities	11. CHANGES IN LIABILITIES ARISING FROM FINANCING ACTIVITIES The table below shows the changes in liabilities arising from financing activities. 2018 2017 Balance sheet line item Balance sheet line item Debt securities in issue £m Subordinated liabilities £m Other equity instruments £m Dividends paid £m Total £m Debt Subordinated Other equity Dividends Total At 1 January 6,256 1,116 2,041 — 9,413 4,464 1,222 1,545 — 7,231 Cash flows from financing activities 2,658 — — (1,268 ) 1,390 2,103 — 496 (964 ) 1,635 Cash flows from operating activities (7 ) — — — (7 ) (3 ) — — — (3 ) Non-cash – Unrealised foreign exchange 418 — — — 418 (324 ) (106 ) — — (430 ) – Other changes (30 ) 69 — 1,268 1,307 16 — — 964 980 At 31 December 9,295 1,185 2,041 — 12,521 6,256 1,116 2,041 — 9,413

Assets Charged As Security For

Assets Charged As Security For Liabilities And Collateral Accepted As Security For Assets	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Assets Charged As Security For Liabilities And Collateral Accepted As Security For Assets	37. 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 2018 2017 On-balance Cash and balances at central banks 1,080 1,010 Trading assets — 17,092 Loans and advances to customers — securitisations and covered bonds (See Note 15) 35,694 35,421 Loans and advances to customers — other 16,402 15,078 Loans and advances to banks 402 105 Other financial assets at amortised cost 3,763 Financial assets at fair value through other comprehensive income 5,825 Financial investments 6,755 Total on-balance 63,166 75,461 Total off-balance 15,221 33,013 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 equity and 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 2018 was £17,485m (2017: £34,310m), of which £2,383m (2017: £2,931m) was classified within ‘Loans and advances to customers – securitisations and covered bonds’ in the table above. Securitisations and covered bonds As described in Note 15, Santander UK plc and certain of its subsidiaries issue securitisations and covered bonds. At 31 December 2018, there were £36,195m (2017: £36,512m) of gross assets in these secured programmes and £501m (2017: £1,091m) of these related to internally retained issuances and were available for use as collateral for liquidity purposes in the future. At 31 December 2018, a total of £4,039m (2017: £4,359m) 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 £1,834m at 31 December 2018 (2017: £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 £25,910m at 31 December 2018 (2017: £38,016m) 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 2018, £1,681m (2017: £3,658m) 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 2018 2017 £m £m On-balance Trading liabilities — 1,911 Deposits by customers — 8 Deposits by banks 4,058 1,760 Total on-balance 4,058 3,679 Total off-balance 23,473 38,655 Purchase and resale agreements The Santander UK group also enters into purchase and resale agreements and similar transactions of equity and 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 2018, the fair value of such collateral received was £15,728m (2017: £16,356m). 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 £7,745m at 31 December 2018 (2017: £22,299m) 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 2018, £4,058m (2017: £3,679m) 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, 2018
Text block [abstract]
Share-Based Compensation	38. 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. The total carrying amount at the end of the year for liabilities arising from share-based payment transactions was £7.7m (2017: £16.7m), of which £0.7m had vested at 31 December 2018 (2017: £nil). a) Sharesave Schemes The Santander UK group launched its eleventh HM Revenue & Customs approved Sharesave Scheme under Banco Santander SA ownership in September 2018. The first ten Sharesave Schemes were launched each year from 2008 to 2017 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. The table below summarises movements in the number of options during the year, and changes in weighted average exercise price over the same period. 2018 2017 2016 Number of Weighted Number of Weighted Number of Weighted Outstanding at 1 January 27,201 3.12 28,916 3.08 24,762 3.53 Granted 6,210 3.46 3,916 4.02 17,296 4.91 Exercised (3,340 ) 3.16 (1,918 ) 3.77 (338 ) 3.67 Forfeited/expired (3,233 ) 3.76 (3,713 ) 3.40 (12,804 ) 3.51 Outstanding at 31 December 26,838 3.12 27,201 3.12 28,916 3.08 Exercisable at 31 December 10,370 2.81 5,200 3.17 2,334 4.30 The weighted average share price at the date the options were exercised was £3.79 (2017: £4.96, 2016: £3.79). The following table summarises the range of exercise prices and weighted average remaining contractual life of the options at 31 December 2018 and 2017. 2018 2017 Weighted average Weighted Weighted average Weighted remaining average remaining average contractual life exercise price contractual life exercise price Range of exercise prices Years £ Years £ £2 to £ 3 2 2.75 3 2.75 £3 to £4 3 3.36 1 3.17 £4 to £5 3 4.11 3 4.21 The fair value of each option for 2018, 2017 and 2016 has been estimated at the date of acquisition or grant using a partial differentiation equation model. This model uses assumptions on the risk free interest rate, dividend yields, the expected volatility of the underlying shares and the expected lives of options granted under 3 and 5 year schemes. The weighted average grant-date fair value of options granted during the year was £0.53 (2017: £1.02, 2016: £0.65). b) LTIP In 2014 and 2015, conditional cash awards were made to certain Executive Directors, Key Management Personnel (as defined in Note 39) 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 involve a one-year The following table summarises the movement in the value of conditional awards in the LTIPs in 2018, 2017 and 2016: 2015 LTIP 2014 LTIP 2018 2017 2016 2018 2017 2016 £000 £000 £000 £000 £000 £000 Outstanding at 1 January 6,503 6,718 6,769 1,910 3,193 5,102 Forfeited/cancelled (129 ) (215 ) (1) (51 ) (1,910 ) (1,283 ) (1) (1,909 ) Outstanding at 31 December 6,374 6,503 6,718 — 1,910 3,193 (1) The outstanding shares have been updated to compensate for the equity dilution caused by the shares issued by Banco Santander SA in July 2017. See Note 39 for details of conditional share awards made to certain Executive Directors, Other Key Management Personnel and other individuals under the LTIP. 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 2017 and 2018, 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 future service. For 2017 and 2018 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, 2018
Statement [LineItems]
Transactions With Directors and Other Key Management Personnel	39. TRANSACTIONS WITH DIRECTORS AND OTHER KEY MANAGEMENT PERSONNEL The Directors of Santander UK Group Holdings plc did not receive any remuneration in respect of their services to the Company. The remuneration disclosures in these financial statements reflect their remuneration in respect of the Santander UK plc group. 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. Directors’ remuneration 2018 £ 2017 2016 Salaries and fees 5,028,434 4,406,908 3,604,999 Performance-related payments (1) 5,194,317 3,685,464 2,330,000 Other fixed remuneration (pension and other allowances & non-cash 1,467,011 1,580,321 635,493 Expenses 25,198 96,358 120,302 Total remuneration 11,714,960 9,769,051 6,690,794 Directors’ and Other Key Management Personnel compensation 2018 £ 2017 2016 Short-term employee benefits (2) 24,445,189 24,642,085 24,757,161 Post-employment benefits (3) 2,399,261 2,292,857 1,918,144 Total compensation 26,844,450 26,934,942 26,675,305 (1) In line with the Code, a proportion of the performance-related payment was deferred. Further details can be found in Note 38. (2) Excludes grants of shares in Banco Santander SA made as buy-outs buy-outs (3) Termination payments of £847,388 were paid in 2018 to two key management persons (2017: nil). In 2018, the remuneration, excluding pension contributions, of the highest paid Director, was £4,635,497 (2017: £4,714,578) of which £2,317,000 (2017: £2,425,000) was performance related. In 2018, 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 £20,402 p.a. (2017: £15,450 p.a.). b) Retirement benefits Defined benefit pension schemes are provided to certain employees. See Note 31 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 2018, which have been provided for previously, amounted to £87,300 (2017: £2,482; 2016: £14,893). 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. 2018 2017 No. £000 No. £000 Secured loans, unsecured loans and overdrafts At 1 January 7 1,216 17 5,195 Net movements 9 1,819 (10 ) (3,979 ) At 31 December 16 3,035 7 1,216 Deposit, bank and instant access accounts and investments At 1 January 25 13,184 26 9,138 Net movements 5 (2,221 ) (1 ) 4,046 At 31 December 30 10,963 25 13,184 In 2018 and 2017, 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 2018 and 2017, no Directors exercised share options over shares in Banco Santander SA, the ultimate parent company of the Company. At 31 December 2018, one interest-free loan from Banco Santander SA had been advanced to a Director, amounting to £344,348 (2017: £510,901). Two Directors and one Key Management Person received benefits in kind from Banco Santander SA totalling £485,334 and £2,024, respectively, in 2018. 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 2018, loans were made to eight Directors (2017: two Directors), with a principal amount of £65,232 outstanding at 31 December 2018 (2017: £53,452). In 2018, loans were made to eight Other Key Management Personnel (2017: five), with a principal amount of £2,969,462 outstanding at 31 December 2018 (2017: £1,162,384). In 2018 and 2017, 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 2018 and 2017, no Director had a material interest in any contract of significance with Santander UK other than a service contract.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Transactions With Directors and Other Key Management Personnel	15. TRANSACTIONS WITH DIRECTORS AND OTHER KEY MANAGEMENT PERSONNEL The Directors of Santander UK Group Holdings plc did not receive any remuneration in respect of their services to the Company. The remuneration disclosures in respect of the Santander UK group are set out in Note 39 to the Consolidated Financial Statements.

Related Party Disclosures

Related Party Disclosures	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Related Party Disclosures	40. RELATED PARTY DISCLOSURES a) Parent undertaking and controlling party The Company’s immediate and 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 Banco Santander SA, 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: Interest, fees and Interest, fees and Amounts owed Amounts owed to 2018 2017 2016 2018 2017 2016 2018 2017 2018 2017 Ultimate parent (73 ) (60 ) (81 ) 231 321 188 2,737 4,398 (3,854 ) (5,082 ) Fellow subsidiaries (81 ) (76 ) (271 ) 169 491 653 39 102 (591 ) (981 ) Associates & joint ventures (28 ) (20 ) (27 ) — — 1 1,986 1,175 (718 ) (33 ) (182 ) (156 ) (379 ) 400 812 842 4,762 5,675 (5,163 ) (6,096 ) 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 31. The above transactions were made in the ordinary course of business, except those carried out with Banco Santander SA as part of our ring-fencing implementation as described in Note 43, 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. For more on ring-fencing, see Note 43.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Related Party Disclosures	16. RELATED PARTY TRANSACTIONS The Company’s only transactions with related parties arise in connection with the receipt of dividends declared by its subsidiaries, payment of dividends on its own ordinary shares and Perpetual Capital Securities, interest payments to its subsidiary on intercompany loans and interest received from its subsidiary relating to downstreamed funding of senior debt, as well as the transactions entered into as part of the implementation of Santander UK’s ring-fencing plans as set in Note 43 to the Consolidated Financial Statements.

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Financial Instruments	41. 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. Level 1 positions include debt securities, equity securities, exchange traded derivatives and short positions in securities. 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 2 positions include loans and advances to banks, loans and advances to customers, equity securities, exchange rate derivatives, interest rate derivatives, equity and credit derivatives, debt securities, deposits by banks and debt securities in issue. 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. Level 3 positions include exchange rate derivatives, property related derivatives, loans and advances to customers, debt securities, equity securities, deposits by customers and debt securities in issue. 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 2018 and 2017 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 2018, 2017 and 2016. A In the valuation of financial instruments requiring static hedging (for example interest rate, currency derivatives and commodity swaps) 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 commodity prices, 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 prices 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. The results of the independent valuation process and any changes to the fair value adjustments methodology are approved in line with the model risk framework and policy. 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 2018 and 2017, 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 and, in 2017, the US Federal Reserve, 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 financial instrument categorised in Level 1 of the fair value hierarchy. 2018 2017 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 — — 204,391 204,391 201,619 — 6,331 195,327 201,658 199,332 Loans and advances to banks — 3,028 448 3,476 3,515 — 2,897 556 3,453 3,466 Reverse repurchase agreements – non trading — 21,130 — 21,130 21,127 — 2,614 — 2,614 2,614 Other financial assets at amortised cost 6,390 720 — 7,110 7,228 Financial investments 6,435 2,211 — 8,646 8,758 6,390 24,878 204,839 236,107 233,489 6,435 14,053 195,883 216,371 214,170 Liabilities Deposits by customers — 21 173,762 173,783 173,692 — — 177,563 177,563 177,421 Deposits by banks — 16,859 977 17,836 17,824 — 12,164 557 12,721 12,708 Repurchase agreements – non trading — 10,923 — 10,923 10,910 — 1,085 — 1,085 1,076 Debt securities in issue — 56,695 — 56,695 55,906 — 50,641 — 50,641 48,860 Subordinated liabilities — 3,825 — 3,825 3,601 — 4,373 — 4,373 3,793 — 88,323 174,739 263,062 261,933 — 68,263 178,120 246,383 243,858 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 fair value exposures set out in the tables above are managed by using a combination of hedging derivatives and offsetting on balance sheet positions. 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 current market rates for lending of a similar credit quality. 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, each representing a LTV band, after taking account of expected customer prepayment rates. The spread is based on new business interest rates derived from competitor market information. Further discounting is applied for certain higher risk mortgage portfolios. ii) Corporate loans The corporate loan portfolio is stratified by product. 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, maturity and structure. 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 the business was written relatively recently. 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 on the basis of spreads on credit default swaps 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. Other financial assets at amortised cost and financial investments These consist of asset backed securities and debt securities. The asset backed securities are 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 valuation technique A as described above. 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. 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. Other market values have been determined using valuation technique A as described above. Repurchase agreements – non trading The fair value of the repurchase agreements – non trading has been estimated using valuation technique A as described above. 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 2018 and 2017, analysed by their levels in the fair value hierarchy – Level 1, Level 2 and Level 3. 2018 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total £m Valuation Assets Trading assets Securities purchased under resale agreements — — — — — 8,870 — 8,870 A Debt securities — — — — 5,156 — — 5,156 — Equity securities — — — — 9,662 — — 9,662 — Cash collateral — — — — — 6,156 — 6,156 A Short-term loans — — — — 656 55 — 711 A — — — — 15,474 15,081 — 30,555 Derivative financial instruments Exchange rate contracts — 4,324 25 4,349 — 6,061 16 6,077 A Interest rate contracts — 2,560 6 2,566 — 23,435 12 23,447 A & C Equity and credit contracts — 194 84 278 — 861 36 897 B & D Netting — (1,872 ) — (1,872 ) — (10,479 ) — (10,479 ) — 5,206 115 5,321 — 19,878 64 19,942 Other financial assets at FVTPL Loans and advances to customers — 427 82 509 — 1,485 64 1,549 A Debt securities 26 2,343 894 3,263 184 187 176 547 A, B & D Equity securities 14 — 79 93 B Reverse repurchase agreements – non trading — 2,272 — 2,272 — — — — A 40 5,042 1,055 6,137 184 1,672 240 2,096 Financial assets at FVOCI Debt securities 12,487 742 — 13,229 D Loans and advances to customers — — 73 73 D 12,487 742 73 13,302 Financial investments Available-for-sale 8,770 2 — 8,772 C Available-for-sale 19 9 53 81 B 8,789 11 53 8,853 Total assets at fair value 12,527 10,990 1,243 24,760 24,447 36,642 357 61,446 Liabilities Trading liabilities Securities sold under repurchase agreements — — — — — 25,504 — 25,504 A Short positions in securities and unsettled trades — — — — 3,694 — — 3,694 — Cash collateral — — — — — 1,911 — 1,911 A Short-term deposits — — — — — — — — — — — — — 3,694 27,415 — 31,109 Derivative financial instruments Exchange rate contracts — 528 23 551 — 4,176 15 4,191 A Interest rate contracts — 2,736 7 2,743 — 23,199 5 23,204 A & C Equity and credit contracts — 132 40 172 1 653 43 697 B & D Netting — (1,872 ) — (1,872 ) — (10,479 ) — (10,479 ) — 1,524 70 1,594 1 17,549 63 17,613 Other financial liabilities at FVTPL Debt securities in issue — 983 7 990 — 1,629 6 1,635 A Structured deposits — 104 29 133 — 680 — 680 A Repurchase agreements – non trading — 2,110 — 2,110 — — — — A Collateral and associated financial guarantees — 3,040 13 3,053 D — 6,237 49 6,286 — 2,309 6 2,315 Total liabilities at fair value — 7,761 119 7,880 3,695 47,273 69 51,037 Transfers between levels of the fair value hierarchy Transfers between levels of the fair value hierarchy are reported at the beginning of the period in which they occur. In 2018, there were no significant (2017: none) transfers of financial instruments between Levels 1 and 2. In 2018, the main transfers of financial instruments between Levels 2 and 3 were Derivatives assets of £56m and Derivative liabilities of £35m 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: 2018 2017 Risk-related: – Bid-offer 13 34 – Uncertainty 36 43 – Credit risk adjustment 9 36 – Funding fair value adjustment 4 6 62 119 Model-related 5 8 Day One profit — 1 67 128 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. For certain types of exotic derivatives where the products are not currently supported by the standard methodology, Santander UK adopts alternative methodologies. These may involve mapping transactions against the results for similar products which are valued using the standard methodology. In other cases, a simplified version of the standard methodology is applied. The calculation is applied at a trade level, with more limited recognition of credit mitigants such as netting or collateral agreements than used in the standard methodology. 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. Day One profit adjustments Day One profit adjustments are adopted where the fair value estimated by a valuation model is based on one or more significant unobservable inputs. Day One profit adjustments are calculated and reported on a portfolio basis. The timing of recognition of deferred Day One profit and loss is determined individually. It is deferred until either the instrument’s fair value can be determined using market observable inputs or is realised through settlement. The financial instrument is subsequently measured at fair value, adjusted for the deferred Day One profit and loss. Subsequent changes in fair value are recognised immediately in the Income Statement without immediate reversal of deferred Day One profits and losses. 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 Balance sheet line item Category Financial instrument product type 2018 2017 £m 2018 2017 2016 1. Derivative assets Equity and credit contracts Reversionary property interests 54 31 30 (6 ) 12 2. FVTPL assets Loans and advances to customers Roll-up 53 64 8 2 4 3. FVTPL assets Debt securities Reversionary property securities 142 176 (28 ) (18 ) — 4. FVTPL assets (1) Equity securities (1) Unlisted equity shares 79 53 19 — — 5. FVTPL assets Debt securities Credit linked notes 752 — 13 — — 6. FVOCI assets Loans and advances to customers Other loans 73 — (5 ) — — 7. Derivative liabilities Equity contracts Property-related options and forwards (35 ) (43 ) — (5 ) (5 ) 8. FVTPL liabilities Financial guarantees Credit protection guarantee (13 ) — (13 ) — — 1,105 281 24 (27 ) 11 Other Level 3 assets 90 33 — (26 ) 6 Other Level 3 liabilities (71 ) (26 ) 1 19 (10 ) Total net assets 1,124 288 Total income/(expense) 25 (34 ) 7 (1) Prior to 1 January 2018, these unlisted equity shares were classified as available-for-sale 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 – 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 2 above. An adjustment is also made to reflect the specific property risk. 4. FVTPL assets – Equity securities (2017: Available-for-sale These consist of unquoted equity investments in companies providing infrastructure services to the financial services industry. In the valuation of equity financial instruments requiring dynamic hedging, 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 equity prices, bid-offer 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 21. 6. FVOCI assets – Loans and advances to customers – other loans The changes to the classification and measurement of financial assets on transition to IFRS 9 as set out in Note 44 resulted in some loans and advances to customers, primarily consisting of utilities and shipping counterparties, being reclassified from amortised cost to FVOCI. The fair value of these loans

Offsetting Financial Assets and

Offsetting Financial Assets and Liabilities	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Offsetting Financial Assets and Liabilities	42. 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 For repurchase and reverse repurchase agreements and other similar secured lending and borrowing, the ‘Financial instruments’ column identifies financial assets and liabilities that are subject to set off under netting agreements, such as global master repurchase agreements and global master securities lending agreements, whereby all outstanding transactions with the same counterparty can be offset and close-out 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. Amounts subject to enforceable netting arrangements Balance (3) Effects of offsetting on balance sheet Related amounts not offset Assets not (2) 2018 Gross Amount Net amount Financial Financial (1) Net Assets Derivative financial instruments 7,088 (1,872 ) 5,216 (933 ) (2,133 ) 2,150 105 5,321 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) 6,820 (1,308 ) 5,512 — — 5,512 199,622 205,134 40,913 (6,786 ) 34,127 (3,654 ) (22,811 ) 7,662 199,727 233,854 Liabilities Derivative financial instruments 3,412 (1,872 ) 1,540 (933 ) (303 ) 304 54 1,594 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) 2,879 (1,308 ) 1,571 — (502 ) 1,069 189,945 191,516 22,917 (6,786 ) 16,131 (3,654 ) (11,104 ) 1,373 189,999 206,130 2017 Assets Derivative financial instruments 30,155 (10,479 ) 19,676 (14,772 ) (2,785 ) 2,119 266 19,942 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 2,614 — 2,614 — (2,614 ) — — 2,614 – Fair value 15,224 (6,354 ) 8,870 (355 ) (8,515 ) — — 8,870 Loans and advances to customers and banks (4) 5,974 (1,459 ) 4,515 — — 4,515 198,283 202,798 53,967 (18,292 ) 35,675 (15,127 ) (13,914 ) 6,634 198,549 234,224 Liabilities Derivative financial instruments 27,839 (10,479 ) 17,360 (14,772 ) (1,951 ) 637 253 17,613 Repurchase, securities lending & similar agreements: – Amortised cost 1,076 — 1,076 — (1,076 ) — — 1,076 – Fair value 31,858 (6,354 ) 25,504 (355 ) (25,149 ) — — 25,504 Deposits by customers and banks (4) 2,688 (1,459 ) 1,229 — (502 ) 727 188,900 190,129 63,461 (18,292 ) 45,169 (15,127 ) (28,678 ) 1,364 189,153 234,322 (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.

Ring-Fencing

Ring-Fencing	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Ring-Fencing	43. RING-FENCING Regulation The Financial Services (Banking Reform) Act 2013 inserted provisions into the Financial Services and Markets Act 2000 (FSMA) and related legislation (the Banking Reform Legislation) requiring the Santander UK group amongst a number of other UK banking groups, to operationally and legally separate certain retail banking activities from certain wholesale or investment banking activities by 1 January 2019. This is known as ‘ring-fencing’. The Banking Reform Legislation specifies: • Certain banking services or activities (principally deposit taking from individuals and SMEs) which must be undertaken by a ring-fenced bank. • Certain banking services and activities, along with certain types of credit risk exposure or off-balance As a result, under the ring-fencing regime, a ring-fenced bank is only permitted to carry on banking services or activities that are not prohibited (permitted business). Santander UK group model Our ring-fence structure was completed ahead of the 1 January 2019 regulatory deadline. Its implementation involved a ring-fencing transfer scheme (RFTS) between Santander UK plc, ANTS and Banco Santander SA, as well as asset sales and the rundown of certain short-term positions. Under our chosen model: • Santander UK plc is the primary ring-fenced bank within a ring-fenced bank sub-group sub-group. sub-group. • ANTS was emptied of most assets and liabilities, except for a small pool of residual assets and liabilities, and became a wholly-owned direct subsidiary of Santander UK Group Holdings plc, outside the ring-fenced bank. The prohibited business of ANTS, which principally included our derivatives business with financial institutions, certain corporates and our short term markets business, was either transferred to Banco Santander London Branch or, in the case of the majority of our short term markets business, was run down. The majority of the permitted business of ANTS transferred to Santander UK plc, with a small amount of the permitted business of ANTS transferring to Banco Santander London Branch. • The business of the Crown Dependency branches (Jersey and Isle of Man) of Santander UK plc was sold to ANTS pursuant to transfer schemes effected under relevant Jersey and Isle of Man law, and therefore transferred out of the ring-fenced bank. Any associated business transfers to Banco Santander London Branch were made for a cash consideration equivalent to the book value of the associated assets and liabilities, which represents a fair value for the Santander UK group. Costs to sell were immaterial. Our ring-fence structure is now in place with all required transfers completed. Compliance with ring-fencing legislation has involved significant effort over a number of years, with a total cost of c£240m.

Transition to IFRS 9

Transition to IFRS 9	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Transition to IFRS 9	44. TRANSITION TO IFRS 9 Statutory balance sheet reconciliation under IAS 39 and IFRS 9 The measurement categories and carrying amounts of financial assets determined in accordance with IAS 39 and IFRS 9 are compared below, illustrating a total net assets decrease of £192m as a result of the application of IFRS 9: IAS 39 IFRS 9 Assets Measurement category Carrying amount (31 December 2017) £m Reclassifications (1) £m Remeasurement (2) £m Measurement category Carrying amount (1 January 2018) £m Representation (6) £m IFRS 9 Balance Sheet (1 January 2018) £m Cash and balances with central banks Loans & receivables 32,771 — — Amortised cost 32,771 — 32,771 Trading assets FVTPL 30,536 — — FVTPL (Mandatory) 30,536 — 30,536 FVTPL 19 — — FVOCI 19 (19 ) (a) — 30,555 — — 30,555 (19 ) 30,536 Derivative financial instruments FVTPL (Trading) 19,942 — — FVTPL (Mandatory) 19,942 — 19,942 Other financial assets at FVTPL (3) FVTPL (Designated) 1,022 (45 ) (b) — Amortised cost 977 (977 ) (b) — FVTPL (Designated) 836 — — FVTPL (Designated) 836 — 836 FVTPL (Designated) 238 — — FVTPL (Mandatory) 238 (c) 1,181 (d) 1,419 2,096 (45 ) — 2,051 204 2,255 Loans and advances to customers (4) Loans & receivables 199,060 — (211 ) Amortised cost 198,849 977 (b) 199,826 Loans & receivables 181 (1 ) (a) — FVOCI 180 (180 ) (a) — Loans & receivables 91 — — FVTPL (Mandatory) 91 (91 ) (d) — 199,332 (1 ) (211 ) 199,120 706 199,826 Loans and advances to banks Loans & receivables 3,466 — — Amortised cost 3,466 — 3,466 Reverse repurchase agreements – non trading Loans & receivables 2,614 — — Amortised cost 2,614 — 2,614 Other financial assets at amortised cost Amortised cost — 7,776 (e) 7,776 Financial assets at FVOCI FVOCI — 8,942 (a)(f) 8,942 Financial investments Loans & receivables 1,198 — — Amortised cost 1,198 (1,198 ) (e) Loans & receivables 982 (2 ) (d) — FVTPL (Mandatory) 980 (980 ) (d) Available-for-sale 8,743 — — FVOCI 8,743 (8,743 ) (f) Available-for-sale 29 — — FVTPL (Mandatory) 29 (29 ) (d) Held-to-maturity 6,578 — — Amortised cost 6,578 (6,578 ) (e) Available-for-sale 81 — — FVTPL (Mandatory) 81 (81 ) (d) 17,611 (2 ) — 17,609 (17,609 ) Other assets Other assets 6,373 (1 ) Other assets 6,372 — 6,372 Total assets (pre-deferred tax asset ) (5) 314,760 (49 ) (211 ) 314,500 — 314,500 (1) Gross (pre-tax) (2) Gross (pre-tax) non-amortised held-to-maturity available-for-sale (3) The balance sheet category for ‘Financial assets designated at fair value’ has been changed to ‘Other financial assets at fair value through profit or loss’ following the adoption of IFRS 9. (4) Of the £211m increase in loss allowance, £50m related to off-balance (5) The impact of transition to IFRS 9 gave rise to a deferred tax asset of £68m, of which £14m is attributable to ‘Reclassifications’, and £54m to ‘Remeasurement’. This deferred tax asset was offset against our deferred tax liabilities. (6) Gross (pre-tax) re-presentations Reclassification and re-presentation The columns for ‘Reclassifications’ and ‘Re-presentations’ (a) Of the financial assets at FVOCI of £8,942m, £199m was previously classified as trading assets of £19m (measured at FVTPL) and loans and advances to customers of £180m (measured at amortised cost). As these financial assets were held within hold to collect and sell business models, they were re-measured (b) The Santander UK group elected to re-measure (c) Other financial assets of £238m, previously designated at FVTPL under IAS 39, are now mandatorily held at FVTPL, as there is no longer an option to bifurcate embedded derivatives under IFRS 9 and they fail the SPPI test. (d) Other financial assets at FVTPL of £1,181m were previously classified as financial investments of £980m (measured at amortised cost), financial investments of £110m (measured at available-for-sale), (e) Other financial assets at amortised cost of £7,776m were previously classified as financial investments (measured at amortised cost). On adoption of IFRS 9, the Santander UK group split the ‘financial investments’ balance sheet line item between ‘other financial assets at amortised cost’ and ‘financial assets at FVOCI’. This aligned the balance sheet line items to the IFRS 9 accounting classifications and provides a clearer understanding of our financial position. (f) Of the financial assets at FVOCI of £8,942m, £8,743m was previously classified as financial investments (and measured at available-for-sale). Reclassifications of debt instruments For financial assets that were reclassified on transition to IFRS 9, the following table shows their fair value at 31 December 2018 and the fair value gain or loss that would have been recognised if these financial assets had not been reclassified: 2018 To amortised cost from FVTPL: Fair value at 31 December 2018 1,347 Fair value gain that would have been recognised during the year if the financial asset had not been reclassified 120 The effective interest rate of these debt instruments on the date of initial application of IFRS 9 was 3.35%. In 2018, interest income of £21m was recognised for these debt instruments.

Events After the Balance Sheet

Events After the Balance Sheet Date	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Events After the Balance Sheet Date	45. EVENTS AFTER THE BALANCE SHEET DATE There have been no significant events between 31 December 2018 and the date of approval of these financial statements which would require a change to or additional disclosure in the financial statements, except for the following: In January 2019, we announced plans to reshape our branch network and close 140 branches in response to changes in how customers are choosing to carry out their banking. Our future branch network, with approximately 615 branches, will be made up of a combination of larger branches offering improved community facilities to support local businesses and customers, and smaller branches using the latest technology to offer customers more convenient access to banking services. Furthermore, in order to deliver a branch network for the future, 100 branches will be refurbished over the next two years through an investment of £55m. At 31 December 2018, no provision was recognised in respect of these plans as the relevant criteria under IAS 37 ‘Provisions, contingent liabilities and contingent assets’ had not been met.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Events After the Balance Sheet Date	17. EVENTS AFTER THE BALANCE SHEET DATE See Note 45 to the Consolidated Financial Statements.

Loans and Advances to Banks

Loans and Advances to Banks	12 Months Ended
	Dec. 31, 2018
Santander UK Group Holdings plc [member]
Statement [LineItems]
Loans and Advances to Banks	4. LOANS AND ADVANCES TO BANKS 2018 2017 Placements with other banks 8 3 Amounts due from Santander UK group undertakings 9,206 6,257 9,214 6,260 The fair values of loans and advances to banks are equal to their carrying amounts. In 2018 and 2017, no impairment losses were incurred. All of our senior debt issued out of Santander UK Group Holdings plc is downstreamed to our operating company Santander UK plc.

Accounting Policies (Policies)

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
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. The Company financial statements have been prepared in accordance with IFRSs as adopted by the European Union and as applied in accordance with the provision of the UK Companies Act 2006. 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 On 1 January 2018, the Santander UK group adopted IFRS 9 ‘Financial Instruments’ (IFRS 9) and IFRS 15 ‘Revenue from Contracts with Customers’ (IFRS 15). The new or revised accounting policies are set out below. The impact of applying IFRS 9 is disclosed in Note 44. The accounting policy changes for IFRS 9, set out below, have been applied from 1 January 2018. Comparatives have not been restated. As a result of the change from IAS 39 to IFRS 9, some disclosures presented in respect of certain financial assets are not comparable because their classification may have changed between the two standards. This means that some IFRS 9 disclosures are not directly comparable and some disclosures that relate to information presented on an IAS 39 basis are no longer relevant in the current period. As explained in Note 44, the classification and measurement changes to financial assets that arose on adoption of IFRS 9 have been aligned to the presentation in the balance sheet. The Santander UK group decided to continue adopting IAS 39 hedge accounting and consequently there have been no changes to the hedge accounting policies and practices following the adoption of IFRS 9. However, additional hedge accounting disclosure requirements of IFRS 7 ‘Financial Instruments: Disclosures’ (IFRS 7) have been included in these financial statements. In addition, non-trading non-trading non-trading non-trading re-presented re-presentation The application of IFRS 15 had no material impact on the Santander UK group as there were no significant changes in the recognition of in-scope Future accounting developments At 31 December 2018, the Santander UK group has not yet adopted the following significant new or revised standards and interpretations, and amendments thereto, which have been issued but which are not yet effective for the Santander UK group: • IFRS 16 ‘Leases’ (IFRS 16) – In January 2016, the IASB issued IFRS 16. The standard is effective for annual periods beginning on or after 1 January 2019. IFRS 16 sets out the principles for the recognition, measurement, presentation and disclosure of leases for both lessees and lessors. For lessee accounting, IFRS 16 introduces a single lessee accounting model and requires a lessee to recognise a right-of-use The Santander UK group has elected to apply the modified retrospective approach whereby the ROU asset at the date of initial application is measured at an amount equal to the lease liability. The ROU asset is adjusted for any prepaid lease payments and incentives relating to the relevant leases that were recognised on the balance sheet at 31 December 2018. It includes the estimated costs of restoring the underlying assets to the condition required by the lease terms and conditions. For the Santander UK group, the application of IFRS 16 at 1 January 2019 is expected to increase property, plant and equipment by £211m (being the net increase in ROU assets referred to above), reduce other assets by £12m, increase other liabilities by £182m from recognising lease liabilities, and increase provisions by £17m. There is expected to be no impact on shareholders’ equity. In arriving at the estimated impact, as well as excluding leases whose terms end within 12 months, the Santander UK group applies a single discount rate to a portfolio of leases with similar remaining lease terms. 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 • Amendment to IAS 12 ‘Income Taxes’ (part of ‘Annual Improvements to IFRS Standards 2015-2017 Cycle’) – In December 2017, as part of its annual improvements project, the IASB issued an amendment to IAS 12 to clarify 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 is applied retrospectively and is effective for annual reporting periods beginning on or after 1 January 2019, is awaiting EU endorsement at the time of approving these Consolidated Financial Statements. The effects of the amendment are expected to lead to a reduction in the effective tax rate where the tax relief on coupons in respect of AT1 capital securities would be recognised in the income statement rather than in equity. 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 has (i) 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 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. Interests in subsidiaries in the Company unconsolidated financial statements are held at cost subject to impairment. 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 (including foreign branch operations) 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 FVOCI (2017: available-for-sale), 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) 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) and interest expense on financial liabilities other than those at fair value through profit or loss (FVTPL) is determined using the effective interest rate method. 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 date for equity securities. 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.
Share-based payments	Share-based payments The Santander UK group engages in cash-settled and equity-settled share-based payment transactions in respect of services received from certain of its employees. Shares of the Santander UK group’s parent, Banco Santander SA are purchased in the open market by the Santander UK group (for the Employee Sharesave scheme) or are purchased by Banco Santander SA or another Banco Santander company (for awards granted under the Long-Term Incentive Plan and the Deferred Shares Bonus Plan) to satisfy share options as they vest. 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 payment transactions. 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 goods or services received is recognised at the fair value determined at each balance sheet date for cash-settled share-based payments. A liability equal to the amount to be reimbursed to Banco Santander SA is recognised at the fair value determined at the grant date for equity-settled share-based payments. 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 non-market 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 at each balance sheet date, 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 basis over their useful life of three to seven years, unless the software is an integral part of the related computer hardware, in which case it is treated as property, plant and equipment as described below. Capitalisation of costs ceases when the software is capable of operating as intended. Costs of maintaining software are expensed as incurred.
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 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 Depreciation is not charged on freehold land and assets under construction.
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 fair value through profit or loss 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 From 1 January 2018, the Santander UK group has applied IFRS 9 Financial Instruments and 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 14. 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, financial liabilities held for trading 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 basis the ECL associated with its debt instrument assets carried at amortised cost and FVOCI and with the exposure arising from financial guarantee contracts and loan commitments. The Santander UK group recognises a loss allowance for such losses at each reporting date. The measurement of ECL reflects: • 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 factors and circumstances. We then probability-weight the net present value of the cash flows under each scenario to arrive at a weighted average provision requirement. We update our assessment process every quarter and more frequently if there are changes in circumstances that might affect the scenarios, cash flows or probabilities we apply. 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 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 All write-offs are assessed / made on a case-by-case write-off, write-off write-off 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. The Santander UK group has not provided any commitment to provide loans at a below-market interest rate, or that can be settled net in cash or by delivering or issuing another financial instrument. 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 and foreign currency risk on its fixed rate debt issuances denominated in foreign currency. Cash flow hedging is used to hedge the variability in cash flows arising from both these risks.
Impairment of non-financial assets	Impairment of non-financial 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 unit’s fair value less costs to sell and its value in use. The cash-generating unit represents the lowest level at which non-financial 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 RV. Operating lease rental income and depreciation is recognised on a straight-line basis over the life of the asset. 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 so as 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 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.
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 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 represent amounts held at the Bank of England and the US Federal Reserve 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, based on conclusions regarding the number of claims that will be received, including 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. Provisions include amounts in respect of irrevocable loan commitments. The provision is the present value of the difference between the contractual cash flows based on the expected drawdowns and the cash flows that the Santander UK group expects to receive. 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, Santander UK group adopted IFRS 9, which replaced IAS 39. In accordance with the transition requirements of IFRS 9, comparatives were not restated. The accounting policies applied in accordance with IAS 39 for periods before the adoption of IFRS 9 are set out below: 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, available-for-sale held-to-maturity available-for-sale, available-for-sale held-to-maturity a) Financial assets and liabilities at fair value through profit or loss Financial assets and financial liabilities are classified as FVTPL if they are either held for trading or otherwise designated at FVTPL on initial recognition. 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, financial assets and financial liabilities other than those that are held for trading are designated at FVTPL where this results in more relevant information 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 or liabilities are managed and their performance evaluated on a fair value basis, or where a financial asset or financial liability contains one or more embedded derivatives which are not closely related to the host contract. 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. b) Loans and receivables Loans and receivables are non-derivative available-for-sale c) Available-for-sale Available-for-sale non-derivative available-for-sale d) Held-to-maturity Held-to-maturity non-derivative available-for-sale. held-to-maturity held-to-maturity available-for-sale 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, a) Assets carried at amortised cost For loans and advances, loans and receivables securities and held-to-maturity held-to-maturity Subsequent to the recognition of an impairment loss on a financial asset or a group of financial assets, interest income continues to be recognised on an effective interest rate basis, on the asset’s carrying value net of impairment provisions. If, in a subsequent period, the amount of the impairment loss decreases and the decrease can be related objectively to an event occurring after the impairment was recognised (such as an improvement in the debtor’s credit rating), the reversal of the previously recognised impairment loss is recognised in profit or loss. Impairment allowances are assessed individually for financial assets that are individually significant. Impairment allowances for portfolios of smaller balance homogenous loans such as most residential mortgages, personal loans and credit card balances that are below the individual assessment thresholds, and for loan losses that have been incurred but not separately identified at the balance sheet date, are determined on a collective basis. Individual assessment For individually assessed assets, the Santander UK group measures the amount of the loss as the difference between the carrying amount of the asset and the present value of the estimated future cash flows from the asset discounted at the asset’s original effective interest rate. The factors considered in determining whether a loan is individually significant for the purpose of assessing impairment include the size of the loan, the number of loans in the portfolio, the importance of the individual loan relationship and how this is managed. Potential indicators of loss events which may be evidence of impairment for retail borrowers may include missed payments of capital and interest and borrowers notifying the Santander UK group of current or likely financial stress. For corporate assets, when a specific observed impairment is established, the asset is transferred to the Corporate & Commercial Banking Restructuring & Recoveries team. As part of their impairment reviews, an assessment is undertaken of the expected future cash flows (including, where appropriate, cash flows through enforcement of any applicable security held) in relation to the relevant asset, discounted at the loan’s original effective interest rate. The result is compared to the current carrying value of the asset. Any shortfall evidenced as a result of such a review will be assessed and recorded as an observed specific loss allowance. Collective assessment In making a collective assessment for impairment, financial assets are grouped together according to their credit risk characteristics. These can include grouping by product, loan-to-value, sub-segment Observed impairment loss allowance An impairment loss allowance for observed losses is established for all NPLs where it is increasingly probable that some of the capital or interest will not be repaid or recovered through enforcement of any applicable security. The allowance for observed losses is determined on a collective (or portfolio) basis for groups of loans with similar credit risk characteristics. For more on the definition of NPLs, see ‘Credit risk management – risk measurement and control’ in the Risk review. For mortgages and other secured advances, the allowance for observed losses is calculated as the product of the account outstanding balance (exposure) at the reporting date, the estimated proportion that will be repossessed (the loss propensity) and the percentage of exposure which will result in a loss (the loss ratio). The loss propensities for the observed segment (i.e. where the loan is classified as non-performing) IBNO impairment loss allowances An allowance for IBNO losses is established for loans which are either: • Performing and no evidence of loss has been specifically identified on an individual basis but because the loans that are not yet past due are known from past experience to have deteriorated since the initial decision to lend was made (for example, where a borrower has not yet missed a payment but is experiencing financial difficulties at the reporting date, for example due to a loss of employment, divorce or bereavement), or • In arrears and not classified as non-performing. The impairment loss calculation resembles the one explained above for the observed segment except that for the IBNO segment, where the account is currently up to date, the loss propensity represents the percentage of such cases that are expected to miss a payment in the appropriate emergence period and which will ultimately be written off. Where the account is delinquent, the loss propensity represents the percentage of such cases that will ultimately be written off. b) Loans and receivables securities and held-to-maturity Loans and receivables securities and held-to-maturity Loans and receivables securities and held-to-maturity c) Assets classified as available-for-sale The Santander UK group assesses at each balance sheet date whether there is objective evidence that an available-for-sale If, in a subsequent period, the fair value of a debt instrument classified as available-for-sale available-for-sale
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 2018, the probability-weighted ECL allowance totalled £807m, of which £789m related to exposures in Retail Banking, Corporate & Commercial Banking and Corporate Centre, and £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 stage allocation used to determine the ECL allowance shown above. For exposures subject to individual assessment, the distribution of ECL which could reasonably be expected has also been considered, assuming no change in the number of cases subject to individual assessment, and within the context of a potential best to worst case outcome. Upside 2 Upside 1 Base case Downside 1 Downside 2 Retail Banking, Corporate & Commercial Banking and Corporate Centre £m £m £m £m £m ECL 554 596 648 843 1,930 Upside Base case Downside Corporate & Investment Banking (1) £m £m £m ECL 8 17 27 (1) As described in more detail in the ‘Santander UK Group Level – Credit Risk Management’ section, our Corporate & Investment Banking segment uses three forward-looking economic scenarios, whereas our other segments use five scenarios. The results of the 100% weighting ECL for the Corporate & Investment Banking segment are therefore presented separately. 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 £237m at 31 December 2018 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 +10% -10% -20% +20% £m £m £m Increase/(decrease) in profit before tax 20 12 (20 ) (52 ) b) Provisions (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. In setting the provision, management estimated the total claims that were likely to be received to the end of the time-bar 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, which include the level of complaints expected to be received, of those, the number that will be upheld and redressed (reflecting legal and regulatory responsibilities, including the determination of liability and the effect of the time bar), as well as the redress costs for each of the different populations of customers identified. These are described in more detail in the ‘PPI assumptions’ section in Note 30. Sensitivity of PPI conduct remediation provision We made no additional provision charges for PPI conduct remediation relating to past activities and products sold recognised in 2018 (2017: £109m, 2016: £144m). The balance sheet provision amounted to £246m (2017: £356m, 2016: £457m). Detailed disclosures on the provision for PPI conduct remediation can be found in Note 30. 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. Detailed disclosures on the assumptions used, including sensitivities, can be found in Note 30. (ii) Other As set out in Note 30, an amount of £58m (2017: £nil) was charged in 2018 and arose from a systems-related historical issue identified by Santander UK, relating to compliance with certain requirements of the Consumer Credit Act (CCA). 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 2018 of potential costs in respect of the identified issue. However, as detailed in Note 32, these reviews and the related analysis are not yet complete, such that the approach and timing to any remediation has not yet been finalised, although it is expected to commence in 2019. c) Pensions The Santander UK group operates a number of defined benefit pension schemes as described in Note 31 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 31. Sensitivity of defined benefit pension scheme estimates The defined benefit pension schemes which were in a net asset position at 31 December 2018 had a surplus of £842m (2017: £449m) and the defined benefit pension schemes which were in a net liability position at 31 December 2018 had a deficit of £115m (2017: £286m). 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 31.
Santander UK Group Holdings plc [member]
Statement [LineItems]
Basis of preparation	Basis of preparation This basis of preparation differs from that applied in the Consolidated Financial Statements. See Note 1 to the Consolidated Financial Statements for details of the periods for which the Consolidated Financial Statements have been prepared. The accounting policies of the Company are the same as those of the Santander UK Group Holdings plc group which are set out in Note 1 to the Consolidated Financial Statements, to the extent that the Company has similar transactions to the Santander UK Group Holdings plc group. The financial statements have been prepared on the going concern basis using the historical cost convention. An assessment of the appropriateness of the adoption of the going concern basis of accounting is disclosed in the Directors’ statement of going concern set out in the Directors’ Report. Compliance with International Financial Reporting Standards The Company’s financial statements have been prepared in accordance with International Financial Reporting Standards as issued by the IASB, including interpretations issued by the IFRS Interpretations Committee (IFRIC) of the IASB (together IFRS). The Company has also complied with IFRS as adopted by the European Union as there are no applicable differences between the two frameworks for the period presented.

Credit risk (Tables)

Credit risk (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Summary of Annual Growth Rates	The annual growth rates over the 5 year forecast for each of our scenarios are: Upside 2 Upside 1 Base case Downside 1 Downside 2 Assumption % % % % % House price index (1) 3.40 2.30 2.00 (2.00 ) (9.50 ) GDP (1) 2.50 2.10 1.60 0.70 0.30 Unemployment rate 2.80 3.80 4.30 6.90 8.60 Interest rate 1.00 1.25 1.50 2.50 2.25 (1) Compound annual growth rate
Summary of Residential Mortgages by Loan Size	The mortgage asset stock of larger loans was: South East including London UK Individual mortgage loan size 2018 £m 2017 2018 £m 2017 <£0.25m 45,851 46,766 105,181 106,838 £0.25m to £0.50m 30,488 27,562 39,841 36,036 £0.50m to £1.0m 10,103 9,214 11,551 10,532 £1.0m to £2.0m 1,168 1,046 1,236 1,111 >£2.0m 146 163 148 165 87,756 84,751 157,957 154,682
Summary of Types of Credit Risk Mitigation	The types of credit risk mitigation, including collateral, across each of our portfolios is: Portfolio Description Residential mortgages 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. Business banking 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 secured against a tangible asset. 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. Consumer (auto) 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. Unsecured lending 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.
Summary of Exposures to Credit Risk in Business Segments	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, treasury products, and treasury markets activities. •  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, as well as sovereigns and other international organisations. •  Exposures include sovereign and other international organisation assets that we hold for liquidity.
Types Of Customers And HowTo 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 across the lifecycle 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 corporate clients) and Corporate Centre (for our 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 analysts who specialise in this type of risk. •  We manage risk through expert analysis. We support this with decision-making tools based on internal risk assessment models.
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 non–performing by portfolio at 31 December 2018 and 2017. Committed exposure Watchlist Non– Fully Enhanced Proactive performing Loss performing monitoring management exposure (1) Total (2) allowances (3) 2018 £m £m £m £m £m £m 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 Sovereign and Supranational 4,200 — — — 4,200 — Large Corporate 15,304 548 186 26 16,064 18 Financial Institutions 3,814 — — — 3,814 — 23,318 548 186 26 24,078 18 Corporate Centre Sovereign and Supranational 34,604 — — — 34,604 — Structured Products 4,840 — — — 4,840 — Social Housing 4,321 22 — — 4,343 — Legacy Portfolios in run–off 809 26 7 16 858 13 Derivatives 147 — — — 147 — Crown Dependencies 281 — — 2 283 — 45,002 48 7 18 45,075 13 Total loss allowances (3) 213 2017 Corporate & Commercial Banking SME and mid corporate 11,185 815 296 334 12,630 128 Commercial Real Estate 8,254 160 133 59 8,606 27 Social Housing 3,274 — — — 3,274 — 22,713 975 429 393 24,510 155 Corporate & Investment Banking Sovereign and Supranational 4,355 — — — 4,355 — Large Corporate 20,757 284 8 390 21,439 236 Financial Institutions 6,354 1 100 — 6,455 — 31,466 285 108 390 32,249 236 Corporate Centre Sovereign and Supranational 44,495 — — — 44,495 — Structured Products 4,379 — — — 4,379 — Social Housing 5,972 4 — — 5,976 — Legacy Portfolios in run–off 977 22 6 20 1,025 6 Derivatives 212 — — — 212 — Crown Dependencies 261 — — 1 262 — 56,296 26 6 21 56,349 6 Total observed impairment loss allowances 397 Allowance for IBNO (4) 52 Total loss allowances 449 (1) Non–performing exposure includes committed facilities and derivative exposures. So it can exceed NPLs which only include on-balance (2) Includes committed facilities and derivatives. We define ‘Enhanced Monitoring’ and ‘Proactive Management’ in the ‘Monitoring‘ section. (3) Loss allowances for 2017 were on an incurred loss basis per IAS 39, whilst for 2018 they are on an ECL basis per IFRS 9. The ECL allowance is for both on and off–balance sheet exposures. (4) Allowance for IBNO losses as described in Note 1 to the Consolidated Financial Statements.
Summary of Other Segments by Forbearance Applied	Forbearance We only make forbearance arrangements for lending to customers. The balances at 31 December 2018 and 2017, analysed by their staging (2017: payment status) at the year–end and the forbearance we applied, were: 2018 2017 Corporate & Corporate & Corporate & Corporate & Commercial Investment Corporate Commercial Investment Corporate Banking Banking Centre Banking Banking Centre (1) £m £m £m £m £m £m Stock: (1) – Term extension 67 42 — 136 55 — – Interest–only 112 — 8 152 — 14 – Other payment rescheduling 163 26 10 127 299 13 342 68 18 415 354 27 Of which: – Stage 1 43 — 3 – Stage 2 78 42 8 – Stage 3 221 26 7 – NPL 273 347 11 – Performing 142 7 16 342 68 18 415 354 27 Proportion of portfolio 1.5 % 0.3 % 2.1 % 1.7 % 1.1 % 2.6 % (1) We base forbearance type on the first forbearance we applied. Tables only show accounts open at the year–end. Amounts are drawn balances and include off balance sheet balances.
Summary of Commercial Real Estate by Loan to Value	The table below shows the LTV distribution for our CRE loan stock and NPL stock (based on the drawn balance and our latest estimate of the property’s current value) of the portfolio at 31 December 2018 and 2017. 2018 2017 Total stock NPL stock Total Stock NPL stock Loans and advances to customers £m % £m % £m % £m % <=50% 3,663 56 3 11 4,146 51 6 9 >50–70% 2,039 32 4 14 3,035 37 2 3 >70–100% 47 1 1 3 36 — 1 1 >100% i.e. negative equity 18 — 16 55 52 1 48 70 Standardised portfolio (1) 631 10 5 17 629 8 12 17 Total with collateral 6,398 99 29 100 7,898 97 69 100 Development loans 61 1 — — 246 3 — — 6,459 100 29 100 8,144 100 69 100 (1) Smaller value transactions, mainly commercial mortgages.
Summary of Commercial Real Estate by Sector	Sector analysis 2018 2017 Sector £m % £m % Office 1,556 24 2,181 27 Retail 1,004 16 1,389 17 Industrial 888 14 1,176 14 Residential 927 14 1,001 12 Mixed use 932 14 1,146 14 Student accommodation 123 2 133 2 Hotels and leisure 309 5 304 4 Other 89 1 185 2 Standardised portfolio (1) 631 10 629 8 6,459 100 8,144 100 (1) Smaller value transactions, mainly commercial mortgages.
Summary of Key Metrics to Measure and Control Credit Risk	We use a number of key metrics to measure and control credit risk, as follows: Metric Description 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. 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. Non-Performing We use NPLs to monitor how our portfolios behave. We classify loans as NPLs when customers do not make a payment for three months or more, or if we have data to make us doubt they can keep up with their payments. There are differences between NPL and Stage 3, which we set out in the ‘Definition of default used for NPL’ section below. Although we adopted IFRS 9 from 1 January 2018, we continued to monitor NPLs as a key metric in 2018 as the NPL ratio was one of Santander UK’s Key Performance Indicators for 2016-2018.
Summary of Probability Weightings Applied to Scenarios	The probability weights we applied to the scenarios are: Scenario type Probability % Upside 2 5 Upside 1 15 Base case 40 Downside 1 30 Downside 2 10
Summary of Quantitative Criteria to Measure Significant Increase in Credit Risk	For each portfolio, the quantitative criteria are: Retail Banking (1) Consumer (auto) Other unsecured Corporate & Corporate & Mortgages finance (2) Personal loans (2) Credit cards Overdrafts Commercial Banking (2) Investment Banking 30bps 300bps 400bps 340bps 260bps 400bps Internal rating method (1) In Business banking, for larger customers we apply the same criteria that we use for Corporate & Commercial Banking. (2) Consumer (auto) finance, Personal loans and Corporate & Commercial Banking use the comparison of lifetime PDs to determine Stage allocation, unlike other products which first turn the lifetime PD into an average yearly PD (annualised) and then do the comparison.
Summary of Qualitative Criteria to Measure Significant Increase in Credit Risk	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 qualitative criteria are: Retail Banking (1) Consumer (auto) Other unsecured Corporate & Corporate & Mortgages finance Personal loans Credit cards Overdrafts Commercial Banking Investment Banking In forbearance Default in last 24m In forbearance Deceased or Insolvent In Collections Default in last 12m In Fees In Watchlist – >30 Days past due (DPD) in last 12m Court ‘Return of goods’ order or Police watchlist NPL in last 12m In Debit NPL in last Bankrupt Agreement terminated Default at £100+ arrears Payment holiday £50+ arrears £100+ Any Cash Collection Behaviour (1) In Business banking, for larger customers we apply the same criteria that we use for Corporate & Commercial Banking.
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 (2017: IAS 39) are applied. Maximum exposure Balance sheet asset Off-balance sheet Collateral (1) 2018 Gross Loss (2) Net Gross Loss (2) £bn Net Cash Non-cash Netting (3) Net exposure Cash and balances at central banks 24.2 — 24.2 — — — — — — 24.2 Financial assets at amortised cost: – Loans and advances to customers: (4) – Loans secured on residential properties (5) 158.2 (0.2 ) 158.0 11.2 — 11.2 — (164.1 ) — 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 202.4 (0.7 ) 201.7 40.0 (0.1 ) 39.9 (0.1 ) (191.0 ) — 50.5 – Loans and advances to banks 3.5 — 3.5 1.6 — 1.6 — — — 5.1 – Reverse repurchase agreements – non trading (6) 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: 234.2 (0.7 ) 233.5 41.6 (0.1 ) 41.5 (0.1 ) (209.4 ) (2.7 ) 62.8 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 271.7 (0.7 ) 271.0 41.7 (0.1 ) 41.6 (0.1 ) (209.4 ) (2.7 ) 100.4 2017 Cash and balances at central banks 32.8 — 32.8 — — — — 32.8 Loans and advances to customers: (4) (6) – Advances secured on residential property (5) 155.4 (0.2 ) 155.2 12.4 — (167.4 ) — 0.2 – Corporate loans 30.9 (0.5 ) 30.4 17.1 — (21.8 ) — 25.7 – Finance leases 6.7 — 6.7 0.6 (0.1 ) (5.8 ) — 1.4 – Other unsecured loans 6.2 (0.2 ) 6.0 11.1 — (0.1 ) — 17.0 – Amounts due from fellow Banco Santander group subsidiaries and joint ventures 1.2 — 1.2 — — — — 1.2 Total loans and advances to customers (6) 200.4 (0.9 ) 199.5 41.2 (0.1 ) (195.1 ) — 45.5 Loans and advances to banks (6) 3.5 — 3.5 1.6 — — — 5.1 Reverse repurchase agreements – non trading (6) 2.6 — 2.6 — — (2.5 ) — 0.1 Financial investments: – Loans and receivables securities (4) 2.2 — 2.2 0.7 — — — 2.9 – Available–for–sale debt securities 8.8 — 8.8 — — — — 8.8 – Held–to–maturity debt securities 6.5 — 6.5 — — — — 6.5 Total financial investments 17.5 — 17.5 0.7 — — — 18.2 Total 256.8 (0.9 ) 255.9 43.5 (0.1 ) (197.6 ) — 101.7 (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) Loss allowances for 2017 were on an incurred loss basis per IAS 39, whilst for 2018 they are on an ECL basis per IFRS 9. The loss allowance for off–balance sheet assets is classified in the balance sheet in provisions – other liabilities. (3) 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. (4) Balances include interest we have charged to the customer’s account and accrued interest that we have not charged to the account yet. (5) 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. (6) From 1 January 2018, the non-trading re-presented
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 gross Collateral (1) Net amount Cash Non-cash Netting (2) exposure 2018 £bn £bn £bn £bn £bn Financial assets at FVTPL – Derivative financial instruments 5.3 — (2.1 ) (0.9 ) 2.3 – Other financial assets at FVTPL 6.1 — (2.3 ) — 3.8 Total 11.4 — (4.4 ) (0.9 ) 6.1 2017 Financial assets designated at fair value – Trading assets: – Securities repurchased under resale agreements 8.9 — (8.5 ) (0.4 ) — – Debt securities 5.2 — — — 5.2 – Cash collateral 6.2 — — — 6.2 – Short–term loans 0.7 — — — 0.7 – Total trading assets 21.0 — (8.5 ) (0.4 ) 12.1 – Derivative financial instruments 19.9 (2.8 ) — (14.8 ) 2.3 – Financial assets designated at fair value: – Loans and advances to customers 1.6 — (1.6 ) — — – Debt securities 0.5 — — — 0.5 Total financial assets designated at fair value 2.1 — (1.6 ) — 0.5 Total 43.0 (2.8 ) (10.1 ) (15.2 ) 14.9 (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.
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 (2017: IAS 39) 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 2018 9 £bn 8 £bn 7 £bn 6 £bn 5 £bn 4 £bn 3 to 1 £bn Other (1) £bn Loss (2) Total £bn Cash and balances at central banks 24.2 — — — — — — — — 24.2 – Stage 1 24.2 — — — — — — — — 24.2 Financial assets at amortised cost: – Loans and advances to customers (3) 10.0 27.5 72.4 51.6 20.3 11.4 6.3 2.9 (0.7 ) 201.7 – Stage 1 10.0 27.5 72.2 50.3 17.6 6.9 1.1 2.8 (0.1 ) 188.3 – 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 – Loans and advances to banks 0.9 0.2 1.4 — — — — 1.0 — 3.5 – Stage 1 0.9 0.2 1.4 — — — — 1.0 — 3.5 – Reverse repo agreements – non trading (4) 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 33.3 31.5 75.1 52.0 20.3 11.4 6.3 4.3 (0.7 ) 233.5 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 exposures 64.1 37.3 75.8 52.0 20.3 11.4 6.3 4.5 (0.7 ) 271.0 Off–balance sheet exposures 0.7 8.0 8.9 9.0 5.4 1.3 0.5 7.9 (0.1 ) (5) 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 64.8 45.3 84.7 61.0 25.7 12.7 6.8 12.4 (0.8 ) 312.6 2017 Cash and balances at central banks 31.8 — — — — — — 1.0 — 32.8 Loans and advances to banks 1.3 0.2 0.7 — — — — 1.3 — 3.5 Loans and advances to customers: (3) – Loans secured on residential property 3.2 26.7 75.2 35.2 6.2 4.5 4.4 — (0.2 ) 155.2 – Corporate loans 1.7 5.1 2.1 4.6 9.6 5.1 1.5 1.3 (0.5 ) 30.5 – Finance leases — — 0.4 1.3 2.0 1.8 1.1 0.1 (0.1 ) 6.6 – Other unsecured loans — 0.1 0.8 1.6 1.6 0.7 0.5 0.9 (0.2 ) 6.0 – Amounts due from fellow Banco Santander group subsidiaries and JVs — — — — — — — 1.2 — 1.2 Total loans and advances to customers 4.9 31.9 78.5 42.7 19.4 12.1 7.5 3.5 (1.0 ) 199.5 Reverse repo agreements – non trading (4) — 1.5 0.4 0.4 — — — 0.1 — 2.4 Financial investments: – Loans and receivables securities (2) 1.9 0.1 0.2 — — — — — — 2.2 – Available–for–sale debt securities 6.5 1.9 0.4 — — — — — — 8.8 – Held–to–maturity debt securities 6.5 — — — — — — — — 6.5 Total financial investments 14.9 2.0 0.6 — — — — — — 17.5 Total 52.9 35.6 80.2 43.1 19.4 12.1 7.5 5.9 (1.0 ) 255.7 (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) Loss allowances for 2017 were on an incurred loss basis per IAS 39, whilst for 2018 they are on an ECL basis per IFRS 9. (3) Includes interest we have charged to the customer’s account and accrued interest we have not charged to the account yet. (4) From 1 January 2018, the non-trading non-trading (5) 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 ‘IFRS 9 Credit Quality’ section.
Summary of Credit Performance	The customer loans in the tables below and in the remainder 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 Gross write- Loss loans NPLs (1)(2) NPL ratio (3) offs allowances (4) 2018 £bn £m % £m £m Retail Banking: 172.8 2,126 1.23 182 594 - of which mortgages 158.0 1,907 1.21 18 237 Corporate & Commercial Banking 17.7 264 1.49 97 182 Corporate & Investment Banking 4.6 — — 252 18 Corporate Centre 4.8 18 0.38 3 13 199.9 2,408 1.20 534 807 2017 Retail Banking: 168.7 2,104 1.25 195 491 - of which mortgages 154.7 1,867 1.21 22 225 Corporate & Commercial Banking 19.4 383 1.97 35 195 Corporate & Investment Banking 6.0 340 5.67 — 236 Corporate Centre 6.2 21 0.34 23 18 200.3 2,848 1.42 253 940 Of which: Corporate lending 2018 24.1 353 1.46 364 253 2017 27.3 838 3.07 56 485 (1) We define NPLs in the ‘Credit risk management’ section. (2) All NPLs (excluding personal bank accounts) continue accruing interest. (3) NPLs as a percentage of customer loans. (4) Loss allowances for 2017 were on an incurred loss basis per IAS 39, whilst for 2018 they are on an ECL basis per IFRS 9. The ECL allowance is for both on and off–balance sheet exposures.
Summary of IFRS 9 Credit Quality	Stage 2 31 December 2018 (unaudited) Average PD (1) % Stage 1 £m £ 30 DPD £m >30 DPD £m Sub total £m Stage 3 (2) £m Total £m Exposures On-balance Retail Banking 0.53 160,212 9,375 949 10,324 2,211 172,747 – of which mortgages 0.48 146,619 8,466 890 9,356 1,982 157,957 Corporate & Commercial Banking 0.92 16,394 1,044 — 1,044 264 17,702 Corporate & Investment Banking 0.36 29,177 78 — 78 — 29,255 Corporate Centre 0.14 49,368 122 11 133 16 49,517 Total on-balance 255,151 10,619 960 11,579 2,491 269,221 Off–balance sheet Retail Banking (3) 22,819 196 — 196 43 23,058 – of which mortgages (3) 11,120 76 — 76 17 11,213 Corporate & Commercial Banking 4,939 182 — 182 12 5,133 Corporate & Investment Banking 12,923 56 — 56 26 13,005 Corporate Centre 531 — — — — 531 Total off–balance sheet (4) 41,212 434 — 434 81 41,727 Total exposures 296,363 11,053 960 12,013 2,572 310,948 ECL On-balance Retail Banking 84 217 39 256 228 568 – of which mortgages 10 98 20 118 106 234 Corporate & Commercial Banking 31 26 — 26 111 168 Corporate & Investment Banking 1 1 — 1 — 2 Corporate Centre 5 3 — 3 5 13 Total on-balance 121 247 39 286 344 751 Off–balance sheet Retail Banking 12 13 — 13 1 26 – of which mortgages 2 1 — 1 — 3 Corporate & Commercial Banking 6 6 — 6 2 14 Corporate & Investment Banking 4 2 — 2 10 16 Total off–balance sheet 22 21 — 21 13 56 Total ECL 143 268 39 307 357 807 Coverage ratio (5) % % % % % % On-balance Retail Banking 0.1 2.3 4.1 2.5 10.3 0.3 – of which mortgages — 1.2 2.2 1.3 5.3 0.1 Corporate & Commercial Banking 0.2 2.5 — 2.5 42.0 0.9 Corporate & Investment Banking — 1.3 — 1.3 — — Corporate Centre — 2.5 — 2.3 31.3 — Total on-balance — 2.3 4.1 2.5 13.8 0.3 Off–balance sheet Retail Banking 0.1 6.6 — 6.6 2.3 0.1 – of which mortgages — 1.3 — 1.3 — — Corporate & Commercial Banking 0.1 3.3 — 3.3 16.7 0.3 Corporate & Investment Banking — 3.6 — 3.6 38.5 0.1 Total off-balance 0.1 4.8 — 4.8 16.0 0.1 Total coverage — 2.4 4.1 2.6 13.9 0.3 (1) Average IFRS 9 PDs are 12-month, (2) Stage 3 exposures under IFRS 9 and NPLs used in our NPL ratio metric are subject to different criteria. These criteria are under review in parallel with the ongoing regulatory changes to the default definition. (3) Off-balance (4) Off-balance Stage 2 analysis Exposure 31 December 2018 £m Currently in arrears 960 Currently up–to–date: – PD deterioration 8,509 – Other (1) 2,544 Total Stage 2 12,013 (1) Mainly due to forbearance. Total on-balance Stage 2 1 January 2018 (unaudited) Average PD (1) % Stage 1 £m £ 30 DPD £m >30 DPD £m Sub total £m Stage 3 (2) £m Total £m Exposures On-balance Retail Banking 0.61 155,845 9,537 1,120 10,657 2,222 168,724 – of which mortgages 0.55 142,940 8,765 991 9,756 1,986 154,682 Corporate & Commercial Banking 0.79 18,362 575 71 646 383 19,391 Corporate & Investment Banking 0.17 11,684 93 — 93 340 12,117 Corporate Centre 0.07 56,325 172 38 210 20 56,555 Total on-balance 242,216 10,377 1,229 11,606 2,965 256,787 Off–balance sheet Retail Banking (3) 23,133 223 5 228 41 23,402 – of which mortgages (3) 12,215 126 2 128 18 12,361 Corporate & Commercial Banking 4,055 211 9 220 5 4,280 Corporate & Investment Banking 14,899 16 — 16 32 14,947 Corporate Centre 830 40 — 40 — 870 Total off–balance sheet (4) 42,917 490 14 504 78 43,499 Total exposures 285,133 10,867 1,243 12,110 3,043 300,286 ECL On-balance Retail Banking 97 206 28 234 266 597 – of which mortgages 20 113 16 129 121 270 Corporate & Commercial Banking 38 17 8 25 173 236 Corporate & Investment Banking 8 — — — 242 250 Corporate Centre 7 2 2 4 8 19 Total on-balance 150 225 38 263 689 1,102 Off-balance Retail Banking 13 13 — 13 2 28 – of which mortgages — 2 — 2 — 2 Corporate & Commercial Banking 5 8 — 8 — 13 Corporate & Investment Banking 8 — — — — 8 Total off-balance 26 21 — 21 2 49 Total ECL 176 246 38 284 691 1,151 Coverage ratio (5) % % % % % % On-balance Retail Banking 0.1 2.2 2.5 2.2 12.0 0.4 – of which mortgages — 1.3 1.6 1.3 6.1 0.2 Corporate & Commercial Banking 0.2 3.0 11.3 3.9 45.2 1.2 Corporate & Investment Banking 0.1 — — — 71.2 2.1 Corporate Centre — 1.2 5.3 1.9 40.0 — Total on-balance 0.1 2.2 3.1 2.3 23.2 0.4 Off-balance Retail Banking 0.1 5.8 — 5.7 4.9 0.1 – of which mortgages — 1.6 — 1.6 — — Corporate & Commercial Banking 0.1 3.8 — 3.6 — 0.3 Corporate & Investment Banking 0.1 — — — — 0.1 Total off-balance 0.1 4.3 — 4.2 2.6 0.1 Total coverage 0.1 2.3 3.1 2.3 22.7 0.4 (1) Average IFRS 9 PDs are 12-month, (2) Stage 3 exposures under IFRS 9 and NPLs used in our NPL ratio metric are subject to different criteria. These criteria are under review in parallel with the ongoing regulatory changes to the default definition. (3) Off-balance (4) Off-balance
Summary of Stage 2 Decomposition	Stage 2 analysis Exposure 31 December 2018 £m Currently in arrears 960 Currently up–to–date: – PD deterioration 8,509 – Other (1) 2,544 Total Stage 2 12,013 (1) Mainly due to forbearance.
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 2018 Exposures Loss Net carrying £m Exposures Loss 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 29,255 2 29,253 13,005 16 Corporate Centre 49,517 13 49,504 531 — Total exposures presented in IFRS 9 Credit Quality tables 269,221 751 268,470 41,727 56 Other items (1) 2,501 Adjusted net carrying amount 270,971 Assets classified at FVTPL 11,458 Non-financial assets 6,952 Total assets per the Consolidated Balance Sheet at 31 December 2018 289,381 (1) These assets carry low credit risk and therefore have an immaterial ECL.
Summary of ECL Reconciliation	The following table shows changes in total exposures subject to ECL assessment, and the corresponding ECL, during the year. The table presents total gross carrying amounts and ECLs at a Santander UK group level. We present segmental views in the sections below. Non-credit Credit impaired Stage 1 Subject to 12-month ECL Stage 2 Stage 3 Total Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL At 1 January 2018 285,133 176 12,110 284 3,043 691 300,286 1,151 Change in economic scenarios (2) — 4 — (12 ) — (8 ) — (16 ) Changes to model — (1 ) — 2 — (8 ) — (7 ) Transfer to lifetime ECL (not–credit impaired) (3) (4,190 ) (11 ) 4,190 11 — — — — Transfer to credit impaired (3) (445 ) (8 ) (603 ) (23 ) 1,048 31 — — Transfer to 12–month ECL ((3) 3,325 68 (3,325 ) (68 ) — — — — Transfer from credit impaired (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 New assets originated or purchased (5) 85,933 43 1,087 34 19 13 87,039 90 Other (6) (19,867 ) (20 ) (295 ) (11 ) 52 170 (20,110 ) 139 Assets derecognised – closed good (7) (53,543 ) (51 ) (1,594 ) (20 ) (474 ) (44 ) (55,611 ) (115 ) Assets derecognised – written off (7) — — — — (656 ) (534 ) (656 ) (534 ) At 31 December 2018 296,363 143 12,013 307 2,572 357 310,948 807 Net movement in the year 11,230 (33 ) (97 ) 23 (471 ) (334 ) 10,662 (344 ) Income statement charge/(release) for the year (33 ) 23 200 190 Recoveries net of collection costs — — (36 ) (36 ) Charge/(release) to the Income Statement (33 ) 23 164 154 (1) Exposures that have attracted an ECL, and as reported in the IFRS 9 Credit Quality table above. (2) Changes to assumptions from the start of the year to the end of 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 each Stage 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 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. Includes the impact of changes in risk parameters in the year, repayments, draw downs on accounts open at the start and end of 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.
Summary of Country Risk Explosures	The tables below exclude balances with other Banco Santander companies. We show them separately in the ‘Balances with other Banco Santander companies’ section. 2018 2017 Financial Financial Governments Government Banks (1) Other £bn Retail Corporate £bn Total (2) £bn Governments Government Banks (1) Other Retail Corporate Total (2) Eurozone Ireland — — — 12.3 — 0.4 12.7 — — 0.2 1.1 — 0.8 2.1 Italy — — — 0.1 — 0.2 0.3 0.4 — — 0.1 — 0.1 0.6 Spain (excl. Santander) — — — 0.2 — — 0.2 — — 0.3 0.1 — 0.1 0.5 Portugal — — — — — — — — — 0.1 — — — 0.1 France — — 1.0 — — — 1.0 — 0.3 2.0 0.2 — 2.2 4.7 Germany — — 1.6 — — — 1.6 — — 2.8 — — 0.1 2.9 Luxembourg — — — 0.9 — 0.2 1.1 — — — 1.3 — 0.4 1.7 Other (3) 0.3 — 1.2 0.2 — 1.1 2.8 0.3 — 1.1 0.2 — 1.4 3.0 0.3 — 3.8 13.7 — 1.9 19.7 0.7 0.3 6.5 3.0 — 5.1 15.6 Other countries UK 32.1 — 4.3 16.3 194.2 37.5 284.4 44.7 — 9.1 13.0 191.3 42.9 301.0 US 1.1 — 1.5 1.5 — 0.3 4.4 6.3 0.1 8.2 2.3 — 0.1 17.0 Japan (4) 3.8 — 2.6 — — — 6.4 3.0 — 2.6 0.2 — 0.8 6.6 Switzerland — — — — — 0.1 0.1 0.2 — 0.2 — — 0.2 0.6 Denmark — — 0.2 — — 0.5 0.7 — — 0.1 — — 0.4 0.5 Other 0.1 — 1.9 0.4 0.3 1.0 3.7 0.1 — 2.3 0.9 — 1.9 5.2 37.1 — 10.5 18.2 194.5 39.4 299.7 54.3 0.1 22.5 16.4 191.3 46.3 330.9 Total 37.4 — 14.3 31.9 194.5 41.3 319.4 55.0 0.4 29.0 19.4 191.3 51.4 346.5 (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 £1.2bn (2017: £1.8bn), Belgium of £0.9bn (2017: £nil), Greece of £nil (2017: £nil). (4) Mainly equity instruments listed in Japan and reverse repos with Japanese banks, held as part of our Short Term Markets business. The equity exposures are hedged using derivatives and the additional reverse repos are fully collateralised.
Summary of Balances with Other Banco Santander Companies	At 31 December 2018 and 2017, we had gross balances with other Banco Santander companies as follows: 2018 2017 Financial institutions Financial institutions Banks Other Corporate Total Banks Other Corporate Total Assets Spain 2.7 — — 2.7 4.4 — — 4.4 UK — 2.0 — 2.0 — 1.3 — 1.3 2.7 2.0 — 4.7 4.4 1.3 — 5.7 Liabilities Spain 3.9 0.1 — 4.0 5.1 0.3 0.1 5.5 UK — 1.0 — 1.0 0.1 0.2 0.1 0.4 Uruguay 0.2 — — 0.2 0.1 — — 0.1 Other <£100m — — — — — 0.1 — 0.1 4.1 1.1 — 5.2 5.3 0.6 0.2 6.1
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 external customers who are remortgaging with us. Stock New business 2018 2017 2018 2017 £m % £m % £m % £m % Home movers 69,198 44 68,752 44 10,854 39 10,704 44 Remortgagers 51,272 32 50,424 33 9,237 34 8,065 33 First-time buyers 29,235 19 28,704 19 4,848 18 4,034 17 Buy-to-let 8,252 5 6,802 4 2,335 9 1,371 6 157,957 100 154,682 100 27,274 100 24,174 100
Summary of Residential Mortgages by Interest Rate Profile	The interest rate profile of our mortgage asset stock was: 2018 2017 £m % £m % Fixed rate 115,178 73 102,036 66 Variable rate 24,396 15 29,370 19 Standard Variable Rate (SVR) 18,383 12 23,276 15 157,957 100 154,682 100
Summary of Residential Mortgages by Geographical Distribution	The geographical distribution of our mortgage asset stock was: Stock New business UK region 2018 £bn 2017 2018 £bn 2017 London 39.0 37.6 7.1 5.8 Midlands and East Anglia 21.1 20.6 3.8 3.4 North 22.2 22.2 3.4 3.0 Northern Ireland 3.4 3.6 0.2 0.2 Scotland 6.7 6.8 1.0 1.0 South East excluding London 48.7 47.2 9.0 8.2 South West, Wales and other 16.9 16.7 2.8 2.6 158.0 154.7 27.3 24.2
Summary of Residential Mortgages by Average Loan Size for New Business	Average loan size for new business £’000 £’000 South East including London 270 260 Rest of the UK 150 146 UK as a whole 203 196
Summary of Residential Mortgages by Loan to Value	This table shows the LTV distribution for our mortgage stock, NPL 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. 2018 2017 Of which: Of which: Stock NPL stock New business Stock NPL stock New business LTV % % % % % % Up to 50% 45 43 20 49 44 19 >50-75% 41 35 41 39 34 43 >75- 9 8 22 7 8 19 >85-100% 4 7 17 4 7 19 >100% 1 7 — 1 7 — 100 100 100 100 100 100 Collateral value of residential properties (1) £ 157,787m £ 1,850m £ 27,274m £ 154,459m £ 1,823m £ 24,174m % % % % % % Simple average (2) 42 43 63 42 44 62 Valuation weighted average (3) 39 38 59 38 38 58 (1) Collateral value shown is limited to the balance of each associated loan. Excludes the impact of over-collateralisation (where the collateral is higher than the loan balance). Includes collateral against loans in negative equity of £969m (2017: £1,248m). (2) Total of all LTV% divided by the total of all accounts. (3) Total of all loan values divided by the total of all valuations.
Summary of Business Banking by Credit Performance	Credit performance 2018 2017 £m £m Loans and advances to customers of which: 1,802 1,912 - Stage 1 1,548 - Stage 2 165 - Stage 3 89 - Performing (1) 1,793 - Early arrears 4 - NPLs (2) 89 115 Loss allowances (3) 53 54 Stage 3 ratio (4) 4.94 % NPL ratio (5) 4.94 % 6.01 % Gross write offs 15 21 (1) Excludes loans and advances to customers where the customer did not pay for between 0 and 90 days and NPLs. (2) We define NPLs in the ‘Credit risk management’ section. (3) Loss allowances for 2017 were on an incurred loss basis per IAS 39, whilst for 2018 they are on an ECL basis per IFRS 9. (4) Stage 3 as a percentage of loans and advances to customers. (5) NPLs as a percentage of loans and advances to customers.
Summary of Residential Mortgages Portfolios of Particular Interest by Credit Performance	Credit performance Portfolio of particular interest (1) Part interest- Other Total Interest-only repayment (2) (3) Flexible (3) LTV >100% Buy-to-let portfolio 2018 £m £m £m £m £m £m £m 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 1.25 % 2.64 % 1.98 % 2.21 % 11.14 % 0.35 % 0.58 % PIPs 25 12 5 3 8 — 7 2017 Mortgage portfolio 154,682 38,885 13,785 14,785 1,471 6,802 95,535 Performing 151,688 37,497 13,372 14,438 1,302 6,768 94,530 Early arrears: - 31 to 60 days 700 317 93 67 22 9 295 - 61 to 90 days 426 203 57 35 15 4 167 NPLs 1,868 868 263 245 132 21 543 NPL ratio 1.21 % 2.23 % 1.91 % 1.66 % 8.97 % 0.31 % 0.57 % PIPs 29 17 5 3 10 1 6 (1) Where a loan falls into more than one category, we have included 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 £9,756m (2017: £10,116m) 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.
Summary of Residential Mortgages Portfolios of Particular Interest by Forbearance Applied	Forbearance (1) The balances at 31 December 2018 and 2017 were: Interest-only (2) Flexible LTV >100% Buy-to-Let £m £m £m £m 2018 229 32 10 9 - Stage 2 136 18 3 6 - Stage 3 93 14 7 3 2017 208 34 13 8 (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 Consumer Personal Credit Total other (auto) finance loans cards Overdrafts unsecured Total 2018 £m £m £m £m £m £m 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 NPLs (1) 43 16 49 22 87 130 Loss allowances 85 47 112 61 220 305 Stage 3 ratio (2) 0.59 % 1.72 % 1.08 % NPL ratio (3) 0.59 % 1.54 % 1.00 % Gross write-offs 24 125 149 (1) We define NPLs in the ‘Credit risk management’ section. (2) Stage 3 as a percentage of loans and advances to customers. (3) NPLs as a percentage of loans and advances to customers. Other unsecured Consumer Personal Credit Total other (auto) finance loans cards Overdrafts unsecured Total 2017 £m £m £m £m £m £m Loans and advances to customers of which: 6,957 2,169 2,444 565 5,178 12,135 - Performing (1) 6,861 2,129 2,377 516 5,022 11,883 - Early arrears 62 24 19 25 68 130 - NPLs (2) 34 16 48 24 88 122 Loss allowances 77 44 62 29 135 212 NPL ratio (3) 0.49 % 1.69 % 1.00 % Gross write-offs 32 120 152 (1) Excludes loans and advances to customers where the customer did not pay for between 0 and 90 days and NPLs. (2) We define NPLs in the ‘Credit risk management’ section. (3) NPLs as a percentage of loans and advances to customers.
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 2018 £m £m £m £m £m £m £m £m £m 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 Sovereign and Supranational 393 3,807 — — — — — — 4,200 Large Corporate 12 3,187 5,535 6,361 888 3 78 — 16,064 Financial Institutions 856 1,392 1,490 76 — — — — 3,814 1,261 8,386 7,025 6,437 888 3 78 — 24,078 Corporate Centre Sovereign and Supranational 34,512 91 — 1 — — — — 34,604 Structured Products 2,436 2,062 318 24 — — — — 4,840 Social Housing 1,377 2,847 76 43 — — — — 4,343 Legacy Portfolios in run-off (2) — — — 203 35 137 126 357 858 Derivatives — 147 — — — — — — 147 Crown Dependencies 14 39 124 77 14 8 7 — 283 38,339 5,186 518 348 49 145 133 357 45,075 Total 40,280 17,471 7,747 8,832 11,250 5,422 1,152 393 92,547 Of which: Stage 1 40,280 17,471 7,747 8,759 10,802 4,780 527 377 90,743 Stage 2 — — — 73 448 635 318 16 1,490 Stage 3 — — — — — 7 307 — 314 2017 Corporate & Commercial Banking SME and mid corporate — — 259 2,183 5,402 3,574 998 214 12,630 Commercial Real Estate — — — 395 6,135 2,014 60 2 8,606 Social Housing 499 2,600 171 — — — 4 — 3,274 499 2,600 430 2,578 11,537 5,588 1,062 216 24,510 Corporate & Investment Banking Sovereign and Supranational 590 3,321 444 — — — — — 4,355 Large Corporate 260 2,979 8,391 8,879 573 2 355 — 21,439 Financial Institutions 2,362 1,463 2,494 33 103 — — — 6,455 3,212 7,763 11,329 8,912 676 2 355 — 32,249 Corporate Centre Sovereign and Supranational 44,477 18 — — — — — — 44,495 Structured Products 2,487 1,560 300 32 — — — — 4,379 Social Housing 1,841 3,641 451 43 — — — — 5,976 Legacy Portfolios in run-off (2) — — 1 359 104 124 37 400 1,025 Derivatives — 212 — — — — — — 212 Crown Dependencies 13 36 115 71 13 8 6 — 262 48,818 5,467 867 505 117 132 43 400 56,349 Total 52,529 15,830 12,626 11,995 12,330 5,722 1,460 616 113,108 (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 Consumer (Auto) Finance and Other Unsecured Lending By Forbearance	Forbearance The balances at 31 December 2018 and 2017 were: Other unsecured Consumer Personal Credit Total other (auto) finance loans cards Overdrafts unsecured Total £m £m £m £m £m £m 2018 — — 53 26 79 79 - Stage 2 — — 10 7 17 17 - Stage 3 — — 43 19 62 62 2017 — 1 48 28 77 77
Summary of Residential Mortgages by Credit Performance	Credit performance 2018 £m 2017 Mortgage loans and advances to customers of which: 157,957 154,682 - Stage 1 146,619 - Stage 2 9,356 - Stage 3 1,982 Performing (1) 151,688 Early arrears: 1,126 - 31 to 60 days 700 - 61 to 90 days 426 NPLs: (2) 1,907 1,868 - By arrears 1,392 1,427 - By bankruptcy 18 14 - By maturity default 392 303 - By forbearance 80 95 - By properties in possession (PIPs) 25 29 Loss allowances (3) 234 225 Stage 2 ratio 5.92 % Stage 3 ratio 1.25 % Early arrears ratio (4) 0.73 % NPL ratio (5) 1.21 % 1.21 % (1) Excludes mortgages where the customer did not pay for between 31 and 90 days, arrears, bankruptcy, maturity default, forbearance and PIPs NPLs. Includes £2,661m of mortgages at 31 December 2017 where the customer did not pay for 30 days or less. (2) We define NPLs in the ‘Credit risk management’ section. All NPLs are in the UK and continue accruing interest. Our Stage 3 exposures under IFRS 9 and NPLs are subject to different criteria. These criteria are under review in parallel with the ongoing regulatory changes to the default definition. (3) Loss allowances for 2017 were on an incurred loss basis per IAS 39, whilst for 2018 they are on an ECL basis per IFRS 9. The loss allowance is for both on and off-balance (4) Mortgages in early arrears as a percentage of mortgages. (5) Mortgage NPLs as a percentage of mortgages.
Summary of Business Banking by Forbearance	Forbearance The balances at 31 December 2018 and 2017 were: £m 2018 74 - Stage 2 20 - Stage 3 54 2017 85
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. 2018 2017 Rest of Rest of UK Europe US World Total UK Europe US World Total £m £m £m £m £m £m £m £m £m £m Corporate & Commercial Banking SME and mid corporate 11,833 74 — 1 11,908 12,513 116 1 — 12,630 Commercial Real Estate 6,743 — — — 6,743 8,606 — — — 8,606 Social Housing 4,743 — — — 4,743 3,274 — — — 3,274 23,319 74 — 1 23,394 24,393 116 1 — 24,510 Corporate & Investment Banking Sovereign and Supranational — 393 — 3,807 4,200 — 1,032 1 3,322 4,355 Large Corporate 13,080 2,752 124 108 16,064 17,430 3,699 111 199 21,439 Financial Institutions 1,237 1,886 198 493 3,814 3,102 2,121 614 618 6,455 14,317 5,031 322 4,408 24,078 20,532 6,852 726 4,139 32,249 Corporate Centre Sovereign and Supranational 30,587 1,409 965 1,643 34,604 35,659 1,514 6,091 1,231 44,495 Structured Products 2,576 1,142 — 1,122 4,840 2,086 1,217 — 1,076 4,379 Social Housing 4,343 — — — 4,343 5,976 — — — 5,976 Legacy Portfolios in run—off 744 — — 114 858 909 — — 116 1,025 Derivatives — — 147 — 147 — 63 149 — 212 Crown Dependencies 283 — — — 283 262 — — — 262 38,533 2,551 1,112 2,879 45,075 44,892 2,794 6,240 2,423 56,349
Summary of Commercial Real Estate by Credit Performance	The table below shows the main CRE credit performance metrics at 31 December 2018 and 2017 Customer Gross write - Loss loans (1) NPLs (2) NPL ratio (3) offs allowances (4) £m £m % £m £m 2018 6,459 29 0.45 23 26 2017 8,144 69 0.85 11 54 (1) CRE drawn loans in the business banking portfolio of our Retail Banking segment of £257m (2017: £257m) and in the CRE portfolio of our Corporate & Commercial Banking segment of £6,202m (2017: £7,886m). (2) We define NPLs in the ‘Credit risk management’ section. All NPLs continue accruing interest. (3) NPLs as a percentage of customer loans. (4) Loss allowances for 2017 were on an incurred loss basis per IAS 39, whilst for 2018 they are on an ECL basis per IFRS 9. The ECL allowance is for both on and off–balance sheet exposures.
Social Housing Exposure	At 31 December 2018 and 2017, our total Social Housing exposure in Corporate & Commercial Banking and Corporate Centre was: 2018 2017 On-balance Total On-balance Total £m £m £m £m Corporate & Commercial Banking 2,844 4,743 2,118 3,274 Corporate Centre 3,780 4,343 5,060 5,976 6,624 9,086 7,178 9,250
Mortgages [member]
Statement [LineItems]
Summary of ECL Reconciliation	The following table shows changes in total exposures subject to ECL assessment, and the corresponding ECL, for residential mortgages in the period. The footnotes to the Santander UK group level analysis on page 83 are also applicable to this table. Non-credit Credit impaired Stage 1 Subject to 12-month ECL Stage 2 Stage 3 Mortgages Exposures (1) ECL Exposures (1) £m ECL Exposures (1) £m ECL Exposures (1) £m ECL At 1 January 2018 155,155 20 9,884 131 2,004 121 167,043 272 Change in economic scenarios (2) — (6 ) — (7 ) — (8 ) — (21 ) Changes to model — — — 2 — 2 — 4 Transfer to lifetime ECL (not-credit (3) (2,941 ) (1 ) 2,941 1 — — — — Transfer to credit impaired (3) (329 ) (6 ) (512 ) (12 ) 841 18 — — Transfer to 12-month (3) 2,628 21 (2,628 ) (21 ) — — — — Transfer from credit impaired (3) 4 — 405 14 (409 ) (14 ) — — Transfers of financial instruments (638 ) 14 206 (18 ) 432 4 — — Net remeasurement of ECL on stage transfer (4) — (20 ) — 20 — 14 — 14 New assets originated or purchased (5) 28,330 2 446 5 3 1 28,779 8 Other (6) (7,327 ) 6 (244 ) (4 ) (36 ) 3 (7,607 ) 5 Assets derecognised - closed good (7) (17,781 ) (4 ) (860 ) (10 ) (327 ) (13 ) (18,968 ) (27 ) Assets derecognised - 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 ) 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 tables provide information on financial assets that were forborne while they had a loss allowance measured at an amount equal to lifetime ECL. £m Financial assets modified during the period: - Amortised cost before modification 207 - Net modification loss 3 Financial assets modified since initial recognition: - Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month 158
Summary of Residential Mortgages by Forbearance Applied	The balances at 31 December 2018 and 2017, analysed by their staging (2017: payment status) at the year-end Capitalisation Term extension Interest-only Total Loss allowance 2018 £m £m £m £m £m 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 % 0.9 % 2017 In arrears 260 63 175 498 22 Performing 392 178 407 977 5 652 241 582 1,475 27 Proportion of portfolio 0.4 % 0.2 % 0.4 % 1.0 % (1) We base forbearance type on the first forbearance on the accounts.
Other business segments [member]
Statement [LineItems]
Summary of ECL Reconciliation	The following tables show changes in total exposures and ECL in the year. The footnotes to the Santander UK group level table on page 83 also apply to these tables. Non-credit impaired Credit impaired Stage 1 Subject to 12-month ECL Stage 2 Stage 3 Subject to lifetime ECL 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 Change in economic scenarios (2) — 5 — (3 ) — — — 2 Transfer to lifetime ECL (not-credit impaired) (3) (670 ) (3 ) 670 3 — — — — Transfer to credit impaired (3) (41 ) — (31 ) (1 ) 72 1 — — Transfer to 12-month ECL (3) 200 8 (200 ) (8 ) — — — — Transfer from credit impaired (3) 2 1 2 1 (4 ) (2 ) — — Transfers of financial instruments (509 ) 6 441 (5 ) 68 (1 ) — — Net remeasurement of ECL on stage transfer (4) — (7 ) — 10 — 18 — 21 New assets originated or purchased (5) 9,115 12 281 5 3 1 9,399 18 Other (6) 879 (3 ) (58 ) (3 ) (2 ) 37 819 31 Assets derecognised - closed good (7) (10,569 ) (19 ) (304 ) (5 ) (76 ) (18 ) (10,949 ) (42 ) Assets derecognised - 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 ) Charge/(release) to the Income Statement (6 ) (1 ) 37 30 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 26,583 16 109 — 372 242 27,064 258 Changes to model — — — — — (9 ) — (9 ) Transfer to lifetime ECL (not-credit impaired) (3) (2 ) — 2 — — — — — New assets originated or purchased (5) 35,926 4 133 3 — — 36,059 7 Other (6) (2,306 ) (1 ) 83 1 (47 ) 29 (2,270 ) 29 Assets derecognised - closed good (7) (18,101 ) (14 ) (193 ) (1 ) — — (18,294 ) (15 ) Assets derecognised - written off (7) — — — — (299 ) (252 ) (299 ) (252 ) At 31 December 2018 42,100 5 134 3 26 10 42,260 18 Net movement in the year 15,517 (11 ) 25 3 (346 ) (232 ) 15,196 (240 ) Charge/(release) to the Income Statement (11 ) 3 20 12 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 57,155 7 250 4 20 8 57,425 19 Change in economic scenarios (2) — 1 — — — — — 1 Transfer to lifetime ECL (not-credit impaired) (3) (111 ) (1 ) 111 1 — — — — Transfer to credit impaired (3) — — (4 ) — 4 — — — Transfer to 12-month ECL (3) 133 3 (133 ) (3 ) — — — — Transfer from credit impaired (3) — — 3 1 (3 ) (1 ) — — Transfers of financial instruments 22 2 (23 ) (1 ) 1 (1 ) — — Net remeasurement of ECL on stage transfer (4) — (2 ) — — — 1 — (1 ) New assets originated or purchased (5) 7,526 1 2 — 2 1 7,530 2 Other (6) (10,187 ) (2 ) (6 ) — 3 1 (10,190 ) (1 ) Assets derecognised - closed good (7) (4,617 ) (2 ) (90 ) — (7 ) (2 ) (4,714 ) (4 ) Assets derecognised - written off (7) — — — — (3 ) (3 ) (3 ) (3 ) At 31 December 2018 49,899 5 133 3 16 5 50,048 13 Net movement in the year (7,256 ) (2 ) (117 ) (1 ) (4 ) (3 ) (7,377 ) (6 ) Charge/(release) to the Income Statement (2 ) (1 ) — (3 ) Recoveries net of collection costs — — (4 ) (4 ) Income statement charge/(release) for the year (2 ) (1 ) (4 ) (7 )
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. Corporate & Corporate & Commercial Investment Corporate Banking Banking Centre £m £m £m Financial assets modified during the period: – Amortised cost before modification 104 — 2 – Net modification loss 10 — — Financial assets modified since initial recognition: – Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month 8 7 4
Corporate and investment banking [member]
Statement [LineItems]
Summary of Annual Growth Rates	The average annual growth rates over a 4 year forecast for each of the scenarios for our CIB portfolio are: Upside Base case Downside Assumption % % % GDP 4.2 3.6 2.7
Summary of Probability Weightings Applied to Scenarios	The probability weights we applied to the scenarios for our CIB portfolio are: Scenario type Probability % Upside 20 Base case 60 Downside 20
Retail banking [member]
Statement [LineItems]
Summary of ECL Reconciliation	The following table shows changes in total exposures subject to ECL assessment, and the corresponding ECL in the period. The footnotes to the Santander UK group level table on page 83 also apply to this table. Non-credit Credit impaired Stage 1 Subject to 12-month ECL Stage 2 Stage 3 Total Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL Exposures (1) ECL At 1 January 2018 178,978 110 10,885 247 2,263 268 192,126 625 Change in economic scenarios (2) — (1 ) — (9 ) — (8 ) — (18 ) Changes to model — (1 ) — 2 — 1 — 2 Transfer to lifetime ECL (not-credit (3) (3,407 ) (7 ) 3,407 7 — — — — Transfer to credit impaired (3) (403 ) (7 ) (569 ) (22 ) 972 29 — — Transfer to 12-month (3) 2,992 58 (2,992 ) (58 ) — — — — Transfer from credit impaired (3) 15 5 438 26 (453 ) (31 ) — — Transfers of financial instruments (803 ) 49 284 (47 ) 519 (2 ) — — Net remeasurement of ECL on stage transfer (4) — (54 ) — 73 — 60 — 79 New assets originated or purchased (5) 33,366 26 670 26 15 11 34,051 63 Other (6) (8,253 ) (15 ) (312 ) (10 ) 97 104 (8,468 ) 79 Assets derecognised - closed good (7) (20,257 ) (18 ) (1,007 ) (13 ) (390 ) (23 ) (21,654 ) (54 ) Assets derecognised - 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 ) Charge/(release) to the Income Statement (14 ) 22 143 151 Recoveries net of collection costs — — (27 ) (27 ) Income Statement charge/(release) for the year (14 ) 22 116 124
Consumer (auto) finance [member]
Statement [LineItems]
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. Credit Overdrafts Total Financial assets modified during the period: - 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 ECL allowance has changed to 12-month 2 3 5
Business Banking [member]
Statement [LineItems]
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. £m Financial assets modified during the period: - Amortised cost before modification 14 - Net modification loss 1 Financial assets modified since initial recognition: - Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month 3

Market risk (Tables)

Market risk (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Balance Sheet Allocation by Market Risk Classification	We analyse our assets and liabilities exposed to market risk between banking and trading market risk as follows: 2018 2017 Banking Trading Total Banking Trading Total £m £m £m £m £m £m Key risk factors Assets subject to market risk Cash and balances at central banks 24,180 — 24,180 32,771 — 32,771 FX, Interest rate Financial assets at FVTPL: – Trading assets — — — — 30,555 30,555 Equity, FX, interest rate – Derivative financial instruments 4,621 700 5, 321 5,198 14,744 19,942 Equity, FX, interest rate – Other financial assets at FVTPL 6,137 — 6,137 2,096 — 2,096 Interest rate, credit spread Financial assets at amortised cost: – Loans and advances to customers (1) 201, — 201,619 199, — 199, Interest rate – Loans and advances to banks (1) 3,515 — 3,515 3,466 — 3,466 FX, interest rate – Reverse repurchase agreements – non trading (1) 21,127 — 21,127 2,614 — 2,614 FX, Interest rate – Other financial assets at amortised cost 7,228 — 7,228 FX, interest rate, inflation, credit spread Financial assets at FVOCI 13,302 — 13,302 FX, interest rate, inflation, credit spread Financial investments 17,611 — 17,611 FX, interest rate, inflation, credit spread Macro hedge of interest rate risk (2) 697 — 697 833 — 833 Interest rate Retirement benefit assets 842 — 842 449 — 449 Equity, FX, interest rate, inflation, credit spread Total assets 283,268 700 283,968 264,370 45,299 309,669 Liabilities subject to market risk Financial liabilities at FVTPL: – Trading liabilities — — — — 31,109 31,109 Equity, FX, interest rate – Derivative financial instruments 875 719 1,594 722 16,891 17,613 Equity, FX, interest rate – Other financial liabilities at FVTPL 6,286 — 6,286 703 1,612 2,315 Interest rate, credit spread Financial Liabilities at amortised cost: – Deposits by customers 173,692 — 173,692 177,421 — 177,421 Interest rate – Deposits by banks (1) 17,824 — 17,824 12,708 — 12,708 FX, interest rate – Repurchase agreements – non trading (1) 10,910 — 10,910 1,076 — 1,076 FX, Interest rate – Debt securities in issue 55,906 — 55,906 48,860 — 48,860 FX, interest rate – Subordinated liabilities 3,601 — 3,601 3,793 — 3,793 FX, interest rate Macro hedge of interest rate risk (3) 242 — 242 — — — Interest rate Retirement benefit obligations 115 — 115 286 — 286 Equity, FX, interest rate, inflation, credit spread Total liabilities 269,451 719 270,170 245,569 49,612 295,181 (1) From 1 January 2018, the non-trading non-trading (2) This is included in Other assets of £2,267m (2017: £2,511m). (3) This is included in Other liabilities of £2,507m (2017: £2,728m).
Summary of NIM and EVE Sensitivity of Interest Rate 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 2018 and 2017. 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 2018 2017 +50bps -50bps +50bps -50bps NIM sensitivity 207 (23 ) 212 (125 ) EVE sensitivity (unaudited) 162 (124 ) 95 (213 )
Summary of Internal VaR for Exposure to Main Classes of Risk	This table and graph shows our Internal VaR for exposure to each of the main classes of risk for 2018 and 2017. Year-end exposure Average exposure Highest exposure Lowest exposure Trading instruments 2018 2017 2018 2017 2018 2017 2018 2017 Interest rate risks 0.5 2.6 1.4 2.5 3.9 3.5 0.2 1.8 Equity risks — 0.3 0.2 0.6 0.6 2.0 — 0.2 Foreign exchange risks 0.1 0.3 0.3 0.4 0.9 1.6 — — Diversification offsets (1) (0.2 ) (0.7 ) (0.5 ) (0.8 ) — — — — Total correlated one-day 0.4 2.5 1.4 2.7 3.8 3.7 0.3 2.0 (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, 2018
Text block [abstract]
Summary of Reconciliation of Wholesale Funding to Balance Sheet	This table reconciles our wholesale funding to our balance sheet at 31 December 2018 and 2017. Balance sheet line item 2018 Funding Deposits by banks £bn Defined by customers (1) £bn Repurchase (2) Trading Financial Debt securities in issue £bn Subordinated £bn Other equity (3) £bn Deposits 1.0 1.0 — — — — — — — Certificates of deposit and commercial paper 6.4 — — — — — 6.4 — — Senior unsecured – public benchmark 21.3 — — — — — 21.3 — — Senior unsecured – privately placed 4.0 — — — — 1.0 3.0 — — 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 5.3 — — — — — — 3.0 2.3 Total wholesale funding 73.2 11.8 0.5 2.2 — 1.0 52.4 3.0 2.3 Repos 10.8 — — 8.7 — 2.1 — — — Foreign exchange and hedge accounting 4.1 — — — — — 3.5 0.6 — Other 9.2 6.0 (4) — — — 3.2 — — — Balance sheet total 97.3 17.8 0.5 10.9 — 6.3 55.9 3.6 2.3 2017 Deposits by banks 0.3 0.2 — — — 0.1 — — — Certificates of deposit and commercial paper 8.0 — — — — 0.4 7.6 — — Senior unsecured – public benchmark 17.8 — — — — — 17.8 — — Senior unsecured – privately placed 3.1 — — — — 1.1 2.0 — — Covered bonds 14.2 — — — — — 14.2 — — Securitisation and structured issuance 5.5 — 0.5 1.0 — — 4.0 — — Term Funding Scheme 8.5 8.5 — — — — — — — Subordinated liabilities and equity 5.5 — — — — — — 3.2 2.3 Total wholesale funding 62.9 8.7 0.5 1.0 — 1.6 45.6 3.2 2.3 Repos 25.6 — — 0.1 25.5 — — — — Foreign exchange and hedge accounting 3.9 — — — — — 3.3 0.6 — Other 10.3 4.0 (4) — — 5.6 (5) 0.7 — — — Balance sheet total 102.7 12.7 0.5 1.1 31.1 2.3 48.9 3.8 2.3 (1) This is included in our balance sheet total of £173,692m (2017: £177,421m). (2) From 1 January 2018, the non-trading re-presented (3) Consists of £14m (2017: £14m) fixed/floating rate non-cumulative Step-up (4) Other consists of items in the course of transmission and other deposits, excluding the TFS. See Note 26 to the Consolidated Financial Statements. (5) Short positions in securities and unsettled trades, cash collateral and short-term deposits. 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 financing repurchase 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 and >6 and >9 and Sub-total >1 and >2 and month £ 3 months £ 6 months £ 9 months £ 12 months £ 1 year £ 2 years £ 5 years >5 years Total 2018 £bn £bn £bn £bn £bn £bn £bn £bn £bn £bn Santander UK Group Holdings plc (1) Senior unsecured – public benchmark — — — — — — 0.8 6.2 1.7 8.7 Senior unsecured – privately placed — — — — — — — — 0.1 0.1 Subordinated liabilities and equity (incl. AT1) — — 0.5 — 0.3 0.8 — 0.8 1.5 3.1 — — 0.5 — 0.3 0.8 0.8 7.0 3.3 11.9 Santander UK plc Deposits by banks — 1.0 — — — 1.0 — — — 1.0 Certificates of deposit and commercial paper 1.5 3.6 1.1 0.1 0.1 6.4 — — — 6.4 Senior unsecured – public benchmark 0.8 1.5 — 0.6 — 2.9 4.8 3.5 1.4 12.6 Senior unsecured – privately placed — — 1.0 0.3 — 1.3 1.8 0.4 0.4 3.9 Covered bonds — — — 1.4 — 1.4 2.8 8.4 4.0 16.6 Securitisation and structured issuance (2) 0.8 0.6 0.6 0.2 0.4 2.6 0.8 2.5 — 5.9 Term Funding Scheme — — — — — — 4.5 6.3 — 10.8 Subordinated liabilities — — — — — — — 0.9 1.3 2.2 3.1 6.7 2.7 2.6 0.5 15.6 14.7 22.0 7.1 59.4 Other group entities Securitisation and structured issuance (3) — 0.1 0.1 0.1 0.1 0.4 0.4 1.1 — 1.9 Total at 31 December 2018 3.1 6.8 3.3 2.7 0.9 16.8 15.9 30.1 10.4 73.2 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 2.6 1.0 0.4 12.4 7.4 11.8 6.4 38.0 3.1 6.8 3.3 2.7 0.9 16.8 15.9 30.1 10.4 73.2 Total at 31 December 2017 4.8 3.9 3.3 1.4 1.5 14.9 7.9 28.9 11.2 62.9 Of which: – Secured 0.9 — 1.4 — 1.3 3.6 2.9 18.3 3.4 28.2 – Unsecured 3.9 3.9 1.9 1.4 0.2 11.3 5.0 10.6 7.8 34.7 4.8 3.9 3.3 1.4 1.5 14.9 7.9 28.9 11.2 62.9 (1) 95% 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 2018 and 2017. 2018 2017 Sterling US Dollar Euro Other Sterling US Dollar Euro Other % % % % % % % % Santander UK Group Holdings plc Senior unsecured – public benchmark 11 65 22 2 9 67 22 2 Senior unsecured – privately placed — — — 100 — — — 100 Subordinated liabilities and equity (incl. AT1) 68 32 — — 68 32 — — 26 56 16 2 28 54 14 4 Santander UK plc Deposits by banks 3 97 — — 27 73 — — Certificates of deposit and commercial paper 48 52 — — 89 10 — 1 Senior unsecured – public benchmark 11 56 33 — 9 49 42 — Senior unsecured – privately placed 13 12 72 3 7 19 70 4 Covered bonds 50 — 49 1 47 — 52 1 Securitisation and structured issuance 61 35 4 — 80 20 — — Term Funding Scheme 100 — — — 100 — — — Subordinated liabilities 49 51 — — 52 48 — — 48 25 26 1 49 19 32 — Other group entities Deposits by banks — — — — — 100 — — Certificates of deposit and commercial paper — — — — 34 65 1 — Securitisation and structured issuance 89 11 — — 91 — 9 — 89 11 — — 47 50 3 — Total 46 30 24 — 45 28 25 2
Summary of External Term Issuance (Sterling Equivalent)	In 2018, our external term issuance (sterling equivalent) was: Sterling US Dollar Euro Other Total 2018 Total 2017 £bn £bn £bn £bn £bn £bn Santander UK Group Holdings plc Senior unsecured – public benchmark 0.5 1.5 0.7 — 2.7 2.0 Senior unsecured – privately placed — — — — — 0.1 Subordinated debt and equity (incl. AT1) — — — — — 0.5 0.5 1.5 0.7 — 2.7 2.6 Santander UK plc Securitisations and other secured funding 1.4 1.5 — — 2.9 0.5 Covered bonds 2.5 — 1.8 — 4.3 2.3 Senior unsecured – public benchmark 0.4 2.5 — — 2.9 1.1 Senior unsecured – privately placed 0.3 — 1.3 — 1.6 0.1 Term Funding Scheme 2.3 — — — 2.3 4.0 6.9 4.0 3.1 — 14.0 8.0 Other group entities Securitisations 0.4 — — — 0.4 1.2 Total gross issuances 7.8 5.5 3.8 — 17.1 11.8
Summary of Loan-to-Deposit Ratio	This table shows our customer loans, deposits and LDR at 31 December 2018 and 2017. The business segments data excludes fair value loans, impairment loss allowances, accrued interest and other. The total data includes them but excludes repurchase agreements. 2018 2017 Customer Customer loans deposits LDR LDR £bn £bn % % Retail Banking 172.8 142.1 122 113 Corporate & Commercial Banking 17.7 17.6 101 104 Corporate & Investment Banking 4.6 4.8 96 133 Corporate Centre 4.8 7.6 63 174 Total customer loans and deposits (2) 199.9 172.1 116 113 Adjust for: fair value loans, impairment loss allowances, accrued interest and other 1.7 1.6 Statutory loans and advances to customers/deposits by customers (1) 201.6 173.7 Total 201.6 173.7 (1) The customer loans and customer deposits numbers are the amounts disclosed in the Consolidated Balance Sheet. (2) We calculate the total LDR as loans and advances to customers divided by deposits by customers.

Capital risk (Tables)

Capital risk (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Regulatory Capital Resources	Regulatory capital resources This table shows our regulatory capital. 2018 £m 2017 CET1 capital instruments and reserves: - Capital instruments 7,060 7,060 - Retained earnings 6,439 6,399 - Accumulated other reserves and non-controlling 431 453 CET1 capital before regulatory adjustments 13,930 13,912 CET1 regulatory adjustments: - Additional value adjustments (42 ) (70 ) - Goodwill (net of tax) (1,161 ) (1,165 ) - Other intangibles (610 ) (539 ) - Fair value reserves related to gains or losses on cash flow hedges (251 ) (228 ) - Negative amounts resulting from the calculation of regulatory expected loss amounts (599 ) (748 ) - Gains or losses on liabilities valued at fair value resulting from changes in own credit standing (67 ) (13 ) - Deferred tax assets that rely on future profitability excluding timing differences (20 ) (25 ) - Defined benefit pension fund assets (631 ) (333 ) - Dividend accrual (18 ) (19 ) - IFRS 9 Transitional Adjustment 21 — - Deduction for non-controlling (151 ) (152 ) CET1 capital 10,401 10,620 AT1 capital instruments: - Capital instruments 2,041 2,041 - Amount of qualifying items subject to phase out from AT1 593 707 - Regulatory deductions for instruments issued by subsidiary undertakings (268 ) (301 ) AT1 capital 2,366 2,447 Tier 1 capital 12,767 13,067 Tier 2 capital instruments: - Capital instruments 2,888 2,749 - Amount of qualifying items subject to phase out from Tier 2 369 587 - Regulatory deductions for instruments issued by subsidiary undertakings or subject to CRDIV amortisation (986 ) (915 ) Tier 2 capital 2,271 2,421 Total regulatory capital (1) 15,038 15,488 (1) Capital resources include a transitional IFRS 9 benefit at 31 December 2018 of £21m (1 January 2018: £18m).

Accounting Policies (Tables)

Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2018
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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
Summary of Probability Weights Applied for Each Scenario of Expected Credit Losses Allowance	Upside 2 Upside 1 Base case Downside 1 Downside 2 Retail Banking, Corporate & Commercial Banking and Corporate Centre £m £m £m £m £m ECL 554 596 648 843 1,930 Upside Base case Downside Corporate & Investment Banking (1) £m £m £m ECL 8 17 27 (1) As described in more detail in the ‘Santander UK Group Level – Credit Risk Management’ section, our Corporate & Investment Banking segment uses three forward-looking economic scenarios, whereas our other segments use five scenarios. The results of the 100% weighting ECL for the Corporate & Investment Banking segment are therefore presented separately.

Segments (Tables)

Segments (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Results by Segment	Results by segment Corporate & Corporate & Retail Commercial investment Corporate Banking Banking Banking Centre Total 2018 £m £m £m £m £m Net interest income 3,126 403 69 8 3,606 Non-interest 638 82 272 (55 ) 937 Total operating income/(expense) 3,764 485 341 (47 ) 4,543 Operating expenses before credit impairment losses, provisions and charges (1,929 ) (258 ) (262 ) (114 ) (2,563 ) Credit impairment (losses)/releases (124 ) (23 ) (14 ) 8 (153 ) Provisions for other liabilities and charges (230 ) (14 ) (8 ) (8 ) (260 ) Total operating credit impairment losses, provisions and (charges)/releases (1) (354 ) (37 ) (22 ) — (413 ) Profit/(loss) before tax 1,481 190 57 (161 ) 1,567 Revenue from external customers 4,421 638 386 (902 ) 4,543 Inter-segment revenue (657 ) (153 ) (45 ) 855 — Total operating income/(expense) 3,764 485 341 (47 ) 4,543 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 4,807 199,869 Total assets (4) 201,261 17,702 33,657 36,761 289,381 Customer deposits 142,065 17,606 4,853 7,607 172,131 Total liabilities 142,839 17,634 14,222 98,466 273,161 Average number of staff 20,694 1,732 1,108 114 23,648 (1) Credit impairment losses for 2018 are calculated on an IFRS 9 basis and for 2017 and earlier on an IAS 39 basis. For more on this methodology change, see the IFRS 9 accounting policy changes in Note 1 and the IFRS 9 transition disclosures in Note 44. (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 (4) Includes customer loans, net of credit impairment loss allowances. Corporate & Corporate & Retail Commercial Investment Corporate Banking (5) Banking Banking Centre (5) Total 2017 £m £m £m £m £m Net interest income 3,270 391 74 68 3,803 Non-interest 615 74 364 56 1,109 Total operating income 3,885 465 438 124 4,912 Operating expenses before credit impairment losses, provisions and charges (1,856 ) (223 ) (304 ) (119 ) (2,502 ) 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 (51 ) 40 1,814 Revenue from external customers 4,534 639 506 (767 ) 4,912 Inter-segment revenue (649 ) (174 ) (68 ) 891 — Total operating income 3,885 465 438 124 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 51,078 69,767 314,760 Customer deposits 143,834 17,760 4,546 9,781 175,921 Total liabilities 150,847 18,697 45,603 83,411 298,558 Average number of staff 17,194 1,240 1,006 119 19,559 2016 Net interest income 3,117 380 73 12 3,582 Non-interest 559 76 312 266 1,213 Total operating income 3,676 456 385 278 4,795 Operating expenses before credit impairment losses, provisions and charges (1,785 ) (215 ) (281 ) (136 ) (2,417 ) Credit impairment (losses)/releases (1) (21 ) (29 ) (21 ) 4 (67 ) Provisions for other liabilities and charges (338 ) (26 ) (11 ) (22 ) (397 ) Total operating credit impairment losses, provisions and charges (359 ) (55 ) (32 ) (18 ) (464 ) Profit before tax 1,532 186 72 124 1,914 Revenue from external customers 4,387 651 474 (717 ) 4,795 Inter-segment revenue (711 ) (195 ) (89 ) 995 — Total operating income 3,676 456 385 278 4,795 Revenue from external customers includes the following fee and commission income disaggregated by income type: (2) – Current account and debit card fees 697 27 23 — 747 – Insurance, protection and investments 94 — — — 94 – Credit cards 95 — — — 95 – Non-banking (3) 53 57 132 10 252 Total fee and commission income 939 84 155 10 1,188 Fee and commission expense (369 ) (31 ) (17 ) (1 ) (418 ) Net fee and commission income 570 53 138 9 770 Customer loans 168,389 19,382 5,659 6,726 200,156 Total assets (4) 175,100 19,381 39,777 68,252 302,510 Customer deposits 143,996 16,082 4,054 8,219 172,351 Total liabilities 149,793 17,203 36,506 83,555 287,057 Average number of staff 17,424 1,435 916 88 19,863 (1) Credit impairment losses for 2018 are calculated on an IFRS 9 basis and for 2017 and earlier on an IAS 39 basis. For more on this methodology change, see the IFRS 9 accounting policy changes in Note 1 and the IFRS 9 transition disclosures in Note 44. (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 (4) Includes customer loans, net of credit impairment loss allowances. (5) The re-segmentation re-presented

Net Interest Income (Tables)

Net Interest Income (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Net Interest Income	2018 2017 2016 £m £m £m Interest and similar income: Loans and advances to customers 5,459 5,494 6,198 Loans and advances to banks 207 164 112 Reverse repurchase agreements – non trading 124 20 15 Other 282 227 142 Total interest and similar income (1) 6,072 5,905 6,467 Interest expense and similar charges: Deposits by customers (1,224 ) (1,183 ) (1,809 ) Deposits by banks (120 ) (35 ) (18 ) Repurchase agreements – non trading (37 ) (5 ) (38 ) Debt securities in issue (936 ) (737 ) (853 ) Subordinated liabilities (141 ) (134 ) (143 ) Other (8 ) (8 ) (24 ) Total interest expense and similar charges (2) (2,466 ) (2,102 ) (2,885 ) Net interest income 3,606 3,803 3,582 (1) This includes £209m of interest income on financial assets at fair value through other comprehensive income. (2) This includes £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, 2018
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Summary of Net Fee and Commission Income	2018 2017 2016 £m £m £m Fee and commission income: Current account and debit card fees 753 791 747 Insurance, protection and investments 105 100 94 Credit cards 85 92 95 Non-banking (1) 227 239 252 Total fee and commission income 1,170 1,222 1,188 Total fee and commission expense (421 ) (415 ) (418 ) Net fee and commission income 749 807 770 (1) Non-banking

Net Trading and Other Income (T

Net Trading and Other Income (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Net Trading and Other Income	2018 2017 2016 £m £m £m Net trading and funding of other items by the trading book 263 205 75 Net (losses)/gains on other financial assets at fair value through profit or loss (18 ) 80 253 Net (losses)/gains on other financial liabilities at fair value through profit or loss (44 ) (97 ) 28 Net losses on derivatives managed with assets/liabilities held at fair value through profit or loss (128 ) (17 ) (135 ) Hedge ineffectiveness 34 5 28 Net profit on sale of available-for-sale 54 115 Net profit on sale of financial assets at fair value through other comprehensive income 19 Net income from operating lease assets 86 44 35 Other (24 ) 28 44 188 302 443

Operating Expenses Before Cre_2

Operating Expenses Before Credit Impairment Losses, Provisions and Charges (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Operating Expenses Before Credit Impairment Losses, Provisions and Charges	2018 2017 2016 Staff costs: Wages and salaries 905 746 731 Performance-related payments 160 157 157 Social security costs 111 93 94 Pensions costs – defined contribution plans 66 54 52 – defined benefit plans 81 32 26 Other share-based payments 3 10 3 Other personnel costs 50 45 62 1,376 1,137 1,125 Other administration expenses 809 1,011 970 Depreciation, amortisation and impairment 378 354 322 2,563 2,502 2,417
Summary of Deferred Performance Awards	Costs recognised in 2018 Costs expected to be recognised in 2019 or later Arising from Arising from Total Arising from Arising from Total Cash 4 9 13 10 10 20 Shares 3 10 13 8 9 17 7 19 26 18 19 37
Summary of Amount of Bonus Awarded to Employees	The following table shows the amount of bonus awarded to employees for the performance year 2018. 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 2018 £m 2017 2018 £m 2017 2018 2017 Cash award – not deferred 123 116 — — 123 116 – deferred 13 13 20 17 33 30 Share awards – not deferred 11 12 — — 11 12 – deferred 13 16 17 18 30 34 Total discretionary bonus 160 157 37 35 197 192

Audit and Other Services (Table

Audit and Other Services (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Audit and Other Services	2018 2017 2016 Audit fees: Fees payable to the Company’s auditor and its associates for the audit of the Santander UK group’s annual accounts 7.7 7.8 4.9 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 1.6 1.4 1.1 Total audit fees (1) 9.3 9.2 6.0 Non-audit Audit-related assurance services (2) 2.2 1.6 1.3 Taxation compliance services — — 0.1 Other assurance services 0.1 0.1 — Other non-audit 1.0 0.4 1.9 Total non-audit 3.3 2.1 3.3 (1) 2018 audit fees included £nil (2017: £0.6m) which related to the prior year. (2) 2018 audit-related assurance services included £0.1m (2017: £0.1m) which related to the prior year.

Credit Impairment Losses and _2

Credit Impairment Losses and Provisions (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Impairment Losses and Provisions	2018 2017 2016 Credit impairment losses: Loans and advances to customers (See Note 14) 189 257 132 Recoveries of loans and advances, net of collection costs (See Note 14) (42 ) (54 ) (65 ) Off-balance 6 153 203 67 Provisions for other liabilities and charges (excluding off-balance 260 385 397 Provisions for RV and voluntary termination (See Note 14) — 8 — 260 393 397 413 596 464

Taxation (Tables)

Taxation (Tables)	12 Months Ended
	Dec. 31, 2018
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Disclosure of Tax on Profit	2018 2017 2016 Current tax: UK corporation tax on profit for the year 456 555 610 Adjustments in respect of prior years (22 ) (27 ) (13 ) Total current tax 434 528 597 Deferred tax: Charge/(credit) for the year 11 23 (11 ) Adjustments in respect of prior years 1 9 11 Total deferred tax 12 32 — Tax on profit 446 560 597
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 2018, based on profit before tax, was 28.5% (2017: 30.9%, 2016: 31.2%). 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: 2018 2017 2016 Profit before tax 1,567 1,814 1,914 Tax calculated at a tax rate of 19% (2017: 19.25%, 2016: 20.00%) 298 349 383 Bank surcharge on profits 111 132 134 Non-deductible 8 9 8 Non-deductible 20 25 30 Non-deductible 6 35 39 Other non-deductible non-taxable 26 30 7 Effect of change in tax rate on deferred tax provision (2 ) (2 ) (2 ) Adjustment to prior year provisions (21 ) (18 ) (2 ) Tax charge 446 560 597
Disclosure of Movements in Current Tax Assets and Liabilities	Movements in current tax assets and liabilities during the year were as follows: 2018 2017 Assets — — Liabilities (3 ) (53 ) At 1 January (3 ) (53 ) Income statement charge (434 ) (528 ) Other comprehensive income credit/(charge) 75 44 Corporate income tax paid 445 484 Other movements 23 50 106 (3 ) Assets 106 — Liabilities — (3 ) At 31 December 106 (3 )
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 and Company has the legal right to offset and intends to settle on a net basis. Fair value Pension Cash flow Available- for-sale Fair Tax Accelerated Other Total At 31 December 2017 (41 ) (41 ) 3 (26 ) 25 (4 ) (4 ) (88 ) Adoption of IFRS 9 (see Note 1) — — — 26 (26 ) — — 68 68 At 1 January 2018 (41 ) (41 ) 3 (26 ) 25 (4 ) 64 (20 ) Income statement (charge)/credit (10 ) (24 ) — — (5 ) — 27 (12 ) Transfers/reclassifications — — — — — — (9 ) (9 ) Credited/(charged) to other comprehensive income — (117 ) (46 ) 14 — — (21 ) (170 ) At 31 December 2018 (51 ) (182 ) (43 ) (12 ) 20 (4 ) 61 (211 ) At 1 January 2017 (31 ) (35 ) (50 ) (27 ) 5 (5 ) 15 (128 ) Income statement (charge)/credit (10 ) (32 ) — — 20 1 (11 ) (32 ) Transfers/reclassifications — — — 7 — — (7 ) — Credited/(charged) to other comprehensive income — 26 53 (6 ) — — (1 ) 72 At 31 December 2017 (41 ) (41 ) 3 (26 ) 25 (4 ) (4 ) (88 )

Dividends on Ordinary Shares (T

Dividends on Ordinary Shares (Tables)	12 Months Ended
	Dec. 31, 2018
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Disclosure of Dividends on Ordinary Shares Declared and Paid	Dividends on ordinary shares declared and paid during the year were as follows: 2018 2017 2016 2018 2017 2016 In respect of current year – first interim 3.54 4.58 4.49 250 323 317 – second interim 9.46 3.26 3.91 668 230 276 – third interim 2.90 — — 205 — — 15.90 7.84 8.40 1,123 553 593

Trading Assets (Tables)

Trading Assets (Tables)	12 Months Ended
	Dec. 31, 2018
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Disclosure of Trading Assets	2018 2017 Securities purchased under resale agreements — 8,870 Debt securities — 5,156 Equity securities — 9,662 Cash collateral associated with trading balances — 6,156 Short-term loans — 711 — 30,555

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
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Notional Amounts and Fair Values of Derivatives	The notional amounts in the tables below indicate the nominal value of transactions outstanding at the balance sheet date; they do not represent actual exposures. 2018 2017 Fair value Fair value Notional amount Assets Liabilities Notional amount Assets Liabilities £m £m £m £m £m £m Derivatives held for trading Exchange rate contracts 14,165 455 351 144,160 2,559 4,130 Interest rate contracts 79,522 1,455 1,326 863,151 22,091 21,619 Equity and credit contracts 2,854 278 168 19,814 888 693 Total derivatives held for trading 96,541 2,188 1,845 1,027,125 25,538 26,442 Derivatives held for hedging Designated as fair value hedges: Exchange rate contracts 3,010 357 — 2,641 312 6 Interest rate contracts 86,422 1,065 1,315 59,610 1,272 1,470 Equity derivative contracts — — — 16 — 4 89,432 1,422 1,315 62,267 1,584 1,480 Designated as cash flow hedges: Exchange rate contracts 33,901 3,537 200 23,117 3,206 55 Interest rate contracts 18,808 46 102 12,884 84 115 Equity derivative contracts 69 — 4 26 9 — 52,778 3,583 306 36,027 3,299 170 Total derivatives held for hedging 142,210 5,005 1,621 98,294 4,883 1,650 Derivative netting (1) (1,872 ) (1,872 ) (10,479 ) (10,479 ) Total derivatives 238,751 5,321 1,594 1,125,419 19,942 17,613 (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 £9m (2017: £333m) and the amount of cash collateral paid that had been offset against the gross derivative liabilities was £354m (2017: £706m).
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 2018 Traded on Settled by Not settled by Total £m Traded on Traded Traded on Traded Exchange rate contracts — — 51,076 51,076 — 4,349 — 551 Interest rate contracts — 154,106 30,646 184,752 — 694 — 871 Equity and credit contracts — — 2,923 2,923 — 278 — 172 — 154,106 84,645 238,751 — 5,321 — 1,594 2017 Exchange rate contracts — — 169,918 169,918 — 6,077 — 4,191 Interest rate contracts 71,618 626,600 237,427 935,645 — 12,968 — 12,725 Equity and credit contracts 30 — 19,826 19,856 — 897 1 696 71,648 626,600 427,171 1,125,419 — 19,942 1 17,612
Summary of Fixed Rate Hedged Instruments	The following table shows the fixed rate instruments hedged, their underlying currency and the respective hedged benchmark rates: Instrument Currency Designated benchmark instrument rate Fixed rate mortgages GBP 3-month Fixed rate loans GBP, EUR 3-month Reverse repurchase agreements GBP, USD SONIA, USD Fed Funds Investment assets GBP, EUR, USD SONIA, 3-month Fixed rate savings GBP, USD 3-month
Summary of Possible Sources of Hedge ineffectiveness	Possible sources of hedge ineffectiveness for each type of hedge relationship are set out below: Fair value hedges Cash flow hedges Possible sources of ineffectiveness Portfolio hedges Micro hedges of Micro hedges Micro hedges Equity risk on Hedging derivatives with a non-zero • • • • • Differences in discounting between hedged item and hedging instrument as cash collateralised swaps discount using Overnight Indexed Swaps (OIS) discount curves, not applied to underlying hedged item • • Counterparty credit risk impacts fair value of derivative but not hedged item • • Differences in expected and actual volume of prepayments • Differences in discounting between hedged item and hedging instrument as cash collateralised cross currency swaps discount using OIS discount curves, not applied to underlying hedged item • Differences in timing of cash flows between hedged item and hedging instrument • • • Differences in basis of cash flows between hedged items and hedging instruments • Changes in the expected number of Sharesave options to be exercised •
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: 2018 Hedging Instruments Less than one Later than one Later than Later than Later than Total Fair value hedges: Interest rate risk Interest rate contracts: – Nominal 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/foreign currency (FX) risk Exchange rate contracts: – Nominal amount (£m) 392 1,295 — 1,101 222 3,010 Interest rate contracts: – Nominal 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: – Nominal 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: – Nominal amount (£m) 3,916 2,552 2,961 5,596 — 15,025 Interest rate contracts: – Nominal 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 — Equity risk Equity derivative contracts – Nominal amount (£m) — — 37 32 — 69 Interest rate/FX risk Exchange rate contracts: – Nominal amount (£m) — — 1,773 11,481 5,622 18,876 Interest rate contracts: – Nominal 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 2018 2017 2016 Fair value hedging: Gains/(losses) on hedging instruments 4 56 (274 ) (Losses)/gains on hedged items attributable to hedged risks 75 (2 ) 335 Fair value hedging ineffectiveness 79 54 61 Cash flow hedging ineffectiveness (45 ) (49 ) (33 ) 34 5 28
Summary of Information About Hedging Ineffectiveness by Risk Category	Hedge ineffectiveness can be analysed by risk category as follows: 2018 Changes in FV of hedging Changes in FV of hedged Hedge Fair value hedges: Interest rate risk 26 15 41 Interest rate/FX risk (22 ) 60 38 4 75 79 2018 Income statement line item affected Changes in FV of hedging instruments to calculate hedge ineffectiveness Changes in value of Hedge ineffectiveness Amount reclassified from Cash flow hedges: Interest rate risk Net interest income 20 (14) 6 26 FX risk Net interest income/net trading and other income 17 (19) (2) 9 Equity risk Operating expenses (16) 16 — (10) Interest rate/FX risk Net interest income/net trading and other income 722 (771) (49) 726 743 (788) (45) 751
Summary of Reconciliation by Risk Category of Components of Equity and Analysis of Other Comprehensive Income Items Resulting from Hedge Accounting	Cash flow 2018 £m Balance at 1 January 2018 285 Effective portion of changes in fair value: – Interest rate risk 14 – Foreign currency risk 19 – Equity risk (16 ) – Interest rate/foreign currency risk 771 788 Income statement transfers – Interest rate risk (26 ) – Foreign currency risk (9 ) – Equity risk 10 – Interest rate/foreign currency risk (726 ) (751 ) Balance at 31 December 2018 322
Summary of Details of Hedged Exposures by Hedging Strategies	The following table sets out the exposures covered by the Santander UK group’s hedging strategies: Carrying value Accumulated amount of FV Accumulated amount of FV interest rate Change in Accumulated 2018 Hedged item balance sheet line item Assets Liabilities Assets £m Liabilities Assets £m Liabilities calculating -ness £m balance sheet £m Fair value hedges: Interest rate risk: Loans and advances to customers 42,075 — — — 638 — (149) 729 Other financial assets at amortised cost 6,640 — — — 59 — 59 — Reverse repo agreements – non trading 10,954 — — — — — — — Other financial assets at FVOCI 7,447 — 10 — — — (46) 123 Deposits by customers — 702 — — — (1) — — Deposits by banks — 516 — 15 — — 9 (23) Interest rate/FX risk: Debt securities in issue — 15,112 — 369 — 191 158 (548) Subordinated liabilities — 685 — 152 — 52 44 (214) 67,116 17,015 10 536 697 242 75 67 2018 Hedged item balance sheet line item Change in value used for Cash flow Balances on cash flow Cash flow hedges: Interest rate risk: Loans and advances to customers (19 ) (4 ) (2 ) Loans and advances to banks — (2 ) — Deposits by banks 6 (1 ) — Debt securities in issue (1 ) — — FX risk: Other financial assets at FVOCI 199 (1 ) — Not applicable – highly probable forecast transactions (1 ) — — Debt securities in issue (217 ) 21 3 Equity risk: Other liabilities 16 (3 ) (2 ) Interest rate/FX risk: Debt securities in issue/loans and advances to customers (564 ) 233 50 Subordinated liabilities/loans and advances to customers (207 ) 79 — (788 ) 322 49

Other Financial Assets At Fai_2

Other Financial Assets At Fair Value Through Profit Or Loss (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Other Financial Assets at Fair Value Through Profit or Loss	2018 2017 Loans and advances to customers: Loans to housing associations 13 1,034 Other loans 496 515 509 1,549 Debt securities 3,263 547 Equity securities 93 — Reverse repurchase agreements – non trading 2,272 — 6,137 (1) 2,096 (1) For the Santander UK group, this comprises £1,521m of financial assets designated at FVTPL and £4,616m of financial assets mandatorily at FVTPL.

Loans and Advances to Custome_2

Loans and Advances to Customers (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Net Loans and Advances to Customers	2018 £m 2017 £m Loans secured on residential properties 158,248 155,355 Corporate loans 27,819 30,856 Finance leases 6,821 6,710 Secured advances — — Other unsecured loans 7,554 6,230 Amounts due from fellow Banco Santander subsidiaries and joint ventures 1,997 1,199 Loans and advances to customers 202,439 200,350 Credit impairment loss allowances on loans and advances to customers (751 ) (940 ) RV and voluntary termination provisions on finance leases (69 ) (78 ) Net loans and advances to customers 201,619 199,332
Summary of Movement in Impairment Loss Allowances	Movement in credit impairment loss allowances: Loans secured Other on residential Corporate Finance unsecured properties loans leases loans Total £m £m £m £m £m At 31 December 2017 225 490 46 179 940 Adoption of IFRS 9 (see Note 1) (1) 47 99 11 54 211 Re-allocation off-balance (1) (3 ) (25 ) — (22 ) (50 ) At 1 January 2018 269 564 57 211 1,101 (Release)/charge to the income statement (see Note 8) (18 ) 17 51 139 189 Write-offs and other items (2) (3) (17 ) (355 ) (23 ) (144 ) (539 ) At 31 December 2018 234 226 85 206 751 Recoveries, net of collection costs (see Note 8) 2 1 6 33 42 At 1 January 2017 279 382 45 215 921 (Release)/charge to the income statement (see Note 8) (37 ) 172 20 102 257 Write-offs and other items (2) (17 ) (64 ) (19 ) (138 ) (238 ) At 31 December 2017 225 490 46 179 940 Of which: – Observed 105 433 12 59 609 – Incurred but not yet observed 120 57 34 120 331 225 490 46 179 940 Recoveries, net of collection costs (see Note 8) 3 1 6 44 54 At 1 January 2016 424 395 20 269 1,108 (Release)/charge to the income statement (see Note 8) (116 ) 59 47 142 132 Write-offs and other items (2) (29 ) (72 ) (22 ) (196 ) (319 ) At 31 December 2016 279 382 45 215 921 Of which: – Observed 130 287 13 73 503 – Incurred but not yet observed 149 95 32 142 418 279 382 45 215 921 Recoveries, net of collection costs (see Note 8) 4 3 2 56 65 (1) The adjustment for the adoption of IFRS 9 related to the re-measurement re-allocation off-balance (2) Mortgage write-offs exclude the effect of the unwind over time of the discounting in estimating losses, as described in the accounting policy ‘Financial instruments’ in Note 1. Mortgage write-offs including this effect were £18m (2017: £22m, 2016: £33m) (3) The contractual amount outstanding on financial assets that were written off in the year, and are still subject to enforcement activity was £76m.
Summary of Finance Lease and Hire Purchase Contract Receivables	Finance lease and hire purchase contract receivables may be analysed as follows: 2018 2017 Gross Unearned Net Gross Unearned Net Not later than one year 3,730 (210 ) 3,520 3,633 (177 ) 3,456 Later than one year and not later than five years 3,415 (278 ) 3,137 3,316 (226 ) 3,090 Later than five years 210 (46 ) 164 214 (50 ) 164 7,355 (534 ) 6,821 7,163 (453 ) 6,710

Securitisations and Covered B_2

Securitisations and Covered Bonds (Tables)	12 Months Ended
	Dec. 31, 2018
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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 and the carrying value of the notes in issue at 31 December 2018 and 2017 are listed below. Gross assets External notes in issue Notes issued to Santander UK 2018 2017 2018 2017 2018 £m 2017 Mortgage-backed master trust structures: – Holmes 4,414 4,299 3,182 1,400 463 389 – Fosse 4,646 5,732 199 616 34 34 – Langton 3,034 3,893 — — 2,354 2,355 12,094 13,924 3,381 2,016 2,851 2,778 Other asset-backed securitisation structures: – Motor 1,055 1,318 738 852 374 514 – Auto ABS UK Loans 1,468 1,498 1,212 1,240 316 306 2,523 2,816 1,950 2,092 690 820 Total securitisation programmes 14,617 16,740 5,331 4,108 3,541 3,598 Covered bond programme: – Euro 35bn Global Covered Bond Programme 21,578 19,772 18,653 16,866 — — Total securitisation and covered bond programmes 36,195 36,512 23,984 20,974 3,541 3,598 Less: held by the Santander UK group: – Euro 35bn Global Covered Bond Programme (539 ) (1,067 ) Total securitisation and covered bond programmes (see Note 28) 23,445 19,907
Summary of Issuances and Redemptions of Securitisation and Covered Bond Programme	The following table sets out the internal and external issuances and redemptions in 2018 and 2017 for each securitisation and covered bond programme. Internal issuances External issuances Internal External 2018 2017 2018 2017 2018 2017 2018 2017 £bn £bn £bn £bn £bn £bn £bn £bn Mortgage-backed master trust structures: – Holmes 0.1 — 1.8 0.5 — 0.2 0.1 1.8 – Fosse — — — — — 0.1 0.4 1.8 Other asset-backed securitisation structures: – Motor — 0.1 — 0.5 0.1 0.1 0.1 0.3 – Auto ABS UK Loans — 0.2 0.4 0.7 — — 0.4 0.7 Covered bond programme — — 4.3 2.3 0.5 0.3 1.9 3.2 0.1 0.3 6.5 4.0 0.6 0.7 2.9 7.8

Transfers of Financial Assets_2

Transfers of Financial Assets Not Qualifying for Derecognition (Tables)	12 Months Ended
	Dec. 31, 2018
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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: 2018 2017 Assets Liabilities Assets Liabilities Nature of transaction £m £m £m £m Sale and repurchase agreements 7,642 (7,188 ) 10,808 (7,734 ) Securities lending agreements 144 (120 ) 302 (235 ) Securitisations (See Notes 15 and 28) 11,583 (5,331 ) 12,847 (4,108 ) 19,369 (12,639 ) 23,957 (12,077 )

Reverse Repurchase Agreements_2

Reverse Repurchase Agreements - Non Trading (Tables)	12 Months Ended
	Dec. 31, 2018
Reverse repurchase agreements - non-trading [member]
Statement [LineItems]
Summary of Reverse Repurchase Agreements - Non Trading	2018 2017 Agreements with banks 3,254 2,464 Agreements with customers 17,873 150 21,127 2,614

Other Financial Assets At Amo_2

Other Financial Assets At Amortised Cost (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Other Financial Assets at Amortised Cost	2018 2017 Asset backed securities (1) 719 Debt securities (2) 6,509 7,228 (1) These securities were previously classified as ‘Financial investments’ under IAS 39. See Note 44. (2) These debt securities were previously classified as held-to-maturity

Financial Assets At Fair Valu_2

Financial Assets At Fair Value Through Other Comprehensive Income (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Financial Assets at Fair Value Through Other Comprehensive Income	2018 2017 Debt securities (1) 13,229 Loans and advances to customers (2) 73 13,302 (1) These debt securities were previously classified as available-for-sale (2) These comprise other loans and receivables mainly held within hold to collect and sell business models that were moved from trading assets and loans and advances to customers at amortised cost, to ‘Financial assets at FVOCI’, due to their reclassification to FVOCI on adoption of IFRS 9. See Note 44.

Financial Investments (Tables)

Financial Investments (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Financial Investments	2018 2017 Asset backed securities (1) 2,180 Debt securities: – Available-for-sale (2) 8,772 – Held-to-maturity (3) 6,578 Available-for-sale (4) 81 17,611 (1) These were reclassified to ‘Other financial assets at amortised cost’ and ‘Other financial assets at fair value through profit or loss’ on adoption of IFRS 9. See Note 44. (2) These were reclassified to ‘Financial assets at FVOCI’ and ‘Other financial assets at fair value through profit or loss’ on adoption of IFRS 9. See Note 44. (3) These were reclassified to ‘Other financial assets at amortised cost’ on adoption of IFRS 9. See Note 44. (4) These were reclassified to ‘Other financial assets at fair value through profit or loss’ on adoption of IFRS 9. See Note 44.

Interests in Other Entities (Ta

Interests in Other Entities (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Schedule of Interests in Other Entities	2018 2017 Joint ventures 88 73 88 73
Schedule of Subsidiaries With Significant Non-Controlling Interests	2018 2017 Profit attributable to non-controlling 22 21 Accumulated non-controlling 151 152 Dividends paid to non-controlling 22 19 Summarised financial information: – Total assets 3,289 3,215 – Total liabilities 2,987 2,909 – Profit for the year 43 43 – Total comprehensive income for the year 43 43
Santander UK Group Holdings plc [member]
Statement [LineItems]
Summary of Interest in Other Entities	2018 2017 Interests in ordinary shares of subsidiaries 11,645 11,268 £500m Fixed Rate Reset Perpetual AT1 Capital Securities 495 495 £750m Fixed Rate Reset Perpetual AT1 Capital Securities 750 750 £300m Perpetual Capital Securities 300 300 £500m Perpetual Capital Securities 210 500 13,400 13,313
Summary of companys interests in subsidiaries	The movement in the Company’s interests in subsidiaries was as follows: Cost £m Impairment Net book At 1 January 2017, 31 December 2017 and 1 January 2018 11,268 — 11,268 Additions 377 — 377 At 31 December 2018 11,645 — 11,645

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2018
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Schedule of Goodwill	a) Goodwill Cost Accumulated Net book value £m £m £m At 31 December 2017, 1 January 2018 and 31 December 2018 1,285 (82 ) 1,203
Schedule of Goodwill for Cash Generating Units	The following CGUs (all within Retail Banking) 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 (1) 2018 2017 2018 2017 2018 2017 CGU £m £m % % % % Personal financial services 1,169 1,169 10.5 10.8 2 1 Private banking 30 30 10.5 10.8 2 1 Other 4 4 10.5 10.8 2 1 1,203 1,203 (1) Average growth rate based on the five-year plan for the first five years and a growth rate of 2.0 % (2017: 1.5%) applied thereafter.
Schedule of Other Intangibles	b) Other intangibles Cost Accumulated Net book value At 1 January 2018 962 (423 ) 539 Additions 213 — 213 Write offs (76 ) 76 — Charge — (141 ) (141 ) Sales — — — At 31 December 2018 1,099 (488 ) 611 At 1 January 2017 760 (278 ) 482 Additions 205 — 205 Disposals (3 ) 3 — Charge — (116 ) (116 ) Impairment — (32 ) (32 ) At 31 December 2017 962 (423 ) 539

Trading Liabilities (Tables)

Trading Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Schedule of Trading Liabilities	2018 2017 Securities sold under repurchase agreements — 25,504 Short positions in securities and unsettled trades — 3,694 Cash collateral — 1,911 — 31,109

Other Financial Liabilities a_2

Other Financial Liabilities at Fair Value Through Profit or Loss (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Other Financial Liabilities at Fair Value Through Profit or Loss	2018 2017 US$10bn Euro Commercial Paper Programme — 387 US$30bn Euro Medium Term Note Programme 165 169 Structured Notes Programmes 696 932 Eurobonds 129 147 Structured deposits 133 680 Collateral and associated financial guarantees 3,053 — Repurchase agreements – non trading 2,110 — 6,286 (1) 2,315 (1) For the Santander UK group, this comprises £6,286m of financial liabilities designated at fair value through profit or loss and £nil of financial liabilities mandatorily at fair value through profit or loss.

Deposits by Customers (Tables)

Deposits by Customers (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Schedule of Deposits by Customers	2018 £m 2017 Current and demand accounts 87,316 85,780 Savings accounts (1) 69,102 70,461 Time deposits 16,204 20,453 Amounts due to fellow Banco Santander subsidiaries and joint ventures 1,070 727 173,692 177,421 (1) Includes equity index-linked deposits of £1,176m (2017: £1,301m). The capital amount guaranteed/protected and the amount of return guaranteed in respect of the equity index-linked deposits were £1,176m and £28m (2017: £1,301m and £67m) respectively.

Deposits by Banks (Tables)

Deposits by Banks (Tables)	12 Months Ended
	Dec. 31, 2018
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Schedule of Deposits by Banks	2018 2017 Items in the course of transmission 262 303 Deposits held as collateral 4,058 1,760 Other deposits (1) 13,504 10,645 17,824 12,708 (1) Includes drawdown from the TFS of £10.8bn (2017: £8.5bn).

Repurchase Agreements - Non T_2

Repurchase Agreements - Non Trading (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Repurchase Agreements - Non Trading	2018 2017 Agreements with banks 5,865 1,076 Agreements with customers 5,045 — 10,910 1,076

Debt Securities in Issue (Table

Debt Securities in Issue (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Debt Securities in Issue	2018 2017 Medium-term notes: – US$30bn Euro Medium Term Note Programme 7,229 8,816 – Euro 30bn Euro Medium Term Note Programme 5,348 2,177 – US SEC-registered 5,841 4,050 – US SEC-registered 7,649 6,280 – US$20bn Commercial Paper Programmes 3,131 2,906 29,198 24,229 Euro 35bn Global Covered Bond Programme (See Note 15) 18,114 15,799 Certificates of deposit 3,221 4,681 Credit linked notes 42 43 Securitisation programmes (See Note 15) 5,331 4,108 55,906 48,860

Subordinated Liabilities (Table

Subordinated Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Schedule of Subordinated Liabilities	2018 2017 £325m Sterling Preference Shares 344 344 £175m Fixed/Floating Rate Tier One Preferred Income Capital Securities — 2 Undated subordinated liabilities 574 584 Dated subordinated liabilities 2,683 2,863 3,601 3,793
Summary of Undated Subordinated Liabilities	First call date 2018 2017 10.0625% Exchangeable capital securities n/a 205 205 7.375% 20 Year Step-up 2020 16 17 7.125% 30 Year Step-up 2030 353 362 574 584
Summary of Dated Subordinated Liabilities	Dated subordinated liabilities Maturity 2018 2017 10.125% Subordinated guaranteed bonds 2023 — 78 9.625% Subordinated notes 2023 — 129 5% Subordinated notes (US$1,500m) 2023 1,173 1,103 4.75% Subordinated notes (US$1,000m) 2025 791 745 7.95% Subordinated notes (US$1,000m) 2029 278 275 6.50% Subordinated notes 2030 38 40 8.963% Subordinated notes (US$1,000m) 2045 — 113 5.875% Subordinated notes 2031 9 9 5.625% Subordinated notes (US$500m) 2045 394 371 2,683 2,863
Santander UK Group Holdings plc [member]
Statement [LineItems]
Schedule of Subordinated Liabilities	Dated subordinated liabilities Maturity 2018 2017 4.75% Subordinated notes (US$1,000m) 2025 791 745 5.625% Subordinated notes (US$500m) 2045 394 371 1,185 1,116

Provisions (Tables)

Provisions (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Provisions Reconciliation	Conduct remediation PPI Other FSCS and Vacant Off-balance Regulatory Total At 31 December 2017 356 47 57 39 59 558 Reallocation of ECL on off-balance (1) — — — — 50 — 50 At 1 January 2018 356 47 57 39 50 59 608 Additional provisions (see Note 8) — — 69 15 6 208 298 Provisions released (see Note 8) — (14 ) (4 ) — — (14 ) (32 ) Utilisation (110 ) (3 ) (92 ) (14 ) — (154 ) (373 ) Other — — 14 (2) — — — 14 At 31 December 2018 246 30 44 40 56 99 515 To be settled: – Within 12 months 246 22 44 25 56 99 492 – In more than 12 months — 8 — 15 — — 23 246 30 44 40 56 99 515 At 1 January 2017 457 36 96 47 64 700 Additional provisions 109 35 93 4 144 385 Utilisation (210 ) (34 ) (132 ) (12 ) (149 ) (537 ) Transfers — 10 — — — 10 At 31 December 2017 356 47 57 39 59 558 To be settled: – Within 12 months 167 38 57 23 59 344 – In more than 12 months 189 9 — 16 — 214 356 47 57 39 59 558 (1) ECL on off-balance (2) Santander UK plc recharged £14m (2017: £nil) in respect of the UK Bank Levy paid on behalf of other UK entities of Banco Santander SA.
Summary of Key Drivers of PPI Provision Balance and Forecast Assumptions Used in Calculating Provision	The remainder of the provision relates to portfolios of complaints which were on hold pending further regulatory clarification in respect of which utilisation will begin in 2019, and to our best estimate of liability in respect of a legal dispute regarding allocation of responsibility for a specific portfolio further described in Note 32. No further information regarding the best estimate has been provided on the basis it would be seriously prejudicial. Cumulative to Future expected Sensitivity analysis Inbound complaints (1) 2,141 415 25 = £7.4m Outbound contact (‘000) 488 217 25 = £5.4m Response rate to outbound contact 54 % 64 % 1% = £0.8m Average uphold rate per claim (2) 37 % 76 % 1% = £2.7m Average redress per claim (3) £ 1,474 £ 545 £ 50 = £16.4m (1) Includes all claims, including the specific portfolio of complaints referred to above, regardless of the likelihood of the Santander UK group incurring a liability. Excludes claims where the complainant has not held a PPI policy. (2) Claims include inbound and responses to outbound contact. (3) The average redress per claim reduced from the cumulative average value at 31 December 2018 of £1,474 to a future average value of £545 due to the inclusion of Plevin cases in the provision, as well as a shift in the complaint mix to a greater proportion of storecards, which typically held lower average balances.

Retirement Benefit Plans (Table

Retirement Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2018
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Summary of Retirement Benefit Plans	The amounts recognised in the balance sheet were as follows: 2018 2017 £m £m Assets/(liabilities) Funded defined benefit pension scheme – surplus 842 449 Funded defined benefit pension scheme – deficit (76 ) (245 ) Unfunded defined benefit pension scheme (39 ) (41 ) Total net assets 727 163
Summary of Pension Remeasurement (Gains)/Losses Recognised In Other Comprehensive Income	Remeasurement (gains)/losses recognised in other comprehensive income during the year were as follows: 2018 2017 2016 £m £m £m Pension remeasurement (469 ) 103 528
Total defined benefit plan amount charged to the income statement	The total amount charged to the income statement was as follows: 2018 2017 2016 £m £m £m Net interest income (7 ) (5 ) (18 ) Current service cost 41 31 33 Past service and GMP costs 41 1 1 Administration costs 8 8 8 83 35 24
Summary of Amounts Recognised in Other Comprehensive Income	The amounts recognised in other comprehensive income were as follows: 2018 2017 2016 £m £m £m Return on plan assets (excluding amounts included in net interest expense) 246 (435 ) (1,447 ) Actuarial (gains)/losses arising from changes in demographic assumptions (56 ) (151 ) 30 Actuarial gains arising from experience adjustments 15 (11 ) (80 ) Actuarial (gains)/losses arising from changes in financial assumptions (674 ) 700 2,025 Pension remeasurement (469 ) 103 528
Disclosure of Movements in Present Value of Defined Benefit Obligations	Movements in the present value of defined benefit scheme obligations were as follows: 2018 2017 £m £m At 1 January (11,583 ) (11,082 ) Current service cost paid by Santander UK plc (27 ) (30 ) Current service cost paid by other subsidiaries (14 ) (1 ) Current service cost paid by fellow Banco Santander subsidiaries — (12 ) Interest cost (282 ) (305 ) Employer salary sacrifice contributions (6 ) (6 ) Past service cost (1 ) (1 ) GMP equalisation cost (40 ) — Remeasurement due to actuarial movements arising from: – Changes in demographic assumptions 56 151 – Experience adjustments (15 ) 11 – Changes in financial assumptions 674 (700 ) Benefits paid 433 392 At 31 December (10,805 ) (11,583 )
Disclosure of Movements in Fair Value of Schemes' Assets	Movements in the fair value of the schemes’ assets were as follows: 2018 2017 £m £m At 1 January 11,746 11,218 Interest income 289 310 Contributions paid by employer and scheme members 184 171 Contributions paid by fellow Banco Santander subsidiaries — 12 Administration costs paid (8 ) (8 ) Return on plan assets (excluding amounts included in net interest expense) (246 ) 435 Benefits paid (433 ) (392 ) At 31 December 11,532 11,746
Summary of Composition and Fair Value of Plan Assets	The composition and fair value of the schemes’ assets by category was: Quoted prices in Prices not quoted in Total 2018 £m % £m % £m % 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 — — (2,981 ) (26 ) (2,981 ) (26 ) Other — — 1,021 9 1,021 9 10,433 90 1,099 10 11,532 100 2017 UK equities 187 1 — — 187 1 Overseas equities 2,204 19 706 6 2,910 25 Corporate bonds 1,665 14 209 2 1,874 16 Government fixed interest bonds 255 2 — — 255 2 Government index-linked bonds 3,506 30 — — 3,506 30 Property — — 1,547 13 1,547 13 Derivatives — — 512 4 512 4 Cash — — 206 2 206 2 Other — — 749 7 749 7 7,817 66 3,929 34 11,746 100
Summary of Principal Actuarial Assumptions Used for Defined Benefit Schemes	The principal actuarial assumptions used for the defined benefit schemes were: 2018 2017 2016 To determine benefit obligations: – Discount rate for scheme liabilities 2.9 2.5 2.8 – General price inflation 3.2 3.2 3.1 – 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 27.4 27.8 – Females 30.1 30.1 30.3 Longevity at 60 for future pensioners currently aged 40, on the valuation date: – Males 28.7 28.9 30.0 – Females 31.6 31.7 32.2
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. Increase/(decrease) Assumption Change in pension obligation at year-end from 2018 2017 Discount rate 25 bps increase (483 ) (550 ) General price inflation 25 bps increase 350 365 General salary increase 25 bps increase n/a n/a Mortality Each additional year of longevity assumed 335 367
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 2019 266 2020 269 2021 287 2022 309 2023 325 Five years ending 2028 1,903

Contingent Liabilities And Co_2

Contingent Liabilities And Commitments (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Contingent Liabilities and Commitments	2018 (1) 2017 Guarantees given to third parties 1,611 1,557 Formal standby facilities, credit lines and other commitments with original term to maturity of: – One year or less 8,560 10,664 – Later than one year 31,566 31,278 41,737 43,499 (1) For segmental and credit risk staging analysis relating to off-balance
Operating Lease Commitments	Operating lease commitments Rental commitments under non-cancellable 2018 2017 Not later than one year 73 73 Later than one year and not later than five years 114 160 Later than five years 60 70 247 303

Share Capital (Tables)

Share Capital (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Schedule of Share Capital Issued and Fully Paid	Ordinary shares of £1 each Issued and fully paid share capital No. £m At 31 December 2017, 1 January 2018 and 31 December 2018 7,060,000,000 7,060

Other Equity Instruments (Table

Other Equity Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of other equity instruments	Initial interest rate First call date 2018 2017 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 745 745 – £300m Perpetual Capital Securities 7.60 December 2019 300 300 – £500m Perpetual Capital Securities 6.625 June 2019 500 500 2,041 2,041

Non-Controlling Interests (Tabl

Non-Controlling Interests (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Schedule of Amounts Attributable to Non-Controlling Interests	Initial interest rate First call date 2018 2017 Santander UK plc issued: – £300m Fixed/Floating Rate Non-Cumulative 6.222 May 2019 14 14 – £300m Step-up 7.037 February 2026 235 235 PSA Finance UK Limited 151 152 400 401

Changes in Liabilities Arisin_2

Changes in Liabilities Arising from Financing Activities (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Summary of Changes in Liabilities Arising from Financing Activities	The table below shows the changes in liabilities arising from financing activities. 2018 2017 Balance sheet line item Balance sheet line item Debt Subordinated £m Other instruments Dividends Total Debt Subordinated Other Dividends Total At 1 January 48,860 3,793 2,041 — 54,694 54,792 4,303 1,545 — 60,640 Cash flows from financing activities 7,272 (277 ) — (1,308 ) 5,687 (4,986 ) (52 ) 496 (1,001 ) (5,543 ) Cash flows from operating activities (2,760 ) (2 ) — — (2,762 ) 112 254 — — 366 Non-cash – Unrealised foreign exchange (2,085 ) 149 — — (1,936 ) (685 ) (235 ) — — (920 ) – Other changes 4,619 (62 ) — 1,308 5,865 (373 ) (477 ) — 1,001 151 At 31 December 55,906 3,601 2,041 — 61,548 48,860 3,793 2,041 — 54,694
Santander UK Group Holdings plc [member]
Statement [LineItems]
Summary of Changes in Liabilities Arising from Financing Activities	The table below shows the changes in liabilities arising from financing activities. 2018 2017 Balance sheet line item Balance sheet line item Debt securities in issue £m Subordinated liabilities £m Other equity instruments £m Dividends paid £m Total £m Debt Subordinated Other equity Dividends Total At 1 January 6,256 1,116 2,041 — 9,413 4,464 1,222 1,545 — 7,231 Cash flows from financing activities 2,658 — — (1,268 ) 1,390 2,103 — 496 (964 ) 1,635 Cash flows from operating activities (7 ) — — — (7 ) (3 ) — — — (3 ) Non-cash – Unrealised foreign exchange 418 — — — 418 (324 ) (106 ) — — (430 ) – Other changes (30 ) 69 — 1,268 1,307 16 — — 964 980 At 31 December 9,295 1,185 2,041 — 12,521 6,256 1,116 2,041 — 9,413

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, 2018
Text block [abstract]
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 2018 2017 On-balance Cash and balances at central banks 1,080 1,010 Trading assets — 17,092 Loans and advances to customers — securitisations and covered bonds (See Note 15) 35,694 35,421 Loans and advances to customers — other 16,402 15,078 Loans and advances to banks 402 105 Other financial assets at amortised cost 3,763 Financial assets at fair value through other comprehensive income 5,825 Financial investments 6,755 Total on-balance 63,166 75,461 Total off-balance 15,221 33,013
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 2018 2017 £m £m On-balance Trading liabilities — 1,911 Deposits by customers — 8 Deposits by banks 4,058 1,760 Total on-balance 4,058 3,679 Total off-balance 23,473 38,655

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Summary of Movement in Share Options	The table below summarises movements in the number of options during the year, and changes in weighted average exercise price over the same period. 2018 2017 2016 Number of Weighted Number of Weighted Number of Weighted Outstanding at 1 January 27,201 3.12 28,916 3.08 24,762 3.53 Granted 6,210 3.46 3,916 4.02 17,296 4.91 Exercised (3,340 ) 3.16 (1,918 ) 3.77 (338 ) 3.67 Forfeited/expired (3,233 ) 3.76 (3,713 ) 3.40 (12,804 ) 3.51 Outstanding at 31 December 26,838 3.12 27,201 3.12 28,916 3.08 Exercisable at 31 December 10,370 2.81 5,200 3.17 2,334 4.30
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 2018 and 2017. 2018 2017 Weighted average Weighted Weighted average Weighted remaining average remaining average contractual life exercise price contractual life exercise price Range of exercise prices Years £ Years £ £2 to £ 3 2 2.75 3 2.75 £3 to £4 3 3.36 1 3.17 £4 to £5 3 4.11 3 4.21
2015 LTIP [member]
Statement [LineItems]
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 2018, 2017 and 2016: 2015 LTIP 2014 LTIP 2018 2017 2016 2018 2017 2016 £000 £000 £000 £000 £000 £000 Outstanding at 1 January 6,503 6,718 6,769 1,910 3,193 5,102 Forfeited/cancelled (129 ) (215 ) (1) (51 ) (1,910 ) (1,283 ) (1) (1,909 ) Outstanding at 31 December 6,374 6,503 6,718 — 1,910 3,193 (1) The outstanding shares have been updated to compensate for the equity dilution caused by the shares issued by Banco Santander SA in July 2017.

Transactions With Directors a_2

Transactions With Directors and Other Key Management Personnel (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
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. Directors’ remuneration 2018 £ 2017 2016 Salaries and fees 5,028,434 4,406,908 3,604,999 Performance-related payments (1) 5,194,317 3,685,464 2,330,000 Other fixed remuneration (pension and other allowances & non-cash 1,467,011 1,580,321 635,493 Expenses 25,198 96,358 120,302 Total remuneration 11,714,960 9,769,051 6,690,794 Directors’ and Other Key Management Personnel compensation 2018 £ 2017 2016 Short-term employee benefits (2) 24,445,189 24,642,085 24,757,161 Post-employment benefits (3) 2,399,261 2,292,857 1,918,144 Total compensation 26,844,450 26,934,942 26,675,305 (1) In line with the Code, a proportion of the performance-related payment was deferred. Further details can be found in Note 38. (2) Excludes grants of shares in Banco Santander SA made as buy-outs buy-outs (3) Termination payments of £847,388 were paid in 2018 to two key management persons (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. 2018 2017 No. £000 No. £000 Secured loans, unsecured loans and overdrafts At 1 January 7 1,216 17 5,195 Net movements 9 1,819 (10 ) (3,979 ) At 31 December 16 3,035 7 1,216 Deposit, bank and instant access accounts and investments At 1 January 25 13,184 26 9,138 Net movements 5 (2,221 ) (1 ) 4,046 At 31 December 30 10,963 25 13,184

Related Party Disclosures (Tabl

Related Party Disclosures (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Transactions With Related Parties	Transactions with related parties during the year and balances outstanding at the year-end: Interest, fees and Interest, fees and Amounts owed Amounts owed to 2018 2017 2016 2018 2017 2016 2018 2017 2018 2017 Ultimate parent (73 ) (60 ) (81 ) 231 321 188 2,737 4,398 (3,854 ) (5,082 ) Fellow subsidiaries (81 ) (76 ) (271 ) 169 491 653 39 102 (591 ) (981 ) Associates & joint ventures (28 ) (20 ) (27 ) — — 1 1,986 1,175 (718 ) (33 ) (182 ) (156 ) (379 ) 400 812 842 4,762 5,675 (5,163 ) (6,096 )

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Fair Values of Financial Instruments Carried at Amortised Cost	2018 2017 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 — — 204,391 204,391 201,619 — 6,331 195,327 201,658 199,332 Loans and advances to banks — 3,028 448 3,476 3,515 — 2,897 556 3,453 3,466 Reverse repurchase agreements – non trading — 21,130 — 21,130 21,127 — 2,614 — 2,614 2,614 Other financial assets at amortised cost 6,390 720 — 7,110 7,228 Financial investments 6,435 2,211 — 8,646 8,758 6,390 24,878 204,839 236,107 233,489 6,435 14,053 195,883 216,371 214,170 Liabilities Deposits by customers — 21 173,762 173,783 173,692 — — 177,563 177,563 177,421 Deposits by banks — 16,859 977 17,836 17,824 — 12,164 557 12,721 12,708 Repurchase agreements – non trading — 10,923 — 10,923 10,910 — 1,085 — 1,085 1,076 Debt securities in issue — 56,695 — 56,695 55,906 — 50,641 — 50,641 48,860 Subordinated liabilities — 3,825 — 3,825 3,601 — 4,373 — 4,373 3,793 — 88,323 174,739 263,062 261,933 — 68,263 178,120 246,383 243,858
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 2018 and 2017, analysed by their levels in the fair value hierarchy – Level 1, Level 2 and Level 3. 2018 2017 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total £m Valuation Assets Trading assets Securities purchased under resale agreements — — — — — 8,870 — 8,870 A Debt securities — — — — 5,156 — — 5,156 — Equity securities — — — — 9,662 — — 9,662 — Cash collateral — — — — — 6,156 — 6,156 A Short-term loans — — — — 656 55 — 711 A — — — — 15,474 15,081 — 30,555 Derivative financial instruments Exchange rate contracts — 4,324 25 4,349 — 6,061 16 6,077 A Interest rate contracts — 2,560 6 2,566 — 23,435 12 23,447 A & C Equity and credit contracts — 194 84 278 — 861 36 897 B & D Netting — (1,872 ) — (1,872 ) — (10,479 ) — (10,479 ) — 5,206 115 5,321 — 19,878 64 19,942 Other financial assets at FVTPL Loans and advances to customers — 427 82 509 — 1,485 64 1,549 A Debt securities 26 2,343 894 3,263 184 187 176 547 A, B & D Equity securities 14 — 79 93 B Reverse repurchase agreements – non trading — 2,272 — 2,272 — — — — A 40 5,042 1,055 6,137 184 1,672 240 2,096 Financial assets at FVOCI Debt securities 12,487 742 — 13,229 D Loans and advances to customers — — 73 73 D 12,487 742 73 13,302 Financial investments Available-for-sale 8,770 2 — 8,772 C Available-for-sale 19 9 53 81 B 8,789 11 53 8,853 Total assets at fair value 12,527 10,990 1,243 24,760 24,447 36,642 357 61,446 Liabilities Trading liabilities Securities sold under repurchase agreements — — — — — 25,504 — 25,504 A Short positions in securities and unsettled trades — — — — 3,694 — — 3,694 — Cash collateral — — — — — 1,911 — 1,911 A Short-term deposits — — — — — — — — — — — — — 3,694 27,415 — 31,109 Derivative financial instruments Exchange rate contracts — 528 23 551 — 4,176 15 4,191 A Interest rate contracts — 2,736 7 2,743 — 23,199 5 23,204 A & C Equity and credit contracts — 132 40 172 1 653 43 697 B & D Netting — (1,872 ) — (1,872 ) — (10,479 ) — (10,479 ) — 1,524 70 1,594 1 17,549 63 17,613 Other financial liabilities at FVTPL Debt securities in issue — 983 7 990 — 1,629 6 1,635 A Structured deposits — 104 29 133 — 680 — 680 A Repurchase agreements – non trading — 2,110 — 2,110 — — — — A Collateral and associated financial guarantees — 3,040 13 3,053 D — 6,237 49 6,286 — 2,309 6 2,315 Total liabilities at fair value — 7,761 119 7,880 3,695 47,273 69 51,037
Summary of Fair Value Adjustment	The magnitude and types of fair value adjustment are listed in the following table: 2018 2017 Risk-related: – Bid-offer 13 34 – Uncertainty 36 43 – Credit risk adjustment 9 36 – Funding fair value adjustment 4 6 62 119 Model-related 5 8 Day One profit — 1 67 128
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 Balance sheet line item Category Financial instrument product type 2018 2017 £m 2018 2017 2016 1. Derivative assets Equity and credit contracts Reversionary property interests 54 31 30 (6 ) 12 2. FVTPL assets Loans and advances to customers Roll-up 53 64 8 2 4 3. FVTPL assets Debt securities Reversionary property securities 142 176 (28 ) (18 ) — 4. FVTPL assets (1) Equity securities (1) Unlisted equity shares 79 53 19 — — 5. FVTPL assets Debt securities Credit linked notes 752 — 13 — — 6. FVOCI assets Loans and advances to customers Other loans 73 — (5 ) — — 7. Derivative liabilities Equity contracts Property-related options and forwards (35 ) (43 ) — (5 ) (5 ) 8. FVTPL liabilities Financial guarantees Credit protection guarantee (13 ) — (13 ) — — 1,105 281 24 (27 ) 11 Other Level 3 assets 90 33 — (26 ) 6 Other Level 3 liabilities (71 ) (26 ) 1 19 (10 ) Total net assets 1,124 288 Total income/(expense) 25 (34 ) 7 (1) Prior to 1 January 2018, these unlisted equity shares were classified as available-for-sale
Reconciliation of Fair Value Measurements in Level 3 of the Fair Value Hierarchy	The following table sets out the movements in Level 3 financial instruments in 2018 and 2017: Assets Liabilities Derivatives Other financial Financial Financial Total Derivatives Other financial Total At 31 December 2017 64 240 53 357 (63 ) (6 ) (69 ) Adoption of IFRS 9 – 598 199 (53 ) 744 — — — At 1 January 2018 64 838 199 — 1,101 (63 ) (6 ) (69 ) Total (losses)/gains recognised in profit or loss: – Fair value movements 28 14 (5 ) 37 1 (13 ) (12 ) – Foreign exchange and other movements (5 ) — — (5 ) 5 (1 ) 4 Transfers in 56 18 — 74 (35 ) (29 ) (64 ) Additions — 280 17 297 — — — Sales — (95 ) — (95 ) — — — Settlements (28 ) — (138 ) (166 ) 22 — 22 At 31 December 2018 115 1,055 73 1,243 (70 ) (49 ) (119 ) (Losses)/gains recognised in profit or loss relating to assets and liabilities held at the end of the year 23 14 (5 ) 32 6 (14 ) (8 ) At 1 January 2017 103 264 32 399 (74 ) (6 ) (80 ) Total (losses)/gains recognised in profit or loss: – Fair value movements (32 ) (16 ) — (48 ) 14 — 14 – Foreign exchange and other movements 32 — — 32 (32 ) — (32 ) Gains recognised in other comprehensive income — — 21 21 — — — Additions 9 — — 9 (2 ) — (2 ) Sales — (8 ) — (8 ) — — — Settlements (48 ) — — (48 ) 31 — 31 At 31 December 2017 64 240 53 357 (63 ) (6 ) (69 ) (Losses)/gains recognised in profit or loss relating to assets and liabilities held at the end of the year — (16 ) — (16 ) (18 ) — (18 )
Effects of Changes in Significant Unobservable Assumptions to Reasonably Possible Alternatives (Level 3)	Significant unobservable input Shift Sensitivity Assumption value Favourable Unfavourable 2018 Fair value Assumption description Range (1) Weighted 1. Derivative assets 54 HPI Forward growth rate 0% – 5% 2.68 % 1 % 8 (8 ) – Reversionary property derivatives HPI Spot rate n/a 783 10 % 7 (7 ) 2. FVTPL 53 HPI Forward growth rate 0% – 5% 2.77 % 1 % 2 (2 ) – Roll-up 3. FVTPL 142 HPI Forward growth rate 0% – 5% 2.68 % 1 % 6 (6 ) – Reversionary property securities HPI Spot rate n/a 783 (2) 10 % 10 (10 ) 4. FVTPL 79 Contingent litigation risk 0% – 100% 29 % 20 % 6 (6 ) – Unlisted equity shares 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 n/a 722 (2) 10 % 3 (4 ) 2017 1. Derivative assets 31 HPI Forward growth rate 0% – 5% 2.42 % 1 % 10 (10 ) – Reversionary property derivatives HPI Spot rate n/a 773 10 % 8 (8 ) 2. FVTPL 64 HPI Forward growth rate 0% – 5% 2.57 % 1 % 2 (2 ) – Roll-up 3. FVTPL 176 HPI Forward growth rate 0% – 5% 2.42 % 1 % 3 (3 ) – Reversionary property securities HPI Spot rate n/a 773 (2) 10 % 11 (11 ) 4. Financial investments 53 Contingent litigation risk 0% – 100% 35 % 20 % 6 (6 ) – Unlisted equity shares 7. Derivative liabilities (43 ) HPI Forward growth rate 0% – 5% 2.32 % 1 % 3 (3 ) – Property-related options and forwards HPI Spot rate n/a 727 (2) 10 % 7 (8 ) (1) The range of actual assumption values used to calculate the weighted average disclosure. (2) Represents the HPI spot rate index level at 31 December 2018 and 2017.
Maturities of Undiscounted Cash Flows for Financial Liabilities and Off Balance Sheet Commitments	2018 On demand Not later than Later than Later than Later than Total Financial liabilities Trading liabilities — — — — — — Derivative financial instruments — 431 61 104 1,170 1,766 Other financial liabilities at fair value through profit or loss 11 2,146 76 408 3,855 6,496 Deposits by customers 151,284 4,640 11,350 5,328 1,373 173,975 Deposits by banks 5,692 1,108 93 11,106 52 18,051 Repurchase agreements – non trading 2 9,101 972 849 517 11,441 Debt securities in issue — 9,194 5,677 28,553 15,384 58,808 Subordinated liabilities — 255 134 709 5,279 6,377 Total financial liabilities 156,989 26,875 18,363 47,057 27,630 276,914 Off-balance 1,106 5,843 670 13,418 18,987 40,024 2017 Financial liabilities Trading liabilities 1,520 26,914 152 161 2,580 31,327 Derivative financial instruments: 15 631 1,230 2,925 14,001 18,802 Other financial liabilities at fair value through profit or loss 7 545 222 789 814 2,377 Deposits by customers 154,114 4,754 13,811 3,454 1,490 177,623 Deposits by banks 2,452 1,465 82 8,626 208 12,833 Repurchase agreements – non trading — 1 832 248 — 1,081 Debt securities in issue — 8,419 4,940 25,950 11,644 50,953 Subordinated liabilities — 289 147 783 5,571 6,790 Total financial liabilities 158,108 43,018 21,416 42,936 36,308 301,786 Off-balance 2,082 6,874 1,844 12,399 18,860 42,059

Offsetting Financial Assets a_2

Offsetting Financial Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2018
Text block [abstract]
Summary of Information about Impact of Offsetting of Financial Assets and Liabilities	Amounts subject to enforceable netting arrangements Balance (3) Effects of offsetting on balance sheet Related amounts not offset Assets not (2) 2018 Gross Amount Net amount Financial Financial (1) Net Assets Derivative financial instruments 7,088 (1,872 ) 5,216 (933 ) (2,133 ) 2,150 105 5,321 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) 6,820 (1,308 ) 5,512 — — 5,512 199,622 205,134 40,913 (6,786 ) 34,127 (3,654 ) (22,811 ) 7,662 199,727 233,854 Liabilities Derivative financial instruments 3,412 (1,872 ) 1,540 (933 ) (303 ) 304 54 1,594 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) 2,879 (1,308 ) 1,571 — (502 ) 1,069 189,945 191,516 22,917 (6,786 ) 16,131 (3,654 ) (11,104 ) 1,373 189,999 206,130 2017 Assets Derivative financial instruments 30,155 (10,479 ) 19,676 (14,772 ) (2,785 ) 2,119 266 19,942 Reverse repurchase, securities borrowing & similar agreements: – Amortised cost 2,614 — 2,614 — (2,614 ) — — 2,614 – Fair value 15,224 (6,354 ) 8,870 (355 ) (8,515 ) — — 8,870 Loans and advances to customers and banks (4) 5,974 (1,459 ) 4,515 — — 4,515 198,283 202,798 53,967 (18,292 ) 35,675 (15,127 ) (13,914 ) 6,634 198,549 234,224 Liabilities Derivative financial instruments 27,839 (10,479 ) 17,360 (14,772 ) (1,951 ) 637 253 17,613 Repurchase, securities lending & similar agreements: – Amortised cost 1,076 — 1,076 — (1,076 ) — — 1,076 – Fair value 31,858 (6,354 ) 25,504 (355 ) (25,149 ) — — 25,504 Deposits by customers and banks (4) 2,688 (1,459 ) 1,229 — (502 ) 727 188,900 190,129 63,461 (18,292 ) 45,169 (15,127 ) (28,678 ) 1,364 189,153 234,322 (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.

Transition to IFRS 9 (Tables)

Transition to IFRS 9 (Tables)	12 Months Ended
	Dec. 31, 2018
Statement [LineItems]
Disclosure of Statutory Balance Sheet Reconciliation under IAS 39 and IFRS 9	For financial assets that were reclassified on transition to IFRS 9, the following table shows their fair value at 31 December 2018 and the fair value gain or loss that would have been recognised if these financial assets had not been reclassified: 2018 To amortised cost from FVTPL: Fair value at 31 December 2018 1,347 Fair value gain that would have been recognised during the year if the financial asset had not been reclassified 120
IFRS 9 [member]
Statement [LineItems]
Summary of Measurement Categories and Carrying Amounts of Financial Assets Determined in Accordance with IAS 39 and IFRS 9	The measurement categories and carrying amounts of financial assets determined in accordance with IAS 39 and IFRS 9 are compared below, illustrating a total net assets decrease of £192m as a result of the application of IFRS 9: IAS 39 IFRS 9 Assets Measurement category Carrying amount (31 December 2017) £m Reclassifications (1) £m Remeasurement (2) £m Measurement category Carrying amount (1 January 2018) £m Representation (6) £m IFRS 9 Balance Sheet (1 January 2018) £m Cash and balances with central banks Loans & receivables 32,771 — — Amortised cost 32,771 — 32,771 Trading assets FVTPL 30,536 — — FVTPL (Mandatory) 30,536 — 30,536 FVTPL 19 — — FVOCI 19 (19 ) (a) — 30,555 — — 30,555 (19 ) 30,536 Derivative financial instruments FVTPL (Trading) 19,942 — — FVTPL (Mandatory) 19,942 — 19,942 Other financial assets at FVTPL (3) FVTPL (Designated) 1,022 (45 ) (b) — Amortised cost 977 (977 ) (b) — FVTPL (Designated) 836 — — FVTPL (Designated) 836 — 836 FVTPL (Designated) 238 — — FVTPL (Mandatory) 238 (c) 1,181 (d) 1,419 2,096 (45 ) — 2,051 204 2,255 Loans and advances to customers (4) Loans & receivables 199,060 — (211 ) Amortised cost 198,849 977 (b) 199,826 Loans & receivables 181 (1 ) (a) — FVOCI 180 (180 ) (a) — Loans & receivables 91 — — FVTPL (Mandatory) 91 (91 ) (d) — 199,332 (1 ) (211 ) 199,120 706 199,826 Loans and advances to banks Loans & receivables 3,466 — — Amortised cost 3,466 — 3,466 Reverse repurchase agreements – non trading Loans & receivables 2,614 — — Amortised cost 2,614 — 2,614 Other financial assets at amortised cost Amortised cost — 7,776 (e) 7,776 Financial assets at FVOCI FVOCI — 8,942 (a)(f) 8,942 Financial investments Loans & receivables 1,198 — — Amortised cost 1,198 (1,198 ) (e) Loans & receivables 982 (2 ) (d) — FVTPL (Mandatory) 980 (980 ) (d) Available-for-sale 8,743 — — FVOCI 8,743 (8,743 ) (f) Available-for-sale 29 — — FVTPL (Mandatory) 29 (29 ) (d) Held-to-maturity 6,578 — — Amortised cost 6,578 (6,578 ) (e) Available-for-sale 81 — — FVTPL (Mandatory) 81 (81 ) (d) 17,611 (2 ) — 17,609 (17,609 ) Other assets Other assets 6,373 (1 ) Other assets 6,372 — 6,372 Total assets (pre-deferred tax asset ) (5) 314,760 (49 ) (211 ) 314,500 — 314,500 (1) Gross (pre-tax) (2) Gross (pre-tax) non-amortised held-to-maturity available-for-sale (3) The balance sheet category for ‘Financial assets designated at fair value’ has been changed to ‘Other financial assets at fair value through profit or loss’ following the adoption of IFRS 9. (4) Of the £211m increase in loss allowance, £50m related to off-balance (5) The impact of transition to IFRS 9 gave rise to a deferred tax asset of £68m, of which £14m is attributable to ‘Reclassifications’, and £54m to ‘Remeasurement’. This deferred tax asset was offset against our deferred tax liabilities. (6) Gross (pre-tax) re-presentations

Loans and Advances to Banks (Ta

Loans and Advances to Banks (Tables)	12 Months Ended
	Dec. 31, 2018
Santander UK Group Holdings plc [member]
Statement [LineItems]
Summary of Loans and Advances to Banks - Parent	2018 2017 Placements with other banks 8 3 Amounts due from Santander UK group undertakings 9,206 6,257 9,214 6,260

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, 2018
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, treasury products, and treasury markets activities. We provide these to large corporates, as well as sovereigns and other international organisations.
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, 2018
Non performing loans [member]
Disclosure of credit risk exposure [line items]
Metric	Non-Performing Loans (NPLs)
Description	We use NPLs to monitor how our portfolios behave. We classify loans as NPLs when customers do not make a payment for three months or more, or if we have data to make us doubt they can keep up with their payments. There are differences between NPL and Stage 3, which we set out in the 'Definition of default used for NPL' section below. Although we adopted IFRS 9 from 1 January 2018, we continued to monitor NPLs as a key metric in 2018 as the NPL ratio was one of Santander UK's Key Performance Indicators for 2016-2018.
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.
Expected credit losses [member]
Disclosure of credit risk exposure [line items]
Metric	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.

Credit Risk - Summary of Compou

Credit Risk - Summary of Compound Annual Growth Rates Over 5 Year Forecast (Detail)	12 Months Ended
	Dec. 31, 2018
Upside 2 [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House price index	3.40%
GDP	2.50%
Unemployment rate	2.80%
Interest rate	1.00%
Upside 1 [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House price index	2.30%
GDP	2.10%
Unemployment rate	3.80%
Interest rate	1.25%
Base case [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House price index	2.00%
GDP	1.60%
Unemployment rate	4.30%
Interest rate	1.50%
Downside 1 [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House price index	(2.00%)
GDP	0.70%
Unemployment rate	6.90%
Interest rate	2.50%
Downside 2 [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
House price index	(9.50%)
GDP	0.30%
Unemployment rate	8.60%
Interest rate	2.25%

Credit Risk - Summary of Probab

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

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, 2018
Upside Scenario [member] | Corporate and investment banking [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	4.20%
Base case [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	1.60%
Base case [member] | Corporate and investment banking [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	3.60%
Downside Scenario [member] | Corporate and investment banking [member]
Disclosure of forward looking information used in the determination of expected credit losses [line items]
GDP	2.70%

Credit Risk - Summary of Prob_2

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

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, 2018
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Other unsecured loans	4.00%
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	4.00%
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, 2018
Disclosure of credit risk exposure [line items]
Qualitative Criteria For Measuring SICR	In forbearance Watchlist - proactive management NPL in last 12m 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 NPL 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 Behaviour score <565
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 - Summary of Differ

Credit Risk - Summary of Difference Between Maximum and Net Exposure to Credit Risk - IFRS 9 (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	£ 92,547		£ 113,108
Collateral cash	11,104		28,678
Netting	3,654		15,127
Net exposure	310,948	£ 300,286	346,500
Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	271,000		255,900
Collateral cash	(100)		(100)
Collateral non-cash	(209,400)		(197,600)
Netting	(2,700)
Net exposure	100,400		101,700
Credit risk [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	271,700		256,800
Credit risk [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(700)		(900)
Credit risk [member] | Cash and balances at central banks [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	24,200		32,800
Net exposure	24,200		32,800
Credit risk [member] | Cash and balances at central banks [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	24,200		32,800
Credit risk [member] | Loans and Advances to Customers [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			199,500
Collateral cash			(100)
Collateral non-cash			(195,100)
Net exposure			45,500
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			155,200
Collateral non-cash			(167,400)
Net exposure			200
Credit risk [member] | Loans and Advances to Customers [member] | Corporate loans [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			30,400
Collateral non-cash			(21,800)
Net exposure			25,700
Credit risk [member] | Loans and Advances to Customers [member] | Finance leases [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			6,700
Collateral cash			(100)
Collateral non-cash			(5,800)
Net exposure			1,400
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			6,000
Collateral non-cash			(100)
Net exposure			17,000
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			1,200
Net exposure			1,200
Credit risk [member] | Loans and Advances to Customers [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			200,400
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			155,400
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			30,900
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			6,700
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			6,200
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			1,200
Credit risk [member] | Loans and Advances to Customers [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			(900)
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)
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			(500)
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)
Credit risk [member] | Loans and advances to banks [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			3,500
Net exposure			5,100
Credit risk [member] | Loans and advances to banks [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			3,500
Credit risk [member] | Reverse repurchase agreements - non-trading [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			2,600
Collateral non-cash			(2,500)
Net exposure			100
Credit risk [member] | Reverse repurchase agreements - non-trading [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			2,600
Credit risk [member] | Financial assets at FVOCI [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	13,300
Net exposure	13,400
Credit risk [member] | Financial assets at FVOCI [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	13,300
Credit risk [member] | Financial investments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			17,500
Net exposure			18,200
Credit risk [member] | Financial investments [member] | Loans and receivables securities [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			2,200
Net exposure			2,900
Credit risk [member] | Financial investments [member] | Available-for-sale [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			8,800
Net exposure			8,800
Credit risk [member] | Financial investments [member] | Held-to-maturity debt securities [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			6,500
Net exposure			6,500
Credit risk [member] | Financial investments [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			17,500
Credit risk [member] | Financial investments [member] | Cost [member] | Loans and receivables securities [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			2,200
Credit risk [member] | Financial investments [member] | Cost [member] | Available-for-sale [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			8,800
Credit risk [member] | Financial investments [member] | Cost [member] | Held-to-maturity debt securities [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			6,500
Off-Balance Sheet [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	41,600
Off-Balance Sheet [member] | Credit risk [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	41,700		43,500
Off-Balance Sheet [member] | Credit risk [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(100)
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			41,200
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			12,400
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			17,100
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			600
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			11,100
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			1,600
Off-Balance Sheet [member] | Credit risk [member] | Financial assets at FVOCI [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	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	100
Off-Balance Sheet [member] | Credit risk [member] | Financial investments [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			700
Off-Balance Sheet [member] | Credit risk [member] | Financial investments [member] | Cost [member] | Loans and receivables securities [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			£ 700
Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	233,500
Collateral cash	(100)
Collateral non-cash	(209,400)
Netting	(2,700)
Net exposure	62,800
Financial assets at amortised cost [member] | Credit risk [member] | Cost [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	234,200
Financial assets at amortised cost [member] | Credit risk [member] | Accumulated Impairment [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	(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	201,700
Collateral cash	(100)
Collateral non-cash	(191,000)
Net exposure	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	158,000
Collateral non-cash	(164,100)
Net exposure	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	27,600
Collateral non-cash	(20,200)
Net exposure	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	6,700
Collateral cash	(100)
Collateral non-cash	(6,100)
Net exposure	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	7,400
Net exposure	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	2,000
Collateral non-cash	(600)
Net exposure	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	202,400
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	158,200
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	27,800
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	6,800
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	7,600
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	2,000
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	(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)
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)
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	(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)
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	3,500
Net exposure	5,100
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	3,500
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	21,100
Collateral non-cash	(18,400)
Netting	(2,700)
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	21,100
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	7,200
Net exposure	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	7,200
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
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
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)
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	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	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	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	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	11,500
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	40,000
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	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	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	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	11,600
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)
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	(100)
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	1,600
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	1,600
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
Net exposure	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
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	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	100
Debt Securities [member] | Credit risk [member] | Financial assets at FVOCI [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	13,200
Net exposure	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	£ 13,200

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, 2018	Jan. 01, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	£ 92,547		£ 113,108
Collateral cash	11,104		28,678
Netting	3,654		15,127
Net exposure	310,948	£ 300,286	346,500
Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	271,000		255,900
Collateral cash	(100)		(100)
Collateral non-cash	(209,400)		(197,600)
Netting	(2,700)
Net exposure	100,400		101,700
Trading Assets [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			21,000
Collateral non-cash			(8,500)
Netting			(400)
Net exposure			12,100
Derivative Financial Instruments [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	5,300		19,900
Collateral cash			(2,800)
Collateral non-cash	(2,100)
Netting	(900)		(14,800)
Net exposure	2,300		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	6,100
Collateral non-cash	(2,300)
Net exposure	3,800
Financial assets at fair value through profit loss [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet	11,400		43,000
Collateral cash			(2,800)
Collateral non-cash	(4,400)		(10,100)
Netting	(900)		(15,200)
Net exposure	£ 6,100		14,900
Financial Assets Designated at Fair Value [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			2,100
Collateral non-cash			(1,600)
Net exposure			500
Securities Repurchased Under Resale Agreements [member] | Trading Assets [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			8,900
Collateral non-cash			(8,500)
Netting			(400)
Debt Securities [member] | Trading Assets [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			5,200
Net exposure			5,200
Debt Securities [member] | Financial Assets Designated at Fair Value [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			500
Net exposure			500
Cash Collateral [member] | Trading Assets [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			6,200
Net exposure			6,200
Short-term loans [member] | Trading Assets [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			700
Net exposure			700
Loans and Advances to Customers [member] | Financial Assets Designated at Fair Value [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to balance sheet			1,600
Collateral non-cash			£ (1,600)

Credit Risk - Summary of Credit

Credit Risk - Summary of Credit Rating of Financial Assets Subject to Credit Risk (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of internal credit grades [line items]
Loss allowance	£ 751	£ 940	£ 921	£ 1,108
Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance	(800)	(1,000)
Financial assets	312,600	255,700
Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance	(700)
Financial assets	233,500
Cash and balances at central banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	24,200	32,800
Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance		(1,000)
Financial assets		199,500
Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance	(700)
Financial assets	201,700
Loans and advances to banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		3,500
Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	3,500
Reverse repurchase agreements - non-trading [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		2,400
Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	21,100
Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	7,200
Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	13,300
Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		17,500
Internal grade 9 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	64,800	52,900
Internal grade 9 [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	33,300
Internal grade 9 [member] | Cash and balances at central banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	24,200	31,800
Internal grade 9 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		4,900
Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	10,000
Internal grade 9 [member] | Loans and advances to banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,300
Internal grade 9 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	900
Internal grade 9 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	15,200
Internal grade 9 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	7,200
Internal grade 9 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	6,600
Internal grade 9 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		14,900
Internal grade 8 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	45,300	35,600
Internal grade 8 [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	31,500
Internal grade 8 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		31,900
Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	27,500
Internal grade 8 [member] | Loans and advances to banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		200
Internal grade 8 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	200
Internal grade 8 [member] | Reverse repurchase agreements - non-trading [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,500
Internal grade 8 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	3,800
Internal grade 8 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	5,800
Internal grade 8 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		2,000
Internal grade 7 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	84,700	80,200
Internal grade 7 [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	75,100
Internal grade 7 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		78,500
Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	72,400
Internal grade 7 [member] | Loans and advances to banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		700
Internal grade 7 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,400
Internal grade 7 [member] | Reverse repurchase agreements - non-trading [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		400
Internal grade 7 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,300
Internal grade 7 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	700
Internal grade 7 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		600
Internal grade 6 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	61,000	43,100
Internal grade 6 [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	52,000
Internal grade 6 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		42,700
Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	51,600
Internal grade 6 [member] | Reverse repurchase agreements - non-trading [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		400
Internal grade 6 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	400
Internal grade 5 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	25,700	19,400
Internal grade 5 [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	20,300
Internal grade 5 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		19,400
Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	20,300
Internal grade 4 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	12,700	12,100
Internal grade 4 [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	11,400
Internal grade 4 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		12,100
Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	11,400
Internal grade 3 to 1 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	6,800	7,500
Internal grade 3 to 1 [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	6,300
Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		7,500
Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	6,300
Other [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	12,400	5,900
Other [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	4,300
Other [member] | Cash and balances at central banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,000
Other [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		3,500
Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	2,900
Other [member] | Loans and advances to banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,300
Other [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,000
Other [member] | Reverse repurchase agreements - non-trading [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Other [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	400
Other [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	200
Balance sheet exposures [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance	(700)
Financial assets	271,000
Balance sheet exposures [member] | Internal grade 9 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	64,100
Balance sheet exposures [member] | Internal grade 8 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	37,300
Balance sheet exposures [member] | Internal grade 7 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	75,800
Balance sheet exposures [member] | Internal grade 6 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	52,000
Balance sheet exposures [member] | Internal grade 5 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	20,300
Balance sheet exposures [member] | Internal grade 4 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	11,400
Balance sheet exposures [member] | Internal grade 3 to 1 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	6,300
Balance sheet exposures [member] | Other [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	4,500
Off-Balance Sheet [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance	(100)
Financial assets	41,600
Off-Balance Sheet [member] | Internal grade 9 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	700
Off-Balance Sheet [member] | Internal grade 8 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	8,000
Off-Balance Sheet [member] | Internal grade 7 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	8,900
Off-Balance Sheet [member] | Internal grade 6 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	9,000
Off-Balance Sheet [member] | Internal grade 5 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	5,400
Off-Balance Sheet [member] | Internal grade 4 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,300
Off-Balance Sheet [member] | Internal grade 3 to 1 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	500
Off-Balance Sheet [member] | Other [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	7,900
Advances secured on residential property [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance		(200)
Financial assets		155,200
Advances secured on residential property [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		3,200
Advances secured on residential property [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		26,700
Advances secured on residential property [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		75,200
Advances secured on residential property [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		35,200
Advances secured on residential property [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		6,200
Advances secured on residential property [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		4,500
Advances secured on residential property [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		4,400
Corporate loans [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance		(500)
Financial assets		30,500
Corporate loans [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,700
Corporate loans [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		5,100
Corporate loans [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		2,100
Corporate loans [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		4,600
Corporate loans [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		9,600
Corporate loans [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		5,100
Corporate loans [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,500
Corporate loans [member] | Other [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,300
Finance leases [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance		(100)
Financial assets		6,600
Finance leases [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		400
Finance leases [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,300
Finance leases [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		2,000
Finance leases [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,800
Finance leases [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,100
Finance leases [member] | Other [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Other unsecured advances [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance		(200)
Financial assets		6,000
Other unsecured advances [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Other unsecured advances [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		800
Other unsecured advances [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,600
Other unsecured advances [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,600
Other unsecured advances [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		700
Other unsecured advances [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		500
Other unsecured advances [member] | Other [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		900
Amounts due from fellow banco santander group subsidiaries and joint ventures [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,200
Amounts due from fellow banco santander group subsidiaries and joint ventures [member] | Other [member] | Loans and Advances to Customers [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,200
Stage 1 [member] | Cash and balances at central banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	24,200
Stage 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance	(100)
Financial assets	188,300
Stage 1 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	3,500
Stage 1 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	21,100
Stage 1 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	7,200
Stage 1 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	13,300
Stage 1 [member] | Internal grade 9 [member] | Cash and balances at central banks [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	24,200
Stage 1 [member] | Internal grade 9 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	10,000
Stage 1 [member] | Internal grade 9 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	900
Stage 1 [member] | Internal grade 9 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	15,200
Stage 1 [member] | Internal grade 9 [member] | Other financial assets at amortised cost [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	7,200
Stage 1 [member] | Internal grade 9 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	6,600
Stage 1 [member] | Internal grade 8 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	27,500
Stage 1 [member] | Internal grade 8 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	200
Stage 1 [member] | Internal grade 8 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	3,800
Stage 1 [member] | Internal grade 8 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	5,800
Stage 1 [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	72,200
Stage 1 [member] | Internal grade 7 [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,400
Stage 1 [member] | Internal grade 7 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,300
Stage 1 [member] | Internal grade 7 [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	700
Stage 1 [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	50,300
Stage 1 [member] | Internal grade 6 [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	400
Stage 1 [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	17,600
Stage 1 [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	6,900
Stage 1 [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,100
Stage 1 [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	2,800
Stage 1 [member] | Other [member] | Loans and advances to banks [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,000
Stage 1 [member] | Other [member] | Reverse repurchase agreements - non-trading [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	400
Stage 1 [member] | Other [member] | Financial assets at fair value through other comprehensive income [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	200
Stage 1 [member] | Off-Balance Sheet [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance	(100)
Financial assets	41,100
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 9 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	700
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 8 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	8,000
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 7 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	8,900
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 6 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	8,900
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 5 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	5,300
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 4 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,200
Stage 1 [member] | Off-Balance Sheet [member] | Internal grade 3 to 1 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	300
Stage 1 [member] | Off-Balance Sheet [member] | Other [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	7,900
Stage 2 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance	(300)
Financial assets	11,300
Stage 2 [member] | Internal grade 7 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	200
Stage 2 [member] | Internal grade 6 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	1,300
Stage 2 [member] | Internal grade 5 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	2,700
Stage 2 [member] | Internal grade 4 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	4,500
Stage 2 [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	2,800
Stage 2 [member] | Other [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	100
Stage 2 [member] | Off-Balance Sheet [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	400
Stage 2 [member] | Off-Balance Sheet [member] | Internal grade 6 [member] | Credit risk [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]
Disclosure of internal credit grades [line items]
Financial assets	100
Stage 2 [member] | Off-Balance Sheet [member] | Internal grade 4 [member] | Credit risk [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]
Disclosure of internal credit grades [line items]
Financial assets	100
Stage 3 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Loss allowance	(300)
Financial assets	2,100
Stage 3 [member] | Internal grade 3 to 1 [member] | Loans and Advances to Customers [member] | Financial assets at amortised cost [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	2,400
Stage 3 [member] | Off-Balance Sheet [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	100
Stage 3 [member] | Off-Balance Sheet [member] | Internal grade 3 to 1 [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets	£ 100
Loans and receivables securities [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		2,200
Loans and receivables securities [member] | Internal grade 9 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,900
Loans and receivables securities [member] | Internal grade 8 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		100
Loans and receivables securities [member] | Internal grade 7 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		200
Available-for-sale [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		8,800
Available-for-sale [member] | Internal grade 9 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		6,500
Available-for-sale [member] | Internal grade 8 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		1,900
Available-for-sale [member] | Internal grade 7 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		400
Held-to-maturity debt securities [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		6,500
Held-to-maturity debt securities [member] | Internal grade 9 [member] | Financial investments [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Financial assets		£ 6,500

Credit Risk - Summary of Cred_2

Credit Risk - Summary of Credit Performance (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of credit risk exposure [line items]
Customer loans	£ 201,619	£ 199,332
NPLs		£ 1,868
NPL ratio		1.21%
Loss allowances	751	£ 940	£ 921	£ 1,108
Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	199,900	200,300
NPLs	£ 2,408	£ 2,848
NPL ratio	1.20%	1.42%
Gross write-offs	£ 534	£ 253
Loss allowances	807	940
Retail banking [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	172,800	168,700
NPLs	£ 2,126	£ 2,104
NPL ratio	1.23%	1.25%
Gross write-offs	£ 182	£ 195
Loss allowances	594	491
Corporate and commercial banking [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	17,700	19,400
NPLs	£ 264	£ 383
NPL ratio	1.49%	1.97%
Gross write-offs	£ 97	£ 35
Loss allowances	182	195
Corporate and investment banking [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	4,600	6,000
NPLs		£ 340
NPL ratio		5.67%
Gross write-offs	252
Loss allowances	18	£ 236
Corporate centre [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	4,800	6,200
NPLs	£ 18	£ 21
NPL ratio	0.38%	0.34%
Gross write-offs	£ 3	£ 23
Loss allowances	13	18
Mortgages [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	158,000	154,700
NPLs	£ 1,907	£ 1,867
NPL ratio	1.21%	1.21%
Gross write-offs	£ 18	£ 22
Loss allowances	237	225
Corporate loans [member] | Loans to Customers [member]
Disclosure of credit risk exposure [line items]
Customer loans	24,100	27,300
NPLs	£ 353	£ 838
NPL ratio	1.46%	3.07%
Gross write-offs	£ 364	£ 56
Loss allowances	£ 253	£ 485

Credit Risk - Summary of IFRS 9

Credit Risk - Summary of IFRS 9 Credit Quality (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of credit risk exposure [line items]
Total exposures	£ 310,948	£ 300,286	£ 346,500
Loss Impairment: On Balance Sheet ECL	751		940	£ 921	£ 1,108
Loss Impairment: Off Balance Sheet ECL	515		£ 558	£ 700
Total ECL	£ 807	£ 1,151
Total coverage ratio	0.30%	0.40%
Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 269,221	£ 256,787
Loss Impairment: On Balance Sheet ECL	£ 751	£ 1,102
Total coverage ratio	0.30%	0.40%
Drawn exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 172,747	£ 168,724
Loss Impairment: On Balance Sheet ECL	£ 568	£ 597
Total coverage ratio	0.30%	0.40%
Drawn exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 157,957	£ 154,682
Loss Impairment: On Balance Sheet ECL	£ 234	£ 270
Total coverage ratio	0.10%	0.20%
Drawn exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 17,702	£ 19,391
Loss Impairment: On Balance Sheet ECL	£ 168	£ 236
Total coverage ratio	0.90%	1.20%
Drawn exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 29,255	£ 12,117
Loss Impairment: On Balance Sheet ECL	2	£ 250
Total coverage ratio		2.10%
Drawn exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	49,517	£ 56,555
Loss Impairment: On Balance Sheet ECL	13	19
Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	41,727	43,499
Loss Impairment: Off Balance Sheet ECL	£ 56	£ 49
Total coverage ratio	0.10%	0.10%
Off-Balance Sheet Exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 23,058	£ 23,402
Loss Impairment: Off Balance Sheet ECL	£ 26	£ 28
Total coverage ratio	0.10%	0.10%
Off-Balance Sheet Exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 11,213	£ 12,361
Loss Impairment: Off Balance Sheet ECL	3	2
Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	5,133	4,280
Loss Impairment: Off Balance Sheet ECL	£ 14	£ 13
Total coverage ratio	0.30%	0.30%
Off-Balance Sheet Exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 13,005	£ 14,947
Loss Impairment: Off Balance Sheet ECL	£ 16	£ 8
Total coverage ratio	0.10%	0.10%
Off-Balance Sheet Exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 531	£ 870
Stage 1 [member]
Disclosure of credit risk exposure [line items]
Total exposures	296,363	285,133
Total ECL	143	£ 176
Total coverage ratio		0.10%
Stage 1 [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	255,151	£ 242,216
Loss Impairment: On Balance Sheet ECL	121	£ 150
Total coverage ratio		0.10%
Stage 1 [member] | Drawn exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	160,212	£ 155,845
Loss Impairment: On Balance Sheet ECL	£ 84	£ 97
Total coverage ratio	0.10%	0.10%
Stage 1 [member] | Drawn exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 146,619	£ 142,940
Loss Impairment: On Balance Sheet ECL	10	20
Stage 1 [member] | Drawn exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	16,394	18,362
Loss Impairment: On Balance Sheet ECL	£ 31	£ 38
Total coverage ratio	0.20%	0.20%
Stage 1 [member] | Drawn exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 29,177	£ 11,684
Loss Impairment: On Balance Sheet ECL	1	£ 8
Total coverage ratio		0.10%
Stage 1 [member] | Drawn exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	49,368	£ 56,325
Loss Impairment: On Balance Sheet ECL	5	7
Stage 1 [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	41,212	42,917
Loss Impairment: Off Balance Sheet ECL	£ 22	£ 26
Total coverage ratio	0.10%	0.10%
Stage 1 [member] | Off-Balance Sheet Exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 22,819	£ 23,133
Loss Impairment: Off Balance Sheet ECL	£ 12	£ 13
Total coverage ratio	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	£ 11,120	£ 12,215
Loss Impairment: Off Balance Sheet ECL	2
Stage 1 [member] | Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	4,939	4,055
Loss Impairment: Off Balance Sheet ECL	£ 6	£ 5
Total coverage ratio	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	£ 12,923	£ 14,899
Loss Impairment: Off Balance Sheet ECL	4	£ 8
Total coverage ratio		0.10%
Stage 1 [member] | Off-Balance Sheet Exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	531	£ 830
Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total exposures	12,013	12,110
Total ECL	£ 307	£ 284
Total coverage ratio	2.60%	2.30%
Stage 2 [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 11,053	£ 10,867
Total ECL	£ 268	£ 246
Total coverage ratio	2.40%	2.30%
Stage 2 [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 960	£ 1,243
Total ECL	£ 39	£ 38
Total coverage ratio	4.10%	3.10%
Stage 2 [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 11,579	£ 11,606
Loss Impairment: On Balance Sheet ECL	£ 286	£ 263
Total coverage ratio	2.50%	2.30%
Stage 2 [member] | Drawn exposures [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 10,619	£ 10,377
Loss Impairment: On Balance Sheet ECL	£ 247	£ 225
Total coverage ratio	2.30%	2.20%
Stage 2 [member] | Drawn exposures [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 960	£ 1,229
Loss Impairment: On Balance Sheet ECL	£ 39	£ 38
Total coverage ratio	4.10%	3.10%
Stage 2 [member] | Drawn exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 10,324	£ 10,657
Loss Impairment: On Balance Sheet ECL	£ 256	£ 234
Total coverage ratio	2.50%	2.20%
Stage 2 [member] | Drawn exposures [member] | Retail banking [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 9,375	£ 9,537
Loss Impairment: On Balance Sheet ECL	£ 217	£ 206
Total coverage ratio	2.30%	2.20%
Stage 2 [member] | Drawn exposures [member] | Retail banking [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 949	£ 1,120
Loss Impairment: On Balance Sheet ECL	£ 39	£ 28
Total coverage ratio	4.10%	2.50%
Stage 2 [member] | Drawn exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 9,356	£ 9,756
Loss Impairment: On Balance Sheet ECL	£ 118	£ 129
Total coverage ratio	1.30%	1.30%
Stage 2 [member] | Drawn exposures [member] | Retail banking mortgages [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 8,466	£ 8,765
Loss Impairment: On Balance Sheet ECL	£ 98	£ 113
Total coverage ratio	1.20%	1.30%
Stage 2 [member] | Drawn exposures [member] | Retail banking mortgages [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 890	£ 991
Loss Impairment: On Balance Sheet ECL	£ 20	£ 16
Total coverage ratio	2.20%	1.60%
Stage 2 [member] | Drawn exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 1,044	£ 646
Loss Impairment: On Balance Sheet ECL	£ 26	£ 25
Total coverage ratio	2.50%	3.90%
Stage 2 [member] | Drawn exposures [member] | Corporate and commercial banking [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 1,044	£ 575
Loss Impairment: On Balance Sheet ECL	£ 26	£ 17
Total coverage ratio	2.50%	3.00%
Stage 2 [member] | Drawn exposures [member] | Corporate and commercial banking [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures		£ 71
Loss Impairment: On Balance Sheet ECL		£ 8
Total coverage ratio		11.30%
Stage 2 [member] | Drawn exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 78	£ 93
Loss Impairment: On Balance Sheet ECL	£ 1
Total coverage ratio	1.30%
Stage 2 [member] | Drawn exposures [member] | Corporate and investment banking [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 78	93
Loss Impairment: On Balance Sheet ECL	£ 1
Total coverage ratio	1.30%
Stage 2 [member] | Drawn exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 133	210
Loss Impairment: On Balance Sheet ECL	£ 3	£ 4
Total coverage ratio	2.30%	1.90%
Stage 2 [member] | Drawn exposures [member] | Corporate centre [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 122	£ 172
Loss Impairment: On Balance Sheet ECL	£ 3	£ 2
Total coverage ratio	2.50%	1.20%
Stage 2 [member] | Drawn exposures [member] | Corporate centre [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 11	£ 38
Loss Impairment: On Balance Sheet ECL		£ 2
Total coverage ratio		5.30%
Stage 2 [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	434	£ 504
Loss Impairment: Off Balance Sheet ECL	£ 21	£ 21
Total coverage ratio	4.80%	4.20%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 434	£ 490
Loss Impairment: Off Balance Sheet ECL	£ 21	£ 21
Total coverage ratio	4.80%	4.30%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures		£ 14
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 196	228
Loss Impairment: Off Balance Sheet ECL	£ 13	£ 13
Total coverage ratio	6.60%	5.70%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Retail banking [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 196	£ 223
Loss Impairment: Off Balance Sheet ECL	£ 13	£ 13
Total coverage ratio	6.60%	5.80%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Retail banking [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures		£ 5
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 76	128
Loss Impairment: Off Balance Sheet ECL	£ 1	£ 2
Total coverage ratio	1.30%	1.60%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Retail banking mortgages [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 76	£ 126
Loss Impairment: Off Balance Sheet ECL	£ 1	£ 2
Total coverage ratio	1.30%	1.60%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Retail banking mortgages [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures		£ 2
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 182	220
Loss Impairment: Off Balance Sheet ECL	£ 6	£ 8
Total coverage ratio	3.30%	3.60%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 182	£ 211
Loss Impairment: Off Balance Sheet ECL	£ 6	£ 8
Total coverage ratio	3.30%	3.80%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member] | Stage 2, above 30 DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures		£ 9
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 56	16
Loss Impairment: Off Balance Sheet ECL	£ 2
Total coverage ratio	3.60%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate and investment banking [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 56	16
Loss Impairment: Off Balance Sheet ECL	£ 2
Total coverage ratio	3.60%
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures		40
Stage 2 [member] | Off-Balance Sheet Exposures [member] | Corporate centre [member] | Stage two below or equal to thirty DPD [member]
Disclosure of credit risk exposure [line items]
Total exposures		40
Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 2,572	3,043
Total ECL	£ 357	£ 691
Total coverage ratio	13.90%	22.70%
Stage 3 [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 2,491	£ 2,965
Loss Impairment: On Balance Sheet ECL	£ 344	£ 689
Total coverage ratio	13.80%	23.20%
Stage 3 [member] | Drawn exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 2,211	£ 2,222
Loss Impairment: On Balance Sheet ECL	£ 228	£ 266
Total coverage ratio	10.30%	12.00%
Stage 3 [member] | Drawn exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 1,982	£ 1,986
Loss Impairment: On Balance Sheet ECL	£ 106	£ 121
Total coverage ratio	5.30%	6.10%
Stage 3 [member] | Drawn exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 264	£ 383
Loss Impairment: On Balance Sheet ECL	£ 111	£ 173
Total coverage ratio	42.00%	45.20%
Stage 3 [member] | Drawn exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures		£ 340
Loss Impairment: On Balance Sheet ECL		£ 242
Total coverage ratio		71.20%
Stage 3 [member] | Drawn exposures [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 16	£ 20
Loss Impairment: On Balance Sheet ECL	£ 5	£ 8
Total coverage ratio	31.30%	40.00%
Stage 3 [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 81	£ 78
Loss Impairment: Off Balance Sheet ECL	£ 13	£ 2
Total coverage ratio	16.00%	2.60%
Stage 3 [member] | Off-Balance Sheet Exposures [member] | Retail banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 43	£ 41
Loss Impairment: Off Balance Sheet ECL	£ 1	£ 2
Total coverage ratio	2.30%	4.90%
Stage 3 [member] | Off-Balance Sheet Exposures [member] | Retail banking mortgages [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 17	£ 18
Stage 3 [member] | Off-Balance Sheet Exposures [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	12	5
Loss Impairment: Off Balance Sheet ECL	£ 2
Total coverage ratio	16.70%
Stage 3 [member] | Off-Balance Sheet Exposures [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 26	£ 32
Loss Impairment: Off Balance Sheet ECL	£ 10
Total coverage ratio	38.50%

Credit Risk - Summary of IFRS_2

Credit Risk - Summary of IFRS 9 Credit Quality (Parenthetical) (Detail) - GBP (£) £ in Billions	Jan. 01, 2018	Dec. 31, 2018
Disclosure of credit risk exposure [abstract]
Average PD percentage	100.00%	100.00%
Retail mortgage offers in pipeline	£ 6.2	£ 5.2

Credit Risk - Summary of Stage

Credit Risk - Summary of Stage 2 Decomposition (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Exposure	£ 310,948	£ 300,286	£ 346,500
Stage 2 [member]
Disclosure of credit risk exposure [line items]
Exposure	12,013	£ 12,110
Currently in Arrears [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Exposure	960
Deterioation in probability of default [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Exposure	8,509
Other [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Exposure	£ 2,544

Credit Risk - Summary of Reconc

Credit Risk - Summary of Reconciliation of Exposures, ECL and Net Carrying Amounts (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of credit risk exposure [line items]
Total exposures	£ 310,948	£ 300,286	£ 346,500
Total ECL on drawn exposures	751		940	£ 921	£ 1,108
Total ECL on off-balance sheet exposures	515		558	700
Assets classified at FVTPL	4,616
Total assets	289,381	£ 314,500	314,760	302,510
Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	269,221
Total ECL on drawn exposures	751
On-balance sheet net carrying amount	268,470
Other items	2,501
Adjusted net carrying amount	270,971
Assets classified at FVTPL	11,458
Non-financial assets	6,952
Total assets	289,381
Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	41,727
Total ECL on off-balance sheet exposures	56
Retail banking [member]
Disclosure of credit risk exposure [line items]
Total assets	201,261		174,524	175,100
Retail banking [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	172,747
Total ECL on drawn exposures	568
On-balance sheet net carrying amount	172,179
Retail banking [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	23,058
Total ECL on off-balance sheet exposures	26
Mortgages [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	157,957
Total ECL on drawn exposures	234
On-balance sheet net carrying amount	157,723
Mortgages [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	11,213
Total ECL on off-balance sheet exposures	3
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Total assets	17,702		19,391	19,381
Corporate and commercial banking [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	17,702
Total ECL on drawn exposures	168
On-balance sheet net carrying amount	17,534
Corporate and commercial banking [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	5,133
Total ECL on off-balance sheet exposures	14
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Total assets	33,657		51,078	39,777
Corporate and investment banking [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	29,255
Total ECL on drawn exposures	2
On-balance sheet net carrying amount	29,253
Corporate and investment banking [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	13,005
Total ECL on off-balance sheet exposures	16
Corporate centre [member]
Disclosure of credit risk exposure [line items]
Total assets	36,761		£ 69,767	£ 68,252
Corporate centre [member] | Drawn exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	49,517
Total ECL on drawn exposures	13
On-balance sheet net carrying amount	49,504
Corporate centre [member] | Off-Balance Sheet Exposures [member]
Disclosure of credit risk exposure [line items]
Total exposures	£ 531

Credit Risk - Summary of ECL Re

Credit Risk - Summary of ECL Reconciliation (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending balance	£ 807
Recoveries net of collection costs	(42)	£ (54)	£ (65)
Charge/(release) to the Income Statement	153	203	£ 67
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	300,286
New assets originated or purchased	87,039
Other	(20,110)
Assets derecognised - closed good	(55,611)
Assets derecognised - written off	(656)
Ending balance	310,948	300,286
Net movement in the year	10,662
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	1,151
Change in economic scenarios	(16)
Changes to model	(7)
Net re-measurement of ECL arising from transfer of stage	99
New assets originated or purchased	90
Other	139
Assets derecognised - closed good	(115)
Assets derecognised - written off	(534)
Ending balance	807	1,151
Net movement in the year	(344)
Income statement charge/(release) for the year	190
Recoveries net of collection costs	(36)
Charge/(release) to the Income Statement	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]
Ending balance	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]
Ending balance	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]
Ending balance	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	176
Change in economic scenarios	4
Changes to model	(1)
Transfer to lifetime ECL (not-credit impaired)	(11)
Transfer to credit impaired	(8)
Transfer to 12-month ECL	68
Transfer from credit impaired	6
Transfer of financial instruments	55
Net re-measurement of ECL arising from transfer of stage	(63)
New assets originated or purchased	43
Other	(20)
Assets derecognised - closed good	(51)
Ending balance	143	176
Net movement in the year	(33)
Income statement charge/(release) for the year	(33)
Charge/(release) to the Income Statement	(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	285,133
Transfer to lifetime ECL (not-credit impaired)	(4,190)
Transfer to credit impaired	(445)
Transfer to 12-month ECL	3,325
Transfer from credit impaired	17
Transfer of financial instruments	(1,293)
New assets originated or purchased	85,933
Other	(19,867)
Assets derecognised - closed good	(53,543)
Ending balance	296,363	285,133
Net movement in the year	11,230
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	284
Change in economic scenarios	(12)
Changes to model	2
Transfer to lifetime ECL (not-credit impaired)	11
Transfer to credit impaired	(23)
Transfer to 12-month ECL	(68)
Transfer from credit impaired	27
Transfer of financial instruments	(53)
Net re-measurement of ECL arising from transfer of stage	83
New assets originated or purchased	34
Other	(11)
Assets derecognised - closed good	(20)
Ending balance	307	284
Net movement in the year	23
Income statement charge/(release) for the year	23
Charge/(release) to the Income Statement	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	12,110
Transfer to lifetime ECL (not-credit impaired)	4,190
Transfer to credit impaired	(603)
Transfer to 12-month ECL	(3,325)
Transfer from credit impaired	443
Transfer of financial instruments	705
New assets originated or purchased	1,087
Other	(295)
Assets derecognised - closed good	(1,594)
Ending balance	12,013	12,110
Net movement in the year	(97)
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	691
Change in economic scenarios	(8)
Changes to model	(8)
Transfer to credit impaired	31
Transfer from credit impaired	(33)
Transfer of financial instruments	(2)
Net re-measurement of ECL arising from transfer of stage	79
New assets originated or purchased	13
Other	170
Assets derecognised - closed good	(44)
Assets derecognised - written off	(534)
Ending balance	357	691
Net movement in the year	(334)
Income statement charge/(release) for the year	200
Recoveries net of collection costs	(36)
Charge/(release) to the Income Statement	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	3,043
Transfer to credit impaired	1,048
Transfer from credit impaired	(460)
Transfer of financial instruments	588
New assets originated or purchased	19
Other	52
Assets derecognised - closed good	(474)
Assets derecognised - written off	(656)
Ending balance	2,572	£ 3,043
Net movement in the year	£ (471)

Credit Risk - Summary of Countr

Credit Risk - Summary of Country Risk Exposure (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Risk exposures	£ 310,948	£ 300,286	£ 346,500
Governments [member]
Disclosure of credit risk exposure [line items]
Risk exposures	37,400		55,000
Government Guaranteed [member]
Disclosure of credit risk exposure [line items]
Risk exposures			400
Banks [member]
Disclosure of credit risk exposure [line items]
Risk exposures	14,300		29,000
Other Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Risk exposures	31,900		19,400
Retail [member]
Disclosure of credit risk exposure [line items]
Risk exposures	194,500		191,300
Corporate counterparty [member]
Disclosure of credit risk exposure [line items]
Risk exposures	41,300		51,400
Eurozone Countries [member]
Disclosure of credit risk exposure [line items]
Risk exposures	19,700		15,600
Eurozone Countries [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	12,700		2,100
Eurozone Countries [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures	300		600
Eurozone Countries [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures	200		500
Eurozone Countries [member] | Portugal [member]
Disclosure of credit risk exposure [line items]
Risk exposures			100
Eurozone Countries [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,000		4,700
Eurozone Countries [member] | Germany [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,600		2,900
Eurozone Countries [member] | Luxembourg [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,100		1,700
Eurozone Countries [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	2,800		3,000
Eurozone Countries [member] | Governments [member]
Disclosure of credit risk exposure [line items]
Risk exposures	300		700
Eurozone Countries [member] | Governments [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures			400
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			300
Eurozone Countries [member] | Government Guaranteed [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures			300
Eurozone Countries [member] | Banks [member]
Disclosure of credit risk exposure [line items]
Risk exposures	3,800		6,500
Eurozone Countries [member] | Banks [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures			200
Eurozone Countries [member] | Banks [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures			300
Eurozone Countries [member] | Banks [member] | Portugal [member]
Disclosure of credit risk exposure [line items]
Risk exposures			100
Eurozone Countries [member] | Banks [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,000		2,000
Eurozone Countries [member] | Banks [member] | Germany [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,600		2,800
Eurozone Countries [member] | Banks [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,200		1,100
Eurozone Countries [member] | Other Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Risk exposures	13,700		3,000
Eurozone Countries [member] | Other Financial Institutions [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	12,300		1,100
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	200		100
Eurozone Countries [member] | Other Financial Institutions [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures			200
Eurozone Countries [member] | Other Financial Institutions [member] | Luxembourg [member]
Disclosure of credit risk exposure [line items]
Risk exposures	900		1,300
Eurozone Countries [member] | Other Financial Institutions [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	200		200
Eurozone Countries [member] | Corporate counterparty [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,900		5,100
Eurozone Countries [member] | Corporate counterparty [member] | Ireland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	400		800
Eurozone Countries [member] | Corporate counterparty [member] | Italy [member]
Disclosure of credit risk exposure [line items]
Risk exposures	200		100
Eurozone Countries [member] | Corporate counterparty [member] | Spain (excl. Banco Santander) [member]
Disclosure of credit risk exposure [line items]
Risk exposures			100
Eurozone Countries [member] | Corporate counterparty [member] | France [member]
Disclosure of credit risk exposure [line items]
Risk exposures			2,200
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	200		400
Eurozone Countries [member] | Corporate counterparty [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,100		1,400
All Other Countries [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	3,700		5,200
All Other Countries [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	284,400		301,000
All Other Countries [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	4,400		17,000
All Other Countries [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	6,400		6,600
All Other Countries [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100		600
All Other Countries [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	700		500
All Other Countries [member] | Governments [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100		100
All Other Countries [member] | Governments [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	32,100		44,700
All Other Countries [member] | Governments [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,100		6,300
All Other Countries [member] | Governments [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	3,800		3,000
All Other Countries [member] | Governments [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures			200
All Other Countries [member] | Government Guaranteed [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures			100
All Other Countries [member] | Banks [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,900		2,300
All Other Countries [member] | Banks [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	4,300		9,100
All Other Countries [member] | Banks [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,500		8,200
All Other Countries [member] | Banks [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures	2,600		2,600
All Other Countries [member] | Banks [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures			200
All Other Countries [member] | Banks [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	200		100
All Other Countries [member] | Other Financial Institutions [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	400		900
All Other Countries [member] | Other Financial Institutions [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	16,300		13,000
All Other Countries [member] | Other Financial Institutions [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,500		2,300
All Other Countries [member] | Other Financial Institutions [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures			200
All Other Countries [member] | Retail [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	300
All Other Countries [member] | Retail [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	194,200		191,300
All Other Countries [member] | Corporate counterparty [member] | Other [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,000		1,900
All Other Countries [member] | Corporate counterparty [member] | UK [member]
Disclosure of credit risk exposure [line items]
Risk exposures	37,500		42,900
All Other Countries [member] | Corporate counterparty [member] | US [member]
Disclosure of credit risk exposure [line items]
Risk exposures	300		100
All Other Countries [member] | Corporate counterparty [member] | Japan [member]
Disclosure of credit risk exposure [line items]
Risk exposures			800
All Other Countries [member] | Corporate counterparty [member] | Switzerland [member]
Disclosure of credit risk exposure [line items]
Risk exposures	100		200
All Other Countries [member] | Corporate counterparty [member] | Denmark [member]
Disclosure of credit risk exposure [line items]
Risk exposures	500		400
All Countries Excluding Eurozone Countries [member]
Disclosure of credit risk exposure [line items]
Risk exposures	299,700		330,900
All Countries Excluding Eurozone Countries [member] | Governments [member]
Disclosure of credit risk exposure [line items]
Risk exposures	37,100		54,300
All Countries Excluding Eurozone Countries [member] | Government Guaranteed [member]
Disclosure of credit risk exposure [line items]
Risk exposures			100
All Countries Excluding Eurozone Countries [member] | Banks [member]
Disclosure of credit risk exposure [line items]
Risk exposures	10,500		22,500
All Countries Excluding Eurozone Countries [member] | Other Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Risk exposures	18,200		16,400
All Countries Excluding Eurozone Countries [member] | Retail [member]
Disclosure of credit risk exposure [line items]
Risk exposures	194,500		191,300
All Countries Excluding Eurozone Countries [member] | Corporate counterparty [member]
Disclosure of credit risk exposure [line items]
Risk exposures	£ 39,400		£ 46,300

Credit Risk - Summary of Coun_2

Credit Risk - Summary of Country Risk Exposure (Parenthetical) (Detail) - GBP (£)	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Risk exposures	£ 310,948,000,000	£ 300,286,000,000	£ 346,500,000,000
Eurozone Countries [member] | Netherlands [member]
Disclosure of credit risk exposure [line items]
Risk exposures	1,200,000,000		1,800,000,000
Eurozone Countries [member] | Belgium [Member]
Disclosure of credit risk exposure [line items]
Risk exposures	900,000,000		0
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, 2018	Dec. 31, 2017
Disclosure of detailed information about financial instruments [line items]
Financial assets	£ 4.7	£ 5.7
Financial liabilities	5.2	6.1
Spain (excl. Banco Santander) [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	2.7	4.4
Financial liabilities	4	5.5
UK [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	2	1.3
Financial liabilities	1	0.4
Other [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities		0.1
Uruguay [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0.2	0.1
Banks [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	2.7	4.4
Financial liabilities	4.1	5.3
Banks [member] | Spain (excl. Banco Santander) [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	2.7	4.4
Financial liabilities	3.9	5.1
Banks [member] | UK [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities		0.1
Banks [member] | Uruguay [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0.2	0.1
Other Financial Institutions [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	2	1.3
Financial liabilities	1.1	0.6
Other Financial Institutions [member] | Spain (excl. Banco Santander) [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities	0.1	0.3
Other Financial Institutions [member] | UK [member]
Disclosure of detailed information about financial instruments [line items]
Financial assets	2	1.3
Financial liabilities	£ 1	0.2
Other Financial Institutions [member] | Other [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities		0.1
Corporate counterparty [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities		0.2
Corporate counterparty [member] | Spain (excl. Banco Santander) [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities		0.1
Corporate counterparty [member] | UK [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities		£ 0.1

Credit Risk - Summary of Bala_2

Credit Risk - Summary of Balances with Other Banco Santander Companies (Parenthetical) (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Santander UK Group Holdings plc [member] | Top of Range [member]
Disclosure of detailed information about financial instruments [line items]
Financial liabilities allocated to other countries	£ 100,000,000	£ 100,000,000

Credit Risk - Summary of Types

Credit Risk - Summary of Types of Credit Risk Mitigation (Detail)	12 Months Ended
	Dec. 31, 2018
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.
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 secured against a tangible asset. 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.
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.
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.

Credit Risk - Summary of ECL _2

Credit Risk - Summary of ECL Reconciliation for Retail Segment (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending balance	£ 807
Recoveries net of collection costs	(42)	£ (54)	£ (65)
Income statement charge/(release) for the year	153	203	67
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	124	36	£ 21
Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending balance	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]
Ending balance	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]
Ending balance	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	300,286
New assets originated or purchased	87,039
Other	(20,110)
Assets derecognised - closed good	(55,611)
Assets derecognised - written off	(656)
Ending balance	310,948	300,286
Net movement in the year	10,662
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	192,126
New assets originated or purchased	34,051
Other	(8,468)
Assets derecognised - closed good	(21,654)
Assets derecognised - written off	(250)
Ending balance	195,805	192,126
Net movement in the year	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	1,151
Change in economic scenarios	(16)
Changes to model	(7)
Net remeasurement of ECL on stage transfer	99
New assets originated or purchased	90
Other	139
Assets derecognised - closed good	(115)
Assets derecognised - written off	(534)
Ending balance	807	1,151
Net movement in the year	(344)
Charge/(release) to the Income Statement	190
Recoveries net of collection costs	(36)
Income statement charge/(release) for the year	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	625
Change in economic scenarios	(18)
Changes to model	2
Net remeasurement of ECL on stage transfer	79
New assets originated or purchased	63
Other	79
Assets derecognised - closed good	(54)
Assets derecognised - written off	(182)
Ending balance	594	625
Net movement in the year	(31)
Charge/(release) to the Income Statement	151
Recoveries net of collection costs	(27)
Income statement charge/(release) for the year	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	285,133
Transfer to lifetime ECL (not-credit impaired)	(4,190)
Transfer to credit impaired	(445)
Transfer to 12-monthECL	3,325
Transfer from credit impaired	17
Transfers of financial instruments	(1,293)
New assets originated or purchased	85,933
Other	(19,867)
Assets derecognised - closed good	(53,543)
Ending balance	296,363	285,133
Net movement in the year	11,230
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	178,978
Transfer to lifetime ECL (not-credit impaired)	(3,407)
Transfer to credit impaired	(403)
Transfer to 12-monthECL	2,992
Transfer from credit impaired	15
Transfers of financial instruments	(803)
New assets originated or purchased	33,366
Other	(8,253)
Assets derecognised - closed good	(20,257)
Ending balance	183,031	178,978
Net movement in the year	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	12,110
Transfer to lifetime ECL (not-credit impaired)	4,190
Transfer to credit impaired	(603)
Transfer to 12-monthECL	(3,325)
Transfer from credit impaired	443
Transfers of financial instruments	705
New assets originated or purchased	1,087
Other	(295)
Assets derecognised - closed good	(1,594)
Ending balance	12,013	12,110
Net movement in the year	(97)
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	10,885
Transfer to lifetime ECL (not-credit impaired)	3,407
Transfer to credit impaired	(569)
Transfer to 12-monthECL	(2,992)
Transfer from credit impaired	438
Transfers of financial instruments	284
New assets originated or purchased	670
Other	(312)
Assets derecognised - closed good	(1,007)
Ending balance	10,520	10,885
Net movement in the year	(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	176
Change in economic scenarios	4
Changes to model	(1)
Transfer to lifetime ECL (not-credit impaired)	(11)
Transfer to credit impaired	(8)
Transfer to 12-monthECL	68
Transfer from credit impaired	6
Transfers of financial instruments	55
Net remeasurement of ECL on stage transfer	(63)
New assets originated or purchased	43
Other	(20)
Assets derecognised - closed good	(51)
Ending balance	143	176
Net movement in the year	(33)
Charge/(release) to the Income Statement	(33)
Income statement charge/(release) for the year	(33)
Financial instruments not credit-impaired [member] | Stage 1 ECL [member] | Subject to 12-month ECL [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	110
Change in economic scenarios	(1)
Changes to model	(1)
Transfer to lifetime ECL (not-credit impaired)	(7)
Transfer to credit impaired	(7)
Transfer to 12-monthECL	58
Transfer from credit impaired	5
Transfers of financial instruments	49
Net remeasurement of ECL on stage transfer	(54)
New assets originated or purchased	26
Other	(15)
Assets derecognised - closed good	(18)
Ending balance	96	110
Net movement in the year	(14)
Charge/(release) to the Income Statement	(14)
Income statement charge/(release) for the year	(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	284
Change in economic scenarios	(12)
Changes to model	2
Transfer to lifetime ECL (not-credit impaired)	11
Transfer to credit impaired	(23)
Transfer to 12-monthECL	(68)
Transfer from credit impaired	27
Transfers of financial instruments	(53)
Net remeasurement of ECL on stage transfer	83
New assets originated or purchased	34
Other	(11)
Assets derecognised - closed good	(20)
Ending balance	307	284
Net movement in the year	23
Charge/(release) to the Income Statement	23
Income statement charge/(release) for the year	23
Financial instruments not credit-impaired [member] | Stage 2 ECL [member] | Subject to Lifetime ECL [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	247
Change in economic scenarios	(9)
Changes to model	2
Transfer to lifetime ECL (not-credit impaired)	7
Transfer to credit impaired	(22)
Transfer to 12-monthECL	(58)
Transfer from credit impaired	26
Transfers of financial instruments	(47)
Net remeasurement of ECL on stage transfer	73
New assets originated or purchased	26
Other	(10)
Assets derecognised - closed good	(13)
Ending balance	269	247
Net movement in the year	22
Charge/(release) to the Income Statement	22
Income statement charge/(release) for the year	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	3,043
Transfer to credit impaired	1,048
Transfer from credit impaired	(460)
Transfers of financial instruments	588
New assets originated or purchased	19
Other	52
Assets derecognised - closed good	(474)
Assets derecognised - written off	(656)
Ending balance	2,572	3,043
Net movement in the year	(471)
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	2,263
Transfer to credit impaired	972
Transfer from credit impaired	(453)
Transfers of financial instruments	519
New assets originated or purchased	15
Other	97
Assets derecognised - closed good	(390)
Assets derecognised - written off	(250)
Ending balance	2,254	2,263
Net movement in the year	(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	691
Change in economic scenarios	(8)
Changes to model	(8)
Transfer to credit impaired	31
Transfer from credit impaired	(33)
Transfers of financial instruments	(2)
Net remeasurement of ECL on stage transfer	79
New assets originated or purchased	13
Other	170
Assets derecognised - closed good	(44)
Assets derecognised - written off	(534)
Ending balance	357	691
Net movement in the year	(334)
Charge/(release) to the Income Statement	200
Recoveries net of collection costs	(36)
Income statement charge/(release) for the year	164
Financial instruments credit-impaired [member] | Stage 3 ECL [member] | Subject to Lifetime ECL [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	268
Change in economic scenarios	(8)
Changes to model	1
Transfer to credit impaired	29
Transfer from credit impaired	(31)
Transfers of financial instruments	(2)
Net remeasurement of ECL on stage transfer	60
New assets originated or purchased	11
Other	104
Assets derecognised - closed good	(23)
Assets derecognised - written off	(182)
Ending balance	229	£ 268
Net movement in the year	(39)
Charge/(release) to the Income Statement	143
Recoveries net of collection costs	(27)
Income statement charge/(release) for the year	£ 116

Credit Risk - Summary of Reside

Credit Risk - Summary of Residential Mortgages by Borrower Profile (Detail) - Credit risk [member] - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 157,957	£ 154,682
Percentage of residential mortgage loans	100.00%	100.00%
New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 27,274	£ 24,174
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	£ 29,235	£ 28,704
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	£ 4,848	£ 4,034
Percentage of residential mortgage loans	18.00%	17.00%
Home Movers [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 69,198	£ 68,752
Percentage of residential mortgage loans	44.00%	44.00%
Home Movers [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 10,854	£ 10,704
Percentage of residential mortgage loans	39.00%	44.00%
Remortgagers [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 51,272	£ 50,424
Percentage of residential mortgage loans	32.00%	33.00%
Remortgagers [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 9,237	£ 8,065
Percentage of residential mortgage loans	34.00%	33.00%
Buy-To-Let [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 8,252	£ 6,802
Percentage of residential mortgage loans	5.00%	4.00%
Buy-To-Let [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 2,335	£ 1,371
Percentage of residential mortgage loans	9.00%	6.00%

Credit Risk - Additional Inform

Credit Risk - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018GBP (£)MortgageLoanClients	Dec. 31, 2017GBP (£)MortgageLoanClients
Disclosure of internal credit grades [line items]
Advances and flexible mortgage drawdowns	£ 1,500,000,000	£ 1,300,000,000
Average consumer finance loan size	11,400	12,500
Average unsecured loan	9,500	9,300
Credit card balances	£ 1,500	1,200
Percenatage of reverse repos to exposure	100.00%
Cash collateral held against portfolio	£ 11,104,000,000	28,678,000,000
Loans and advances to customers	201,619,000,000	199,332,000,000
Credit risk [member]
Disclosure of internal credit grades [line items]
Cash collateral held against portfolio	£ (100,000,000)	£ (100,000,000)
Corporate and commercial banking [member]
Disclosure of internal credit grades [line items]
Percentage of collateral held against impaired loans	43.00%	15.00%
Collateral held against Credit impaired assets	£ 69,000,000	£ 134,000,000
Credit impaired assets	276,000,000	393,000,000
Mortgages [member]
Disclosure of internal credit grades [line items]
Parts of the loans in negative equity that were effectively uncollateralised	170,000,000	223,000,000
Legacy Portfolios in Run-Off [member]
Disclosure of internal credit grades [line items]
Collateral held against Credit impaired assets	10,000,000	13,000,000
Credit impaired assets	16,000,000	20,000,000
Cash collateral held against portfolio	£ 265,000,000	£ 348,000,000
Corporate and investment banking [member]
Disclosure of internal credit grades [line items]
Number of clients | Clients	20	20
Rate of derivative exposure with client	85.00%	65.00%
Weighted-average credit rating percent	7.10%	7.20%
Commercial Real Estate [member]
Disclosure of internal credit grades [line items]
Loans and advances to customers	£ 6,459,000,000	£ 8,144,000,000
Percentage of loan to value	100.00%	100.00%
Commercial Real Estate [member] | Not Later Than 1 Year [member]
Disclosure of internal credit grades [line items]
Loans and advances to customers	£ 1,144,000,000	£ 1,090,000,000
Loans and advances to customers with higher LTV ratio	£ 30,000,000	£ 59,000,000
Percentage of maximum acceptable LTV ratio	3.00%	5.00%
Commercial Real Estate [member] | Non performing loans [member] | Not Later Than 1 Year [member]
Disclosure of internal credit grades [line items]
Loans and advances to customers	£ 10,000,000	£ 53,000,000
Impairment loss allowance	5,000,000	27,000,000
Commercial Real Estate [member] | Pre Two Thousand Nine Loans [member]
Disclosure of internal credit grades [line items]
Loans written down	£ 190,000,000	£ 380,000,000
Commercial Real Estate [member] | Corporate loans [member]
Disclosure of internal credit grades [line items]
Loan percentage	27.00%	30.00%
Commercial Real Estate [member] | Customer Loans [member]
Disclosure of internal credit grades [line items]
Loan percentage	3.00%	4.00%
Development Loans [member] | Commercial Real Estate [member]
Disclosure of internal credit grades [line items]
Loans and advances to customers	£ 61,000,000	£ 246,000,000
Percentage of loan to value	1.00%	3.00%
Loan percentage	1.00%	3.00%
Average loan balance	£ 3,200,000	£ 4,700,000
Internal Remortgages [member]
Disclosure of internal credit grades [line items]
Internal remortgages	£ 27,200,000,000	£ 26,000,000,000
Greater Than 2.0m [member] | Credit risk [member]
Disclosure of internal credit grades [line items]
Number of individual mortgage loans | MortgageLoan	57	64
New business number of individual mortgage loans | MortgageLoan	9	13
Less Than 70% [member]
Disclosure of internal credit grades [line items]
Loans and advances to customers	£ 5,702,000,000	£ 7,181,000,000
Percentage of loan to value	70.00%	70.00%

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, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 157,957	£ 154,682
Percentage of residential mortgage loans	100.00%	100.00%
Fixed Rate [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 115,178	£ 102,036
Percentage of residential mortgage loans	73.00%	66.00%
Variable Rate [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 24,396	£ 29,370
Percentage of residential mortgage loans	15.00%	19.00%
Standard Variable Rate [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 18,383	£ 23,276
Percentage of residential mortgage loans	12.00%	15.00%

Credit Risk - Summary of Resi_3

Credit Risk - Summary of Residential Mortgages by Geographical Distribution (Detail) - Credit risk [member] - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 157,957	£ 154,682
New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	27,274	24,174
London [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	39,000	37,600
London [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	7,100	5,800
Midlands and East Anglia [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	21,100	20,600
Midlands and East Anglia [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	3,800	3,400
North UK [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	22,200	22,200
North UK [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	3,400	3,000
Northern Ireland [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	3,400	3,600
Northern Ireland [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	200	200
Scotland [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	6,700	6,800
Scotland [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	1,000	1,000
South East Excluding London [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	48,700	47,200
South East Excluding London [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	9,000	8,200
South West and Wales and Other [member] | Stock [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	16,900	16,700
South West and Wales and Other [member] | New Business [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 2,800	£ 2,600

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, 2018	Dec. 31, 2017
South East Including London [member]
Disclosure of credit risk exposure [line items]
New business residential mortgage loans average size	£ 270	£ 260
Rest of UK [member]
Disclosure of credit risk exposure [line items]
New business residential mortgage loans average size	150	146
UK [member]
Disclosure of credit risk exposure [line items]
New business residential mortgage loans average size	£ 203	£ 196

Credit Risk - Summary of Resi_5

Credit Risk - Summary of Residential Mortgages by Loan Size (Detail) - Credit risk [member] - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 87,756	£ 84,751
UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	157,957	154,682
Less Than 0.25m [member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	45,851	46,766
Less Than 0.25m [member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	105,181	106,838
0.25m-0.50m[member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	30,488	27,562
0.25m-0.50m[member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	39,841	36,036
0.50m-1.0m [member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	10,103	9,214
0.50m-1.0m [member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	11,551	10,532
1.0m-2.0m [member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	1,168	1,046
1.0m-2.0m [member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	1,236	1,111
Greater Than 2.0m [member] | South East Including London [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	146	163
Greater Than 2.0m [member] | UK [member]
Disclosure of credit risk exposure [line items]
Residential mortgage loans	£ 148	£ 165

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, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Percentage of loan to value, Stock	100.00%	100.00%
Collateral value of residential properties, Stock	£ 157,787	£ 154,459
Percentage of loan to value, NPL stock	100.00%	100.00%
Collateral value of residential properties, NPL stock	£ 1,850	£ 1,823
Percentage of loan to value, New business	100.00%	100.00%
Collateral value of residential properties, New business	£ 27,274	£ 24,174
Up to 50% [member]
Disclosure of credit risk exposure [line items]
Percentage of loan to value, Stock	45.00%	49.00%
Percentage of loan to value, NPL stock	43.00%	44.00%
Percentage of loan to value, New business	20.00%	19.00%
50 - 75% [member]
Disclosure of credit risk exposure [line items]
Percentage of loan to value, Stock	41.00%	39.00%
Percentage of loan to value, NPL stock	35.00%	34.00%
Percentage of loan to value, New business	41.00%	43.00%
75 - 85% [member]
Disclosure of credit risk exposure [line items]
Percentage of loan to value, Stock	9.00%	7.00%
Percentage of loan to value, NPL stock	8.00%	8.00%
Percentage of loan to value, New business	22.00%	19.00%
85 - 100% [member]
Disclosure of credit risk exposure [line items]
Percentage of loan to value, Stock	4.00%	4.00%
Percentage of loan to value, NPL stock	7.00%	7.00%
Percentage of loan to value, New business	17.00%	19.00%
Greater Than 100% [member]
Disclosure of credit risk exposure [line items]
Percentage of loan to value, Stock	1.00%	1.00%
Percentage of loan to value, NPL stock	7.00%	7.00%
Simple Average [member]
Disclosure of credit risk exposure [line items]
Percentage of loan to value, Stock	42.00%	42.00%
Percentage of loan to value, NPL stock	43.00%	44.00%
Percentage of loan to value, New business	63.00%	62.00%
Valuation Weighted Average LTV [member]
Disclosure of credit risk exposure [line items]
Percentage of loan to value, Stock	39.00%	38.00%
Percentage of loan to value, NPL stock	38.00%	38.00%
Percentage of loan to value, New business	59.00%	58.00%

Credit Risk - Summary of Resi_7

Credit Risk - Summary of Residential Mortgages by Loan to Value (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Credit risk [member]
Disclosure of credit risk exposure [line items]
Collateral against loans in negative equity	£ 969	£ 1,248

Credit Risk - Summary of Resi_8

Credit Risk - Summary of Residential Mortgages by Credit Performance (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 201,619	£ 199,332
Non performing loans		1,868
Impairment loss allowances	751	£ 940	£ 921	£ 1,108
NPL ratio		1.21%
Credit risk [member]
Disclosure of credit risk exposure [line items]
Impairment loss allowances	(800)	£ (1,000)
Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	157,957	154,682
Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	157,957	154,682
Non performing loans	1,907	1,868
Impairment loss allowances	£ 234	£ 225
Stage 2 ratio	5.92%
Stage 3 ratio	1.25%
Early arrears ratio		0.73%
NPL ratio	1.21%	1.21%
Stage 1 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 146,619
Stage 1 [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	146,619
Stage 2 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	9,356
Stage 2 [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	9,356
Stage 3 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 1,982
Stage 3 ratio	1.25%
Stage 3 [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 1,982
Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		£ 151,688
Performing Loans [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		151,688
Early Arrear Loans [member] | Later Than 1 Month and Not Later Than 2 Months [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		700
Early Arrear Loans [member] | Later Than 2 Months And Not Later Than 3 Months [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		426
Early Arrear Loans [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		1,126
Early Arrear Loans [member] | Mortgages [member] | Credit risk [member] | Later Than 1 Month and Not Later Than 2 Months [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		700
Early Arrear Loans [member] | Mortgages [member] | Credit risk [member] | Later Than 2 Months And Not Later Than 3 Months [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		426
Non Performing Loans by Arrears [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Non performing loans	1,392	1,427
Non Performing Loans by Bankruptcy [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Non performing loans	18	14
Non Performing Loans by Maturity Default [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Non performing loans	392	303
Non-performing loans by forbearance [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Non performing loans	80	95
Non Performing Loans by Properties in Possession [member] | Mortgages [member] | Credit risk [member]
Disclosure of credit risk exposure [line items]
Non performing loans	£ 25	£ 29

Credit Risk - Summary of Resi_9

Credit Risk - Summary of Residential Mortgages by Credit Performance (Parenthetical) (Detail) £ in Millions	Dec. 31, 2017GBP (£)
Disclosure of credit risk exposure [line items]
Non performing loans	£ 1,868
Later Than 1 day and Not Later Than 1 Month [member]
Disclosure of credit risk exposure [line items]
Non performing loans	£ 2,661

Credit Risk - Summary of ECL _3

Credit Risk - Summary of ECL Reconciliation (Residential Mortgages) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending balance	£ 807
Recoveries net of collection costs	(42)	£ (54)	£ (65)
Income statement charge/(release) for the year	153	203	£ 67
Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending balance	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	285,133
Transfer to lifetime ECL (not-credit impaired)	(4,190)
Transfer to credit impaired	(445)
Transfer to 12-monthECL	3,325
Transfer from credit impaired	17
Transfers of financial instruments	(1,293)
New assets originated or purchased	85,933
Other	(19,867)
Assets derecognised - closed good	(53,543)
Ending balance	296,363	285,133
Net movement in the year	11,230
Stage 2 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending balance	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	12,110
Transfer to lifetime ECL (not-credit impaired)	4,190
Transfer to credit impaired	(603)
Transfer to 12-monthECL	(3,325)
Transfer from credit impaired	443
Transfers of financial instruments	705
New assets originated or purchased	1,087
Other	(295)
Assets derecognised - closed good	(1,594)
Ending balance	12,013	12,110
Net movement in the year	(97)
Stage 3 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending balance	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	3,043
Transfer to credit impaired	1,048
Transfer from credit impaired	(460)
Transfers of financial instruments	588
New assets originated or purchased	19
Other	52
Assets derecognised - closed good	(474)
Assets derecognised - written off	(656)
Ending balance	2,572	3,043
Net movement in the year	(471)
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	176
Change in economic scenarios	4
Changes to model	(1)
Transfer to lifetime ECL (not-credit impaired)	(11)
Transfer to credit impaired	(8)
Transfer to 12-monthECL	68
Transfer from credit impaired	6
Transfers of financial instruments	55
Net remeasurement of ECL on stage transfer	(63)
New assets originated or purchased	43
Other	(20)
Assets derecognised - closed good	(51)
Ending balance	143	176
Net movement in the year	(33)
Charge/(release) to the Income Statement	(33)
Income statement charge/(release) for the year	(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	284
Change in economic scenarios	(12)
Changes to model	2
Transfer to lifetime ECL (not-credit impaired)	11
Transfer to credit impaired	(23)
Transfer to 12-monthECL	(68)
Transfer from credit impaired	27
Transfers of financial instruments	(53)
Net remeasurement of ECL on stage transfer	83
New assets originated or purchased	34
Other	(11)
Assets derecognised - closed good	(20)
Ending balance	307	284
Net movement in the year	23
Charge/(release) to the Income Statement	23
Income statement charge/(release) for the year	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	691
Change in economic scenarios	(8)
Changes to model	(8)
Transfer to credit impaired	31
Transfer from credit impaired	(33)
Transfers of financial instruments	(2)
Net remeasurement of ECL on stage transfer	79
New assets originated or purchased	13
Other	170
Assets derecognised - closed good	(44)
Assets derecognised - written off	(534)
Ending balance	357	691
Net movement in the year	(334)
Charge/(release) to the Income Statement	200
Recoveries net of collection costs	(36)
Income statement charge/(release) for the year	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	300,286
New assets originated or purchased	87,039
Other	(20,110)
Assets derecognised - closed good	(55,611)
Assets derecognised - written off	(656)
Ending balance	310,948	300,286
Net movement in the year	10,662
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	1,151
Change in economic scenarios	(16)
Changes to model	(7)
Net remeasurement of ECL on stage transfer	99
New assets originated or purchased	90
Other	139
Assets derecognised - closed good	(115)
Assets derecognised - written off	(534)
Ending balance	807	1,151
Net movement in the year	(344)
Charge/(release) to the Income Statement	190
Recoveries net of collection costs	(36)
Income statement charge/(release) for the year	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	155,155
Transfer to lifetime ECL (not-credit impaired)	(2,941)
Transfer to credit impaired	(329)
Transfer to 12-monthECL	2,628
Transfer from credit impaired	4
Transfers of financial instruments	(638)
New assets originated or purchased	28,330
Other	(7,327)
Assets derecognised - closed good	(17,781)
Ending balance	157,739	155,155
Net movement in the year	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	9,884
Transfer to lifetime ECL (not-credit impaired)	2,941
Transfer to credit impaired	(512)
Transfer to 12-monthECL	(2,628)
Transfer from credit impaired	405
Transfers of financial instruments	206
New assets originated or purchased	446
Other	(244)
Assets derecognised - closed good	(860)
Ending balance	9,432	9,884
Net movement in the year	(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	2,004
Transfer to credit impaired	841
Transfer from credit impaired	(409)
Transfers of financial instruments	432
New assets originated or purchased	3
Other	(36)
Assets derecognised - closed good	(327)
Assets derecognised - written off	(77)
Ending balance	1,999	2,004
Net movement in the year	(5)
Residential mortgages [member] | 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	20
Change in economic scenarios	(6)
Transfer to lifetime ECL (not-credit impaired)	(1)
Transfer to credit impaired	(6)
Transfer to 12-monthECL	21
Transfers of financial instruments	14
Net remeasurement of ECL on stage transfer	(20)
New assets originated or purchased	2
Other	6
Assets derecognised - closed good	(4)
Ending balance	12	20
Net movement in the year	(8)
Charge/(release) to the Income Statement	(8)
Income statement charge/(release) for the year	(8)
Residential mortgages [member] | 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	131
Change in economic scenarios	(7)
Changes to model	2
Transfer to lifetime ECL (not-credit impaired)	1
Transfer to credit impaired	(12)
Transfer to 12-monthECL	(21)
Transfer from credit impaired	14
Transfers of financial instruments	(18)
Net remeasurement of ECL on stage transfer	20
New assets originated or purchased	5
Other	(4)
Assets derecognised - closed good	(10)
Ending balance	119	131
Net movement in the year	(12)
Charge/(release) to the Income Statement	(12)
Income statement charge/(release) for the year	(12)
Residential mortgages [member] | 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	121
Change in economic scenarios	(8)
Changes to model	2
Transfer to credit impaired	18
Transfer from credit impaired	(14)
Transfers of financial instruments	4
Net remeasurement of ECL on stage transfer	14
New assets originated or purchased	1
Other	3
Assets derecognised - closed good	(13)
Assets derecognised - written off	(18)
Ending balance	106	121
Net movement in the year	(15)
Charge/(release) to the Income Statement	3
Recoveries net of collection costs	(4)
Income statement charge/(release) for the year	(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	167,043
New assets originated or purchased	28,779
Other	(7,607)
Assets derecognised - closed good	(18,968)
Assets derecognised - written off	(77)
Ending balance	169,170	167,043
Net movement in the year	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	272
Change in economic scenarios	(21)
Changes to model	4
Net remeasurement of ECL on stage transfer	14
New assets originated or purchased	8
Other	5
Assets derecognised - closed good	(27)
Assets derecognised - written off	(18)
Ending balance	237	£ 272
Net movement in the year	(35)
Charge/(release) to the Income Statement	(17)
Recoveries net of collection costs	(4)
Income statement charge/(release) for the year	£ (21)

Credit Risk - Summary of Modifi

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

Credit Risk - Summary of Res_10

Credit Risk - Summary of Residential Mortgages by Forbearance Applied (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Capitalisation	£ 587	£ 652
Term extension	256	241
Interest-only	502	582
Total	1,345	1,475
Impairment loss allowances	£ 29	£ 27
Loans capitalisation forbearance Percentage	0.40%	0.40%
Loans term extension forbearance percentage	0.20%	0.20%
Loans interest only forbearance percentage	0.30%	0.40%
Loans forbearance percentage	0.90%	1.00%
Stage 2 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Capitalisation	£ 375
Term extension	161
Interest-only	389
Total	925
Impairment loss allowances	9
Stage 3 [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Capitalisation	212
Term extension	95
Interest-only	113
Total	420
Impairment loss allowances	£ 20
Forbearance in Arrears [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Capitalisation		£ 260
Term extension		63
Interest-only		175
Total		498
Impairment loss allowances		22
Performing [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Capitalisation		392
Term extension		178
Interest-only		407
Total		977
Impairment loss allowances		£ 5

Credit Risk - Summary of Res_11

Credit Risk - Summary of Residential Mortgages Portfolios of Particular Interest by Credit Performance (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 201,619	£ 199,332
NPLs		£ 1,868
NPL ratio		1.21%
PIPs	25	£ 29
Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
NPLs		£ 868
NPL ratio		2.23%
PIPs	12	£ 17
Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
NPLs		£ 263
NPL ratio		1.91%
PIPs	5	£ 5
Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
NPLs		£ 245
NPL ratio		1.66%
PIPs	3	£ 3
Loan To Value Greater Than 100% Loan [member]
Disclosure of credit risk exposure [line items]
NPLs		£ 132
NPL ratio		8.97%
PIPs	8	£ 10
Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
NPLs		£ 21
NPL ratio		0.31%
PIPs		£ 1
Other [member]
Disclosure of credit risk exposure [line items]
NPLs		£ 543
NPL ratio		0.57%
PIPs	7	£ 6
Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		151,688
Performing Loans [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		37,497
Performing Loans [member] | Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		13,372
Performing Loans [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		14,438
Performing Loans [member] | Loan To Value Greater Than 100% Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		1,302
Performing Loans [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		6,768
Performing Loans [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		94,530
Later Than 1 Month and Not Later Than 2 Months [member] | Early Arrear Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		700
Later Than 1 Month and Not Later Than 2 Months [member] | Early Arrear Loans [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		317
Later Than 1 Month and Not Later Than 2 Months [member] | Early Arrear Loans [member] | Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		93
Later Than 1 Month and Not Later Than 2 Months [member] | Early Arrear Loans [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		67
Later Than 1 Month and Not Later Than 2 Months [member] | Early Arrear Loans [member] | Loan To Value Greater Than 100% Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		22
Later Than 1 Month and Not Later Than 2 Months [member] | Early Arrear Loans [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		9
Later Than 1 Month and Not Later Than 2 Months [member] | Early Arrear Loans [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		295
Later Than 2 Months And Not Later Than 3 Months [member] | Early Arrear Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		426
Later Than 2 Months And Not Later Than 3 Months [member] | Early Arrear Loans [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		203
Later Than 2 Months And Not Later Than 3 Months [member] | Early Arrear Loans [member] | Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		57
Later Than 2 Months And Not Later Than 3 Months [member] | Early Arrear Loans [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		35
Later Than 2 Months And Not Later Than 3 Months [member] | Early Arrear Loans [member] | Loan To Value Greater Than 100% Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		15
Later Than 2 Months And Not Later Than 3 Months [member] | Early Arrear Loans [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		4
Later Than 2 Months And Not Later Than 3 Months [member] | Early Arrear Loans [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		167
Mortgages [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	157,957	154,682
Mortgages [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	38,035	38,885
Mortgages [member] | Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	13,201	13,785
Mortgages [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	12,926	14,785
Mortgages [member] | Loan To Value Greater Than 100% Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,140	1,471
Mortgages [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	8,252	6,802
Mortgages [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	101,158	£ 95,535
Mortgages [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	146,619
Mortgages [member] | Stage 1 [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	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	11,824
Mortgages [member] | Stage 1 [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	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	740
Mortgages [member] | Stage 1 [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	7,906
Mortgages [member] | Stage 1 [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	96,767
Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	9,356
Mortgages [member] | Stage 2 [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	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	1,115
Mortgages [member] | Stage 2 [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	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	273
Mortgages [member] | Stage 2 [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	317
Mortgages [member] | Stage 2 [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	3,802
Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 1,982
Stage 3 ratio	1.25%
Mortgages [member] | Stage 3 [member] | Interest Only Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 1,005
Stage 3 ratio	2.64%
Mortgages [member] | Stage 3 [member] | Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 262
Stage 3 ratio	1.98%
Mortgages [member] | Stage 3 [member] | Flexible Interest Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 286
Stage 3 ratio	2.21%
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	£ 127
Stage 3 ratio	11.14%
Mortgages [member] | Stage 3 [member] | Buy To Let Loan [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 29
Stage 3 ratio	0.35%
Mortgages [member] | Stage 3 [member] | Other [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 589
Stage 3 ratio	0.58%

Credit Risk - Summary of Res_12

Credit Risk - Summary of Residential Mortgages Portfolios of Particular Interest by Credit Performance (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Part Interest Only Part Repayment [member]
Disclosure of credit risk exposure [line items]
Mortgage loan including interest-only part	£ 9,756	£ 10,116

Credit Risk - Summary of Res_13

Credit Risk - Summary of Residential Mortgages Portfolios of Particular Interest by Forbearance Applied (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Total value	£ 1,345	£ 1,475
Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	925
Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	420
Interest Only Loan [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Total value	229	208
Interest Only Loan [member] | Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	136
Interest Only Loan [member] | Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	93
Flexible Interest Loan [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Total value	32	34
Flexible Interest Loan [member] | Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	18
Flexible Interest Loan [member] | Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	14
Loan To Value Greater Than 100% Loan [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Total value	10	13
Loan To Value Greater Than 100% Loan [member] | Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	3
Loan To Value Greater Than 100% Loan [member] | Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	7
Buy To Let Loan [member] | Mortgages [member]
Disclosure of credit risk exposure [line items]
Total value	9	£ 8
Buy To Let Loan [member] | Mortgages [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	6
Buy To Let Loan [member] | Mortgages [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	£ 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, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 201,619	£ 199,332
NPL		1,868
Loss allowances	751	£ 940	£ 921	£ 1,108
NPL ratio		1.21%
Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		£ 151,688
Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	12,987	12,135
NPL	130	122
Loss allowances	£ 305	£ 212
NPL ratio	1.00%	1.00%
Gross write-offs	£ 149	£ 152
Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	12,045
Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	802
Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 140
Stage 3 ratio	1.08%
Consumer finance and unsecured lending [member] | Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		11,883
Consumer finance and unsecured lending [member] | Early Arrear Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		130
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 7,347	6,957
NPL	43	34
Loss allowances	£ 85	£ 77
NPL ratio	0.59%	0.49%
Gross write-offs	£ 24	£ 32
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	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	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	£ 43
Stage 3 ratio	0.59%
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member] | Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		6,861
Consumer (auto) finance [member] | Consumer finance and unsecured lending [member] | Early Arrear Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		62
Personal loans [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 2,182	2,169
NPL	16	16
Loss allowances	47	44
Personal loans [member] | Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,113
Personal loans [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	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	21
Personal loans [member] | Consumer finance and unsecured lending [member] | Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		2,129
Personal loans [member] | Consumer finance and unsecured lending [member] | Early Arrear Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		24
Credit Card [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,865	2,444
NPL	49	48
Loss allowances	112	62
Credit Card [member] | Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	2,560
Credit Card [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	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	49
Credit Card [member] | Consumer finance and unsecured lending [member] | Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		2,377
Credit Card [member] | Consumer finance and unsecured lending [member] | Early Arrear Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		19
Overdrafts [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	593	565
NPL	22	24
Loss allowances	61	29
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	422
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	144
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	27
Overdrafts [member] | Consumer finance and unsecured lending [member] | Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		516
Overdrafts [member] | Consumer finance and unsecured lending [member] | Early Arrear Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		25
Other unsecured advances [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	5,640	5,178
NPL	87	88
Loss allowances	£ 220	£ 135
NPL ratio	1.54%	1.69%
Gross write-offs	£ 125	£ 120
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	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	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	£ 97
Stage 3 ratio	1.72%
Other unsecured advances [member] | Consumer finance and unsecured lending [member] | Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		5,022
Other unsecured advances [member] | Consumer finance and unsecured lending [member] | Early Arrear Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		£ 68

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] £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of credit risk exposure [line items]
Amortised cost before modification	£ 43
Net modification loss	20
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	5
Credit cards [member]
Disclosure of credit risk exposure [line items]
Amortised cost before modification	26
Net modification loss	12
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	2
Overdrafts [member]
Disclosure of credit risk exposure [line items]
Amortised cost before modification	17
Net modification loss	8
Gross carrying amount of financial assets for which the ECL allowance has changed to 12-month measurement during the year	£ 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, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Forbearance	£ 1,345	£ 1,475
Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	79	77
Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	17
Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	62
Personal loans [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance		1
Credit cards [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	53	48
Credit cards [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	10
Credit cards [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	43
Overdrafts [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	26	28
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	7
Overdrafts [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	19
Total other unsecured [member] | Consumer finance and unsecured lending [member]
Disclosure of credit risk exposure [line items]
Forbearance	79	£ 77
Total other unsecured [member] | Consumer finance and unsecured lending [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Forbearance	17
Total other unsecured [member] | Consumer finance and unsecured lending [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Forbearance	£ 62

Credit Risk - Summary of Busine

Credit Risk - Summary of Business Banking by Credit Performance (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 201,619	£ 199,332
Loss allowances	751	£ 940	£ 921	£ 1,108
NPL ratio		1.21%
Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		£ 151,688
Credit risk [member]
Disclosure of credit risk exposure [line items]
Loss allowances	(800)	(1,000)
Credit risk [member] | Business Banking [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,802	1,912
Loss allowances	£ 53	£ 54
NPL ratio	4.94%	6.01%
Gross write offs	£ 15	£ 21
Credit risk [member] | Business Banking [member] | Performing Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		1,793
Credit risk [member] | Business Banking [member] | Early Arrear Loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers		4
Credit risk [member] | Business Banking [member] | Non performing loans [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	89	£ 115
Credit risk [member] | Business Banking [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	1,548
Credit risk [member] | Business Banking [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	165
Credit risk [member] | Business Banking [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Loans and advances to customers	£ 89
Stage 3 ratio	4.94%

Credit Risk - Summary of Modi_3

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

Credit Risk - Summary of Busi_2

Credit Risk - Summary of Business Banking by Forbearance (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Total value	£ 1,345	£ 1,475
Business Banking [member]
Disclosure of credit risk exposure [line items]
Total value	74	£ 85
Business Banking [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Total value	20
Business Banking [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Total value	£ 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending balance	£ 807
Recoveries net of collection costs	(42)	£ (54)	£ (65)
Income statement charge/(release) for the year	153	203	67
Stage 1 [member]
Disclosure of reconciliation of changes in loss allowance and explanation of changes in gross carrying amount for financial instruments [line items]
Ending balance	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]
Ending balance	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]
Ending balance	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	300,286
New assets originated or purchased	87,039
Other	(20,110)
Assets derecognised - closed good	(55,611)
Assets derecognised - written off	(656)
Ending balance	310,948	300,286
Net movement in the year	10,662
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	1,151
Change in economic scenarios	(16)
Changes to model	(7)
Net remeasurement of ECL on stage transfer	99
New assets originated or purchased	90
Other	139
Assets derecognised - closed good	(115)
Assets derecognised - written off	(534)
Ending balance	807	1,151
Net movement in the year	(344)
Charge/(release) to the Income Statement	190
Recoveries net of collection costs	(36)
Income statement charge/(release) for the year	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	23	13	29
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	23,671
New assets originated or purchased	9,399
Other	819
Assets derecognised - closed good	(10,949)
Assets derecognised - written off	(105)
Ending balance	22,835	23,671
Net movement in the year	(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	249
Change in economic scenarios	2
Net remeasurement of ECL on stage transfer	21
New assets originated or purchased	18
Other	31
Assets derecognised - closed good	(42)
Assets derecognised - written off	(97)
Ending balance	182	249
Net movement in the year	(67)
Charge/(release) to the Income Statement	30
Recoveries net of collection costs	(7)
Income statement charge/(release) for the year	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	14	174	21
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	27,064
New assets originated or purchased	36,059
Other	(2,270)
Assets derecognised - closed good	(18,294)
Assets derecognised - written off	(299)
Ending balance	42,260	27,064
Net movement in the year	15,196
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	258
Changes to model	(9)
New assets originated or purchased	7
Other	29
Assets derecognised - closed good	(15)
Assets derecognised - written off	(252)
Ending balance	18	258
Net movement in the year	(240)
Charge/(release) to the Income Statement	12
Recoveries net of collection costs	2
Income statement charge/(release) for the year	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	(8)	(20)	£ (4)
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	57,425
New assets originated or purchased	7,530
Other	(10,190)
Assets derecognised - closed good	(4,714)
Assets derecognised - written off	(3)
Ending balance	50,048	57,425
Net movement in the year	(7,377)
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	19
Change in economic scenarios	1
Net remeasurement of ECL on stage transfer	(1)
New assets originated or purchased	2
Other	(1)
Assets derecognised - closed good	(4)
Assets derecognised - written off	(3)
Ending balance	13	19
Net movement in the year	(6)
Charge/(release) to the Income Statement	(3)
Recoveries net of collection costs	(4)
Income statement charge/(release) for the year	(7)
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	285,133
Transfer to lifetime ECL (not-credit impaired)	(4,190)
Transfer to credit impaired	(445)
Transfer to 12-month ECL	3,325
Transfer from credit impaired	17
Transfers of financial instruments	(1,293)
New assets originated or purchased	85,933
Other	(19,867)
Assets derecognised - closed good	(53,543)
Ending balance	296,363	285,133
Net movement in the year	11,230
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	12,110
Transfer to lifetime ECL (not-credit impaired)	4,190
Transfer to credit impaired	(603)
Transfer to 12-month ECL	(3,325)
Transfer from credit impaired	443
Transfers of financial instruments	705
New assets originated or purchased	1,087
Other	(295)
Assets derecognised - closed good	(1,594)
Ending balance	12,013	12,110
Net movement in the year	(97)
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	176
Change in economic scenarios	4
Changes to model	(1)
Transfer to lifetime ECL (not-credit impaired)	(11)
Transfer to credit impaired	(8)
Transfer to 12-month ECL	68
Transfer from credit impaired	6
Transfers of financial instruments	55
Net remeasurement of ECL on stage transfer	(63)
New assets originated or purchased	43
Other	(20)
Assets derecognised - closed good	(51)
Ending balance	143	176
Net movement in the year	(33)
Charge/(release) to the Income Statement	(33)
Income statement charge/(release) for the year	(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	284
Change in economic scenarios	(12)
Changes to model	2
Transfer to lifetime ECL (not-credit impaired)	11
Transfer to credit impaired	(23)
Transfer to 12-month ECL	(68)
Transfer from credit impaired	27
Transfers of financial instruments	(53)
Net remeasurement of ECL on stage transfer	83
New assets originated or purchased	34
Other	(11)
Assets derecognised - closed good	(20)
Ending balance	307	284
Net movement in the year	23
Charge/(release) to the Income Statement	23
Income statement charge/(release) for the year	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	22,417
Transfer to lifetime ECL (not-credit impaired)	(670)
Transfer to credit impaired	(41)
Transfer to 12-month ECL	200
Transfer from credit impaired	2
Transfers of financial instruments	(509)
New assets originated or purchased	9,115
Other	879
Assets derecognised - closed good	(10,569)
Ending balance	21,333	22,417
Net movement in the year	(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	866
Transfer to lifetime ECL (not-credit impaired)	670
Transfer to credit impaired	(31)
Transfer to 12-month ECL	(200)
Transfer from credit impaired	2
Transfers of financial instruments	441
New assets originated or purchased	281
Other	(58)
Assets derecognised - closed good	(304)
Ending balance	1,226	866
Net movement in the year	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	43
Change in economic scenarios	5
Transfer to lifetime ECL (not-credit impaired)	(3)
Transfer to 12-month ECL	8
Transfer from credit impaired	1
Transfers of financial instruments	6
Net remeasurement of ECL on stage transfer	(7)
New assets originated or purchased	12
Other	(3)
Assets derecognised - closed good	(19)
Ending balance	37	43
Net movement in the year	(6)
Charge/(release) to the Income Statement	(6)
Income statement charge/(release) for the year	(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	33
Change in economic scenarios	(3)
Transfer to lifetime ECL (not-credit impaired)	3
Transfer to credit impaired	(1)
Transfer to 12-month ECL	(8)
Transfer from credit impaired	1
Transfers of financial instruments	(5)
Net remeasurement of ECL on stage transfer	10
New assets originated or purchased	5
Other	(3)
Assets derecognised - closed good	(5)
Ending balance	32	33
Net movement in the year	(1)
Charge/(release) to the Income Statement	(1)
Income statement charge/(release) for the year	(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	26,583
Transfer to lifetime ECL (not-credit impaired)	(2)
New assets originated or purchased	35,926
Other	(2,306)
Assets derecognised - closed good	(18,101)
Ending balance	42,100	26,583
Net movement in the year	15,517
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	109
Transfer to lifetime ECL (not-credit impaired)	2
New assets originated or purchased	133
Other	83
Assets derecognised - closed good	(193)
Ending balance	134	109
Net movement in the year	25
Financial instruments not credit-impaired [member] | Corporate and investment 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	16
New assets originated or purchased	4
Other	(1)
Assets derecognised - closed good	(14)
Ending balance	5	16
Net movement in the year	(11)
Charge/(release) to the Income Statement	(11)
Income statement charge/(release) for the year	(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]
New assets originated or purchased	3
Other	1
Assets derecognised - closed good	(1)
Ending balance	3
Net movement in the year	3
Charge/(release) to the Income Statement	3
Income statement charge/(release) for the year	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	57,155
Transfer to lifetime ECL (not-credit impaired)	(111)
Transfer to 12-month ECL	133
Transfers of financial instruments	22
New assets originated or purchased	7,526
Other	(10,187)
Assets derecognised - closed good	(4,617)
Ending balance	49,899	57,155
Net movement in the year	(7,256)
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	250
Transfer to lifetime ECL (not-credit impaired)	111
Transfer to credit impaired	(4)
Transfer to 12-month ECL	(133)
Transfer from credit impaired	3
Transfers of financial instruments	(23)
New assets originated or purchased	2
Other	(6)
Assets derecognised - closed good	(90)
Ending balance	133	250
Net movement in the year	(117)
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	7
Change in economic scenarios	1
Transfer to lifetime ECL (not-credit impaired)	(1)
Transfer to 12-month ECL	3
Transfers of financial instruments	2
Net remeasurement of ECL on stage transfer	(2)
New assets originated or purchased	1
Other	(2)
Assets derecognised - closed good	(2)
Ending balance	5	7
Net movement in the year	(2)
Charge/(release) to the Income Statement	(2)
Income statement charge/(release) for the year	(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	4
Transfer to lifetime ECL (not-credit impaired)	1
Transfer to 12-month ECL	(3)
Transfer from credit impaired	1
Transfers of financial instruments	(1)
Ending balance	3	4
Net movement in the year	(1)
Charge/(release) to the Income Statement	(1)
Income statement charge/(release) for the year	(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	3,043
Transfer to credit impaired	1,048
Transfer from credit impaired	(460)
Transfers of financial instruments	588
New assets originated or purchased	19
Other	52
Assets derecognised - closed good	(474)
Assets derecognised - written off	(656)
Ending balance	2,572	3,043
Net movement in the year	(471)
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	691
Change in economic scenarios	(8)
Changes to model	(8)
Transfer to credit impaired	31
Transfer from credit impaired	(33)
Transfers of financial instruments	(2)
Net remeasurement of ECL on stage transfer	79
New assets originated or purchased	13
Other	170
Assets derecognised - closed good	(44)
Assets derecognised - written off	(534)
Ending balance	357	691
Net movement in the year	(334)
Charge/(release) to the Income Statement	200
Recoveries net of collection costs	(36)
Income statement charge/(release) for the year	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	388
Transfer to credit impaired	72
Transfer from credit impaired	(4)
Transfers of financial instruments	68
New assets originated or purchased	3
Other	(2)
Assets derecognised - closed good	(76)
Assets derecognised - written off	(105)
Ending balance	276	388
Net movement in the year	(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	173
Transfer to credit impaired	1
Transfer from credit impaired	(2)
Transfers of financial instruments	(1)
Net remeasurement of ECL on stage transfer	18
New assets originated or purchased	1
Other	37
Assets derecognised - closed good	(18)
Assets derecognised - written off	(97)
Ending balance	113	173
Net movement in the year	(60)
Charge/(release) to the Income Statement	37
Recoveries net of collection costs	(7)
Income statement charge/(release) for the year	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	372
Other	(47)
Assets derecognised - written off	(299)
Ending balance	26	372
Net movement in the year	(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	242
Changes to model	(9)
Other	29
Assets derecognised - written off	(252)
Ending balance	10	242
Net movement in the year	(232)
Charge/(release) to the Income Statement	20
Recoveries net of collection costs	2
Income statement charge/(release) for the year	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	20
Transfer to credit impaired	4
Transfer from credit impaired	(3)
Transfers of financial instruments	1
New assets originated or purchased	2
Other	3
Assets derecognised - closed good	(7)
Assets derecognised - written off	(3)
Ending balance	16	20
Net movement in the year	(4)
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	8
Transfer from credit impaired	(1)
Transfers of financial instruments	(1)
Net remeasurement of ECL on stage transfer	1
New assets originated or purchased	1
Other	1
Assets derecognised - closed good	(2)
Assets derecognised - written off	(3)
Ending balance	5	£ 8
Net movement in the year	(3)
Recoveries net of collection costs	(4)
Income statement charge/(release) for the year	£ (4)

Credit Risk - Summary of Other

Credit Risk - Summary of Other Segments Exposures by Credit Rating (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 92,547	£ 113,108
Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	90,743
Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,490
Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	314
Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	9,086	9,250
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	24,078	32,249
Corporate and investment banking [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,200	4,355
Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	16,064	21,439
Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,814	6,455
Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	45,075	56,349
Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,343	5,976
Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,604	44,495
Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,840	4,379
Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	147	212
Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	858	1,025
Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	283	262
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	23,394	24,510
Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,908	12,630
Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,743	8,606
Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,743	3,274
Internal grade 9 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	40,280	52,529
Internal grade 9 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	40,280
Internal grade 9 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,261	3,212
Internal grade 9 [member] | Corporate and investment banking [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	393	590
Internal grade 9 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	12	260
Internal grade 9 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	856	2,362
Internal grade 9 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	38,339	48,818
Internal grade 9 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,377	1,841
Internal grade 9 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,512	44,477
Internal grade 9 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,436	2,487
Internal grade 9 [member] | Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	14	13
Internal grade 9 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	680	499
Internal grade 9 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	680	499
Internal grade 8 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	17,471	15,830
Internal grade 8 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	17,471
Internal grade 8 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8,386	7,763
Internal grade 8 [member] | Corporate and investment banking [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,807	3,321
Internal grade 8 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,187	2,979
Internal grade 8 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,392	1,463
Internal grade 8 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,186	5,467
Internal grade 8 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,847	3,641
Internal grade 8 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	91	18
Internal grade 8 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,062	1,560
Internal grade 8 [member] | Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	147	212
Internal grade 8 [member] | Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	39	36
Internal grade 8 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,899	2,600
Internal grade 8 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,899	2,600
Internal grade 7 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7,747	12,626
Internal grade 7 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7,747
Internal grade 7 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7,025	11,329
Internal grade 7 [member] | Corporate and investment banking [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk		444
Internal grade 7 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,535	8,391
Internal grade 7 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,490	2,494
Internal grade 7 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	518	867
Internal grade 7 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	76	451
Internal grade 7 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	318	300
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		1
Internal grade 7 [member] | Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	124	115
Internal grade 7 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	204	430
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	66	259
Internal grade 7 [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	138	171
Internal grade 6 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8,832	11,995
Internal grade 6 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8,759
Internal grade 6 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	73
Internal grade 6 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,437	8,912
Internal grade 6 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,361	8,879
Internal grade 6 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	76	33
Internal grade 6 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	348	505
Internal grade 6 [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	43	43
Internal grade 6 [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1
Internal grade 6 [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	24	32
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	203	359
Internal grade 6 [member] | Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	77	71
Internal grade 6 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,047	2,578
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	1,745	2,183
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	302	395
Internal grade 5 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,250	12,330
Internal grade 5 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	10,802
Internal grade 5 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	448
Internal grade 5 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	888	676
Internal grade 5 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	888	573
Internal grade 5 [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk		103
Internal grade 5 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	49	117
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	35	104
Internal grade 5 [member] | Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	14	13
Internal grade 5 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	10,313	11,537
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	5,749	5,402
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	4,564	6,135
Internal grade 4 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,422	5,722
Internal grade 4 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,780
Internal grade 4 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	635
Internal grade 4 [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7
Internal grade 4 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3	2
Internal grade 4 [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3	2
Internal grade 4 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	145	132
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	137	124
Internal grade 4 [member] | Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	8	8
Internal grade 4 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,274	5,588
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	3,426	3,574
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	1,846	2,014
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
Internal grade 3 to 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,152	1,460
Internal grade 3 to 1 [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	527
Internal grade 3 to 1 [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	318
Internal grade 3 to 1 [member] | Stage 3 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	307
Internal grade 3 to 1 [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	78	355
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	78	355
Internal grade 3 to 1 [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	133	43
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	126	37
Internal grade 3 to 1 [member] | Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7	6
Internal grade 3 to 1 [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	941	1,062
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	886	998
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	31	60
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	24	4
Other [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	393	616
Other [member] | Stage 1 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	377
Other [member] | Stage 2 [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	16
Other [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	357	400
Other [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	357	400
Other [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	36	216
Other [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 36	214
Other [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk		£ 2

Credit Risk - Summary of Othe_2

Credit Risk - Summary of Other Segments Exposures by Geographical Distribution (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 92,547	£ 113,108
Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	9,086	9,250
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	23,394	24,510
Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,908	12,630
Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,743	8,606
Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,743	3,274
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	24,078	32,249
Corporate and investment banking [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,200	4,355
Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	16,064	21,439
Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,814	6,455
Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	45,075	56,349
Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,343	5,976
Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,604	44,495
Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,840	4,379
Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	147	212
Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	858	1,025
Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	283	262
UK [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	23,319	24,393
UK [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,833	12,513
UK [member] | Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,743	8,606
UK [member] | Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,743	3,274
UK [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	14,317	20,532
UK [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	13,080	17,430
UK [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,237	3,102
UK [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	38,533	44,892
UK [member] | Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,343	5,976
UK [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	30,587	35,659
UK [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,576	2,086
UK [member] | Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	744	909
UK [member] | Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	283	262
Europe [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	74	116
Europe [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	74	116
Europe [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	5,031	6,852
Europe [member] | Corporate and investment banking [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	393	1,032
Europe [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,752	3,699
Europe [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,886	2,121
Europe [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,551	2,794
Europe [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,409	1,514
Europe [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,142	1,217
Europe [member] | Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk		63
US [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk		1
US [member] | Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk		1
US [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	322	726
US [member] | Corporate and investment banking [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk		1
US [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	124	111
US [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	198	614
US [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,112	6,240
US [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	965	6,091
US [member] | Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	147	149
Rest Of World [member] | Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	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
Rest Of World [member] | Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,408	4,139
Rest Of World [member] | Corporate and investment banking [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,807	3,322
Rest Of World [member] | Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	108	199
Rest Of World [member] | Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	493	618
Rest Of World [member] | Corporate centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	2,879	2,423
Rest Of World [member] | Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,643	1,231
Rest Of World [member] | Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,122	1,076
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	£ 114	£ 116

Credit Risk - Summary of Othe_3

Credit Risk - Summary of Other Segments Exposures by Credit Performance (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 92,547	£ 113,108
Observed impairment loss allowances	213	449
Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	9,086	9,250
Observed Impairment Loss Allowances [Member]
Disclosure of credit risk exposure [line items]
Observed impairment loss allowances		397
Allowance for IBNO [member]
Disclosure of credit risk exposure [line items]
Observed impairment loss allowances		52
Corporate and commercial banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	23,394	24,510
Observed impairment loss allowances	182	155
Corporate and commercial banking [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	21,402	22,713
Corporate and commercial banking [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	1,336	975
Corporate and commercial banking [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	380	429
Corporate and commercial banking [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	276	393
Corporate and commercial banking [member] | SME and Mid Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	11,908	12,630
Observed impairment loss allowances	160	128
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	10,350	11,185
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	972	815
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	333	296
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	253	334
Corporate and commercial banking [member] | Commercial Real Estate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,743	8,606
Observed impairment loss allowances	22	27
Corporate and commercial banking [member] | Commercial Real Estate [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	6,426	8,254
Corporate and commercial banking [member] | Commercial Real Estate [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	247	160
Corporate and commercial banking [member] | Commercial Real Estate [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	47	133
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	23	59
Corporate and commercial banking [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,743	3,274
Corporate and commercial banking [member] | Social Housing [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,626	3,274
Corporate and commercial banking [member] | Social Housing [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	117
Corporate and investment banking [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	24,078	32,249
Observed impairment loss allowances	18	236
Corporate and investment banking [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	23,318	31,466
Corporate and investment banking [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	548	285
Corporate and investment banking [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	186	108
Corporate and investment banking [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	26	390
Corporate and investment banking [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,200	4,355
Corporate and investment banking [member] | Sovereign And Supranational [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,200	4,355
Corporate and investment banking [member] | Large Corporate [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	16,064	21,439
Observed impairment loss allowances	18	236
Corporate and investment banking [member] | Large Corporate [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	15,304	20,757
Corporate and investment banking [member] | Large Corporate [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	548	284
Corporate and investment banking [member] | Large Corporate [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	186	8
Corporate and investment banking [member] | Large Corporate [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	26	390
Corporate and investment banking [member] | Financial Institutions [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,814	6,455
Corporate and investment banking [member] | Financial Institutions [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	3,814	6,354
Corporate and investment banking [member] | Financial Institutions [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk		1
Corporate and investment banking [member] | Financial Institutions [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	0	100
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 centre [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	45,075	56,349
Observed impairment loss allowances	13	6
Corporate centre [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	45,002	56,296
Corporate centre [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	48	26
Corporate centre [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7	6
Corporate centre [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	18	21
Corporate centre [member] | Social Housing [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,343	5,976
Corporate centre [member] | Social Housing [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,321	5,972
Corporate centre [member] | Social Housing [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	22	4
Corporate centre [member] | Sovereign And Supranational [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,604	44,495
Corporate centre [member] | Sovereign And Supranational [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	34,604	44,495
Corporate centre [member] | Structured Products [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,840	4,379
Corporate centre [member] | Structured Products [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	4,840	4,379
Corporate centre [member] | Derivative Financial Instruments [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	147	212
Corporate centre [member] | Derivative Financial Instruments [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	147	212
Corporate centre [member] | Legacy Portfolios in Run-Off [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	858	1,025
Observed impairment loss allowances	13	6
Corporate centre [member] | Legacy Portfolios in Run-Off [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	809	977
Corporate centre [member] | Legacy Portfolios in Run-Off [member] | Enhanced Monitoring [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	26	22
Corporate centre [member] | Legacy Portfolios in Run-Off [member] | Proactive Management [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	7	6
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	16	20
Corporate centre [member] | Crown dependency branch [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	283	262
Corporate centre [member] | Crown dependency branch [member] | Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	281	261
Corporate centre [member] | Crown dependency branch [member] | Non-Performing Exposure [member]
Disclosure of credit risk exposure [line items]
Maximum exposure to credit risk	£ 2	£ 1

Credit Risk - Summary of Modi_4

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

Credit Risk - Summary of Othe_4

Credit Risk - Summary of Other Segments by Forbearance Applied (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Forbearance [line items]
- Term extension	£ 256	£ 241
- Interest-only	502	582
- Other payment rescheduling	587	652
Loans forbearance	1,345	1,475
Corporate and commercial banking [member]
Disclosure Of Forbearance [line items]
- Term extension	67	136
- Interest-only	112	152
- Other payment rescheduling	163	127
Loans forbearance	£ 342	£ 415
Proportion of portfolio	1.50%	1.70%
Corporate and commercial banking [member] | Non-performing loans by forbearance [member]
Disclosure Of Forbearance [line items]
Loans forbearance		£ 273
Corporate and commercial banking [member] | Performing [member]
Disclosure Of Forbearance [line items]
Loans forbearance		142
Corporate and commercial banking [member] | Stage 1 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	£ 43
Corporate and commercial banking [member] | Stage 2 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	78
Corporate and commercial banking [member] | Stage 3 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	221
Corporate and investment banking [member]
Disclosure Of Forbearance [line items]
- Term extension	42	55
- Other payment rescheduling	26	299
Loans forbearance	£ 68	£ 354
Proportion of portfolio	0.30%	1.10%
Corporate and investment banking [member] | Non-performing loans by forbearance [member]
Disclosure Of Forbearance [line items]
Loans forbearance		£ 347
Corporate and investment banking [member] | Performing [member]
Disclosure Of Forbearance [line items]
Loans forbearance		7
Corporate and investment banking [member] | Stage 2 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	£ 42
Corporate and investment banking [member] | Stage 3 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	26
Corporate centre [member]
Disclosure Of Forbearance [line items]
- Interest-only	8	14
- Other payment rescheduling	10	13
Loans forbearance	£ 18	£ 27
Proportion of portfolio	2.10%	2.60%
Corporate centre [member] | Non-performing loans by forbearance [member]
Disclosure Of Forbearance [line items]
Loans forbearance		£ 11
Corporate centre [member] | Performing [member]
Disclosure Of Forbearance [line items]
Loans forbearance		£ 16
Corporate centre [member] | Stage 1 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	£ 3
Corporate centre [member] | Stage 2 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	8
Corporate centre [member] | Stage 3 [member]
Disclosure Of Forbearance [line items]
Loans forbearance	£ 7

Credit Risk - Summary of Commer

Credit Risk - Summary of Commercial Real Estate by Credit Performance (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of performance obligations [line items]
Customer loans	£ 201,619	£ 199,332
NPLs		1,868
Commercial Real Estate [member]
Disclosure of performance obligations [line items]
Customer loans	6,459	8,144
NPLs	£ 29	£ 69
NPL ratio	0.45%	0.85%
Gross write-offs	£ 23	£ 11
Impairment loss allowances	£ 26	£ 54

Credit Risk - Summary of Comm_2

Credit Risk - Summary of Commercial Real Estate by Credit Performance (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Retail Banking Segment [member]
Disclosure of performance obligations [line items]
Consumer loans	£ 257	£ 257
Commercial Real Estate [member]
Disclosure of performance obligations [line items]
Consumer loans	£ 6,202	£ 7,886

Credit Risk - Summary of Comm_3

Credit Risk - Summary of Commercial Real Estate by Loan to Value (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 201,619	£ 199,332
Commercial Real Estate [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 6,459	£ 8,144
Percentage of loan to value	100.00%	100.00%
Commercial Real Estate [member] | Development Loans [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 61	£ 246
Percentage of loan to value	1.00%	3.00%
Commercial Real Estate [member] | Less Than Or Equal To Fifty Percentage [Member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 3,663	£ 4,146
Percentage of loan to value	56.00%	51.00%
Commercial Real Estate [member] | Greater than fifty percentage to seventy percentage [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 2,039	£ 3,035
Percentage of loan to value	32.00%	37.00%
Commercial Real Estate [member] | Greater Than 70-100% [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 47	£ 36
Percentage of loan to value	1.00%
Commercial Real Estate [member] | Greater Than 100% [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 18	£ 52
Percentage of loan to value		1.00%
Commercial Real Estate [member] | Standardised Portfolio [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 631	£ 629
Percentage of loan to value	10.00%	8.00%
Commercial Real Estate [member] | Total With Collateral [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 6,398	£ 7,898
Percentage of loan to value	99.00%	97.00%
Commercial Real Estate [member] | Non performing loans [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 29	£ 69
Percentage of loan to value	100.00%	100.00%
Commercial Real Estate [member] | Non performing loans [member] | Less Than Or Equal To Fifty Percentage [Member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 3	£ 6
Percentage of loan to value	11.00%	9.00%
Commercial Real Estate [member] | Non performing loans [member] | Greater than fifty percentage to seventy percentage [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 4	£ 2
Percentage of loan to value	14.00%	3.00%
Commercial Real Estate [member] | Non performing loans [member] | Greater Than 70-100% [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 1	£ 1
Percentage of loan to value	3.00%	1.00%
Commercial Real Estate [member] | Non performing loans [member] | Greater Than 100% [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 16	£ 48
Percentage of loan to value	55.00%	70.00%
Commercial Real Estate [member] | Non performing loans [member] | Standardised Portfolio [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 5	£ 12
Percentage of loan to value	17.00%	17.00%
Commercial Real Estate [member] | Non performing loans [member] | Total With Collateral [member]
Disclosure Of Loan To Value [line items]
Loans and advances to customers	£ 29	£ 69
Percentage of loan to value	100.00%	100.00%

Credit Risk - Summary of Comm_4

Credit Risk - Summary of Commercial Real Estate by Sector (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 201,619	£ 199,332
Commercial Real Estate [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 6,459	£ 8,144
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	£ 1,556	£ 2,181
Percentage of total CRE Portfolio	24.00%	27.00%
Commercial Real Estate [member] | Retail [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 1,004	£ 1,389
Percentage of total CRE Portfolio	16.00%	17.00%
Commercial Real Estate [member] | Industrial [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 888	£ 1,176
Percentage of total CRE Portfolio	14.00%	14.00%
Commercial Real Estate [member] | Residential [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 927	£ 1,001
Percentage of total CRE Portfolio	14.00%	12.00%
Commercial Real Estate [member] | Mixed Use [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 932	£ 1,146
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	£ 123	£ 133
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	£ 309	£ 304
Percentage of total CRE Portfolio	5.00%	4.00%
Commercial Real Estate [member] | Other [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 89	£ 185
Percentage of total CRE Portfolio	1.00%	2.00%
Commercial Real Estate [member] | Standardised Portfolio [member]
Disclosure Of Loans And Advances By Industry Sector [line items]
Loans and advances to customers	£ 631	£ 629
Percentage of total CRE Portfolio	10.00%	8.00%

Credit Risk - Summary of Social

Credit Risk - Summary of Social Housing Exposure (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Social Housing Exposure [line items]
Drawn	£ 201,619	£ 199,332
Total	92,547	113,108
Corporate and commercial banking [member]
Disclosure Of Social Housing Exposure [line items]
Total	23,394	24,510
Corporate centre [member]
Disclosure Of Social Housing Exposure [line items]
Total	45,075	56,349
Social Housing [member]
Disclosure Of Social Housing Exposure [line items]
Drawn	6,624	7,178
Total	9,086	9,250
Social Housing [member] | Corporate and commercial banking [member]
Disclosure Of Social Housing Exposure [line items]
Drawn	2,844	2,118
Total	4,743	3,274
Social Housing [member] | Corporate centre [member]
Disclosure Of Social Housing Exposure [line items]
Drawn	3,780	5,060
Total	£ 4,343	£ 5,976

Market Risk - Summary of Balanc

Market Risk - Summary of Balance Sheet Allocation by Market Risk Classification (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Market Risk [line items]
Cash and balances at central banks	£ 24,180		£ 32,771	£ 17,107
- Trading assets			30,555
- Derivative financial instruments	5,321		19,942
- Other financial assets at FVTPL	6,137		2,096
- Loans and advances to customers	201,619		199,332
- Loans and advances to banks	3,515		3,466
Financial assets at FVOCI	13,302
Financial investments			17,611
Retirement benefit assets	842		449
Total assets	289,381	£ 314,500	314,760	302,510
- Trading liabilities			31,109
- Derivative financial instruments	1,594		17,613
- Other financial liabilities at FVTPL	6,286		2,315
- Deposits by customers	173,692		177,421
- Deposits by banks	17,824		12,708
- Debt securities in issue	55,906		48,860
- Subordinated liabilities	3,601		3,793
Retirement benefit obligations	115		286
Total liabilities	273,161		298,558	£ 287,057
Banking Market Risk [member]
Market Risk [line items]
Cash and balances at central banks	24,180		32,771
- Derivative financial instruments	4,621		5,198
- Other financial assets at FVTPL	6,137		2,096
- Loans and advances to customers	201,619		199,332
- Loans and advances to banks	3,515		3,466
- Reverse repurchase agreements - non trading	21,127		2,614
- Other financial assets at amortised cost	7,228
Financial assets at FVOCI	13,302
Financial investments			17,611
Macro hedge of interest rate risk	697		833
Retirement benefit assets	842		449
Total assets	283,268		264,370
- Derivative financial instruments	875		722
- Other financial liabilities at FVTPL	6,286		703
- Deposits by customers	173,692		177,421
- Deposits by banks	17,824		12,708
- Repurchase agreements - non trading	10,910		1,076
- Debt securities in issue	55,906		48,860
- Subordinated liabilities	3,601		3,793
Macro hedge of interest rate risk	242
Retirement benefit obligations	115		286
Total liabilities	269,451		245,569
Trading Market Risk [member]
Market Risk [line items]
- Trading assets			30,555
- Derivative financial instruments	700		14,744
Total assets	700		45,299
- Trading liabilities			31,109
- Derivative financial instruments	719		16,891
- Other financial liabilities at FVTPL			1,612
Total liabilities	719		49,612
Market Risk [member]
Market Risk [line items]
Cash and balances at central banks	24,180		32,771
- Trading assets			30,555
- Derivative financial instruments	5,321		19,942
- Other financial assets at FVTPL	6,137		2,096
- Loans and advances to customers	201,619		199,332
- Loans and advances to banks	3,515		3,466
- Reverse repurchase agreements - non trading	21,127		2,614
- Other financial assets at amortised cost	7,228
Financial assets at FVOCI	13,302
Financial investments			17,611
Macro hedge of interest rate risk	697		833
Retirement benefit assets	842		449
Total assets	283,968		309,669
- Trading liabilities			31,109
- Derivative financial instruments	1,594		17,613
- Other financial liabilities at FVTPL	6,286		2,315
- Deposits by customers	173,692		177,421
- Deposits by banks	17,824		12,708
- Repurchase agreements - non trading	10,910		1,076
- Debt securities in issue	55,906		48,860
- Subordinated liabilities	3,601		3,793
Macro hedge of interest rate risk	242
Retirement benefit obligations	115		286
Total liabilities	£ 270,170		£ 295,181

Market Risk - Summary of Bala_2

Market Risk - Summary of Balance Sheet Allocation by Market Risk Classification (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other Assets [member]
Market Risk [line items]
Macro hedge of interest rate risk including other assets	£ 2,267	£ 2,511
Other Liabilities [member]
Market Risk [line items]
Macro hedge of interest rate risk including other liabilities	£ 2,507	£ 2,728

Market Risk - Summary of NIM an

Market Risk - Summary of NIM and EVE Sensitivity of Interest Rate Risk (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
+50bps [member]
Disclosure Of Sensitivity Limit Of Risk [line items]
NIM sensitivity	£ 207	£ 212
EVE sensitivity (unaudited)	162	95
-50bps [member]
Disclosure Of Sensitivity Limit Of Risk [line items]
NIM sensitivity	(23)	(125)
EVE sensitivity (unaudited)	£ (124)	£ (213)

Market Risk - Summary of NIM _2

Market Risk - Summary of NIM and EVE Sensitivity of Interest Rate Risk (Parenthetical) (Detail)	Dec. 31, 2018	Dec. 31, 2017
+50bps [member]
Disclosure Of Sensitivity Limit Of Risk [line items]
Shift in basis point	0.50%	0.50%
-50bps [member]
Disclosure Of Sensitivity Limit Of Risk [line items]
Shift in basis point	0.50%	0.50%

Market Risk - Summary of Intern

Market Risk - Summary of Internal VaR for Exposure to Main Classes of Risk (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Market Risk [line items]
Risk exposure	£ 0.4	£ 2.5
Interest Rate Risks [member]
Market Risk [line items]
Risk exposure	0.5	2.6
Equity Risks [member]
Market Risk [line items]
Risk exposure		0.3
Currency Risk [member]
Market Risk [line items]
Risk exposure	0.1	0.3
Diversification Offsets [member]
Market Risk [line items]
Risk exposure	(0.2)	(0.7)
Weighted average [member]
Market Risk [line items]
Risk exposure	1.4	2.7
Weighted average [member] | Interest Rate Risks [member]
Market Risk [line items]
Risk exposure	1.4	2.5
Weighted average [member] | Equity Risks [member]
Market Risk [line items]
Risk exposure	0.2	0.6
Weighted average [member] | Currency Risk [member]
Market Risk [line items]
Risk exposure	0.3	0.4
Weighted average [member] | Diversification Offsets [member]
Market Risk [line items]
Risk exposure	(0.5)	(0.8)
Top of Range [member]
Market Risk [line items]
Risk exposure	3.8	3.7
Top of Range [member] | Interest Rate Risks [member]
Market Risk [line items]
Risk exposure	3.9	3.5
Top of Range [member] | Equity Risks [member]
Market Risk [line items]
Risk exposure	0.6	2
Top of Range [member] | Currency Risk [member]
Market Risk [line items]
Risk exposure	0.9	1.6
Bottom of Range [member]
Market Risk [line items]
Risk exposure	0.3	2
Bottom of Range [member] | Interest Rate Risks [member]
Market Risk [line items]
Risk exposure	£ 0.2	1.8
Bottom of Range [member] | Equity Risks [member]
Market Risk [line items]
Risk exposure		£ 0.2

Liquidity Risk - Summary of Rec

Liquidity Risk - Summary of Reconciliation of Wholesale Funding to Balance Sheet (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Deposits by banks	£ 17,824	£ 12,708
Deposits by customers	173,692	177,421
Repurchase agreements - non trading	10,910	1,076
Trading liabilities		31,109
Financial liabilities at fair value	6,286	2,315
Debt securities in issue	55,906	48,860
Subordinated liabilities	3,601	3,793
Liquidity risk [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	97,300	102,700
Deposits by banks	17,800	12,700
Deposits by customers	500	500
Repurchase agreements - non trading	10,900	1,100
Trading liabilities		31,100
Financial liabilities at fair value	6,300	2,300
Debt securities in issue	55,900	48,900
Subordinated liabilities	3,600	3,800
Other equity and non-controlling interests	2,300	2,300
Liquidity risk [member] | Repurchase Agreement [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	10,800	25,600
Repurchase agreements - non trading	8,700	100
Trading liabilities		25,500
Financial liabilities at fair value	2,100
Liquidity risk [member] | Foreign Exchange And Hedge Accounting [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	4,100	3,900
Debt securities in issue	3,500	3,300
Subordinated liabilities	600	600
Liquidity risk [member] | Other Borrowing [Member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	9,200	10,300
Deposits by banks	6,000	4,000
Trading liabilities		5,600
Financial liabilities at fair value	3,200	700
Liquidity risk [member] | Wholesale Funding [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	73,200	62,900
Deposits by banks	11,800	8,700
Deposits by customers	500	500
Repurchase agreements - non trading	2,200	1,000
Financial liabilities at fair value	1,000	1,600
Debt securities in issue	52,400	45,600
Subordinated liabilities	3,000	3,200
Other equity and non-controlling interests	2,300	2,300
Liquidity risk [member] | Wholesale Funding [member] | Deposits [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	1,000	300
Deposits by banks	1,000	200
Financial liabilities at fair value		100
Liquidity risk [member] | Wholesale Funding [member] | Certificates of Deposit and Commercial Paper [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	6,400	8,000
Financial liabilities at fair value		400
Debt securities in issue	6,400	7,600
Liquidity risk [member] | Wholesale Funding [member] | Senior Unsecured - Public Benchmark [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	21,300	17,800
Debt securities in issue	21,300	17,800
Liquidity risk [member] | Wholesale Funding [member] | Senior Unsecured - Privately Placed [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	4,000	3,100
Financial liabilities at fair value	1,000	1,100
Debt securities in issue	3,000	2,000
Liquidity risk [member] | Wholesale Funding [member] | Covered Bonds [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	16,600	14,200
Debt securities in issue	16,600	14,200
Liquidity risk [member] | Wholesale Funding [member] | Securitisation and Structured Issuance [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	7,800	5,500
Deposits by customers	500	500
Repurchase agreements - non trading	2,200	1,000
Debt securities in issue	5,100	4,000
Liquidity risk [member] | Wholesale Funding [member] | Term Funding Scheme [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	10,800	8,500
Deposits by banks	10,800	8,500
Liquidity risk [member] | Wholesale Funding [member] | Subordinated Liabilities and Equity [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Funding analysis	5,300	5,500
Subordinated liabilities	3,000	3,200
Other equity and non-controlling interests	£ 2,300	£ 2,300

Liquidity Risk - Summary of R_2

Liquidity Risk - Summary of Reconciliation of Wholesale Funding to Balance Sheet (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Deposit from customers	£ 173,692	£ 177,421
Other equity and non-controlling interests	2,041	2,041
Liquidity risk [member]
Reconciliation Of Wholesale Funding To Balance Sheet [line items]
Deposit from customers	500	500
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	14	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	£ 2,041	£ 2,041

Liquidity Risk - Summary of Sou

Liquidity Risk - Summary of Sources of Wholesale Funding by Maturity (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	£ 17,824	£ 12,708
Subordinated liabilities	3,601	3,793
Wholesale fund amount	73,200	62,900
Of which: - secured	35,200	28,200
Of which: - unsecured	38,000	34,700
Downstreamed From Santander UK Group Holdings Plc to Santander UK Plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	8,700
Senior unsecured - privately placed	100
Subordinated liabilities and equity (incl. AT1)	3,100
Other Santander UK Plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	1,000
Certificates of deposit and commercial paper	6,400
Senior unsecured - public benchmark	12,600
Senior unsecured - privately placed	3,900
Covered bonds	16,600
Securitisation and structured issuance	5,900
Term Funding Scheme	10,800
Subordinated liabilities	2,200
Wholesale fund amount	59,400
Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	1,900
Not Later Than One Month [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	3,100	4,800
Of which: - secured	800	900
Of which: - unsecured	2,300	3,900
Not Later Than One Month [member] | Other Santander UK Plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Certificates of deposit and commercial paper	1,500
Senior unsecured - public benchmark	800
Securitisation and structured issuance	800
Wholesale fund amount	3,100
Greater Than 1 and Less Than 3 Months [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	6,800	3,900
Of which: - secured	700
Of which: - unsecured	6,100	3,900
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	1,000
Certificates of deposit and commercial paper	3,600
Senior unsecured - public benchmark	1,500
Securitisation and structured issuance	600
Wholesale fund amount	6,700
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
Greater Than 3 and Less Than 6 Months [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	3,300	3,300
Of which: - secured	700	1,400
Of which: - unsecured	2,600	1,900
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]
Subordinated liabilities and equity (incl. AT1)	500
Greater Than 3 and Less Than 6 Months [member] | Other Santander UK Plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Certificates of deposit and commercial paper	1,100
Senior unsecured - privately placed	1,000
Securitisation and structured issuance	600
Wholesale fund amount	2,700
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
Greater Than 6 and Less Than 9 Months [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	2,700	1,400
Of which: - secured	1,700
Of which: - unsecured	1,000	1,400
Greater Than 6 and Less Than 9 Months [member] | Other Santander UK Plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Certificates of deposit and commercial paper	100
Senior unsecured - public benchmark	600
Senior unsecured - privately placed	300
Covered bonds	1,400
Securitisation and structured issuance	200
Wholesale fund amount	2,600
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
Greater Than 9 and Less Than 12 Months [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	900	1,500
Of which: - secured	500	1,300
Of which: - unsecured	400	200
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]
Subordinated liabilities and equity (incl. AT1)	300
Greater Than 9 and Less Than 12 Months [member] | Other Santander UK Plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Certificates of deposit and commercial paper	100
Securitisation and structured issuance	400
Wholesale fund amount	500
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
Not Later Than 1 Year [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	16,800	14,900
Of which: - secured	4,400	3,600
Of which: - unsecured	12,400	11,300
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]
Subordinated liabilities and equity (incl. AT1)	800
Not Later Than 1 Year [member] | Other Santander UK Plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Deposits by banks	1,000
Certificates of deposit and commercial paper	6,400
Senior unsecured - public benchmark	2,900
Senior unsecured - privately placed	1,300
Covered bonds	1,400
Securitisation and structured issuance	2,600
Wholesale fund amount	15,600
Not Later Than 1 Year [member] | Other Group Entities [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Securitisation and structured issuance	400
Later Than 1 Year and Not Later Than 2 Years [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	15,900	7,900
Of which: - secured	8,500	2,900
Of which: - unsecured	7,400	5,000
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	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]
Senior unsecured - public benchmark	4,800
Senior unsecured - privately placed	1,800
Covered bonds	2,800
Securitisation and structured issuance	800
Term Funding Scheme	4,500
Wholesale fund amount	14,700
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	400
Later Than 2 Year and Not Later Than 5 Years [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	30,100	28,900
Of which: - secured	18,300	18,300
Of which: - unsecured	11,800	10,600
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	6,200
Subordinated liabilities and equity (incl. AT1)	800
Later Than 2 Year and Not Later Than 5 Years [member] | Other Santander UK Plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	3,500
Senior unsecured - privately placed	400
Covered bonds	8,400
Securitisation and structured issuance	2,500
Term Funding Scheme	6,300
Subordinated liabilities	900
Wholesale fund amount	22,000
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	1,100
Later Than Five Years [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Wholesale fund amount	10,400	11,200
Of which: - secured	4,000	3,400
Of which: - unsecured	6,400	£ 7,800
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)	1,500
Later Than Five Years [member] | Other Santander UK Plc [member]
Disclosure of Maturity of Wholesale Funding [Line Items]
Senior unsecured - public benchmark	1,400
Senior unsecured - privately placed	400
Covered bonds	4,000
Subordinated liabilities	1,300
Wholesale fund amount	£ 7,100

Liquidity Risk - Summary of Who

Liquidity Risk - Summary of Wholesale Funding by Currency (Detail) - Liquidity risk [member]	Dec. 31, 2018	Dec. 31, 2017
United Kingdom, Pounds [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	46.00%	45.00%
United Kingdom, Pounds [member] | Santander UK Group Holdings Plc to Santander UK Plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	26.00%	28.00%
United Kingdom, Pounds [member] | 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%	9.00%
United Kingdom, Pounds [member] | 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	68.00%	68.00%
United Kingdom, Pounds [member] | Santander UK Plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	48.00%	49.00%
United Kingdom, Pounds [member] | 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%	9.00%
United Kingdom, Pounds [member] | Santander UK Plc [member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	13.00%	7.00%
United Kingdom, Pounds [member] | Santander UK Plc [member] | Deposits by banks [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	3.00%	27.00%
United Kingdom, Pounds [member] | 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	48.00%	89.00%
United Kingdom, Pounds [member] | Santander UK Plc [member] | Covered Bonds [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	50.00%	47.00%
United Kingdom, Pounds [member] | Santander UK Plc [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	61.00%	80.00%
United Kingdom, Pounds [member] | 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] | Santander UK Plc [member] | Subordinated liabilities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	49.00%	52.00%
United Kingdom, Pounds [member] | Other Group Entities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	89.00%	47.00%
United Kingdom, Pounds [member] | Other Group Entities [member] | Certificates of Deposit and Commercial Paper [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies		34.00%
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	89.00%	91.00%
United States of America, Dollars [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	30.00%	28.00%
United States of America, Dollars [member] | 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%	54.00%
United States of America, Dollars [member] | 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%	67.00%
United States of America, Dollars [member] | 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	32.00%	32.00%
United States of America, Dollars [member] | Santander UK Plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	25.00%	19.00%
United States of America, Dollars [member] | Santander UK Plc [member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	56.00%	49.00%
United States of America, Dollars [member] | Santander UK Plc [member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	12.00%	19.00%
United States of America, Dollars [member] | Santander UK Plc [member] | Deposits by banks [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	97.00%	73.00%
United States of America, Dollars [member] | 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	52.00%	10.00%
United States of America, Dollars [member] | Santander UK Plc [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	35.00%	20.00%
United States of America, Dollars [member] | Santander UK Plc [member] | Subordinated liabilities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	51.00%	48.00%
United States of America, Dollars [member] | Other Group Entities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	11.00%	50.00%
United States of America, Dollars [member] | Other Group Entities [member] | Deposits by banks [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies		100.00%
United States of America, Dollars [member] | Other Group Entities [member] | Certificates of Deposit and Commercial Paper [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies		65.00%
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	11.00%
Euro Member Countries, Euro [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	24.00%	25.00%
Euro Member Countries, Euro [member] | 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%	14.00%
Euro Member Countries, Euro [member] | 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] | Santander UK Plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	26.00%	32.00%
Euro Member Countries, Euro [member] | Santander UK Plc [member] | Senior Unsecured - Public Benchmark [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	33.00%	42.00%
Euro Member Countries, Euro [member] | Santander UK Plc [member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	72.00%	70.00%
Euro Member Countries, Euro [member] | Santander UK Plc [member] | Covered Bonds [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	49.00%	52.00%
Euro Member Countries, Euro [member] | Santander UK Plc [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	4.00%
Euro Member Countries, Euro [member] | Other Group Entities [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies		3.00%
Euro Member Countries, Euro [member] | Other Group Entities [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 Group Entities [member] | Securitisation and Structured Issuance [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies		9.00%
Other [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies		2.00%
Other [member] | Santander UK Group Holdings Plc to Santander UK Plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	2.00%	4.00%
Other [member] | 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] | 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] | Santander UK Plc [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	1.00%
Other [member] | Santander UK Plc [member] | Senior Unsecured - Privately Placed [member]
Currency Composition Of Wholesale Funds [line items]
Percentage of wholesale funding by major currencies	3.00%	4.00%
Other [member] | 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%
Other [member] | 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%

Liquidity Risk - Summary of Ext

Liquidity Risk - Summary of External Term Issuance (Sterling Equivalent) (Detail) - Liquidity risk [member] - GBP (£) £ in Billions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 17.1	£ 11.8
Santander UK Group Holdings Plc to Santander UK Plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.7	2.6
Santander UK Group Holdings Plc to Santander UK Plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.7	2
Santander UK Group Holdings Plc to Santander UK Plc [member] | Senior Unsecured - Privately Placed [member]
Disclosure of detailed information about borrowings [line items]
Borrowings		0.1
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
Santander UK Plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	14	8
Santander UK Plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.9	1.1
Santander UK Plc [member] | Senior Unsecured - Privately Placed [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	1.6	0.1
Santander UK Plc [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.9	0.5
Santander UK Plc [member] | Covered Bonds [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	4.3	2.3
Santander UK Plc [member] | Term Funding Scheme [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.3	4
Other Group Entities [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.4	£ 1.2
United Kingdom, Pounds [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	7.8
United Kingdom, Pounds [member] | 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] | Santander UK Group Holdings Plc to Santander UK Plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.5
United Kingdom, Pounds [member] | Santander UK Plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	6.9
United Kingdom, Pounds [member] | Santander UK Plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.4
United Kingdom, Pounds [member] | Santander UK Plc [member] | Senior Unsecured - Privately Placed [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.3
United Kingdom, Pounds [member] | Santander UK Plc [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	1.4
United Kingdom, Pounds [member] | Santander UK Plc [member] | Covered Bonds [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.5
United Kingdom, Pounds [member] | Santander UK Plc [member] | Term Funding Scheme [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.3
United Kingdom, Pounds [member] | Other Group Entities [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.4
United States of America, Dollars [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	5.5
United States of America, Dollars [member] | Santander UK Group Holdings Plc to Santander UK Plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	1.5
United States of America, Dollars [member] | Santander UK Group Holdings Plc to Santander UK Plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	1.5
United States of America, Dollars [member] | Santander UK Plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	4
United States of America, Dollars [member] | Santander UK Plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	2.5
United States of America, Dollars [member] | Santander UK Plc [member] | Securitisations [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	1.5
Euro Member Countries, Euro [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	3.8
Euro Member Countries, Euro [member] | Santander UK Group Holdings Plc to Santander UK Plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.7
Euro Member Countries, Euro [member] | Santander UK Group Holdings Plc to Santander UK Plc [member] | Senior Unsecured - Public Benchmark [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	0.7
Euro Member Countries, Euro [member] | Santander UK Plc [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	3.1
Euro Member Countries, Euro [member] | Santander UK Plc [member] | Senior Unsecured - Privately Placed [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	1.3
Euro Member Countries, Euro [member] | Santander UK Plc [member] | Covered Bonds [member]
Disclosure of detailed information about borrowings [line items]
Borrowings	£ 1.8

Liquidity Risk - Summary of Loa

Liquidity Risk - Summary of Loan-to-Deposit Ratio (Detail) - GBP (£) £ in Billions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Customer Loans, Customer Deposits and Loan to Deposit Ratio [line items]
Consumer loans gross	£ 199.9
Adjust for: fair value loans, impairment loss allowances, accrued interest and other	1.7
Statutory loans and advances to customers/deposits by customers	201.6
Total	201.6
Deposits from customers gross	172.1
Adjust for: fair value loans, impairment loss allowances, accrued interest and other	1.6
Statutory loans and advances to customers/deposits by customers	173.7
Total	£ 173.7
Percentage of loan to deposit ratio	116.00%	113.00%
Retail banking [member]
Disclosure of Customer Loans, Customer Deposits and Loan to Deposit Ratio [line items]
Consumer loans gross	£ 172.8
Deposits from customers gross	£ 142.1
Percentage of loan to deposit ratio	122.00%	113.00%
Corporate and commercial banking [member]
Disclosure of Customer Loans, Customer Deposits and Loan to Deposit Ratio [line items]
Consumer loans gross	£ 17.7
Deposits from customers gross	£ 17.6
Percentage of loan to deposit ratio	101.00%	104.00%
Corporate and investment banking [member]
Disclosure of Customer Loans, Customer Deposits and Loan to Deposit Ratio [line items]
Consumer loans gross	£ 4.6
Deposits from customers gross	£ 4.8
Percentage of loan to deposit ratio	96.00%	133.00%
Corporate centre [member]
Disclosure of Customer Loans, Customer Deposits and Loan to Deposit Ratio [line items]
Consumer loans gross	£ 4.8
Deposits from customers gross	£ 7.6
Percentage of loan to deposit ratio	63.00%	174.00%

Capital Risk - Summary of Regul

Capital Risk - Summary of Regulatory Capital Resources (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	£ 10,401	£ 10,620
AT1 capital	2,366	2,447
Tier 1 capital	12,767	13,067
Total regulatory capital	15,038	15,488
Capital before regulatory adjustments [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	13,930	13,912
Additional Value Adjustments [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(42)	(70)
Goodwill (Net of Tax) [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(1,161)	(1,165)
Other Intangibles [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(610)	(539)
Fair Value Reserves Related to Gains or Losses on Cash Flow Hedges [Member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(251)	(228)
Negative Amounts Resulting From the Calculation of Regulatory Expected Loss Amounts [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(599)	(748)
Gains or Losses on Liabilities Valued at Fair Value Resulting From Changes in Own Credit Standing [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(67)	(13)
Deferred Tax Assets That Rely on Future Profitability Excluding Timing Differences [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(20)	(25)
Defined Benefit Pension Fund Assets [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(631)	(333)
Dividend Accrual [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(18)	(19)
IFRS 9 Transitional Adjustment [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	21
Non-Controlling Interests [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	(151)	(152)
Regulatory Deductions for Instruments Issued by Subsidiary Undertakings or Subject to CRDIV Amortisation [member]
Disclosure of Regulatory Capital Resources [Line Items]
AT1 capital	(268)	(301)
Tier 2 capital	(986)	(915)
Amount of qualifying items subject to phase out from Tier 2 [member]
Disclosure of Regulatory Capital Resources [Line Items]
Tier 2 capital	369	587
Capital Instruments [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	7,060	7,060
AT1 capital	2,041	2,041
Tier 2 capital	2,888	2,749
Retained Earnings [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	6,439	6,399
Accumulated Other Reserves And Non-Controlling Interests [member]
Disclosure of Regulatory Capital Resources [Line Items]
CET1 capital	431	453
Amount of Qualifying Items Subject to Phase Out From AT1 [member]
Disclosure of Regulatory Capital Resources [Line Items]
AT1 capital	593	707
Tier Two Capital [member]
Disclosure of Regulatory Capital Resources [Line Items]
Total regulatory capital	£ 2,271	£ 2,421

Accounting Policies - Additiona

Accounting Policies - Additional information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2017
Disclosure of changes in accounting estimates [line items]
Loans and advances to banks	£ 3,515	£ 3,466
Reverse repurchase agreements - non trading	21,127	2,614
Deposit by banks	17,824	12,708
Repurchase agreements - non trading	10,910	1,076
Other assets	2,267	2,511
Other liabilities	2,507	2,728
Provisions	515	558	£ 700
Expected credit losses allowance	807
Additional provisions	298	385
Defined benefit pension schemes in net asset having surplus	842	449
Defined benefit pension schemes in net liabilities having deficit	115	286
Miscellaneous other provisions [member]
Disclosure of changes in accounting estimates [line items]
Additional operational risk losses and restructuring charges	58	0
Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of changes in accounting estimates [line items]
Expected credit losses allowance	789
Corporate and investment banking [member]
Disclosure of changes in accounting estimates [line items]
Expected credit losses allowance	18
Payment protection insurance [member]
Disclosure of changes in accounting estimates [line items]
Provisions	246	356	457
Additional provisions	£ 0	£ 109	£ 144
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	£ 237
Stage 2 [member]
Disclosure of changes in accounting estimates [line items]
Probability weight	100.00%
IFRS 9 [member]
Disclosure of changes in accounting estimates [line items]
Loans and advances to banks				£ (1,462)
Reverse repurchase agreements - non trading				1,462
Deposit by banks				(2,384)
Repurchase agreements - non trading				£ 2,384
IFRS 16 [member]
Disclosure of changes in accounting estimates [line items]
Increase Property, plant and equipment	£ 211
Other assets	(12)
Other liabilities	182
Provisions	£ 17

Accounting Policies - Summary o

Accounting Policies - Summary of Useful Lives or Depreciation Rates Used for Property, Plant and Equipment (Detail)	12 Months Ended
	Dec. 31, 2018
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_2

Accounting Policies - Summary of Probability Weights Applied for Each Scenario of Expected Credit Losses Allowance (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of probability weightings of scenarios [line items]
ECL	£ 807
Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	789
Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
ECL	18
Upside 2 [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	554
Upside 1 [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	596
Base case [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	648
Base case [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
ECL	17
Downside 1 [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	843
Downside 2 [member] | Retail banking Corporate and Commercial Banking and Corporate Centre [member]
Disclosure of probability weightings of scenarios [line items]
ECL	1,930
Downside [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
ECL	27
Upside [member] | Corporate and investment banking [member]
Disclosure of probability weightings of scenarios [line items]
ECL	£ 8

Accounting Policies - Summary_3

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

Segments - Additional Informati

Segments - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
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, 2018GBP (£)Employee	Dec. 31, 2017GBP (£)Employee	Dec. 31, 2016GBP (£)Employee	Jan. 01, 2018GBP (£)
Disclosure of operating segments [line items]
Net interest income	£ 3,606	£ 3,803	£ 3,582
Non-interest income	937	1,109	1,213
Total operating income	4,543	4,912	4,795
Operating expenses before credit impairment losses, provisions and charges	(2,563)	(2,502)	(2,417)
Credit impairment (losses)/releases	(153)	(203)	(67)
Provisions for other liabilities and charges	(260)	(393)	(397)
Total operating credit impairment losses, provisions and (charges)/releases	(413)	(596)	(464)
Profit before tax	1,567	1,814	1,914
Revenue from external customers	4,543	4,912	4,795
Inter-segment revenue	4,543	4,912	4,795
Total operating income	4,543	4,912	4,795
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Current account and debit card fees	753	791	747
- Insurance, protection and investments	105	100	94
- Credit cards	85	92	95
- Non-banking and other fees(3)	227	239	252
Total fee and commission income	1,170	1,222	1,188
Fee and commission expense	(421)	(415)	(418)
Net fee and commission income	749	807	770
Customer loans	199,869	200,324	200,156
Total assets	289,381	314,760	302,510	£ 314,500
Customer deposits	172,131	175,921	172,351
Total liabilities	£ 273,161	£ 298,558	£ 287,057
Average number of staff | Employee	23,648	19,559	19,863
Retail banking [member]
Disclosure of operating segments [line items]
Net interest income	£ 3,126	£ 3,270	£ 3,117
Non-interest income	638	615	559
Total operating income	3,764	3,885	3,676
Operating expenses before credit impairment losses, provisions and charges	(1,929)	(1,856)	(1,785)
Credit impairment (losses)/releases	(124)	(36)	(21)
Provisions for other liabilities and charges	(230)	(342)	(338)
Total operating credit impairment losses, provisions and (charges)/releases	(354)	(378)	(359)
Profit before tax	1,481	1,651	1,532
Revenue from external customers	4,421	4,534	4,387
Total operating income	3,764	3,885	3,676
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Current account and debit card fees	697	737	697
- Insurance, protection and investments	105	100	94
- Credit cards	85	92	95
- Non-banking and other fees(3)	75	45	53
Total fee and commission income	962	974	939
Fee and commission expense	(382)	(367)	(369)
Net fee and commission income	580	607	570
Customer loans	172,747	168,729	168,389
Total assets	201,261	174,524	175,100
Customer deposits	142,065	143,834	143,996
Total liabilities	£ 142,839	£ 150,847	£ 149,793
Average number of staff | Employee	20,694	17,194	17,424
Retail banking [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ (657)	£ (649)	£ (711)
Corporate and commercial banking [member]
Disclosure of operating segments [line items]
Net interest income	403	391	380
Non-interest income	82	74	76
Total operating income	485	465	456
Operating expenses before credit impairment losses, provisions and charges	(258)	(223)	(215)
Credit impairment (losses)/releases	(23)	(13)	(29)
Provisions for other liabilities and charges	(14)	(55)	(26)
Total operating credit impairment losses, provisions and (charges)/releases	(37)	(68)	(55)
Profit before tax	190	174	186
Revenue from external customers	638	639	651
Total operating income	485	465	456
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Current account and debit card fees	27	27	27
- Non-banking and other fees(3)	62	63	57
Total fee and commission income	89	90	84
Fee and commission expense	(25)	(31)	(31)
Net fee and commission income	64	59	53
Customer loans	17,702	19,391	19,382
Total assets	17,702	19,391	19,381
Customer deposits	17,606	17,760	16,082
Total liabilities	£ 17,634	£ 18,697	£ 17,203
Average number of staff | Employee	1,732	1,240	1,435
Corporate and commercial banking [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ (153)	£ (174)	£ (195)
Corporate and investment banking [member]
Disclosure of operating segments [line items]
Net interest income	69	74	73
Non-interest income	272	364	312
Total operating income	341	438	385
Operating expenses before credit impairment losses, provisions and charges	(262)	(304)	(281)
Credit impairment (losses)/releases	(14)	(174)	(21)
Provisions for other liabilities and charges	(8)	(11)	(11)
Total operating credit impairment losses, provisions and (charges)/releases	(22)	(185)	(32)
Profit before tax	57	(51)	72
Revenue from external customers	386	506	474
Total operating income	341	438	385
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Current account and debit card fees	29	27	23
- Non-banking and other fees(3)	87	123	132
Total fee and commission income	116	150	155
Fee and commission expense	(14)	(17)	(17)
Net fee and commission income	102	133	138
Customer loans	4,613	6,037	5,659
Total assets	33,657	51,078	39,777
Customer deposits	4,853	4,546	4,054
Total liabilities	£ 14,222	£ 45,603	£ 36,506
Average number of staff | Employee	1,108	1,006	916
Corporate and investment banking [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ (45)	£ (68)	£ (89)
Corporate centre [member]
Disclosure of operating segments [line items]
Net interest income	8	68	12
Non-interest income	(55)	56	266
Total operating income	(47)	124	278
Operating expenses before credit impairment losses, provisions and charges	(114)	(119)	(136)
Credit impairment (losses)/releases	8	20	4
Provisions for other liabilities and charges	(8)	15	(22)
Total operating credit impairment losses, provisions and (charges)/releases		35	(18)
Profit before tax	(161)	40	124
Revenue from external customers	(902)	(767)	(717)
Total operating income	(47)	124	278
Revenue from external customers includes the following fee and commission income disaggregated by income type:
- Non-banking and other fees(3)	3	8	10
Total fee and commission income	3	8	10
Fee and commission expense			(1)
Net fee and commission income	3	8	9
Customer loans	4,807	6,167	6,726
Total assets	36,761	69,767	68,252
Customer deposits	7,607	9,781	8,219
Total liabilities	£ 98,466	£ 83,411	£ 83,555
Average number of staff | Employee	114	119	88
Corporate centre [member] | Elimination of Intersegment Amounts [member]
Disclosure of operating segments [line items]
Inter-segment revenue	£ 855	£ 891	£ 995

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	Dec. 31, 2016
Disclosure of operating segments [line items]
Profit before tax	£ 1,567	£ 1,814	£ 1,914
Customer loans	199,869	200,324	200,156
Customer deposits	172,131	175,921	172,351
Corporate centre [member]
Disclosure of operating segments [line items]
Profit before tax	(161)	40	124
Customer loans	4,807	6,167	6,726
Customer deposits	£ 7,607	9,781	8,219
Reclassification and presentational changes [member] | Corporate centre [member]
Disclosure of operating segments [line items]
Profit before tax		21	15
Customer loans		262	248
Customer deposits		£ 6,418	£ 5,188

Net Interest Income - Summary o

Net Interest Income - Summary of Net Interest Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest and similar income:
Loans and advances to customers	£ 5,459	£ 5,494	£ 6,198
Loans and advances to banks	207	164	112
Reverse repurchase agreements - non trading	124	20	15
Other	282	227	142
Total interest and similar income	6,072	5,905	6,467
Interest expense and similar charges:
Deposits by customers	(1,224)	(1,183)	(1,809)
Deposits by banks	(120)	(35)	(18)
Repurchase agreements - non trading	(37)	(5)	(38)
Debt securities in issue	(936)	(737)	(853)
Subordinated liabilities	(141)	(134)	(143)
Other	(8)	(8)	(24)
Total interest expense and similar charges	(2,466)	(2,102)	(2,885)
Net interest income	£ 3,606	£ 3,803	£ 3,582

Net Interest Income - Summary_2

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

Net Interest Income - Additiona

Net Interest Income - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Interest And Similar Income [abstract]
Interest and similar income on impaired loans	£ 66	£ 79

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Fee And Commission Income [Line Items]
Fee and commission income	£ 1,170	£ 1,222	£ 1,188
Fee and commission expense	(421)	(415)	(418)
Net fee and commission income	749	807	770
Current account and debit card fees [member]
Net Fee And Commission Income [Line Items]
Fee and commission income	753	791	747
Insurance, protection and investments [member]
Net Fee And Commission Income [Line Items]
Fee and commission income	105	100	94
Credit cards [member]
Net Fee And Commission Income [Line Items]
Fee and commission income	85	92	95
Non-banking and other fees [member]
Net Fee And Commission Income [Line Items]
Fee and commission income	£ 227	£ 239	£ 252

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Trading And Other Income [abstract]
Net trading and funding of other items by the trading book	£ 263	£ 205	£ 75
Net (losses)/ gains on other financial assets at fair value through profit or loss	(18)	80	253
Net (losses)/gains on other financial liabilities at fair value through profit or loss	(44)	(97)	28
Net losses on derivatives managed with assets/liabilities held at fair value through profit or loss	(128)	(17)	(135)
Hedge ineffectiveness	34	5	28
Net profit on sale of available-for-sale assets		54	115
Net profit on sale of financial assets at fair value through other comprehensive income	19
Net income from operating lease assets	86	44	35
Other	(24)	28	44
Net trading and other income	£ 188	£ 302	£ 443

Net Trading and Other Income _2

Net Trading and Other Income - Additional Information (Detail) - GBP (£) £ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2018
Disclosure of subordinated liabilities [line items]
Fair value gains/(losses) on net trading and funding of other items by trading book		£ 22	£ (27)	£ (50)
(Losses)/gains on equity derivatives trading desk		(21)	28	51
Net gain on equity index-linked deposits and the related economic hedges		1	1	1
Exchange rate differences recognised		(689)	(109)	(4,051)
Principally offset from cash flow hedge reserve		£ 751	£ 94	4,076
7.375% 20 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Percentage of notes purchased and redeemed	91.00%
Interest rate	7.375%	7.375%	7.375%
Maturity year	20 Year
Non-Cumulative Trust Preferred Securities [member]
Disclosure of subordinated liabilities [line items]
Interest rate					8.963%
Vocalink Holdings Limited [member]
Disclosure of subordinated liabilities [line items]
Gain on sale of shares			£ 48
Visa Europe Ltd [member]
Disclosure of subordinated liabilities [line items]
Gain on sale of shares				£ 119

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Staff costs:
Wages and salaries	£ 905	£ 746	£ 731
Performance-related payments	160	157	157
Social security costs	111	93	94
Pensions costs - defined contribution plans	66	54	52
Pensions costs - defined benefit plans	81	32	26
Other share-based payments	3	10	3
Other personnel costs	50	45	62
Employee benefits expense	1,376	1,137	1,125
Other administration expenses	809	1,011	970
Depreciation, amortisation and impairment	378	354	322
Total operating expenses before impairment losses, provisions and charges	£ 2,563	£ 2,502	£ 2,417

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, 2018	Dec. 31, 2017
Disclosure of deferred performance awards [line Items]
Cash	£ 33	£ 30
Shares	30	34
Not Later Than 1 Year [member]
Disclosure of deferred performance awards [line Items]
Cash	13	13
Shares	13	16
Deferred performance awards	26
Not Later Than 1 Year [member] | Arising From Awards in Current Year [member]
Disclosure of deferred performance awards [line Items]
Cash	4
Shares	3
Deferred performance awards	7
Not Later Than 1 Year [member] | Arising From Awards in Prior Year [member]
Disclosure of deferred performance awards [line Items]
Cash	9
Shares	10
Deferred performance awards	19
More than One Year [member]
Disclosure of deferred performance awards [line Items]
Cash	20	17
Shares	17	£ 18
Deferred performance awards	37
More than One Year [member] | Arising From Awards in Current Year [member]
Disclosure of deferred performance awards [line Items]
Cash	10
Shares	8
Deferred performance awards	18
More than One Year [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, 2018	Dec. 31, 2017
Disclosure of amount of bonus awarded to employees [line items]
Cash award - not deferred	£ 123	£ 116
- deferred	33	30
Share awards - not deferred	11	12
- deferred	30	34
Total discretionary bonus	197	192
Not Later Than 1 Year [member]
Disclosure of amount of bonus awarded to employees [line items]
Cash award - not deferred	123	116
- deferred	13	13
Share awards - not deferred	11	12
- deferred	13	16
Total discretionary bonus	160	157
More than One Year [member]
Disclosure of amount of bonus awarded to employees [line items]
- deferred	20	17
- deferred	17	18
Total discretionary bonus	£ 37	£ 35

Operating Expenses Before Cre_6

Operating Expenses Before Credit Impairment Losses, Provisions and Charges - Additional Information (Detail) £ in Millions	Oct. 26, 2018GBP (£)	Dec. 31, 2018Employee	Dec. 31, 2017GBP (£)Employee	Dec. 31, 2016Employee
Classes of employee benefits expense [abstract]
Increase in liabilities	£ 40
Average number of full-time equivalent staff | Employee		23,648	19,559	19,863
Impairment charge			£ 32

Audit and Other Services - Summ

Audit and Other Services - Summary of Audit and Other Services (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Audit fees:
Fees payable to the Company's auditor and its associates for the audit of the Santander UK group's annual accounts	£ 7.7	£ 7.8	£ 4.9
- Audit of the Santander UK group's subsidiaries	1.6	1.4	1.1
Total audit fees	9.3	9.2	6
Non-audit fees:
Audit-related assurance services	2.2	1.6	1.3
Taxation compliance services			0.1
Other assurance services	0.1	0.1
Other non-audit services	1	0.4	1.9
Total non-audit fees	£ 3.3	£ 2.1	£ 3.3

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of audit fees and non audit fees [Line Items]
Audit-related assurance services	£ 2.2	£ 1.6	£ 1.3
Prior year audit services [member]
Disclosure of audit fees and non audit fees [Line Items]
Auditors fee	0	0.6
Audit-related assurance services	£ 0.1	£ 0.1

Audit and Other Services - Addi

Audit and Other Services - Additional Information (Detail) - GBP (£) £ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of audit fees and non audit fees [Line Items]
Audit fees payable for statutory audit	£ 9,300	£ 9,200	£ 6,000
Audit-related services related to services performed in connection with the statutory and regulatory filings	1,100	800	600
Audit-related services related to services performed in connection with securitisation, debt issuance and related work and reporting to prudential and conduct regulators	1,100	800	700
Santander UK Group Holdings plc [member]
Disclosure of audit fees and non audit fees [Line Items]
Audit fees payable for statutory audit	500	400	£ 300
Corporate and Other Borrowers [member]
Disclosure of audit fees and non audit fees [Line Items]
Audit fees payable for statutory audit	£ 150	£ 45

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of credit impairment loss and provisions [abstract]
Loans and advances to customers (See Note 14)	£ 189	£ 257	£ 132
Recoveries of loans and advances, net of collection costs (See Note 14)	(42)	(54)	(65)
Off-balance sheet exposures (See Note 30)	6
Impairment loss on financial assets	153	203	67
Provisions for other liabilities and charges (excluding off-balance sheet credit exposures) (See Note 30)	260	385	397
Provisions for RV and voluntary termination (See Note 14)		8
Provisions for other liabilities and charges	260	393	397
Total operating impairment losses, provisions and charges	£ 413	£ 596	£ 464

Credit Impairment Losses and _4

Credit Impairment Losses and Provisions - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Current tax:
UK corporation tax on profit for the year	£ 456	£ 555	£ 610
Adjustments in respect of prior years	(22)	(27)	(13)
Total current tax	434	528	597
Deferred tax:
Charge/(credit) for the year	11	23	(11)
Adjustments in respect of prior years	1	9	11
Total deferred tax	12	32
Tax on profit	£ 446	£ 560	£ 597

Taxation - Additional Informati

Taxation - Additional Information (Detail) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)	Dec. 31, 2018USD ($)	Dec. 31, 2017GBP (£)	Dec. 31, 2017USD ($)	Dec. 31, 2016
Income Tax Expense Benefits [line items]
Applicable tax rate	19.00%	19.00%	19.25%	19.25%	20.00%
Bank corporation tax surcharge	8.00%	8.00%			8.00%
Effective tax rate	28.50%	28.50%	30.90%	30.90%	31.20%
Unrecognised capital losses carried forward	£ 0		£ 0
Net operating losses carried forward | $		$ 0		$ 76
Banking Entities [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	27.00%	27.00%	27.25%	27.25%
Non-banking Entities [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	19.00%	19.00%	19.25%	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	£ 17		£ 21
Finance (No.2) Act 2015 [member] | Top of Range [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	20.00%	20.00%
Finance (No.2) Act 2015 [member] | Top of Range [member] | Corporation Tax Rate in 2020 [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	18.00%	18.00%
Finance (No.2) Act 2015 [member] | Bottom of Range [member]
Income Tax Expense Benefits [line items]
Applicable tax rate	19.00%	19.00%
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, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of accounting profit multiplied by applicable tax rates [abstract]
Profit before tax	£ 1,567	£ 1,814	£ 1,914
Tax calculated at a tax rate of 19% (2017: 19.25%, 2016: 20.00%)	298	349	383
Bank surcharge on profits	111	132	134
Non-deductible preference dividends paid	8	9	8
Non-deductible UK Bank Levy	20	25	30
Non-deductible conduct remediation, fines and penalties	6	35	39
Other non-deductible costs and non-taxable income	26	30	7
Effect of change in tax rate on deferred tax provision	(2)	(2)	(2)
Adjustment to prior year provisions	(21)	(18)	(2)
Tax charge	£ 446	£ 560	£ 597

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of accounting profit multiplied by applicable tax rates [abstract]
Standard tax rate	19.00%	19.25%	20.00%

Taxation - Disclosure of Moveme

Taxation - Disclosure of Movements in Current Tax Assets and Liabilities (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Current Tax Assets and Liabilities [abstract]
Liabilities	£ (3)	£ (53)
Beginning Balance	(3)	(53)
Income statement charge	(434)	(528)	£ (597)
Other comprehensive income credit/(charge)	75	44
Corporate income tax paid	445	484	507
Other movements	23	50
Ending Balance	106	(3)	(53)
Assets	£ 106
Liabilities		£ (3)	£ (53)

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, 2018	Dec. 31, 2017
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	£ (88)	£ (128)
Adoption of IFRS 9 (see Note 1)	68
Beginning Balance, After adoption of IFRS 9	(20)
Income statement (charge)/credit	(12)	(32)
Transfers/reclassifications	(9)
Credited/(charged) to other comprehensive income	(170)	72
Ending Balance	(211)	(88)
Fair Value of Financial Instruments [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(41)	(31)
Beginning Balance, After adoption of IFRS 9	(41)
Income statement (charge)/credit	(10)	(10)
Ending Balance	(51)	(41)
Pension Remeasurement [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(41)	(35)
Beginning Balance, After adoption of IFRS 9	(41)
Income statement (charge)/credit	(24)	(32)
Credited/(charged) to other comprehensive income	(117)	26
Ending Balance	(182)	(41)
Cash Flow Hedges [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	3	(50)
Beginning Balance, After adoption of IFRS 9	3
Credited/(charged) to other comprehensive income	(46)	53
Ending Balance	(43)	3
Available-for-Sale [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(26)	(27)
Adoption of IFRS 9 (see Note 1)	26
Transfers/reclassifications		7
Credited/(charged) to other comprehensive income		(6)
Ending Balance		(26)
Fair Value Reserves Related to Gains or Losses on Cash Flow Hedges [Member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Adoption of IFRS 9 (see Note 1)	(26)
Beginning Balance, After adoption of IFRS 9	(26)
Credited/(charged) to other comprehensive income	14
Ending Balance	(12)
Tax Losses Carried Forward [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	25	5
Beginning Balance, After adoption of IFRS 9	25
Income statement (charge)/credit	(5)	20
Ending Balance	20	25
Accelerated Tax Depreciation [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(4)	(5)
Beginning Balance, After adoption of IFRS 9	(4)
Income statement (charge)/credit		1
Ending Balance	(4)	(4)
Other temporary differences [member]
Disclosure of temporary difference, unused tax losses and unused tax credits [line items]
Beginning Balance	(4)	15
Adoption of IFRS 9 (see Note 1)	68
Beginning Balance, After adoption of IFRS 9	64
Income statement (charge)/credit	27	(11)
Transfers/reclassifications	(9)	(7)
Credited/(charged) to other comprehensive income	(21)	(1)
Ending Balance	£ 61	£ (4)

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of Dividends on Ordinary Shares [Line Items]
Dividend per share	£ 15.90	£ 7.84	£ 8.40
Dividends	£ 1,123	£ 553	£ 593
First Interim [member]
Disclosure of Dividends on Ordinary Shares [Line Items]
Dividend per share	£ 3.54	£ 4.58	£ 4.49
Dividends	£ 250	£ 323	£ 317
Second Interim [member]
Disclosure of Dividends on Ordinary Shares [Line Items]
Dividend per share	£ 9.46	£ 3.26	£ 3.91
Dividends	£ 668	£ 230	£ 276
Third Interim [member]
Disclosure of Dividends on Ordinary Shares [Line Items]
Dividend per share	£ 2.90
Dividends	£ 205

Dividends on Ordinary Shares _2

Dividends on Ordinary Shares - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Dividends On Ordinary Shares [abstract]
Dividends declared	£ 250	£ 205
Dividends paid	£ 668
Percentage of dividend on recurring earnings	50.00%

Trading Assets - Disclosure of

Trading Assets - Disclosure of Trading Assets (Detail) £ in Millions	Dec. 31, 2017GBP (£)
Disclosure of financial assets held for trading [line items]
Total trading assets	£ 30,555
Securities Purchased Under Resale Agreements [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	8,870
Debt Securities [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	5,156
Equity securities [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	9,662
Cash Collateral Associated with Trading Balances [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	6,156
Short-term loans [member]
Disclosure of financial assets held for trading [line items]
Total trading assets	£ 711

Derivative Financial Instrume_3

Derivative Financial Instruments - Notional Amounts and Fair Values of Derivatives (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about hedges [line items]
Derivative notional	£ 238,751	£ 1,125,419
Fair value assets	5,321	19,942
Fair value liabilities	1,594	17,613
Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	96,541	1,027,125
Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	142,210	98,294
Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	89,432	62,267
Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	52,778	36,027
Exchange Rate Contracts [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	51,076	169,918
Exchange Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	14,165	144,160
Exchange Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	3,010	2,641
Exchange Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	33,901	23,117
Interest Rate Contracts [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	184,752	935,645
Interest Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	79,522	863,151
Interest Rate Contracts [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	86,422	59,610
Interest Rate Contracts [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	18,808	12,884
Equity and Credit Contracts [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	2,923	19,856
Equity and Credit Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	2,854	19,814
Equity Investments [Member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Derivative notional		16
Equity Investments [Member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Derivative notional	69	26
Fair Value [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	5,321	19,942
Fair value liabilities	1,594	17,613
Fair Value [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	2,188	25,538
Fair value liabilities	1,845	26,442
Fair Value [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	5,005	4,883
Fair value liabilities	1,621	1,650
Fair Value [member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	1,422	1,584
Fair value liabilities	1,315	1,480
Fair Value [member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	3,583	3,299
Fair value liabilities	306	170
Fair Value [member] | Exchange Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	455	2,559
Fair value liabilities	351	4,130
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	357	312
Fair value liabilities		6
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	3,537	3,206
Fair value liabilities	200	55
Fair Value [member] | Interest Rate Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	1,455	22,091
Fair value liabilities	1,326	21,619
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	1,065	1,272
Fair value liabilities	1,315	1,470
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	46	84
Fair value liabilities	102	115
Fair Value [member] | Equity and Credit Contracts [member] | Derivatives Held for Trading [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	278	888
Fair value liabilities	168	693
Fair Value [member] | Equity Investments [Member] | Fair Value Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value liabilities		4
Fair Value [member] | Equity Investments [Member] | Cash Flow Hedges [member] | Derivatives Held for Hedging [member]
Disclosure of detailed information about hedges [line items]
Fair value assets		9
Fair value liabilities	4
Fair Value [member] | Netting adjustments [member]
Disclosure of detailed information about hedges [line items]
Fair value assets	(1,872)	(10,479)
Fair value liabilities	£ (1,872)	£ (10,479)

Derivative Financial Instrume_4

Derivative Financial Instruments - Notional Amounts and Fair Values of Derivatives (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about hedges [line items]
Cash collateral received that had been offset against the gross derivative assets	£ 22,811	£ 13,914
Cash collateral paid that had been offset against the gross derivative liabilities	11,104	28,678
Derivative Assets [member]
Disclosure of detailed information about hedges [line items]
Cash collateral received that had been offset against the gross derivative assets	9	333
Derivative Liabilities [Member]
Disclosure of detailed information about hedges [line items]
Cash collateral paid that had been offset against the gross derivative liabilities	£ 354	£ 706

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, 2018	Dec. 31, 2017
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	£ 238,751	£ 1,125,419
Exchange Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	51,076	169,918
Interest Rate Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	184,752	935,645
Equity and Credit Contracts [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	2,923	19,856
Traded on Recognised Exchanges [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional		71,648
Liabilities traded over the counter		1
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		71,618
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		30
Liabilities traded over the counter		1
Settled by Central Counterparties [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	154,106	626,600
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	154,106	626,600
Not Settled by Central Counterparties [member]
Analysis of notional and fair values of derivatives by trading and settlement method [line item]
Derivative notional	84,645	427,171
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	51,076	169,918
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	30,646	237,427
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	2,923	19,826
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	5,321	19,942
Liabilities traded over the counter	1,594	17,612
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	4,349	6,077
Liabilities traded over the counter	551	4,191
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	694	12,968
Liabilities traded over the counter	871	12,725
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	278	897
Liabilities traded over the counter	£ 172	£ 696

Derivative Financial Instrume_6

Derivative Financial Instruments - Summary of Fixed Rate Instruments Hedged (Detail)	12 Months Ended
	Dec. 31, 2018
Fixed rate mortgages [member]
Disclosure of detailed information about hedged items [line items]
Designated benchmark instrument rate	3-month LIBOR
Currency	GBP
Fixed rate loans [member]
Disclosure of detailed information about hedged items [line items]
Designated benchmark instrument rate	3-month LIBOR & EURIBOR
Currency	GBP, EUR
Reverse repurchase agreements [member]
Disclosure of detailed information about hedged items [line items]
Designated benchmark instrument rate	SONIA, USD Fed Funds
Currency	GBP, USD
Investment assets [member]
Disclosure of detailed information about hedged items [line items]
Designated benchmark instrument rate	SONIA, 3-month LIBOR, Eonia & USD Fed Funds
Currency	GBP, EUR, USD
Fixed rate savings [member]
Disclosure of detailed information about hedged items [line items]
Designated benchmark instrument rate	3-month LIBOR, SONIA
Currency	GBP, USD

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, 2018GBP (£)	Dec. 31, 2017GBP (£)
Disclosure of nature and extent of risks arising from financial instruments [line items]
Nominal amount	£ 238,751	£ 1,125,419
Interest Rate Contracts [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Nominal amount	184,752	935,645
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]
Nominal amount	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]
Nominal amount	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]
Nominal amount	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]
Nominal amount	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]
Nominal amount	785
Exchange Rate Contracts [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Nominal amount	51,076	£ 169,918
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]
Nominal amount	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]
Nominal amount	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]
Nominal amount	15,025
Equity derivative contracts [member] | Equity Risks [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Nominal amount	69
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]
Nominal amount	£ 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	0.0063
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	(0.0022)
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 And Foreign Currency Risk [member] | Fair Value Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Nominal amount	£ 392
Average GBP - USD exchange rate	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] | Currency Risk [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Average GBP - USD exchange rate	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]
Nominal amount	£ 392
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]
Nominal amount	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]
Nominal amount	£ 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	0.0079
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	0.0067
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	0.0131
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]
Nominal amount	£ 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	0.0073
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]
Nominal amount	£ 1,295
Average GBP - USD exchange rate	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	0.0250
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]
Average GBP - JPY exchange rate	147.2149
Average GBP - USD exchange rate	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]
Nominal amount	£ 1,295
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]
Nominal amount	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]
Nominal amount	£ 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	0.0106
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	0.0091
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	0.0134
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]
Nominal amount	£ 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	0.0073
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]
Nominal amount	£ 784
Average GBP - EUR exchange rate	1.2523
Average GBP - USD exchange rate	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	0.0234
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]
Average GBP - JPY exchange rate	146.3718
Average GBP - EUR exchange rate	1.2803
Average GBP - USD exchange rate	1.3099
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]
Nominal amount	£ 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]
Nominal amount	2,961
Later Than Three Months and Not Later Than One Year [member] | Equity derivative contracts [member] | Equity Risks [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Nominal amount	37
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]
Nominal amount	£ 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	0.0159
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	0.0109
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	0.0268
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]
Nominal amount	£ 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	0.0133
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]
Nominal amount	£ 90
Average GBP - EUR exchange rate	1.1827
Average GBP - USD exchange rate	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	0.0389
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]
Nominal amount	£ 7,562
Average GBP - EUR exchange rate	1.2707
Average GBP - USD exchange rate	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	0.0266
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]
Nominal amount	£ 785
Average GBP - JPY exchange rate	145.3191
Average GBP - EUR exchange rate	1.1349
Average GBP - USD exchange rate	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]
Nominal amount	£ 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]
Nominal amount	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]
Nominal amount	5,596
Later Than One Year and Not Later Than Five Years [member] | Equity derivative contracts [member] | Equity Risks [member] | Cash Flow Hedges [member]
Disclosure of nature and extent of risks arising from financial instruments [line items]
Nominal amount	32
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]
Nominal amount	£ 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	0.0285
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	0.0126
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	0.0218
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]
Nominal amount	£ 301
Average GBP - EUR exchange rate	1.1682
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	0.0392
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]
Nominal amount	£ 2,871
Average GBP - EUR exchange rate	1.2167
Average GBP - USD exchange rate	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	0.0290
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]
Nominal amount	£ 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]
Nominal amount	£ 5,622

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of detailed information about hedges [line items]
Hedge ineffectiveness	£ 34	£ 5	£ 28
Fair Value and Cash Flow Hedges [member]
Disclosure of detailed information about hedges [line items]
Gains/(losses) on hedging instruments	4	56	(274)
(Losses)/gains on hedged items attributable to hedged risks	75	(2)	335
Fair value hedging ineffectiveness	79	54	61
Cash flow hedging ineffectiveness	(45)	(49)	(33)
Hedge ineffectiveness	£ 34	£ 5	£ 28

Derivative Financial Instrume_9

Derivative Financial Instruments - Summary of Information About Hedging Ineffectiveness by Risk Category (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Fair Value Hedges [member]
Disclosure of detailed information about hedges [line items]
Changes in FV of hedging instruments to calculate hedge ineffectiveness	£ 4
Changes in FV of hedged items to calculate hedge ineffectiveness	75
Hedge ineffectiveness recognised in income statement	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	26
Changes in FV of hedged items to calculate hedge ineffectiveness	15
Hedge ineffectiveness recognised in income statement	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	(22)
Changes in FV of hedged items to calculate hedge ineffectiveness	60
Hedge ineffectiveness recognised in income statement	38
Cash Flow Hedges [member]
Disclosure of detailed information about hedges [line items]
Changes in FV of hedging instruments to calculate hedge ineffectiveness	743
Changes in value of hedging instrument recognised in OCI	(788)
Hedge ineffectiveness recognised in income statement	(45)
Amount reclassified from cash flow hedging reserve to income statement	£ 751
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	£ 20
Changes in value of hedging instrument recognised in OCI	(14)
Hedge ineffectiveness recognised in income statement	6
Amount reclassified from cash flow hedging reserve to income statement	£ 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	£ 722
Changes in value of hedging instrument recognised in OCI	(771)
Hedge ineffectiveness recognised in income statement	(49)
Amount reclassified from cash flow hedging reserve to income statement	£ 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	£ 17
Changes in value of hedging instrument recognised in OCI	(19)
Hedge ineffectiveness recognised in income statement	(2)
Amount reclassified from cash flow hedging reserve to income statement	£ 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	£ (16)
Changes in value of hedging instrument recognised in OCI	16
Amount reclassified from cash flow hedging reserve to income statement	£ (10)

Derivative Financial Instrum_10

Derivative Financial Instruments - Additional Information (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Derivative Financial Instruments [abstract]
Ceased cash flow hedge accounting	£ 12	£ 0

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) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of detailed information about hedges [line items]
Beginning Balance	£ 285
Effective portion of changes in fair value	788
Income statement transfers	(751)
Ending Balance	322
Interest Rate Risks [member]
Disclosure of detailed information about hedges [line items]
Effective portion of changes in fair value	14
Income statement transfers	(26)
Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Effective portion of changes in fair value	19
Income statement transfers	(9)
Equity Risks [member]
Disclosure of detailed information about hedges [line items]
Effective portion of changes in fair value	(16)
Income statement transfers	10
Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Effective portion of changes in fair value	771
Income statement transfers	£ (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, 2018	Dec. 31, 2017
Disclosure of detailed information about hedges [line items]
Cash flow hedge reserve	£ 322	£ 285
Fair Value Hedges [member]
Disclosure of detailed information about hedges [line items]
Change in value used for calculating hedge ineffectiveness	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	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	60
Santander UK Group [member] | Fair Value Hedges [member] | Interest Rate And Foreign Currency Risk [member]
Disclosure of detailed information about hedges [line items]
Carrying value of assets	67,116
Carrying value of liabilities	17,015
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	10
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	536
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	697
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	242
Change in value used for calculating hedge ineffectiveness	75
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	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	(788)
Cash flow hedge reserve	322
Balances on cash flow hedge reserve where hedge accounting is no longer applied	49
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	42,075
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	638
Change in value used for calculating hedge ineffectiveness	(149)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	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	(19)
Cash flow hedge reserve	(4)
Balances on cash flow hedge reserve where hedge accounting is no longer applied	(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	6,640
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks assets	59
Change in value used for calculating hedge ineffectiveness	59
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	10,954
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	7,447
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item assets	10
Change in value used for calculating hedge ineffectiveness	(46)
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	123
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	702
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	(1)
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	516
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	15
Change in value used for calculating hedge ineffectiveness	9
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(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	6
Cash flow hedge reserve	(1)
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	15,112
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	369
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	191
Change in value used for calculating hedge ineffectiveness	158
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(548)
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	(1)
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	(217)
Cash flow hedge reserve	21
Balances on cash flow hedge reserve where hedge accounting is no longer applied	3
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 liabilities	685
Accumulated amount of FV hedge adjustments on hedged item in carrying value of hedged item liabilities	152
Accumulated amount of FV hedge adjustments for portfolio hedge of interest rate risks liabilities	52
Change in value used for calculating hedge ineffectiveness	44
Accumulated amount of FV hedge adjustments on balance sheet for discontinued hedges	(214)
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]
Cash flow hedge reserve	(2)
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	199
Cash flow hedge reserve	(1)
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	(1)
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	16
Cash flow hedge reserve	(3)
Balances on cash flow hedge reserve where hedge accounting is no longer applied	(2)
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	(564)
Cash flow hedge reserve	233
Balances on cash flow hedge reserve where hedge accounting is no longer applied	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	(207)
Cash flow hedge reserve	£ 79

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, 2018	Dec. 31, 2017
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	£ 6,137	£ 2,096
Loans and Advances to Customers [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	509	1,549
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	13	1,034
Loans and Advances to Customers [member] | Other Loans [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	496	515
Debt Securities [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	3,263	£ 547
Equity Securities [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	93
Reverse repurchase agreements - non-trading [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Loans	£ 2,272

Other Financial Assets at Fai_4

Other Financial Assets at Fair Value Through Profit or Loss - Summary of Other Financial Assets at Fair Value Through Profit or Loss (Parenthetical) (Detail) £ in Millions	Dec. 31, 2018GBP (£)
Financial assets at fair value through profit or loss [abstract]
Financial assets designated at FVTPL	£ 1,521
Financial assets mandatorily at FVTPL	£ 4,616

Other Financial Assets at Fai_5

Other Financial Assets at Fair Value Through Profit or Loss - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Financial assets mandatorily at FVTPL	£ 4,616
Net (loss)/gain attributable to changes in credit risk for loans and advances at fair value through profit or loss	(1)	£ 49	£ 40
Cumulative net loss attributable to changes in credit risk for loans and advances at fair value through profit or loss	2	£ 120
Debt Securities [member]
Disclosure of other financial assets at fair value through profit or loss [Line Items]
Financial assets mandatorily at FVTPL	£ 3,053

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, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Loans and Advances to Customers [abstract]
Loans secured on residential properties	£ 158,248	£ 155,355
Corporate loans	27,819	30,856
Finance leases	6,821	6,710
Other unsecured loans	7,554	6,230
Amounts due from fellow Banco Santander subsidiaries and joint ventures	1,997	1,199
Loans and advances to customers	202,439	200,350
Credit impairment loss allowances on loans and advances to customers	(751)	(940)	£ (921)	£ (1,108)
RV and voluntary termination provisions on finance leases	(69)	(78)
Net loans and advances to customers	£ 201,619	£ 199,332

Loans and Advances to Custome_4

Loans and Advances to Customers - Summary of Movement in Impairment Loss Allowances (Detail) - GBP (£) £ in Millions	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning balance	£ 940	£ 940	£ 921	£ 1,108
Adoption of IFRS 9 (see Note 1)	211	211
Re-allocation of ECL on off-balance sheet exposures		(50)
Balance at 1 January 2018		1,101
(Release)/charge to the income statement (see Note 8)		189	257	132
Write-offs and other items		(539)	(238)	(319)
Ending balance		751	940	921
Observed			609	503
Incurred but not yet observed			331	418
Recoveries, net of collection costs (see Note 8)		42	54	65
Advances secured on residential property [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning balance	225	225	279	424
Adoption of IFRS 9 (see Note 1)		47
Re-allocation of ECL on off-balance sheet exposures		(3)
Balance at 1 January 2018		269
(Release)/charge to the income statement (see Note 8)		(18)	(37)	(116)
Write-offs and other items		(17)	(17)	(29)
Ending balance		234	225	279
Observed			105	130
Incurred but not yet observed			120	149
Recoveries, net of collection costs (see Note 8)		2	3	4
Corporate loans [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning balance	490	490	382	395
Adoption of IFRS 9 (see Note 1)		99
Re-allocation of ECL on off-balance sheet exposures		(25)
Balance at 1 January 2018		564
(Release)/charge to the income statement (see Note 8)		17	172	59
Write-offs and other items		(355)	(64)	(72)
Ending balance		226	490	382
Observed			433	287
Incurred but not yet observed			57	95
Recoveries, net of collection costs (see Note 8)		1	1	3
Finance leases [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning balance	46	46	45	20
Adoption of IFRS 9 (see Note 1)		11
Balance at 1 January 2018		57
(Release)/charge to the income statement (see Note 8)		51	20	47
Write-offs and other items		(23)	(19)	(22)
Ending balance		85	46	45
Observed			12	13
Incurred but not yet observed			34	32
Recoveries, net of collection costs (see Note 8)		6	6	2
Other unsecured advances [member]
Movement in impairment loss allowances for loan and advances to customers [line items]
Beginning balance	£ 179	179	215	269
Adoption of IFRS 9 (see Note 1)		54
Re-allocation of ECL on off-balance sheet exposures		(22)
Balance at 1 January 2018		211
(Release)/charge to the income statement (see Note 8)		139	102	142
Write-offs and other items		(144)	(138)	(196)
Ending balance		206	179	215
Observed			59	73
Incurred but not yet observed			120	142
Recoveries, net of collection costs (see Note 8)		£ 33	£ 44	£ 56

Loans and Advances to Custome_5

Loans and Advances to Customers - Summary of Movement in Impairment Loss Allowances (Parenthetical) (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of impairment loss recognised or reversed for cash-generating unit [abstract]
Mortgage write-offs of financial assets	£ 18	£ 22	£ 33
Contractual amount outstanding on financial assets, written off	£ 76

Loans and Advances to Custome_6

Loans and Advances to Customers - Summary of Finance Lease and Hire Purchase Contract Receivables (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	£ 7,355	£ 7,163
Unearned finance income	(534)	(453)
Net investment	6,821	6,710
Not Later Than 1 Year [member]
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	3,730	3,633
Unearned finance income	(210)	(177)
Net investment	3,520	3,456
Later Than One Year and Not Later Than Five Years [member]
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	3,415	3,316
Unearned finance income	(278)	(226)
Net investment	3,137	3,090
Later Than Five Years [member]
Disclosure of finance lease and hire purchase contract receivables [line items]
Gross investment	210	214
Unearned finance income	(46)	(50)
Net investment	£ 164	£ 164

Loans and Advances To Custome_7

Loans and Advances To Customers - Additional Information (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of finance lease and hire purchase contract receivables [abstract]
Unguaranteed residual value of leases	£ 1,034	£ 886
Contingent rent income	£ 0	£ 5	£ 4

Securitisations and Covered B_3

Securitisations and Covered Bonds - Analysis of Securitisations and Covered Bonds (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of securitisations and covered bonds [line items]
Gross assets	£ 36,195	£ 36,512
External notes in issue	23,984	20,974
Notes issued to Santander UK plc/subsidiaries as collateral	3,541	3,598
Total securitisation and covered bond programmes (see Note 28)	23,445	19,907
Securitisation Programmes [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	14,617	16,740
External notes in issue	5,331	4,108
Notes issued to Santander UK plc/subsidiaries as collateral	3,541	3,598
Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	12,094	13,924
External notes in issue	3,381	2,016
Notes issued to Santander UK plc/subsidiaries as collateral	2,851	2,778
Securitisation Programmes [member] | Other Securitisation Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	2,523	2,816
External notes in issue	1,950	2,092
Notes issued to Santander UK plc/subsidiaries as collateral	690	820
Holmes [member] | Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	4,414	4,299
External notes in issue	3,182	1,400
Notes issued to Santander UK plc/subsidiaries as collateral	463	389
Fosse [member] | Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	4,646	5,732
External notes in issue	199	616
Notes issued to Santander UK plc/subsidiaries as collateral	34	34
Langton [member] | Securitisation Programmes [member] | Master Trust Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	3,034	3,893
Notes issued to Santander UK plc/subsidiaries as collateral	2,354	2,355
Auto ABS UK Loans [member] | Securitisation Programmes [member] | Other Securitisation Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	1,468	1,498
External notes in issue	1,212	1,240
Notes issued to Santander UK plc/subsidiaries as collateral	316	306
Euro 35bn Global Covered Bond Programme [member] | Covered Bond Programme [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	21,578	19,772
External notes in issue	18,653	16,866
held by the Santander UK group	(539)	(1,067)
Motor [member] | Securitisation Programmes [member] | Other Securitisation Structures [member]
Disclosure of securitisations and covered bonds [line items]
Gross assets	1,055	1,318
External notes in issue	738	852
Notes issued to Santander UK plc/subsidiaries as collateral	£ 374	£ 514

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, 2018	Dec. 31, 2017
Internal [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	£ 0.1	£ 0.3
Internal and external redemptions	0.6	0.7
Internal [member] | Master Trust Structures [member] | Holmes [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	0.1
Internal and external redemptions		0.2
Internal [member] | Master Trust Structures [member] | Fosse [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external redemptions		0.1
Internal [member] | Other Securitisation Structures [member] | Motor [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances		0.1
Internal and external redemptions	0.1	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		0.2
Internal [member] | Covered Bond Programme [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external redemptions	0.5	0.3
External [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	6.5	4
Internal and external redemptions	2.9	7.8
External [member] | Master Trust Structures [member] | Holmes [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	1.8	0.5
Internal and external redemptions	0.1	1.8
External [member] | Master Trust Structures [member] | Fosse [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external redemptions	0.4	1.8
External [member] | Other Securitisation Structures [member] | Motor [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances		0.5
Internal and external redemptions	0.1	0.3
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	0.4	0.7
Internal and external redemptions	0.4	0.7
External [member] | Covered Bond Programme [member]
Issuances And Redemptions Of Securitisation And Covered Bond [Line items]
Internal and external issuances	4.3	2.3
Internal and external redemptions	£ 1.9	£ 3.2

Securitisations and Covered B_5

Securitisations and Covered Bonds - Additional Information (Detail) - GBP (£)	Dec. 31, 2018	Dec. 31, 2017
Holmes [member]
Disclosure of gross asset securitised [line items]
Beneficial interest in residential mortgage loans	£ 3,200,000,000	£ 1,700,000,000
Cash deposits	218,000,000	0
Fosse [member]
Disclosure of gross asset securitised [line items]
Beneficial interest in residential mortgage loans	200,000,000	600,000,000
Cash deposits	0	24,000,000
Langton [member]
Disclosure of gross asset securitised [line items]
Beneficial interest in residential mortgage loans	£ 2,300,000,000	£ 2,300,000,000

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, 2018	Dec. 31, 2017
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	£ 19,369	£ 23,957
Carrying amount of associated financial liabilities	(12,639)	(12,077)
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	7,642	10,808
Carrying amount of associated financial liabilities	(7,188)	(7,734)
Securities lending agreements [member]
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	144	302
Carrying amount of associated financial liabilities	(120)	(235)
Securitisations [member]
Disclosure of continuing involvement in derecognised financial assets [line items]
Carrying amount of financial assets not derecognised in their entirety	11,583	12,847
Carrying amount of associated financial liabilities	£ (5,331)	£ (4,108)

Reverse Repurchase Agreements_3

Reverse Repurchase Agreements - Non Trading - Summary of Reverse Repurchase Agreements - Non Trading (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of reserve repurchase agreements non-trading [line items]
Reverse repurchase agreements-non trading	£ 21,127	£ 2,614
Agreements with banks [member]
Disclosure of reserve repurchase agreements non-trading [line items]
Reverse repurchase agreements-non trading	3,254	2,464
Agreements with customers [member]
Disclosure of reserve repurchase agreements non-trading [line items]
Reverse repurchase agreements-non trading	£ 17,873	£ 150

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] £ in Millions	Dec. 31, 2018GBP (£)
Financial assets at amortised cost [line items]
Financial assets at amortised cost	£ 7,228
Asset backed securities [member]
Financial assets at amortised cost [line items]
Financial assets at amortised cost	719
Debt Securities [member]
Financial assets at amortised cost [line items]
Financial assets at amortised cost	£ 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) £ in Millions	Dec. 31, 2018GBP (£)
Financial assets at fair value through other comprehensive income [abstract]
Debt securities	£ 13,229
Loans and advances to customers	73
Financial assets at fair value through other comprehensive income	£ 13,302

Financial Investments - Summary

Financial Investments - Summary of Financial Investments (Detail) £ in Millions	Dec. 31, 2017GBP (£)
Disclosure of financial investments [line items]
Financial investments	£ 17,611
Asset-backed Securities [member]
Disclosure of financial investments [line items]
Financial investments	2,180
Available-for-sale [member] | Debt Securities [member]
Disclosure of financial investments [line items]
Financial investments	8,772
Available-for-sale [member] | Equity Securities [member]
Disclosure of financial investments [line items]
Financial investments	81
Held-to-maturity debt securities [member] | Debt Securities [member]
Disclosure of financial investments [line items]
Financial investments	£ 6,578

Interests in Other Entities - S

Interests in Other Entities - Schedule of Interests in Other Entities (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of interest in other entities [abstract]
Joint ventures	£ 88	£ 73
Total	£ 88	£ 73

Interests In Other Entities - A

Interests In Other Entities - Additional Information (Detail) - GBP (£) £ in Millions	Jan. 01, 2018	Dec. 31, 2018	Jan. 31, 2018	Jan. 31, 2017
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%
Santander UK Operations Ltd [member] | Events After Reporting Period [member]
Disclosure of subsidiaries [line items]
Percentage of ownership in subsidiaries	100.00%
Santander UK Technology Ltd [member] | Events After Reporting Period [member]
Disclosure of subsidiaries [line items]
Cash consideration	£ 66
Produban servicios informaticos generales SI [member] | Events After Reporting Period [member]
Disclosure of subsidiaries [line items]
Cash consideration	£ 13

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, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 01, 2018
Disclosure of subsidiaries [line items]
Profit attributable to non-controlling interests	£ 39	£ 39	£ 45
Accumulated non-controlling interests of the subsidiary	400	401
Total assets	289,381	314,760	302,510	£ 314,500
Total liabilities	273,161	298,558	287,057
Profit for the year	1,121	1,254	1,317
Total comprehensive income for the year	1,520	932	£ 1,132
Subsidiaries with material non-controlling interests [member]
Disclosure of subsidiaries [line items]
Profit attributable to non-controlling interests	22	21
Accumulated non-controlling interests of the subsidiary	151	152
Dividends paid to non-controlling interests	22	19
Total assets	3,289	3,215
Total liabilities	2,987	2,909
Profit for the year	43	43
Total comprehensive income for the year	£ 43	£ 43

Interests In Other Entities - I

Interests In Other Entities - Interests in Consolidated Structured Entities - Additional Information (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Santander UK Foundation Limited [member]
Disclosure of information about consolidated structured entities [line items]
Third party assets	£ 15	£ 16

Interests In Other Entities -_3

Interests In Other Entities - Interests in Joint Ventures - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of joint ventures [line items]
Carrying value of interest in joint venture	£ 88	£ 73
Joint ventures [member]
Disclosure of joint ventures [line items]
Profit after tax	15	12
Carrying value of interest in joint venture	88	73
Commitments and contingent liabilities	£ 0	£ 0

Interests In Other Entities -_4

Interests In Other Entities - Interests in Unconsolidated Structured Entities - Additional Information (Detail) £ in Millions	Feb. 07, 2000USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017GBP (£)	Dec. 31, 2018GBP (£)
Disclosure of information about unconsolidated subsidiaries [line items]
Ownership interest in trust preferred entities by Santander UK plc		100.00%
Non-cumulative trust preferred securities issued | $	$ 1,000,000,000
Non-cumulative trust preferred securities interest rate	8.963%
Number of credit protection vehicles		3	2
Credit Linked Notes issued			£ 830	£ 3,053
Entities with Joint Control or Significant Influence over Entity [Member]
Disclosure of information about unconsolidated subsidiaries [line items]
Credit Linked Notes issued			187	408
Santander (UK) Common Investment Fund [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Defined benefit assets and obligations			£ 11,626	£ 11,433
Name of subsidiary		The Santander (UK) Common Investment Fund
Abbey National Capital Trust I [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Name of subsidiary		Abbey National Capital Trust I
Ownership interest in trust preferred entities by Santander UK plc		100.00%
Non-cumulative trust preferred securities issued | $		$ 104
Non-cumulative trust preferred securities interest rate		8.963%
Abbey National Capital LP I [member]
Disclosure of information about unconsolidated subsidiaries [line items]
Name of subsidiary		Abbey National Capital LP
Ownership interest in trust preferred entities by Santander UK plc		100.00%

Intangible Assets - Schedule of

Intangible Assets - Schedule of Goodwill (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of goodwill [line items]
Carrying amount	£ 1,203	£ 1,203
Cost [member]
Disclosure of goodwill [line items]
Carrying amount		1,285
Accumulated Impairment [member]
Disclosure of goodwill [line items]
Carrying amount		£ (82)

Intangible Assets - Additional

Intangible Assets - Additional Information (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about intangible assets [abstract]
Goodwill impairment recognised	£ 0	£ 0
Increase/(decrease) in discount rate percentage	(0.30%)
Discount rate percentage	10.50%	10.80%

Intangible Assets - Schedule _2

Intangible Assets - Schedule of Goodwill for Cash Generating Units (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of information for cash-generating units [line items]
Goodwill	£ 1,203	£ 1,203
Discount rate	10.50%	10.80%
Personal Financial Services [member]
Disclosure of information for cash-generating units [line items]
Goodwill	£ 1,169	£ 1,169
Discount rate	10.50%	10.80%
Growth rate	2.00%	1.00%
Private Banking [member]
Disclosure of information for cash-generating units [line items]
Goodwill	£ 30	£ 30
Discount rate	10.50%	10.80%
Growth rate	2.00%	1.00%
Other [member]
Disclosure of information for cash-generating units [line items]
Goodwill	£ 4	£ 4
Discount rate	10.50%	10.80%
Growth rate	2.00%	1.00%

Intangible Assets - Schedule _3

Intangible Assets - Schedule of Goodwill for Cash Generating Units (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of information for cash-generating units [abstract]
Terminal growth rate	2.00%	1.50%

Intangible Assets - Schedule _4

Intangible Assets - Schedule of Other Intangibles (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of detailed information about intangible assets [line items]
Beginning balance	£ 539	£ 482
Additions	213	205
Charge	(141)	(116)
Sales	0
Impairment		(32)
Ending balance	611	539
Cost [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	962	760
Additions	213	205
Write offs	(76)
Disposals		(3)
Sales	0
Ending balance	1,099	962
Accumulated amortisation / impairment [member]
Disclosure of detailed information about intangible assets [line items]
Beginning balance	(423)	(278)
Write offs	76
Disposals		3
Charge	(141)	(116)
Sales	0
Impairment		(32)
Ending balance	£ (488)	£ (423)

Trading Liabilities - Schedule

Trading Liabilities - Schedule of Trading Liabilities (Detail) £ in Millions	Dec. 31, 2017GBP (£)
Disclosure of financial liabilities held for trading [line items]
Trading liabilities	£ 31,109
Securities Sold Under Repurchase Agreements [member]
Disclosure of financial liabilities held for trading [line items]
Trading liabilities	25,504
Short Positions in Securities and Unsettled Trades [member]
Disclosure of financial liabilities held for trading [line items]
Trading liabilities	3,694
Cash Collateral [member]
Disclosure of financial liabilities held for trading [line items]
Trading liabilities	£ 1,911

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, 2018	Dec. 31, 2017
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	£ 6,286	£ 2,315
US Dollar Ten Billion Euro commercial paper programmes [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss		387
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	165	169
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	696	932
Eurobonds [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	129	147
Structured Deposits [member]
Disclosure of other financial liabilities at fair value through profit or loss [line items]
Other financial liabilities through profit or loss	133	£ 680
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	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	£ 2,110

Other Financial Liabilities a_4

Other Financial Liabilities at Fair Value Through Profit or Loss - Summary of Other Financial Liabilities at Fair Value Through Profit or Loss (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of financial liabilities [abstract]
Financial liabilities designated at fair value through profit or loss	£ 6,286	£ 2,315
Financial liabilities mandatorily at fair value through profit or loss	£ 0

Other Financial Liabilities a_5

Other Financial Liabilities at Fair Value Through Profit or Loss - Additional Information (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Other financial liabilities at fair value through profit or loss [abstract]
Net gain (loss) on financial liabilities designated at fair value, attributable to changes in credit risk	£ 84	£ (29)	£ 6
Accumulated gain (loss) on financial liabilities designated at fair value, attributable to changes in credit risk	77	(7)
Difference between carrying amount of financial liability and amount contractually required to pay at maturity to holder of obligation	£ 128	£ 4

Deposits by Customers - Schedul

Deposits by Customers - Schedule of Deposits by Customers (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of deposits from customers [line items]
Deposits from customers	£ 173,692	£ 177,421
Current and Demand Accounts - [member]
Disclosure of deposits from customers [line items]
Deposits from customers	87,316	85,780
Savings Accounts [member]
Disclosure of deposits from customers [line items]
Deposits from customers	69,102	70,461
Time Deposits [member]
Disclosure of deposits from customers [line items]
Deposits from customers	16,204	20,453
Amounts Due to Fellow Banco Santander Subsidiaries and Joint Ventures - [member]
Disclosure of deposits from customers [line items]
Deposits from customers	£ 1,070	£ 727

Deposits by Customers - Sched_2

Deposits by Customers - Schedule of Deposits by Customers (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of deposits from customers [line items]
Deposits from customers	£ 173,692	£ 177,421
Equity Index Linked Deposits [member]
Disclosure of deposits from customers [line items]
Deposits from customers	1,176	1,301
Capital amount guaranteed or protected	1,176	1,301
Capital amount of return guaranteed	£ 28	£ 67

Deposits by Banks - Schedule of

Deposits by Banks - Schedule of Deposits by Banks (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of deposits from banks [line items]
Deposits from banks	£ 17,824	£ 12,708
Items in Course of Transmission [member]
Disclosure of deposits from banks [line items]
Deposits from banks	262	303
Deposits Held as Collateral [member]
Disclosure of deposits from banks [line items]
Deposits from banks	4,058	1,760
Other Deposits [member]
Disclosure of deposits from banks [line items]
Deposits from banks	£ 13,504	£ 10,645

Deposits by Banks - Schedule _2

Deposits by Banks - Schedule of Deposits by Banks (Parenthetical) (Detail) - GBP (£) £ in Billions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of deposits from banks [abstract]
Drawdown from TFS	£ 10.8	£ 8.5

Repurchase Agreements - Non T_3

Repurchase Agreements - Non Trading - Summary of Repurchase Agreements Non Trading (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements - non trading	£ 10,910	£ 1,076
Agreements with banks [member]
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements - non trading	5,865	£ 1,076
Agreements with customers [member]
Disclosure Of Repurchase Agreements [line items]
Repurchase agreements - non trading	£ 5,045

Debt Securities In Issue - Summ

Debt Securities In Issue - Summary of Debt Securities in Issue (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt securities in issue [line items]
Debt Securities	£ 55,906	£ 48,860
Credit Linked Notes	3,053	830
Medium Term Notes [member]
Debt securities in issue [line items]
Debt Securities	29,198	24,229
Medium Term Notes [member] | US$30bn Euro Medium Term Note Programme [member]
Debt securities in issue [line items]
Debt Securities	7,229	8,816
Medium Term Notes [member] | Euro 30bn Euro Medium Term Note Programme [member]
Debt securities in issue [line items]
Debt Securities	5,348	2,177
Medium Term Notes [member] | US SEC - Registered - Santander UK Group Holdings Plc [member]
Debt securities in issue [line items]
Debt Securities	5,841	4,050
Medium Term Notes [member] | US SEC - Registered - Santander UK Plc [member]
Debt securities in issue [line items]
Debt Securities	7,649	6,280
Medium Term Notes [member] | US$20bn Commercial Paper Programmes [member]
Debt securities in issue [line items]
Debt Securities	3,131	2,906
Euro 35bn Global Covered Bond Programme [member]
Debt securities in issue [line items]
Debt Securities	18,114	15,799
Certificates of Deposit [member]
Debt securities in issue [line items]
Debt Securities	3,221	4,681
Credit Linked Note [member]
Debt securities in issue [line items]
Credit Linked Notes	42	43
Securitisation Programmes [member]
Debt securities in issue [line items]
Debt Securities	£ 5,331	£ 4,108

Debt Securities In Issue - Su_2

Debt Securities In Issue - Summary of Debt Securities in Issue (Parenthetical) (Detail) £ in Millions, € in Billions, $ in Billions	Dec. 31, 2018GBP (£)	Dec. 31, 2018USD ($)	Dec. 31, 2018EUR (€)	Dec. 31, 2017GBP (£)	Dec. 31, 2017USD ($)	Dec. 31, 2017EUR (€)
Debt securities in issue [line items]
Notional amount | £	£ 238,751			£ 1,125,419
Medium Term Notes [member] | US$30bn Euro Medium Term Note Programme [member]
Debt securities in issue [line items]
Notional amount | $		$ 30			$ 30
Medium Term Notes [member] | Euro 30bn Euro Medium Term Note Programme [member]
Debt securities in issue [line items]
Notional amount | €			€ 30			€ 30
Medium Term Notes [member] | US$20bn Commercial Paper Programmes [member]
Debt securities in issue [line items]
Notional amount | $		$ 20			$ 20
Euro 35bn Global Covered Bond Programme [member]
Debt securities in issue [line items]
Notional amount | €			€ 35			€ 35

Debt Securities In Issue - Addi

Debt Securities In Issue - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018
PSA Finance UK Limited [member]
Debt securities in issue [line items]
Percentage of losses in portfolio having credit protection	7.60%

Subordinated Liabilities - Sche

Subordinated Liabilities - Schedule of Subordinated Liabilities (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Subordinated Liabilities [abstract]
£325m Sterling Preference Shares	£ 344	£ 344
£175m Fixed/Floating Rate Tier One Preferred Income Capital Securities		2
Undated subordinated liabilities	574	584
Dated subordinated liabilities	2,683	2,863
Subordinated liabilities	£ 3,601	£ 3,793

Subordinated Liabilities - Sc_2

Subordinated Liabilities - Schedule of Subordinated Liabilities (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of Subordinated Liabilities [abstract]
325m Sterling Preference Shares, Notional amount	£ 325	£ 325
175m Fixed/Floating Rate Tier One Preferred Income Capital Securities, Notional amount	£ 175	£ 175

Subordinated Liabilities - Addi

Subordinated Liabilities - Additional Information (Detail) - GBP (£)	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017	Sep. 30, 2017
Disclosure of subordinated liabilities [line items]
Notional amount	£ 175,000,000		£ 175,000,000
Defaults of principal, interest or other breaches with respect to subordinated liabilities	£ 0		£ 0
Par value per share	£ 1	£ 1	£ 1
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%
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%
10.125% Subordinated Guaranteed Bond 2023 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	10.125%		10.125%
175m Sterling Fixed/Floating Rate Tier One Preferred Income Capital Securities [member]
Disclosure of subordinated liabilities [line items]
Notional amount			£ 175,000,000
10.0625% non-cumulative non-redeemable sterling preference shares [member]
Disclosure of subordinated liabilities [line items]
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
300m Fixed/Floating Rate Non-Cumulative Callable Preference Shares [member]
Disclosure of subordinated liabilities [line items]
Notional amount	£ 300,000,000
300m Step-up Callable Perpetual Reserve Capital Instruments [member]
Disclosure of subordinated liabilities [line items]
Notional amount	£ 300,000,000

Subordinated Liabilities - Summ

Subordinated Liabilities - Summary of Undated Subordinated Liabilities (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of subordinated liabilities [line items]
Undated subordinated liabilities	£ 574	£ 584
10.0625% Exchangeable Capital Securities [member]
Disclosure of subordinated liabilities [line items]
Undated subordinated liabilities	£ 205	205
First call date	n/a
7.375% 20 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Undated subordinated liabilities	£ 16	£ 17
First call date	2,020	2,020
7.125% 30 Year Step-up Perpetual Callable Subordinated Notes [member]
Disclosure of subordinated liabilities [line items]
Undated subordinated liabilities	£ 353	£ 362
First call date	2,030	2,030

Subordinated Liabilities - Su_2

Subordinated Liabilities - Summary of Undated Subordinated Liabilities (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Sep. 30, 2017
10.0625% Exchangeable Capital Securities [member]
Disclosure of subordinated liabilities [line items]
Interest rate	10.0625%	10.0625%
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%
Notes maturity, year	20 years
Maturity period	2,020	2,020
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
Maturity period	2,030	2,030

Subordinated Liabilities - Su_3

Subordinated Liabilities - Summary of Dated Subordinated Liabilities (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 2,683	£ 2,863
10.125% Subordinated Guaranteed Bond 2023 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities		£ 78
Maturity period	2,023	2,023
9.625% Subordinated Notes 2023 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities		£ 129
Maturity period	2,023	2,023
5% Subordinated Notes 2023 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 1,173	£ 1,103
Maturity period	2,023	2,023
4.75% Subordinated Notes 2025 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 791	£ 745
Maturity period	2,025	2,025
7.95% Subordinated Notes 2029 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 278	£ 275
Maturity period	2,029	2,029
6.50% Subordinated Notes 2030 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 38	£ 40
Maturity period	2,030	2,030
8.963% Subordinated Notes 2045 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities		£ 113
Maturity period	2,045	2,045
5.875% Subordinated Notes 2031 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 9	£ 9
Maturity period	2,031	2,031
5.625% Subordinated Notes 2045 [member]
Disclosure of subordinated liabilities [line items]
Dated subordinated liabilities	£ 394	£ 371
Maturity period	2,045	2,045

Subordinated Liabilities - Su_4

Subordinated Liabilities - Summary of Dated Subordinated Liabilities (Parenthetical) (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
10.125% Subordinated Guaranteed Bond 2023 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	10.125%	10.125%
9.625% Subordinated Notes 2023 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	9.625%	9.625%
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%
8.963% Subordinated Notes 2045 [member]
Disclosure of subordinated liabilities [line items]
Interest rate	8.963%	8.963%
Notional amount	$ 1,000	$ 1,000
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	12 Months Ended
	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of other provisions [line items]
Beginning balance	£ 558	£ 558	£ 700
Reallocation of ECL on off-balance sheet exposures		50
Balance on January 1 2018		608
Additional provisions		298	385
Provisions released (see Note 8)		(32)
Utilisation		(373)	(537)
Other		14
Transfers			10
Ending balance		515	558	£ 700
To be settled:
Ending balance		515	558	700
Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Beginning balance	344	344
Ending balance		492	344
To be settled:
Ending balance		492	344
More than One Year [member]
Disclosure of other provisions [line items]
Beginning balance	214	214
Ending balance		23	214
To be settled:
Ending balance		23	214
PPI [member]
Disclosure of other provisions [line items]
Beginning balance	356	356	457
Balance on January 1 2018		356
Additional provisions		0	109	144
Utilisation		(110)	(210)
Ending balance		246	356	457
To be settled:
Ending balance		246	356	457
PPI [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Beginning balance	167	167
Ending balance		246	167
To be settled:
Ending balance		246	167
PPI [member] | More than One Year [member]
Disclosure of other provisions [line items]
Beginning balance	189	189
Ending balance			189
To be settled:
Ending balance			189
Other products [member]
Disclosure of other provisions [line items]
Beginning balance	47	47	36
Balance on January 1 2018		47
Additional provisions			35
Provisions released (see Note 8)	(11)	(14)
Utilisation		(3)	(34)
Transfers			10
Ending balance		30	47	36
To be settled:
Ending balance		30	47	36
Other products [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Beginning balance	38	38
Ending balance		22	38
To be settled:
Ending balance		22	38
Other products [member] | More than One Year [member]
Disclosure of other provisions [line items]
Beginning balance	9	9
Ending balance		8	9
To be settled:
Ending balance		8	9
FSCS and Bank Levy [member]
Disclosure of other provisions [line items]
Beginning balance	57	57	96
Balance on January 1 2018		57
Additional provisions		69	93
Provisions released (see Note 8)		(4)
Utilisation		(92)	(132)
Other		14
Ending balance		44	57	96
To be settled:
Ending balance		44	57	96
FSCS and Bank Levy [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Beginning balance	57	57
Ending balance		44	57
To be settled:
Ending balance		44	57
Vacant Property [member]
Disclosure of other provisions [line items]
Beginning balance	39	39	47
Balance on January 1 2018		39
Additional provisions		15	4
Utilisation		(14)	(12)
Ending balance		40	39	47
To be settled:
Ending balance		40	39	47
Vacant Property [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Beginning balance	23	23
Ending balance		25	23
To be settled:
Ending balance		25	23
Vacant Property [member] | More than One Year [member]
Disclosure of other provisions [line items]
Beginning balance	16	16
Ending balance		15	16
To be settled:
Ending balance		15	16
Off-Balance Sheet [member]
Disclosure of other provisions [line items]
Reallocation of ECL on off-balance sheet exposures		50
Balance on January 1 2018		50
Additional provisions		6
Ending balance		56
To be settled:
Ending balance		56
Off-Balance Sheet [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Ending balance		56
To be settled:
Ending balance		56
Regulatory and other [member]
Disclosure of other provisions [line items]
Beginning balance	59	59	64
Balance on January 1 2018		59
Additional provisions		208	144
Provisions released (see Note 8)		(14)
Utilisation		(154)	(149)
Ending balance		99	59	64
To be settled:
Ending balance		99	59	£ 64
Regulatory and other [member] | Not Later Than 1 Year [member]
Disclosure of other provisions [line items]
Beginning balance	£ 59	59
Ending balance		99	59
To be settled:
Ending balance		£ 99	£ 59

Provisions - Summary of Provi_2

Provisions - Summary of Provisions Reconciliation (Parenthetical) (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of other provisions [line items]
Other	£ 14
FSCS and Bank Levy [member]
Disclosure of other provisions [line items]
Other	£ 14

Provisions - Additional Informa

Provisions - Additional Information (Detail) - GBP (£) £ in Millions	3 Months Ended	6 Months Ended		12 Months Ended
	Dec. 31, 2018	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Apr. 25, 2017	Apr. 24, 2017
Disclosure of other provisions [line items]
Provisions	£ 515	£ 515		£ 515	£ 558	£ 700
Additional provision charge				298	385
Provisions released				(32)
Reduction in amount that FSCS owes to HM Treasury							£ 4,700	£ 15,700
Financial Ombudsman Service [member]
Disclosure of other provisions [line items]
Overturn rate percentage			16.00%
Average overturn rate percentage		12.00%
PPI [member]
Disclosure of other provisions [line items]
Provisions	246	£ 246		246	356	457
Additional provision charge				0	109	144
PPI [member] | Plevin redress [member]
Disclosure of other provisions [line items]
Provision linked to future claims levels				101
Impact on the PPI misselling element of provision				(16)
Provision for Past Business Review [member]
Disclosure of other provisions [line items]
Additional provision charge						114
August 2016 FCA Papers [member]
Disclosure of other provisions [line items]
Additional provision charge						32
Other products [member]
Disclosure of other provisions [line items]
Provisions	30	30		30	47	36
Additional provision charge					35
Provisions released			£ (11)	(14)
Regulatory Related | Financial Services Compensation Scheme [member]
Disclosure of other provisions [line items]
Regulatory costs related to Financial Services Compensation Scheme (FSCS)				(4)	1	34
Regulatory Related | Financial Services Compensation Scheme [member] | Santander UK Group Holdings plc [member]
Disclosure of other provisions [line items]
Reduction in amount that FSCS owes to HM Treasury	4	4		4	13
Regulatory Related Uk Bank Levy [member]
Disclosure of other provisions [line items]
Provisions	40	£ 40		£ 40	£ 44
Bank levy rate				0.16%	0.17%
Cost of UK Bank Levy Incurred				£ 69	£ 92	£ 107
Amount paid as UK Bank Levy				£ 86	109
Regulatory Related Uk Bank Levy [member] | Top of Range [member]
Disclosure of other provisions [line items]
UK Bank Levy				0.21%
Regulatory Related Uk Bank Levy [member] | Bottom of Range [member]
Disclosure of other provisions [line items]
UK Bank Levy				0.10%
Compliance with Consumer Credit Act [member]
Disclosure of other provisions [line items]
Additional operational risk losses and restructuring charges				£ 58	£ 0
Historical probate and bereavement practices [member]
Disclosure of other provisions [line items]
Additional operational risk losses and restructuring charges	£ 33

Provisions - Summary of Key Dri

Provisions - Summary of Key Drivers of PPI Provision Balance and Forecast Assumptions Used in Calculating Provision (Detail) - PPI [member]	12 Months Ended
	Dec. 31, 2018GBP (£)
Inbound Complaints [member]
Disclosure of other provisions [line items]
Cumulative to 31 December 2018	2,141,000
Future expected (unaudited)	415,000
Sensitivity analysis number	25,000
Sensitivity analysis increase/decrease in provision	£ 7,400,000
Outbound Complaints [member]
Disclosure of other provisions [line items]
Cumulative to 31 December 2018	488,000
Future expected (unaudited)	217,000
Sensitivity analysis number	25,000
Sensitivity analysis increase/decrease in provision	£ 5,400,000
Response Rate to Outbound Contact [member]
Disclosure of other provisions [line items]
Cumulative to 31 December 2018	54.00%
Future expected (unaudited)	64.00%
Sensitivity analysis rate	1.00%
Sensitivity analysis increase/decrease in provision	£ 800,000
Average Uphold Rate Per Claim [member]
Disclosure of other provisions [line items]
Cumulative to 31 December 2018	37.00%
Future expected (unaudited)	76.00%
Sensitivity analysis rate	1.00%
Sensitivity analysis increase/decrease in provision	£ 2,700,000
Average Redress Per Claim [member]
Disclosure of other provisions [line items]
Cumulative to 31 December 2018	1,474
Future expected (unaudited)	545
Sensitivity analysis amount	50
Sensitivity analysis increase/decrease in provision	£ 16,400,000

Provisions - Summary of Key D_2

Provisions - Summary of Key Drivers of PPI Provision Balance and Forecast Assumptions Used in Calculating Provision (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of other provisions [abstract]
Cumulative average value	£ 1,474
Future average value	£ 545

Retirement Benefit Plans - Summ

Retirement Benefit Plans - Summary of Retirement Benefit Plans (Detail) - Santander UK Group [member] - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Assets/(liabilities)
Total net assets	£ 727	£ 163
Unfunded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	(39)	(41)
Surplus [member] | Funded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	842	449
Deficit [member] | Funded Defined Benefit Pension Scheme [member]
Assets/(liabilities)
Surplus (deficit) in plan	£ (76)	£ (245)

Retirement Benefit Plans - Su_2

Retirement Benefit Plans - Summary of Remeasurement (Gains)/Losses Recognised In Other Comprehensive Income (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of net defined benefit liability (asset) [abstract]
Pension remeasurement	£ (469)	£ 103	£ 528

Retirement Benefit Plans - Addi

Retirement Benefit Plans - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018GBP (£)Directors	Dec. 31, 2017GBP (£)	Dec. 31, 2016GBP (£)	Mar. 31, 2017GBP (£)
Disclosure of defined benefit plans [line items]
Defined contribution expense	£ 66,000,000	£ 54,000,000	£ 52,000,000
Key management personnel expense	None	None	None
Percentage of employee covered defined benefit pension schemes	13.00%	17.00%
Number of directors selected | Directors	6
Number of directors nominated | Directors	6
Actuarial valuation deficit				£ (1,739,000,000)
Equity securities hold	£ 0	£ 0
Property occupied	0	0
Other assets occupied	0	0
Contribution to scheme based on agreement	£ 176,000,000	£ 163,000,000
Improvements to life expectancy of female employees	1.25%
Improvements to life expectancy of male employees	1.25%
Average duration of defined benefit obligation	19.1 years	20.1 years
Actuarial Assumption of Discount Rates [member]
Disclosure of defined benefit plans [line items]
Surplus (deficit) in plan	£ 104,000,000
Actuarial Assumption of Expected Rates of Inflation [member]
Disclosure of defined benefit plans [line items]
Surplus (deficit) in plan	(65,000,000)
Actuarial assumption of expected rate of pension increases [member]
Disclosure of defined benefit plans [line items]
Surplus (deficit) in plan	(85,000,000)
Actuarial assumption of mortality rates [member]
Disclosure of defined benefit plans [line items]
Surplus (deficit) in plan	£ 57,000,000
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	£ 1,795,000,000	£ 2,000,000,000
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	£ (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	£ 123,000,000	£ 123,000,000
Deficit Repair Contributions [member] | Santander UK Group [member]
Disclosure of defined benefit plans [line items]
Contributions to defined benefit plans	£ 119,000,000
Annual increase in contibution	5.00%
Maturity date for contribution	31 March 2026
Deficit Repair Group Section Contributions [member] | Santander UK Group [member]
Disclosure of defined benefit plans [line items]
Contributions to defined benefit plans	£ 28,000,000
Annual increase in contibution	5.00%
Maturity date for contribution	1 April 2021 to 31 March 2023
Deficit Group Section Contributions Plan [member] | Santander UK Group [member]
Disclosure of defined benefit plans [line items]
Contributions to defined benefit plans	£ 66,000,000
Annual increase in contibution	5.00%
Maturity date for contribution	1 April 2023 to 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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of net defined benefit liability (asset) [abstract]
Net interest income	£ (7)	£ (5)	£ (18)
Current service cost	41	31	33
Past service cost	41	1	1
Administration costs	8	8	8
Total	£ 83	£ 35	£ 24

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of net defined benefit liability (asset) [abstract]
Return on plan assets (excluding amounts included in net interest expense)	£ 246	£ (435)	£ (1,447)
Actuarial (gains)/losses arising from changes in demographic assumptions	(56)	(151)	30
Actuarial gains arising from experience adjustments	15	(11)	(80)
Actuarial (gains)/losses arising from changes in financial assumptions	(674)	700	2,025
Pension remeasurement	£ (469)	£ 103	£ 528

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of net defined benefit liability (asset) [line items]
Current service cost	£ 41	£ 31	£ 33
Net interest income	(7)	(5)	(18)
Past service cost	41	1	1
Remeasurement due to actuarial movements arising from:
- Changes in demographic assumptions	(56)	(151)	30
- Experience adjustments	15	(11)	(80)
- Changes in financial assumptions	(674)	700	2,025
Present value of defined benefit obligations [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	(11,583)	(11,082)
Current service cost	(27)	(30)
Current service cost paid by other subsidiaries	(14)	(1)
Current service cost paid by fellow Banco Santander subsidiaries		(12)
Net interest income	(282)	(305)
Employer salary sacrifice contributions	(6)	(6)
Past service cost	(1)	(1)
GMP equalisation cost	(40)
Remeasurement due to actuarial movements arising from:
- Changes in demographic assumptions	56	151
- Experience adjustments	(15)	11
- Changes in financial assumptions	674	(700)
Benefits paid	433	392
Ending balance	£ (10,805)	£ (11,583)	£ (11,082)

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of net defined benefit liability (asset) [line items]
Interest income	£ (7)	£ (5)	£ (18)
Return on plan assets (excluding amounts included in net interest expense)	246	(435)	(1,447)
Fair value of scheme assets [member]
Disclosure of net defined benefit liability (asset) [line items]
Beginning balance	11,746	11,218
Interest income	289	310
Contributions paid by employer and scheme members	184	171
Contributions paid by fellow Banco Santander subsidiaries		12
Administration costs paid	(8)	(8)
Return on plan assets (excluding amounts included in net interest expense)	(246)	435
Benefits paid	(433)	(392)
Ending balance	£ 11,532	£ 11,746	£ 11,218

Retirement Benefit Plans - Su_4

Retirement Benefit Plans - Summary of Composition and Fair Value of Plan Assets (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of net defined benefit liability (asset) [line items]
UK equities	1.00%	1.00%
Overseas equities	24.00%	25.00%
Corporate bonds	16.00%	16.00%
Government fixed interest bonds	23.00%	2.00%
Government index-linked bonds	37.00%	30.00%
Property	10.00%	13.00%
Derivatives		4.00%
Cash	6.00%	2.00%
Repurchase agreements	(26.00%)
Other	9.00%	7.00%
Total	100.00%	100.00%
UK equities	£ 159	£ 187
Overseas equities	2,732	2,910
Corporate bonds	1,847	1,874
Government fixed interest bonds	2,636	255
Government index-linked bonds	4,248	3,506
Property	1,143	1,547
Derivatives	65	512
Cash	662	206
Repurchase agreements	(2,981)
Other	1,021	749
Total	£ 11,532	£ 11,746
Quoted Prices in Active Markets [member]
Disclosure of net defined benefit liability (asset) [line items]
UK equities	1.00%	1.00%
Overseas equities	16.00%	19.00%
Corporate bonds	13.00%	14.00%
Government fixed interest bonds	23.00%	2.00%
Government index-linked bonds	37.00%	30.00%
Total	90.00%	66.00%
UK equities	£ 159	£ 187
Overseas equities	1,854	2,204
Corporate bonds	1,536	1,665
Government fixed interest bonds	2,636	255
Government index-linked bonds	4,248	3,506
Total	£ 10,433	£ 7,817
Prices Not Quoted in Active Markets [member]
Disclosure of net defined benefit liability (asset) [line items]
Overseas equities	8.00%	6.00%
Corporate bonds	3.00%	2.00%
Property	10.00%	13.00%
Derivatives		4.00%
Cash	6.00%	2.00%
Repurchase agreements	(26.00%)
Other	9.00%	7.00%
Total	10.00%	34.00%
Overseas equities	£ 878	£ 706
Corporate bonds	311	209
Property	1,143	1,547
Derivatives	65	512
Cash	662	206
Repurchase agreements	(2,981)
Other	1,021	749
Total	£ 1,099	£ 3,929

Retirement Benefit Plans - Su_5

Retirement Benefit Plans - Summary of Principal Actuarial Assumptions Used for Defined Benefit Schemes (Detail)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of sensitivity analysis for actuarial assumptions [abstract]
- Discount rate for scheme liabilities	2.90%	2.50%	2.80%
- General price inflation	3.20%	3.20%	3.10%
- General salary increase	1.00%	1.00%	1.00%
- Expected rate of pension increase	2.90%	2.90%	2.90%
Longevity at 60 for current pensioners, on the valuation date:
- Males	27 years 3 months 18 days	27 years 4 months 24 days	27 years 9 months 18 days
- Females	30 years 1 month 6 days	30 years 1 month 6 days	30 years 3 months 18 days
Longevity at 60 for future pensioners currently aged 40, on the valuation date:
- Males	28 years 8 months 28 days	28 years 10 months 24 days	30 years
- Females	31 years 7 months 6 days	31 years 8 months 12 days	32 years 2 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, 2018	Dec. 31, 2017
Actuarial Assumption of Discount Rates [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
Increase decrease in defined benefit obligation	£ (483)	£ (550)
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	£ 350	365
Description of changes in methods and assumptions	25 bps increase
Actuarial assumption of expected rates of salary increases [member]
Disclosure of sensitivity analysis for actuarial assumptions [line items]
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	£ 335	£ 367
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, 2018GBP (£)
Not Later Than 1 Year [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	£ 266
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	269
2 - 3 years [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	287
3 - 4 years [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	309
4 - 5 years [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	325
Five Years Ending 2028 [member]
Disclosure of net defined benefit liability (asset) [line items]
Benefits expected to be paid	£ 1,903

Contingent Liabilities and Co_3

Contingent Liabilities and Commitments - Summary of Contingent Liabilities and Commitments (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of contingent liabilities and commitments [line items]
Guarantees and formal standby facilities, credit lines and other commitments	£ 41,737	£ 43,499
Contingent Liability for Guarantees [Member]
Disclosure of contingent liabilities and commitments [line items]
Guarantees given to third parties	1,611	1,557
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	8,560	10,664
Loan commitments [member] | More than One Year [member]
Disclosure of contingent liabilities and commitments [line items]
Formal standby facilities, credit lines and other commitments	£ 31,566	£ 31,278

Contingent Liabilities and Co_4

Contingent Liabilities and Commitments - Additional Information (Detail)	Nov. 02, 2015	Dec. 31, 2018GBP (£)	Dec. 31, 2018EUR (€)	Dec. 31, 2017GBP (£)	Dec. 31, 2016GBP (£)
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 whereby the Santander UK group has the right to extend the occupation of properties by a minimum of three years subject to 12 months' notice and a lease renewal being available from external landlords. Where leases expire after the expiry of the outsourcing contract in 2020 and occupation is still required, negotiations will be held with the landlords to agree renewal terms.	The majority of leases are subject to a third party outsourcing contract whereby the Santander UK group has the right to extend the occupation of properties by a minimum of three years subject to 12 months' notice and a lease renewal being available from external landlords. Where leases expire after the expiry of the outsourcing contract in 2020 and occupation is still required, negotiations will be held with the landlords to agree renewal terms.
Minimum lease extension period		3 years	3 years
Terms of notice period		12 months	12 months
Rental expense		£ 61,000,000		£ 61,000,000	£ 61,000,000
Minimum rentals		63,000,000		61,000,000	61,000,000
Sub-lease rental income		2,000,000		0	£ 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 charges		£ 58,000,000		£ 0
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%

Contingent Liabilities and Co_5

Contingent Liabilities and Commitments - Operating Lease Commitments (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of finance lease and operating lease by lessee [line items]
Lease payments	£ 247	£ 303
Not Later Than 1 Year [member]
Disclosure of finance lease and operating lease by lessee [line items]
Lease payments	73	73
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	160
Later Than Five Years [member]
Disclosure of finance lease and operating lease by lessee [line items]
Lease payments	£ 60	£ 70

Share Capital - Schedule of Sha

Share Capital - Schedule of Share Capital Issued and Fully Paid (Detail) - GBP (£) £ / shares in Units, £ in Millions	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Disclosure of classes of share capital [abstract]
Number of shares issued and fully paid	7,060,000,000	7,060,000,000	7,060,000,000
Ordinary shares, price per share	£ 1	£ 1	£ 1
Issued and fully paid share capital	£ 7,060	£ 7,060	£ 7,060

Other Equity Instruments - Summ

Other Equity Instruments - Summary of Other Equity Instruments (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of other equity instruments [line items]
Other equity instruments	£ 2,041	£ 2,041
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Initial interest rate	6.75%
First call date	2024-06
Other equity instruments	£ 496	496
750m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Initial interest rate	7.375%
First call date	2022-06
Other equity instruments	£ 745	745
300m Perpetual Capital Securities [member]
Disclosure of other equity instruments [line items]
Initial interest rate	7.60%
First call date	2019-12
Other equity instruments	£ 300	300
500m Perpetual Capital Securities [member]
Disclosure of other equity instruments [line items]
Initial interest rate	6.625%
First call date	2019-06
Other equity instruments	£ 500	£ 500

Other Equity Instruments - Su_2

Other Equity Instruments - Summary of Other Equity Instruments (Parenthetical) (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities	£ 500
750m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities	750
300m Perpetual Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities	300
500m Perpetual Capital Securities [member]
Disclosure of other equity instruments [line items]
Capital securities	£ 500

Other Equity Instruments - Addi

Other Equity Instruments - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
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
300m Perpetual Capital Securities [member]
Disclosure of other equity instruments [line items]
Perpetual Capital Securities issued	300
500m Perpetual Capital Securities [member]
Disclosure of other equity instruments [line items]
Perpetual Capital Securities issued	500
Hundred Million Of The Seven Hundred And Fifty Million Fixed Rate Reset Perpetual At One Capital Securities [member]
Disclosure of other equity instruments [line items]
Perpetual Capital Securities issued	100
750m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of other equity instruments [line items]
Perpetual Capital Securities issued	£ 750

Non-Controlling Interests - Sch

Non-Controlling Interests - Schedule of Amounts Attributable to Non-Controlling Interests (Detail) - GBP (£) £ in Millions	May 24, 2019	Dec. 31, 2018	Dec. 31, 2017
Disclosure of noncontrolling interests [line items]
Non-controlling interests		£ 400	£ 401
300m Fixed/Floating Rate Non-Cumulative Callable Preference Shares [member]
Disclosure of noncontrolling interests [line items]
Fixed non-cumulative annual dividend payable percentage	6.222%	6.222%	6.222%
First call date		2019-05	2019-05
Non-controlling interests		£ 14	£ 14
300m Step-up Callable Perpetual Reserve Capital Instruments [member]
Disclosure of noncontrolling interests [line items]
Reserve Capital Instruments annual bear interest rate		7.037%	7.037%
First call date		2026-02	2026-02
Non-controlling interests		£ 235	£ 235
PSA Finance UK Limited [member]
Disclosure of noncontrolling interests [line items]
Non-controlling interests		£ 151	£ 152

Non-Controlling Interests - S_2

Non-Controlling Interests - Schedule of Amounts Attributable to Non-Controlling Interests (Parenthetical) (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of noncontrolling interests [line items]
Notional amount	£ 238,751	£ 1,125,419
300m Fixed/Floating Rate Non-Cumulative Callable Preference Shares [member]
Disclosure of noncontrolling interests [line items]
Notional amount	300	300
300m Step-up Callable Perpetual Reserve Capital Instruments [member]
Disclosure of noncontrolling interests [line items]
Notional amount	£ 300	£ 300

Non-Controlling Interests - Add

Non-Controlling Interests - Additional Information (Detail)	Feb. 14, 2026	May 24, 2019	Dec. 31, 2018	Dec. 31, 2017
300m Fixed/Floating Rate Non-Cumulative Callable Preference Shares [member]
Disclosure of noncontrolling interests [line items]
Fixed non-cumulative annual dividend payable percentage		6.222%	6.222%	6.222%
Fixed non-cumulative quarterly dividend payable percentage		1.13%
300m Step-up Callable Perpetual Reserve Capital Instruments [member]
Disclosure of noncontrolling interests [line items]
Reserve Capital Instruments bear interest rate reset period	5 years
Reserve Capital Instruments benchmark gilt rate period	5 years

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	£ 54,694	£ 60,640
Cash flows from financing activities	5,687	(5,543)	£ (3,159)
Cash flows from operating activities	(2,762)	366
- Unrealised foreign exchange	(1,936)	(920)
- Other changes	5,865	151
Ending Balance	61,548	54,694	60,640
Debt Securities [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	48,860	54,792
Cash flows from financing activities	7,272	(4,986)
Cash flows from operating activities	(2,760)	112
- Unrealised foreign exchange	(2,085)	(685)
- Other changes	4,619	(373)
Ending Balance	55,906	48,860	54,792
Subordinated liabilities [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	3,793	4,303
Cash flows from financing activities	(277)	(52)
Cash flows from operating activities	(2)	254
- Unrealised foreign exchange	149	(235)
- Other changes	(62)	(477)
Ending Balance	3,601	3,793	4,303
Other Equity Instruments [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	2,041	1,545
Cash flows from financing activities		496
Ending Balance	2,041	2,041	£ 1,545
Dividends Paid [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Cash flows from financing activities	(1,308)	(1,001)
- Other changes	£ 1,308	£ 1,001

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, 2018	Dec. 31, 2017
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	£ 3,541	£ 3,598
On-Balance Sheet [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	63,166	75,461
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	1,010
On-Balance Sheet [member] | Trading Assets [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities		17,092
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	35,694	35,421
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	16,402	15,078
On-Balance Sheet [member] | Loans and advances to banks [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	402	105
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	3,763
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	5,825
On-Balance Sheet [member] | Financial investments [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities		6,755
Off-Balance Sheet [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	£ 15,221	£ 33,013

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, 2018	Dec. 31, 2017
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	£ 3,541	£ 3,598
Gross assets charged as security for liabilities	36,195	36,512
Notes issued under securitisation and covered bond programmes retained internally	23,984	20,974
Securities Lending [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	25,910	38,016
Collateral accepted as security for assets	7,745	22,299
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	4,039	4,359
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	1,834	1,834
Cash [member] | Derivative Financial Instruments [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	1,681	3,658
Collateral accepted as security for assets	4,058	3,679
Purchase and resale agreements [member]
Disclosure of assets pledged as security [line items]
Collateral accepted as security for assets	15,728	16,356
Fellow Subsidiaries [member] | Sale and Repurchase Agreements [member]
Disclosure of assets pledged as security [line items]
Assets charged as security for liabilities	17,485	34,310
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	2,383	2,931
Santander UK Plc [member] | Securitisations and Covered Bonds [member]
Disclosure of assets pledged as security [line items]
Gross assets charged as security for liabilities	36,195	36,512
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	£ 501	£ 1,091

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, 2018	Dec. 31, 2017
On-Balance Sheet [member]
Disclosure of assets pledged as security [line items]
Total on-balance sheet/ off-balance sheet	£ 4,058	£ 3,679
On-Balance Sheet [member] | Trading Liabilities [member]
Disclosure of assets pledged as security [line items]
Total on-balance sheet/ off-balance sheet		1,911
On-Balance Sheet [member] | Deposits by customers [member]
Disclosure of assets pledged as security [line items]
Total on-balance sheet/ off-balance sheet		8
On-Balance Sheet [member] | Deposits by banks [member]
Disclosure of assets pledged as security [line items]
Total on-balance sheet/ off-balance sheet	4,058	1,760
Off-Balance Sheet [member]
Disclosure of assets pledged as security [line items]
Total on-balance sheet/ off-balance sheet	£ 23,473	£ 38,655

Share-Based Compensation - Addi

Share-Based Compensation - Additional Information (Detail)	1 Months Ended	3 Months Ended	9 Months Ended	12 Months Ended				120 Months Ended
	Jan. 31, 2015	Mar. 31, 2019	Sep. 30, 2018Scheme	Dec. 31, 2018GBP (£)shares	Dec. 31, 2017GBP (£)shares	Dec. 31, 2016GBP (£)	Dec. 31, 2015award	Dec. 31, 2017GBP (£)Scheme
Disclosure of terms and conditions of share-based payment arrangement [line items]
Liabilities arising from share-based payment transactions				£ 7,700,000	£ 16,700,000			£ 16,700,000
Liabilities arising from share-based payment transactions, vested liabilities				£ 700,000	0			£ 0
Number of sharesave schemes launched | Scheme			11					10
Discount percent on share price under share based compensation plan				10.00%
Weighted average share price				£ 3.79	4.96	£ 3.79
Weighted average grant-date fair value				£ 0.53	£ 1.02	£ 0.65		£ 1.02
Number of shares outstanding | shares				2,346,108	2,147,399
Employees [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Deferred shares description				Any deferred awards are dependent on future service. For 2017 and 2018 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	100.00%	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. 2,346,108 shares were outstanding at 31 December 2018 (2017 2,147,399 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				2,008
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				2,017
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] pure in Thousands	12 Months Ended
	Dec. 31, 2018GBP (£)	Dec. 31, 2017GBP (£)	Dec. 31, 2016GBP (£)
Disclosure of terms and conditions of share-based payment arrangement [line items]
Number of options outstanding beginning balance	27,201	28,916	24,762
Number of options granted	6,210	3,916	17,296
Number of options exercised	(3,340)	(1,918)	(338)
Number of options forfeited/expired	(3,233)	(3,713)	(12,804)
Number of options outstanding ending balance	26,838	27,201	28,916
Number of options exercisable	10,370	5,200	2,334
Weighted average exercise price outstanding beginning balance	£ 3.12	£ 3.08	£ 3.53
Weighted average exercise price granted	3.46	4.02	4.91
Weighted average exercise price exercised	3.16	3.77	3.67
Weighted average exercise price forfeited/expired	3.76	3.40	3.51
Weighted average exercise price outstanding ending balance	3.12	3.12	3.08
Weighted average exercise price exercisable ending balance	£ 2.81	£ 3.17	£ 4.30

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] - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of number and weighted average remaining contractual life of outstanding share options [line items]
Option outstanding, Weighted average exercise price	£ 3.12	£ 3.12	£ 3.08	£ 3.53
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	2 years	3 years
Option outstanding, Weighted average exercise price	£ 2.75	£ 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	3 years	1 year
Option outstanding, Weighted average exercise price	£ 3.36	£ 3.17
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	3 years	3 years
Option outstanding, Weighted average exercise price	£ 4.11	£ 4.21

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, 2018GBP (£)
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, 2018	Dec. 31, 2017		Dec. 31, 2016
2015 LTIP [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Conditional awards at the beginning of the year	£ 6,503	£ 6,718		£ 6,769
Conditional awards forfeited or cancelled	(129)	(215)	[1]	(51)
Conditional awards outstanding at the end of the year	6,374	6,503		6,718
2014 LTIP [member]
Disclosure of terms and conditions of share-based payment arrangement [line items]
Conditional awards at the beginning of the year	1,910	3,193		5,102
Conditional awards forfeited or cancelled	£ (1,910)	(1,283)	[1]	(1,909)
Conditional awards outstanding at the end of the year		£ 1,910		£ 3,193
[1]	The outstanding shares have been updated to compensate for the equity dilution caused by the shares issued by Banco Santander SA in July 2017.

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure Of Remuneration Of Directors And Other Key Management Personnel [abstract]
Salaries and fees	£ 5,028,434	£ 4,406,908	£ 3,604,999
Performance-related payments	5,194,317	3,685,464	2,330,000
Other fixed remuneration (pension and other allowances & non-cash benefits)	1,467,011	1,580,321	635,493
Expenses	25,198	96,358	120,302
Total remuneration	11,714,960	9,769,051	6,690,794
Short-term employee benefits	24,445,189	24,642,085	24,757,161
Post-employment benefits	2,399,261	2,292,857	1,918,144
Total compensation	£ 26,844,450	£ 26,934,942	£ 26,675,305

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, 2018GBP (£)IndividualsDirectorsshares	Dec. 31, 2017GBP (£)Individualsshares	Dec. 31, 2016GBP (£)Individualsshares
Disclosure of directors and key management remuneration [line items]
Payments made as buy-outs of deferred performance-related payment | £	£ 266,667	£ 52,100	£ 2,732,357
Number of previously employed individuals for buy-out of deferred performance related payment | Individuals	1	1	5
Termination payment | £	£ 847,388	£ 0
Number key management persons who receives termination benefit | Directors	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	0
Number of previously employed individuals for buy-out of deferred performance related payment | Individuals	5

Transactions With Directors a_5

Transactions With Directors and Other Key Management Personnel - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2018GBP (£)SecurityLoanDirectorManagers	Dec. 31, 2017GBP (£)SecurityLoanDirector	Dec. 31, 2016GBP (£)
Disclosure of transactions between related parties [line items]
Remuneration excluding pension contribution	£ 4,635,497	£ 4,714,578
Remuneration excluding pension contribution performance related	2,317,000	2,425,000
Deferred pension benefit accruing under a defined benefit scheme	20,402	15,450
Ex gratia pensions paid to former Directors	87,300	2,482	£ 14,893
Sharedealing transactions through the Santander UK group's	£ 0	£ 0
Number of Directors undertook sharedealing transactions | Director	0	0
Loans made to directors	£ 65,232	£ 53,452
Number of loan made to directors | SecurityLoan	8	2
Benefits paid in kind for directors	£ 25,198	£ 96,358	120,302
Benefits paid in kind for key management	£ 26,844,450	£ 26,934,942	£ 26,675,305
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
Banco Santander SA [member]
Disclosure of transactions between related parties [line items]
Loans made to directors	£ 344,348	£ 510,901
Number of loan made to directors | SecurityLoan	1	1
Benefits paid in kind for directors	£ 485,334
Number of directors paid in kind | Director	2
Benefits paid in kind for key management	£ 2,024
Number of key management paid in kind | Managers	1
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	£ 2,969,462	£ 1,162,384
Number of loan made to key management personnel | SecurityLoan	8	5

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, 2018GBP (£)DepositsLoans	Dec. 31, 2017GBP (£)DepositsLoans
Disclosure of directors and key management remuneration [line items]
Number of secured loans, unsecured loans and overdrafts, beginning balance | Loans	7	17
Number of secured loans, unsecured loans and overdrafts, net movements | Loans	9	(10)
Number of secured loans, unsecured loans and overdrafts, ending balance | Loans	16	7
Beginning balance	£ 1,216	£ 5,195
Net movements	1,819	(3,979)
Ending balance	£ 3,035	£ 1,216
Number of deposit, bank and instant access accounts and investments, beginning balance | Deposits	25	26
Number of deposit, bank and instant access accounts and investments, net movements | Deposits	5	(1)
Number of deposit, bank and instant access accounts and investments, ending balance | Deposits	30	25
Beginning balance	£ 13,184	£ 9,138
Net movements	(2,221)	4,046
Ending balance	£ 10,963	£ 13,184

Related Party Disclosures - Sum

Related Party Disclosures - Summary of Transactions With Related Parties (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	£ (182)	£ (156)	£ (379)
Interest, fees and other expenses paid	400	812	842
Amounts owed by related parties	4,762	5,675
Amounts owed to related parties	(5,163)	(6,096)
Ultimate Parent [Member]
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(73)	(60)	(81)
Interest, fees and other expenses paid	231	321	188
Amounts owed by related parties	2,737	4,398
Amounts owed to related parties	(3,854)	(5,082)
Fellow Subsidiaries [member]
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(81)	(76)	(271)
Interest, fees and other expenses paid	169	491	653
Amounts owed by related parties	39	102
Amounts owed to related parties	(591)	(981)
Associates and Joint Ventures [Member]
Disclosure of transactions between related parties [line items]
Interest, fees and other income received	(28)	(20)	(27)
Interest, fees and other expenses paid			£ 1
Amounts owed by related parties	1,986	1,175
Amounts owed to related parties	£ (718)	£ (33)

Related Party Disclosures - Add

Related Party Disclosures - Additional Information (Detail) - GBP (£) £ in Millions	1 Months Ended
	Jul. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of transactions between related parties [line items]
Other assets		£ 2,267	£ 2,511
Liabilities		£ 273,161	£ 298,558	£ 287,057
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

Financial Instruments - Analysi

Financial Instruments - Analysis of Fair Value of Financial Instruments Carried at Amortised (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Deposits by customers	£ 173,692	£ 177,421
Deposits by banks	17,824	12,708
Repurchase agreements - non trading	10,910	1,076
Debt securities in issue	55,906	48,860
Financial investments	3,601	3,793
Loans and advances to customers	201,619	199,332
Loans and advances to banks	3,515	3,466
Reverse repurchase agreements - non trading	21,127	2,614
Financial investments		17,611
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	7,228
Financial assets	233,489	214,170
Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial liabilities	261,933	243,858
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	173,692	177,421
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	17,824	12,708
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	10,910	1,076
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	55,906	48,860
Subordinated liabilities [member] | Financial Liabilities at Amortised Cost, Category [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial investments	3,601	3,793
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	201,619	199,332
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	3,515	3,466
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	21,127	2,614
Financial investments [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial investments		8,758
Level 1 [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	6,390
Financial assets	6,390	6,435
Level 1 [member] | Financial investments [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial investments		6,435
Level 2 [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	720
Financial assets	24,878	14,053
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	88,323	68,263
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	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	16,859	12,164
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	10,923	1,085
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	56,695	50,641
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]
Financial investments	3,825	4,373
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		6,331
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	3,028	2,897
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	21,130	2,614
Level 2 [member] | Financial investments [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial investments		2,211
Level 3 [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial assets	204,839	195,883
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	174,739	178,120
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	173,762	177,563
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	977	557
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]
Financial investments	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	204,391	195,327
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	448	556
Fair Value [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
Financial assets	236,107	216,371
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	263,062	246,383
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	173,783	177,563
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	17,836	12,721
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	10,923	1,085
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	56,695	50,641
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]
Financial investments	3,825	4,373
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	204,391	201,658
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	3,476	3,453
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	£ 21,130	2,614
Fair Value [member] | Financial investments [member] | Financial assets at amortised cost [member]
Disclosure Of Fair Values Of Financial Instruments Carried At Amortised Cost [line items]
Financial investments		£ 8,646

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, 2018	Dec. 31, 2017
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 24,760	£ 61,446
Liabilities at fair value	7,880	51,037
Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value		31,109
Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	1,594	17,613
Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	6,286	2,315
Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		30,555
Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	5,321	19,942
Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	6,137	2,096
Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	13,302
Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		8,853
Level 1 [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	12,527	24,447
Liabilities at fair value		3,695
Level 1 [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value		3,694
Level 1 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value		1
Level 1 [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		15,474
Level 1 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	40	184
Level 1 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	12,487
Level 1 [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		8,789
Level 2 [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	10,990	36,642
Liabilities at fair value	7,761	47,273
Level 2 [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value		27,415
Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	1,524	17,549
Level 2 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	6,237	2,309
Level 2 [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		15,081
Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	5,206	19,878
Level 2 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	5,042	1,672
Level 2 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	742
Level 2 [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		11
Level 3 [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	1,243	357
Liabilities at fair value	119	69
Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	70	63
Level 3 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	49	6
Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	115	64
Level 3 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	1,055	240
Level 3 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 73
Level 3 [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		53
Securities Purchased Under Resale Agreements [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		8,870
Valuation technique	A
Securities Purchased Under Resale Agreements [member] | Level 2 [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		8,870
Debt Securities [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		5,156
Valuation technique	-
Debt Securities [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 3,263	547
Valuation technique	A, B & D
Debt Securities [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 13,229
Valuation technique	D
Debt Securities [member] | Level 1 [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		5,156
Debt Securities [member] | Level 1 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 26	184
Debt Securities [member] | Level 1 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	12,487
Debt Securities [member] | Level 2 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	2,343	187
Debt Securities [member] | Level 2 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	742
Debt Securities [member] | Level 3 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 894	176
Equity securities [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		9,662
Valuation technique	-
Equity securities [member] | Level 1 [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		9,662
Cash Collateral [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value		1,911
Cash Collateral [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		6,156
Valuation technique	A
Cash Collateral [member] | Level 2 [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value		1,911
Cash Collateral [member] | Level 2 [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		6,156
Short-term loans [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		711
Valuation technique	A
Short-term loans [member] | Level 1 [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		656
Short-term loans [member] | Level 2 [member] | Trading Assets [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		55
Exchange Rate Contracts [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 551	4,191
Exchange Rate Contracts [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 4,349	6,077
Valuation technique	A
Exchange Rate Contracts [member] | Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	£ 528	4,176
Exchange Rate Contracts [member] | Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	4,324	6,061
Exchange Rate Contracts [member] | Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	23	15
Exchange Rate Contracts [member] | Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 25	16
Interest Rate Contracts [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	A & C
Liabilities at fair value	£ 2,743	23,204
Interest Rate Contracts [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 2,566	23,447
Valuation technique	A & C
Interest Rate Contracts [member] | Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	£ 2,736	23,199
Interest Rate Contracts [member] | Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	2,560	23,435
Interest Rate Contracts [member] | Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	7	5
Interest Rate Contracts [member] | Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	6	12
Equity and Credit Contracts [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 54	31
Equity and Credit Contracts [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	B & D
Liabilities at fair value	£ 172	697
Equity and Credit Contracts [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 278	897
Valuation technique	B & D
Equity and Credit Contracts [member] | Level 1 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value		1
Equity and Credit Contracts [member] | Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	£ 132	653
Equity and Credit Contracts [member] | Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	194	861
Equity and Credit Contracts [member] | Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	40	43
Equity and Credit Contracts [member] | Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	84	36
Netting [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	(1,872)	(10,479)
Netting [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	(1,872)	(10,479)
Netting [member] | Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	(1,872)	(10,479)
Netting [member] | Level 2 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	(1,872)	(10,479)
Netting [member] | Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities 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 measurement of assets and liabilities [line items]
Assets at fair value	£ 509	1,549
Valuation technique	A
Loans and Advances to Customers [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 73
Valuation technique	D
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 measurement of assets and liabilities [line items]
Assets at fair value	£ 427	1,485
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 measurement of assets and liabilities [line items]
Assets at fair value	82	64
Loans and Advances to Customers [member] | Level 3 [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	73
Equity Securities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	35	43
Equity Securities [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 93
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 measurement of assets and liabilities [line items]
Assets at fair value	£ 14
Equity Securities [member] | Level 3 [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 79
Reverse repurchase agreements - non-trading [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 2,110
Reverse repurchase agreements - non-trading [member] | Other Financial assets at fair value through profit or loss, category [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value	£ 2,272
Valuation technique	A
Reverse repurchase agreements - non-trading [member] | Level 2 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	£ 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 measurement of assets and liabilities [line items]
Assets at fair value	2,272
Reverse repurchase agreements - non-trading [member] | Level 3 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	£ 0
Available for sale debt securities [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		8,772
Valuation technique	C
Available for sale debt securities [member] | Level 1 [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		8,770
Available for sale debt securities [member] | Level 2 [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		2
Available for sale equity securities [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		81
Valuation technique	B
Available for sale equity securities [member] | Level 1 [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		19
Available for sale equity securities [member] | Level 2 [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		9
Available for sale equity securities [member] | Level 3 [member] | Financial investments [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Assets at fair value		53
Securities Sold Under Repurchase Agreements [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value		25,504
Securities Sold Under Repurchase Agreements [member] | Level 2 [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value		25,504
Short Positions in Securities and Unsettled Trades [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	-
Liabilities at fair value		3,694
Short Positions in Securities and Unsettled Trades [member] | Level 1 [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value		3,694
Short-term Deposits [member] | Trading Liabilities [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	-
Debt Securities [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 990	1,635
Debt Securities [member] | Level 2 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	983	1,629
Debt Securities [member] | Level 3 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	£ 7	6
Structured Deposits [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	A
Liabilities at fair value	£ 133	680
Structured Deposits [member] | Level 2 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	104	£ 680
Structured Deposits [member] | Level 3 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	£ 29
Collateral and associated financial guarantees [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Valuation technique	D
Liabilities at fair value	£ 3,053
Collateral and associated financial guarantees [member] | Level 2 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	3,040
Collateral and associated financial guarantees [member] | Level 3 [member] | Other financial liabilities designated at fair value through profit or loss [member]
Disclosure of fair value measurement of assets and liabilities [line items]
Liabilities at fair value	£ 13

Financial Instruments - Additio

Financial Instruments - Additional Information (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of financial assets [abstract]
Fair value of financial instruments transferred from Level 1 to Level 2	£ 0	£ 0
Fair value of financial instruments transferred from Level 2 to Level 1	0	0
Fair value of financial instruments transferred from Level 2 to Level 3, Derivative assets	56,000,000
Fair value of financial instruments transferred from Level 2 to Level 3, Derivative liabilities	35,000,000
Exposure to wrong-way risk	£ 0	£ 0

Financial Instruments - Summary

Financial Instruments - Summary of Fair Value Adjustment (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of financial assets [line items]
Fair value adjustments	£ 67	£ 128
Bid-Offer and Trade Specific Adjustments [Member]
Disclosure of financial assets [line items]
Fair value adjustments	13	34
Uncertainty [Member]
Disclosure of financial assets [line items]
Fair value adjustments	36	43
Credit Risk Adjustment [Member]
Disclosure of financial assets [line items]
Fair value adjustments	9	36
Funding Fair Value Adjustment [Member]
Disclosure of financial assets [line items]
Fair value adjustments	4	6
Risk Related Adjustments [Member]
Disclosure of financial assets [line items]
Fair value adjustments	62	119
Model-Related [Member]
Disclosure of financial assets [line items]
Fair value adjustments	£ 5	8
Day One Profit [Member]
Disclosure of financial assets [line items]
Fair value adjustments		£ 1

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, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of financial assets [line items]
FVTPL	£ 6,137	£ 2,096
FVOCI	13,302
Total net assets	1,124	288
Total (expense)/income	25	(34)	£ 7
Level 3 [member]
Disclosure of financial assets [line items]
Other Level 3 liabilities	(71)	(26)
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	37	(48)
Other Level 3 [member]
Disclosure of financial assets [line items]
Financial assets and liabilities	1,105	281
Financial asset liabilities	24	(27)	11
Other Level 3 [member] | Level 3 [member]
Disclosure of financial assets [line items]
Other Level 3 assets	90	33
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)		(26)	6
Derivative liabilities and other Level 3 liabilities, fair value movements recognised in profit/(loss)	1	19	(10)
Reversionary property securities [member] | Equity and Credit Contracts [member]
Disclosure of financial assets [line items]
Derivative assets	54	31
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	30	(6)	12
Reversionary property securities [member] | Debt Securities [member]
Disclosure of financial assets [line items]
FVTPL	142	176
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	(28)	(18)
Loans and Advances to Customers [member] | Roll-up Mortgage Portfolio [member]
Disclosure of financial assets [line items]
FVTPL	53	64
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	8	2	4
Loans and Advances to Customers [member] | Other Loans [member] | Financial assets at fair value through other comprehensive income [member]
Disclosure of financial assets [line items]
FVOCI	73
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	(5)
Unlisted Equity Shares [member] | Equity Securities [member]
Disclosure of financial assets [line items]
FVTPL	79	53
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	19
Credit Linked Note [member] | Debt Securities [member]
Disclosure of financial assets [line items]
FVTPL	752
Derivative assets and other Level 3 assets, fair value movements recognised in profit/(loss)	13
Property Related Options and Forwards [Member] | Equity Securities [member]
Disclosure of financial assets [line items]
Derivative liabilities	(35)	(43)
Derivative liabilities and other Level 3 liabilities, fair value movements recognised in profit/(loss)		£ (5)	£ (5)
Credit Protection Guarantees [member] | Financial Guarantees [member]
Disclosure of financial assets [line items]
FVTPL	(13)
Derivative liabilities and other Level 3 liabilities, fair value movements recognised in profit/(loss)	£ (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, 2018	Dec. 31, 2017
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	£ (298,558)	£ (287,057)
Transfers in	(35)
Ending Balance	(273,161)	(298,558)
Level 3 [member] | Fair Value Through P&L [member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	(6)	(6)
Adoption of IFRS 9	0
At 1 January 2018	(6)
Total (losses)/gains recognised in profit/loss, fair value movements	(13)
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	(1)
Transfers in	(29)
Gains recognised in other comprehensive income		0
Sales	0	0
Ending Balance	(49)	(6)
(Losses)/gains recognised in profit or loss relating to assets and liabilities held at the end of the year	(14)
Level 3 [member] | Financial Liabilities at Fair Value, Class [member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	(69)	(80)
Adoption of IFRS 9	0
At 1 January 2018	(69)
Total (losses)/gains recognised in profit/loss, fair value movements	(12)	14
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	4	(32)
Transfers in	(64)
Gains recognised in other comprehensive income		0
Additions		(2)
Sales	0	0
Settlements	22	31
Ending Balance	(119)	(69)
(Losses)/gains recognised in profit or loss relating to assets and liabilities held at the end of the year	(8)	(18)
Level 3 [member] | Derivative Liabilities [Member]
Disclosure of fair value measurement of liabilities [line items]
Beginning balance	(63)	(74)
Adoption of IFRS 9	0
At 1 January 2018	(63)
Total (losses)/gains recognised in profit/loss, fair value movements	1	14
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	5	(32)
Transfers in	(35)
Gains recognised in other comprehensive income		0
Additions		(2)
Sales	0	0
Settlements	22	31
Ending Balance	(70)	(63)
(Losses)/gains recognised in profit or loss relating to assets and liabilities held at the end of the year	£ 6	£ (18)

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, 2018	Dec. 31, 2017
Disclosure of financial assets [line items]
Beginning balance	£ 314,760	£ 302,510
Transfers in	56
Ending Balance	289,381	314,760
Level 3 [member]
Disclosure of financial assets [line items]
Beginning balance	357	399
Adoption of IFRS 9	744
At 1 January 2018	1,101
Total (losses)/gains recognised in profit/loss, fair value movements	37	(48)
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	(5)	32
Transfers in	74
Gains recognised in other comprehensive income		21
Additions	297	9
Sales	(95)	(8)
Settlements	(166)	(48)
Ending Balance	1,243	357
(Losses)/gains recognised in profit or loss relating to assets and liabilities held at the end of the year	32	(16)
Level 3 [member] | Fair Value Through P&L [Member]
Disclosure of financial assets [line items]
Beginning balance	240	264
Adoption of IFRS 9	598
At 1 January 2018	838
Total (losses)/gains recognised in profit/loss, fair value movements	14	(16)
Transfers in	18
Additions	280
Sales	(95)	(8)
Ending Balance	1,055	240
(Losses)/gains recognised in profit or loss relating to assets and liabilities held at the end of the year	14	(16)
Level 3 [member] | Financial assets at FVOCI [member]
Disclosure of financial assets [line items]
Adoption of IFRS 9	199
At 1 January 2018	199
Total (losses)/gains recognised in profit/loss, fair value movements	(5)
Additions	17
Settlements	(138)
Ending Balance	73
(Losses)/gains recognised in profit or loss relating to assets and liabilities held at the end of the year	(5)
Level 3 [member] | Derivative Financial Instruments [member]
Disclosure of financial assets [line items]
Beginning balance	64	103
At 1 January 2018	64
Total (losses)/gains recognised in profit/loss, fair value movements	28	(32)
Total (losses)/gains recognised in profit/loss, foreign exchange and other movements	(5)	32
Transfers in	56
Additions		9
Sales		0
Settlements	(28)	(48)
Ending Balance	115	64
(Losses)/gains recognised in profit or loss relating to assets and liabilities held at the end of the year	23
Level 3 [member] | Financial investments [member]
Disclosure of financial assets [line items]
Beginning balance	53	32
Adoption of IFRS 9	£ (53)
Gains recognised in other comprehensive income		21
Ending Balance		£ 53

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, 2018GBP (£)Index	Dec. 31, 2017GBP (£)Index
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ (7,880)	£ (51,037)
Fair value	24,760	61,446
Equity and Credit Contracts [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ 54	£ 31
Assumption description	HPI Forward growth rate HPI Spot rate	HPI Forward growth rate HPI Spot rate
Shift	1.00%	1.00%
Favourable changes	£ 8	£ 10
Unfavourable changes	£ (8)	£ (10)
Equity and Credit Contracts [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	£ 7	£ 8
Unfavourable changes	£ (7)	£ (8)
HPI spot rate index level | Index	783	773
Equity Securities [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ (35)	£ (43)
Assumption description	HPI Forward growth rate HPI Spot rate	HPI Forward growth rate HPI Spot rate
Shift	1.00%	1.00%
Favourable changes	£ 2	£ 3
Unfavourable changes	£ (2)	£ (3)
Equity Securities [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	£ 7
Unfavourable changes	£ (4)	£ (8)
HPI spot rate index level | Index	722	727
Bottom of Range [member] | Equity Securities [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]
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 Securities [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	2.68%	2.42%
Weighted average [member] | Equity Securities [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	2.59%	2.32%
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	£ 142	£ 176
Assumption description	HPI Forward growth rate HPI Spot rate	HPI Forward growth rate HPI Spot rate
Shift	1.00%	1.00%
Favourable changes	£ 6	£ 3
Unfavourable changes	£ (6)	£ (3)
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	£ 10	£ 11
Unfavourable changes	£ (10)	£ (11)
HPI spot rate index level | Index	783	773
Fair Value Through P&L [Member] | Equity Securities [member] | Unlisted Equity Shares [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value	£ 79
Assumption description	Contingent litigation risk
Shift	20.00%
Favourable changes	£ 6
Unfavourable changes	(6)
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	£ 53	£ 64
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] | Top of Range [member] | Debt 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] | Equity Securities [member] | Unlisted Equity Shares [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	100.00%
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] | Weighted average [member] | Debt Securities [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	2.68%	2.42%
Fair Value Through P&L [Member] | Weighted average [member] | Equity Securities [member] | Unlisted Equity Shares [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value	29.00%
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	2.77%	2.57%
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	£ 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	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	£ 73
Assumption description	Credit spreads
Shift	20.00%
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	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	0.80%
Available-for-Sale [member] | Equity Securities [member] | Unlisted Equity Shares [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Fair value		£ 53
Assumption description		Contingent litigation risk
Shift		20.00%
Favourable changes		£ 6
Unfavourable changes		£ (6)
Available-for-Sale [member] | Top of Range [member] | Equity Securities [member] | Unlisted Equity Shares [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value		100.00%
Available-for-Sale [member] | Weighted average [member] | Equity Securities [member] | Unlisted Equity Shares [member]
Effect of changes in significant unobservable assumptions to reasonably possible alternatives - Level 3 [line items]
Assumption value		35.00%

Financial Instruments - Maturit

Financial Instruments - Maturities of Undiscounted Cash Flows for Financial Liabilities and Off Balance Sheet Commitments (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Trading liabilities		£ 31,109
Other financial liabilities at fair value through profit or loss	£ 6,286	2,315
Deposits by customers	173,692	177,421
Deposits by banks	17,824	12,708
Repurchase agreements - non trading	10,910	1,076
Debt securities in issue	55,906	48,860
Subordinated liabilities	3,601	3,793
Undiscounted Cash Flow [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Trading liabilities		31,327
Derivative financial instruments	1,766	18,802
Other financial liabilities at fair value through profit or loss	6,496	2,377
Deposits by customers	173,975	177,623
Deposits by banks	18,051	12,833
Repurchase agreements - non trading	11,441	1,081
Debt securities in issue	58,808	50,953
Subordinated liabilities	6,377	6,790
Financial liabilities	276,914	301,786
Off-balance sheet commitments given	40,024	42,059
Undiscounted Cash Flow [member] | On Demand [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Trading liabilities		1,520
Derivative financial instruments		15
Other financial liabilities at fair value through profit or loss	11	7
Deposits by customers	151,284	154,114
Deposits by banks	5,692	2,452
Repurchase agreements - non trading	2
Financial liabilities	156,989	158,108
Off-balance sheet commitments given	1,106	2,082
Undiscounted Cash Flow [member] | Not Later Than Three Months [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Trading liabilities		26,914
Derivative financial instruments	431	631
Other financial liabilities at fair value through profit or loss	2,146	545
Deposits by customers	4,640	4,754
Deposits by banks	1,108	1,465
Repurchase agreements - non trading	9,101	1
Debt securities in issue	9,194	8,419
Subordinated liabilities	255	289
Financial liabilities	26,875	43,018
Off-balance sheet commitments given	5,843	6,874
Undiscounted Cash Flow [member] | Later Than Three Months and Not Later Than One Year [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Trading liabilities		152
Derivative financial instruments	61	1,230
Other financial liabilities at fair value through profit or loss	76	222
Deposits by customers	11,350	13,811
Deposits by banks	93	82
Repurchase agreements - non trading	972	832
Debt securities in issue	5,677	4,940
Subordinated liabilities	134	147
Financial liabilities	18,363	21,416
Off-balance sheet commitments given	670	1,844
Undiscounted Cash Flow [member] | Later Than One Year and Not Later Than Five Years [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Trading liabilities		161
Derivative financial instruments	104	2,925
Other financial liabilities at fair value through profit or loss	408	789
Deposits by customers	5,328	3,454
Deposits by banks	11,106	8,626
Repurchase agreements - non trading	849	248
Debt securities in issue	28,553	25,950
Subordinated liabilities	709	783
Financial liabilities	47,057	42,936
Off-balance sheet commitments given	13,418	12,399
Undiscounted Cash Flow [member] | Later Than Five Years [member]
Disclosure Of Maturity Analysis For Financial Liabilities [line items]
Trading liabilities		2,580
Derivative financial instruments	1,170	14,001
Other financial liabilities at fair value through profit or loss	3,855	814
Deposits by customers	1,373	1,490
Deposits by banks	52	208
Repurchase agreements - non trading	517
Debt securities in issue	15,384	11,644
Subordinated liabilities	5,279	5,571
Financial liabilities	27,630	36,308
Off-balance sheet commitments given	£ 18,987	£ 18,860

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, 2018	Dec. 31, 2017
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	£ 40,913	£ 53,967
Amounts offset, Assets	(6,786)	(18,292)
Net amounts reported on the balance sheet, Assets	34,127	35,675
Financial instruments, Assets	(3,654)	(15,127)
Financial collateral, Assets	(22,811)	(13,914)
Net amount, Assets	7,662	6,634
Assets not subject to enforceable netting arrangements, Assets	199,727	198,549
Balance sheet total, Assets	233,854	234,224
Gross amounts, Liabilities	22,917	63,461
Amounts offset, Liabilities	(6,786)	(18,292)
Net amounts reported on the balance sheet, Liabilities	16,131	45,169
Financial instruments, Liabilities	(3,654)	(15,127)
Financial collateral, Liabilities	(11,104)	(28,678)
Net amount, Liabilities	1,373	1,364
Assets not subject to enforceable netting arrangements, Liabilities	189,999	189,153
Balance sheet total, Liabilities	206,130	234,322
Derivative Financial Liabilities [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Liabilities	3,412	27,839
Amounts offset, Liabilities	(1,872)	(10,479)
Net amounts reported on the balance sheet, Liabilities	1,540	17,360
Financial instruments, Liabilities	(933)	(14,772)
Financial collateral, Liabilities	(303)	(1,951)
Net amount, Liabilities	304	637
Assets not subject to enforceable netting arrangements, Liabilities	54	253
Balance sheet total, Liabilities	1,594	17,613
Amortised cost [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	24,733	2,614
Amounts offset, Assets	(3,606)
Net amounts reported on the balance sheet, Assets	21,127	2,614
Financial instruments, Assets	(2,721)
Financial collateral, Assets	(18,406)	(2,614)
Balance sheet total, Assets	21,127	2,614
Gross amounts, Liabilities	14,516	1,076
Amounts offset, Liabilities	(3,606)
Net amounts reported on the balance sheet, Liabilities	10,910	1,076
Financial instruments, Liabilities	(2,721)
Financial collateral, Liabilities	(8,189)	(1,076)
Balance sheet total, Liabilities	10,910	1,076
Fair Value [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	2,272	15,224
Amounts offset, Assets		(6,354)
Net amounts reported on the balance sheet, Assets	2,272	8,870
Financial instruments, Assets		(355)
Financial collateral, Assets	(2,272)	(8,515)
Balance sheet total, Assets	2,272	8,870
Gross amounts, Liabilities	2,110	31,858
Amounts offset, Liabilities		(6,354)
Net amounts reported on the balance sheet, Liabilities	2,110	25,504
Financial instruments, Liabilities		(355)
Financial collateral, Liabilities	(2,110)	(25,149)
Balance sheet total, Liabilities	2,110	25,504
Deposits by Customers and Banks [Member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Liabilities	2,879	2,688
Amounts offset, Liabilities	(1,308)	(1,459)
Net amounts reported on the balance sheet, Liabilities	1,571	1,229
Financial collateral, Liabilities	(502)	(502)
Net amount, Liabilities	1,069	727
Assets not subject to enforceable netting arrangements, Liabilities	189,945	188,900
Balance sheet total, Liabilities	191,516	190,129
Derivative Financial Instruments [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	7,088	30,155
Amounts offset, Assets	(1,872)	(10,479)
Net amounts reported on the balance sheet, Assets	5,216	19,676
Financial instruments, Assets	(933)	(14,772)
Financial collateral, Assets	(2,133)	(2,785)
Net amount, Assets	2,150	2,119
Assets not subject to enforceable netting arrangements, Assets	105	266
Balance sheet total, Assets	5,321	19,942
Loans and Advances to Customers [member]
Disclosure of offsetting of financial assets and liabilities [line items]
Gross amounts, Assets	6,820	5,974
Amounts offset, Assets	(1,308)	(1,459)
Net amounts reported on the balance sheet, Assets	5,512	4,515
Net amount, Assets	5,512	4,515
Assets not subject to enforceable netting arrangements, Assets	199,622	198,283
Balance sheet total, Assets	£ 205,134	£ 202,798

Ring-Fencing - Additional Infor

Ring-Fencing - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of cost and expenses by nature [abstract]
Total cost incurred in relation to compliance with ring-rencing legislation	£ 240

Transition to IFRS 9 - Summary

Transition to IFRS 9 - Summary of Measurement Categories and Carrying Amounts of Financial Assets Determined in Accordance with IAS 39 and IFRS 9 (Detail) - GBP (£) £ in Millions	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Transition to IFRS 9 [line items]
Re-classifications	£ (49)
Re-measurement	211	£ 211
Ending balance before re-presentation	314,500
Beginning balance	314,500	£ 289,381	£ 314,760	£ 302,510
IFRS 9 [member] | Other financial assets at amortised cost [member]
Transition to IFRS 9 [line items]
Re-presentation	7,776
Beginning balance	7,776
IFRS 9 [member] | Financial assets at FVOCI [member]
Transition to IFRS 9 [line items]
Re-presentation	8,942
Beginning balance	8,942
IFRS 9 [member] | Cash and Balances at Central Banks [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	32,771
Beginning balance	32,771
IFRS 9 [member] | Trading Assets [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	30,555
Re-presentation	(19)
Beginning balance	30,536
IFRS 9 [member] | Trading Assets [member] | FVOCI [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	19
Re-presentation	(19)
IFRS 9 [member] | Trading Assets [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	30,536
Beginning balance	30,536
IFRS 9 [member] | Derivative Financial Instruments [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	19,942
Beginning balance	19,942
IFRS 9 [member] | Financial assets designated at fair value [member]
Transition to IFRS 9 [line items]
Re-classifications	(45)
Ending balance before re-presentation	2,051
Re-presentation	204
Beginning balance	2,255
IFRS 9 [member] | Financial assets designated at fair value [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Re-classifications	(45)
Ending balance before re-presentation	977
Re-presentation	(977)
IFRS 9 [member] | Financial assets designated at fair value [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	238
Re-presentation	1,181
Beginning balance	1,419
IFRS 9 [member] | Financial assets designated at fair value [member] | FVTPL (Designated) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	836
Beginning balance	836
IFRS 9 [member] | Loans and Advances to Customers [member]
Transition to IFRS 9 [line items]
Re-classifications	(1)
Re-measurement	(211)
Ending balance before re-presentation	199,120
Re-presentation	706
Beginning balance	199,826
IFRS 9 [member] | Loans and Advances to Customers [member] | FVOCI [member]
Transition to IFRS 9 [line items]
Re-classifications	(1)
Ending balance before re-presentation	180
Re-presentation	(180)
IFRS 9 [member] | Loans and Advances to Customers [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Re-measurement	(211)
Ending balance before re-presentation	198,849
Re-presentation	977
Beginning balance	199,826
IFRS 9 [member] | Loans and Advances to Customers [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	91
Re-presentation	(91)
IFRS 9 [member] | Loans and advances to banks [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	3,466
Beginning balance	3,466
IFRS 9 [member] | Reverse repurchase agreements - non-trading [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	2,614
Beginning balance	2,614
IFRS 9 [member] | Financial investments [member]
Transition to IFRS 9 [line items]
Re-classifications	(2)
Ending balance before re-presentation	17,609
Re-presentation	(17,609)
IFRS 9 [member] | Financial investments [member] | FVOCI [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	8,743
Re-presentation	(8,743)
IFRS 9 [member] | Financial investments [member] | Amortised cost [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	1,198
Re-presentation	(1,198)
IFRS 9 [member] | Financial investments [member] | FVTPL (Mandatory) [member]
Transition to IFRS 9 [line items]
Re-classifications	(2)
Ending balance before re-presentation	980
Re-presentation	(980)
IFRS 9 [member] | Financial investments [member] | FVTPL (Mandatory)1 [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	29
Re-presentation	(29)
IFRS 9 [member] | Financial investments [member] | Amortised cost1 [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	6,578
Re-presentation	(6,578)
IFRS 9 [member] | Financial investments [member] | FVTPL (Mandatory)2 [member]
Transition to IFRS 9 [line items]
Ending balance before re-presentation	81
Re-presentation	(81)
IFRS 9 [member] | Other Assets [member]
Transition to IFRS 9 [line items]
Re-classifications	(1)
Ending balance before re-presentation	6,372
Beginning balance	6,372
IAS 39 [member] | Cash and Balances at Central Banks [member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	32,771
IAS 39 [member] | Trading Assets [member]
Transition to IFRS 9 [line items]
Beginning balance	30,555
IAS 39 [member] | Trading Assets [member] | FVOCI [member]
Transition to IFRS 9 [line items]
Beginning balance	19
IAS 39 [member] | Trading Assets [member] | FVTPL [member]
Transition to IFRS 9 [line items]
Beginning balance	30,536
IAS 39 [member] | Derivative Financial Instruments [member] | FVTPL (Trading) [member]
Transition to IFRS 9 [line items]
Beginning balance	19,942
IAS 39 [member] | Loans and Advances to Customers [member]
Transition to IFRS 9 [line items]
Beginning balance	199,332
IAS 39 [member] | Loans and Advances to Customers [member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	199,060
IAS 39 [member] | Loans and Advances to Customers [member] | Loans and receivable securities1 [member]
Transition to IFRS 9 [line items]
Beginning balance	181
IAS 39 [member] | Loans and Advances to Customers [member] | Loans and receivable securities2 [member]
Transition to IFRS 9 [line items]
Beginning balance	91
IAS 39 [member] | Loans and advances to banks [member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	3,466
IAS 39 [member] | Reverse repurchase agreements - non-trading [member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	2,614
IAS 39 [member] | Financial investments [member]
Transition to IFRS 9 [line items]
Beginning balance	17,611
IAS 39 [member] | Financial investments [member] | Loans and receivable securities [member]
Transition to IFRS 9 [line items]
Beginning balance	1,198
IAS 39 [member] | Financial investments [member] | Loans and receivable securities1 [member]
Transition to IFRS 9 [line items]
Beginning balance	982
IAS 39 [member] | Financial investments [member] | Available for sale financial assets [member]
Transition to IFRS 9 [line items]
Beginning balance	8,743
IAS 39 [member] | Financial investments [member] | Available for sale financial assets1 [member]
Transition to IFRS 9 [line items]
Beginning balance	29
IAS 39 [member] | Financial investments [member] | Held to maturity investments [member]
Transition to IFRS 9 [line items]
Beginning balance	6,578
IAS 39 [member] | Financial investments [member] | Available for sale financial assets2 [member]
Transition to IFRS 9 [line items]
Beginning balance	81
IAS 39 [member] | Other Assets [member]
Transition to IFRS 9 [line items]
Beginning balance	6,373
IAS 39 [member] | Other financial assets designated at fair value through profit or loss [member]
Transition to IFRS 9 [line items]
Beginning balance	2,096
IAS 39 [member] | Other financial assets designated at fair value through profit or loss [member] | FVTPL (Designated) [member]
Transition to IFRS 9 [line items]
Beginning balance	1,022
IAS 39 [member] | Other financial assets designated at fair value through profit or loss [member] | FVTPL1 (Designated) [member]
Transition to IFRS 9 [line items]
Beginning balance	836
IAS 39 [member] | Other financial assets designated at fair value through profit or loss [member] | FVTPL2 (Designated) [member]
Transition to IFRS 9 [line items]
Beginning balance	£ 238

Transition to IFRS 9 - Summar_2

Transition to IFRS 9 - Summary of Measurement Categories and Carrying Amounts of Financial Assets Determined in Accordance with IAS 39 and IFRS 9 (Parenthetical) (Detail) - GBP (£) £ in Millions	Jan. 01, 2018	Dec. 31, 2018	Dec. 31, 2017
Transition to IFRS 9 [line items]
Re-measurement	£ 211	£ 211
Financial assets at FVOCI		13,302
Financial assets at FVTPL		6,137	£ 2,096
Loans and advances to customers		201,619	199,332
Financial investments			17,611
IFRS 9 [member]
Transition to IFRS 9 [line items]
Increase in deferred tax asset	68
Other financial assets at FVTPL	1,181
IFRS 9 [member] | Allowance for credit losses [member]
Transition to IFRS 9 [line items]
Re-measurement	211
IFRS 9 [member] | Reclassifications [member]
Transition to IFRS 9 [line items]
Increase in deferred tax asset	14
IFRS 9 [member] | Remeasurements [member]
Transition to IFRS 9 [line items]
Increase in deferred tax asset	54
FVOCI [member] | IFRS 9 [member]
Transition to IFRS 9 [line items]
Financial assets at FVOCI	8,942
Downward remeasurement of loans and receivables	1
FVTPL [member]
Transition to IFRS 9 [line items]
Other financial assets at FVTPL	238
FVTPL [member] | IFRS 9 [member]
Transition to IFRS 9 [line items]
Trading assets	199
Financial assets at FVTPL	19
Downward remeasurement of loans and receivables	2
Amortised cost [member] | IFRS 9 [member]
Transition to IFRS 9 [line items]
Loans and advances to customers	180
Other financial assets at FVTPL	7,776
Financial investments	980
Available-for-Sale [member] | IFRS 9 [member]
Transition to IFRS 9 [line items]
Financial investments	110
Santander UK Group [member] | Amortised cost [member] | IFRS 9 [member]
Transition to IFRS 9 [line items]
Downward remeasurement of financial asset	45
Loans and advances to customers	977
Loans and Advances to Customers [member]
Transition to IFRS 9 [line items]
Financial assets at FVTPL		£ 509	£ 1,549
Loans and Advances to Customers [member] | IFRS 9 [member]
Transition to IFRS 9 [line items]
Re-measurement	(211)
Loans and Advances to Customers [member] | Amortised cost [member] | IFRS 9 [member]
Transition to IFRS 9 [line items]
Re-measurement	(211)
Loans and advances to customers	91
Financial investments [member] | Available-for-Sale [member] | IFRS 9 [member]
Transition to IFRS 9 [line items]
Financial investments	8,743
Provisions for off-balance sheet exposures (IAS 37/IFRS 9) [member] | Financial guarantee contracts [member] | IFRS 9 [member] | Allowance for credit losses [member]
Transition to IFRS 9 [line items]
Re-measurement	£ 50

Transition to IFRS 9 - Disclosu

Transition to IFRS 9 - Disclosure of Statutory Balance Sheet Reconciliation under IAS 39 and IFRS 9 (Detail) - IFRS 9 [member] - Financial Assets at Amortised Cost, Category [member] £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of financial assets [line items]
To amortised cost from FVPTL	£ 1,347
Fair value gain that would have been recognised during the year if the financial asset had not been reclassified	£ 120

Transition to IFRS 9 - Addition

Transition to IFRS 9 - Additional Information (Detail) - IFRS 9 [member] £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Transition to IFRS 9 [line items]
Effective interest rate	3.35%
Interest income recognized	£ 21

Events After the Balance Shee_2

Events After the Balance Sheet Date - Additional Information (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)Branch
Disclosure of non-adjusting events after reporting period [abstract]
Description of nature of Non adjusting event after reporting period	There have been no significant events between 31 December 2018 and the date of approval of these financial statements which would require a change to or additional disclosure in the financial statements, except for the following: In January 2019, we announced plans to reshape our branch network and close 140 branches in response to changes in how customers are choosing to carry out their banking. Our future branch network, with approximately 615 branches, will be made up of a combination of larger branches offering improved community facilities to support local businesses and customers, and smaller branches using the latest technology to offer customers more convenient access to banking services. Furthermore, in order to deliver a branch network for the future, 100 branches will be refurbished over the next two years through an investment of £55m. At 31 December 2018, no provision was recognised in respect of these plans as the relevant criteria under IAS 37 ‘Provisions, contingent liabilities and contingent assets’ had not been met.
Estimated investment to refurbish 100 branches | £	£ 55
Number of branches being closed	140
Number of branches in our future branch network	615

Financial Statements - Addition

Financial Statements - Additional Information - Parent (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Profit after tax attributable to shareholders	£ 1,121	£ 1,254	£ 1,317
Profit after tax attributable to shareholders, dividend receipts	668
Santander UK Group Holdings plc [member]
Condensed Financial Statements, Captions [Line Items]
Profit after tax attributable to shareholders	1,253	659
Profit after tax attributable to shareholders, dividend receipts	£ 668	£ 0

Operating Expenses Before Impai

Operating Expenses Before Impairment Losses, Provisions and Charges - Additional Information - Parent (Detail) £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)Employee	Dec. 31, 2017GBP (£)Employee	Dec. 31, 2016GBP (£)
Disclosure Of Operating Expense [line items]
Wages and salaries	£ 905	£ 746	£ 731
Santander UK Group Holdings plc [member]
Disclosure Of Operating Expense [line items]
Wages and salaries	£ 3	£ 3
Number of full-time staff | Employee	0	0

Loans and Advances to Banks - S

Loans and Advances to Banks - Summary of Loans and Advances to Banks - Parent (Detail) - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of loans and advances to banks [line items]
Loans and advances to banks	£ 3,515	£ 3,466
Santander UK Group Holdings plc [member]
Disclosure of loans and advances to banks [line items]
Loans and advances to banks	9,214	6,260
Santander UK Group Holdings plc [member] | Placements with Other Banks [member]
Disclosure of loans and advances to banks [line items]
Loans and advances to banks	8	3
Santander UK Group Holdings plc [member] | Amounts Due from Santander UK Group Undertakings [member]
Disclosure of loans and advances to banks [line items]
Loans and advances to banks	£ 9,206	£ 6,257

Loans and Advances to Banks - A

Loans and Advances to Banks - Additional Information - Parent (Detail) - GBP (£)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Santander UK Group Holdings plc [member]
Disclosure of loans and advances to banks [line items]
Impairment losses	£ 0	£ 0

Other Financial Assets At Amo_4

Other Financial Assets At Amortised Cost - Additional Information - Parent (Detail)	12 Months Ended
	Dec. 31, 2018
Santander UK Group Holdings plc [member] | Later than 10 years [member]
Financial Assets At Fair Value Through Profit Or Loss [line items]
Maturity of financial investments	10 years

Financial Investments - Additio

Financial Investments - Additional Information - Parent (Detail)	12 Months Ended
	Dec. 31, 2018
Santander UK Group Holdings plc [member] | Later than 10 years [member]
Disclosure of financial investments [line items]
Maturity of financial investments	10 years

Interests in Other Entities -_5

Interests in Other Entities - Summary of Interest in Other Entities - Parent (Detail) - Santander UK Group Holdings plc [member] - GBP (£) £ in Millions	Dec. 31, 2018	Dec. 31, 2017
Disclosure of interest in other entities [line items]
Interests in other entities	£ 13,400	£ 13,313
Fellow Subsidiaries [member] | Ordinary Share Capital [member]
Disclosure of interest in other entities [line items]
Interests in other entities	11,645	11,268
500m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of interest in other entities [line items]
Interests in other entities	495	495
750m Fixed Rate Reset Perpetual AT1 Capital Securities [member]
Disclosure of interest in other entities [line items]
Interests in other entities	750	750
300m Perpetual Capital Securities [member]
Disclosure of interest in other entities [line items]
Interests in other entities	300	300
500m Perpetual Capital Securities [member]
Disclosure of interest in other entities [line items]
Interests in other entities	£ 210	£ 500

Interests in Other Entities -_6

Interests in Other Entities - Additional Information - Parent (Detail)	12 Months Ended
	Dec. 31, 2018GBP (£)Associate	Dec. 31, 2017GBP (£)Associate
Disclosure of subsidiaries [line items]
Ownership interest in share capital	100.00%
Santander UK Group Holdings plc [member]
Disclosure of subsidiaries [line items]
Impairment loss	£ 0	£ 0
Number of associates | Associate	0	0
Ownership interest in share capital	100.00%
Santander UK Group Holdings plc [member] | Santander Equity Investments Limited [member]
Disclosure of subsidiaries [line items]
Percentage of share capital acquired	100.00%
Consideration of acquisition equal to book value of the associated assets and liabilities	£ 40,000,000
Santander UK Group Holdings plc [member] | Abbey national treasury services plc [member]
Disclosure of subsidiaries [line items]
Percentage of share capital acquired	100.00%
Consideration of acquisition equal to book value of the associated assets and liabilities	£ 337,000,000

Interest in other entities - Su

Interest in other entities - Summary of interests in subsidiaries (Detail) - Santander UK Group Holdings plc [member] £ in Millions	12 Months Ended
	Dec. 31, 2018GBP (£)
Disclosure of subsidiaries [line items]
At 1 January 2017, 31 December 2017 and 1 January 2018	£ 11,268
Additions	377
At 31 December 2018	11,645
Cost [member]
Disclosure of subsidiaries [line items]
At 1 January 2017, 31 December 2017 and 1 January 2018	11,268
Additions	377
At 31 December 2018	£ 11,645

Subordinated Liabilities - Su_5

Subordinated Liabilities - Summary of Subordinated Liabilities - Parent (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Subordinated liabilities [line items]
Subordinated liabilities	£ 3,601	£ 3,793
Santander UK Group Holdings plc [member]
Subordinated liabilities [line items]
Subordinated liabilities	£ 1,185	1,116
4.75% Subordinated Notes 2025 [member] | Santander UK Group Holdings plc [member]
Subordinated liabilities [line items]
Borrowings maturity	2,025
Subordinated liabilities	£ 791	745
5.625% Subordinated Notes 2045 [member] | Santander UK Group Holdings plc [member]
Subordinated liabilities [line items]
Borrowings maturity	2,045
Subordinated liabilities	£ 394	£ 371

Subordinated Liabilities - Su_6

Subordinated Liabilities - Summary of Subordinated Liabilities - Parent (Parenthetical) (Detail) - Santander UK Group Holdings plc [member] - USD ($)	Dec. 31, 2018	Dec. 31, 2017
4.75% Subordinated Notes 2025 [member]
Subordinated liabilities [line items]
Interest rate	4.75%	4.75%
Notional amount	$ 1,000,000,000	$ 1,000,000,000
5.625% Subordinated Notes 2045 [member]
Subordinated liabilities [line items]
Interest rate	5.625%	5.625%
Notional amount	$ 500,000,000	$ 500,000,000

Changes in Liabilities Arisin_4

Changes in Liabilities Arising From Financing Activities - Summary of Changes in Liabilities Arising from Financing Activities - Parent (Detail) - GBP (£) £ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	£ 54,694	£ 60,640
Cash flows from operating activities	(2,762)	366
- Unrealised foreign exchange	(1,936)	(920)
- Other changes	5,865	151
Ending Balance	61,548	54,694
Debt Securities [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	48,860	54,792
Cash flows from operating activities	(2,760)	112
- Unrealised foreign exchange	(2,085)	(685)
- Other changes	4,619	(373)
Ending Balance	55,906	48,860
Subordinated liabilities [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	3,793	4,303
Cash flows from operating activities	(2)	254
- Unrealised foreign exchange	149	(235)
- Other changes	(62)	(477)
Ending Balance	3,601	3,793
Other Equity Instruments [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	2,041	1,545
Ending Balance	2,041	2,041
Dividends Paid [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
- Other changes	1,308	1,001
Santander UK Group Holdings plc [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	9,413	7,231
Cash flows from financing activities	1,390	1,635
Cash flows from operating activities	(7)	(3)
- Unrealised foreign exchange	418	(430)
- Other changes	1,307	980
Ending Balance	12,521	9,413
Santander UK Group Holdings plc [member] | Debt Securities [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	6,256	4,464
Cash flows from financing activities	2,658	2,103
Cash flows from operating activities	(7)	(3)
- Unrealised foreign exchange	418	(324)
- Other changes	(30)	16
Ending Balance	9,295	6,256
Santander UK Group Holdings plc [member] | Subordinated liabilities [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	1,116	1,222
- Unrealised foreign exchange		(106)
- Other changes	69
Ending Balance	1,185	1,116
Santander UK Group Holdings plc [member] | Other Equity Instruments [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Beginning Balance	2,041	1,545
Cash flows from financing activities		496
Ending Balance	2,041	2,041
Santander UK Group Holdings plc [member] | Dividends Paid [member]
Disclosure of reconciliation of liabilities arising from financing activities [line items]
Cash flows from financing activities	(1,268)	(964)
- Other changes	£ 1,268	£ 964

Related Party Transactions - Ad

Related Party Transactions - Additional Information - Parent (Detail)	12 Months Ended
	Dec. 31, 2018
Santander UK Group Holdings plc [member]
Disclosure of transactions between related parties [line items]
Description related party transactions	The Company’s only transactions with related parties arise in connection with the receipt of dividends declared by its subsidiaries, payment of dividends on its own ordinary shares and Perpetual Capital Securities, interest payments to its subsidiary on intercompany loans and interest received from its subsidiary relating to downstreamed funding of senior debt, as well as the transactions entered into as part of the implementation of Santander UK’s ring-fencing plans as set in Note 43 to the Consolidated Financial Statements.