Northern Trust (NTRS) 10-Q 29 Apr 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information	3 Months Ended
	Mar. 31, 2019shares
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	NTRS
Entity Registrant Name	NORTHERN TRUST CORP
Entity Central Index Key	0000073124
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Entity Common Stock, Shares Outstanding (in shares)	217,676,589

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Assets
Cash and Due from Banks	$ 5,074.1	$ 4,581.6
Federal Reserve and Other Central Bank Deposits	23,422.2	30,080.2
Interest-Bearing Deposits with Banks	3,861.6	4,264.2
Federal Funds Sold and Securities Purchased under Agreements to Resell	552.2	1,165.2
Debt Securities
Available for Sale	37,058.2	36,888.8
Held to Maturity (Fair value of $12,097.7 and $14,267.0)	12,143	14,354
Trading Account	0.3	0.3
Total Debt Securities	49,201.5	51,243.1
Loans and Leases
Total Loans and Leases (Net of unearned income)	30,620.6	32,490
Allowance for Credit Losses Assigned to Loans and Leases	(114.5)	(112.6)
Buildings and Equipment	411.5	428.2
Client Security Settlement Receivables	2,067.3	1,646.1
Goodwill	683	669.3
Other Assets	6,089.9	5,757.2
Total Assets	121,869.4	132,212.5
Deposits
Demand and Other Noninterest-Bearing	14,886.8	14,508
Savings, Money Market and Other Interest-Bearing	14,784.6	14,612
Savings Certificates and Other Time	856.2	688.7
Non U.S. Offices — Noninterest-Bearing	6,977.1	8,220.1
Non U.S. Offices — Interest-Bearing	58,339.5	66,468
Total Deposits	95,844.2	104,496.8
Federal Funds Purchased	651.8	2,594.2
Securities Sold Under Agreements to Repurchase	39.7	168.3
Other Borrowings	7,749.8	7,901.7
Senior Notes	2,024.1	2,011.3
Long-Term Debt	1,125.8	1,112.4
Floating Rate Capital Debt	277.6	277.6
Other Liabilities	3,540.2	3,141.9
Total Liabilities	111,253.2	121,704.2
Stockholders’ Equity
Common Stock	408.6	408.6
Additional Paid-In Capital	1,003.3	1,068.5
Retained Earnings	10,972.9	10,776.8
Accumulated Other Comprehensive Loss	(345.3)	(453.7)
Treasury Stock (27,494,935 and 26,159,474 shares, at cost)	(2,305.3)	(2,173.9)
Total Stockholders’ Equity	10,616.2	10,508.3
Total Liabilities and Stockholders’ Equity	121,869.4	132,212.5
Series C Preferred Stock
Stockholders’ Equity
Preferred Stock	388.5	388.5
Series D Preferred Stock
Stockholders’ Equity
Preferred Stock	493.5	493.5
Total Stockholders’ Equity		493.5
Commercial
Loans and Leases
Total Loans and Leases (Net of unearned income)	13,635.5	15,175.2
Allowance for Credit Losses Assigned to Loans and Leases	(58.1)	(57.6)
Personal
Loans and Leases
Total Loans and Leases (Net of unearned income)	16,985.1	17,314.8
Allowance for Credit Losses Assigned to Loans and Leases	$ (56.4)	$ (55)

Consolidated Balance Sheet (Par

Consolidated Balance Sheet (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Held to maturity, fair value	$ 12,097.7	$ 14,267
Total loans and leases, unearned income	$ 13.3	$ 13.2
Preferred stock, par value (in dollars per share)	$ 0	$ 0
Preferred stock, authorized (in shares)	10,000,000	10,000,000
Common stock, par value (in dollars per share)	$ 1.6667	$ 1.6667
Common stock, authorized (in shares)	560,000,000	560,000,000
Common stock, outstanding (in shares)	217,676,589	219,012,050
Treasury stock (in shares)	27,494,935	26,159,474
Series C Preferred Stock
Preferred stock, outstanding (in shares)	16,000	16,000
Series D Preferred Stock
Preferred stock, outstanding (in shares)	5,000	5,000

Consolidated Statements of Inco

Consolidated Statements of Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Noninterest Income
Foreign Exchange Trading Income	$ 66.2	$ 78.5
Treasury Management Fees	11.7	14
Security Commissions and Trading Income	23.3	27.2
Other Operating Income	29	34.8
Investment Security Gains (Losses), net (Note)	(0.2)	(0.2)
Total Noninterest Income	1,058.9	1,092
Net Interest Income
Interest Income	662.8	505.9
Interest Expense	240.8	121.9
Net Interest Income	422	384
Provision for Credit Losses	0	(3)
Net Interest Income after Provision for Credit Losses	422	387
Noninterest Expense
Compensation	482	471.7
Employee Benefits	85.7	91.7
Outside Services	188.4	171.4
Equipment and Software	148.3	140
Occupancy	51.6	51.5
Other Operating Expense	72.7	69
Total Noninterest Expense	1,028.7	995.3
Income before Income Taxes	452.2	483.7
Provision for Income Taxes	105.1	102.1
Net Income	347.1	381.6
Preferred Stock Dividends	17.3	17.3
Net Income Applicable to Common Stock	$ 329.8	$ 364.3
Per Common Share
Net Income — Basic (in dollars per share)	$ 1.49	$ 1.59
Net Income - Diluted (in dollars per share)	$ 1.48	$ 1.58
Average number of common shares outstanding
Average Number of Common Shares Outstanding - Basic (in shares)	218,236,802	225,681,167
Average Number of Common Shares Outstanding - Diluted (in shares)	219,270,215	227,047,519
Changes in other-than-temporary-impairment (OTTI) losses	$ 0	$ (0.2)
Other Security Gains (Losses), net	(0.2)	0
Investment Security Gains (Losses), net	(0.2)	(0.2)
Total Trust, Investment and Other Servicing Fees
Noninterest Income
Trust, Investment and Other Servicing Fees	$ 928.9	$ 937.7

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net Income	$ 347.1	$ 381.6
Other Comprehensive Income (Loss) (Net of Tax and Reclassifications)
Net Unrealized (Losses) Gains on Debt Securities Available for Sale	85.6	(55)
Net Unrealized (Losses) Gains on Cash Flow Hedges	(4.3)	(3.7)
Foreign Currency Translation Adjustments	14.8	(13.1)
Pension and Other Postretirement Benefit Adjustments	12.3	5.7
Other Comprehensive Income	108.4	(66.1)
Comprehensive Income	$ 455.5	$ 315.5

Consolidated Statements of Chan

Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2017		$ 882	$ 408.6	$ 1,047.3	$ 9,685.1	$ (414.3)	$ (1,392.4)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Options and Awards				(83.5)			102.5
Stock Options and Awards — Amortization				56.6
Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income					25.3	(25.3)
Net Income	$ 381.6				381.6
Dividends Declared — Common Stock					(96.4)
Dividends Declared — Preferred Stock					(17.3)
Net Unrealized (Losses) Gains on Debt Securities Available for Sale	(55)					(55)
Net Unrealized (Losses) Gains on Cash Flow Hedges	(3.7)					(3.7)
Foreign Currency Translation Adjustments	(13.1)					(13.1)
Pension and Other Postretirement Benefit Adjustments	5.7					5.7
Stock Purchased							(263.2)
Ending balance at Mar. 31, 2018	10,226	882	408.6	1,020.4	9,973.8	(505.7)	(1,553.1)
Beginning balance at Dec. 31, 2018	10,508.3	882	408.6	1,068.4	10,776.8	(453.7)	(2,173.9)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock Options and Awards				(120.4)			126
Stock Options and Awards — Amortization				55.3
Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income					0	0
Net Income	347.1				347.1
Dividends Declared — Common Stock					(133.7)
Dividends Declared — Preferred Stock					(17.3)
Net Unrealized (Losses) Gains on Debt Securities Available for Sale	85.6					85.6
Net Unrealized (Losses) Gains on Cash Flow Hedges	(4.3)					(4.3)
Foreign Currency Translation Adjustments	14.8					14.8
Pension and Other Postretirement Benefit Adjustments	12.3					12.3
Stock Purchased	(257.4)						(257.4)
Ending balance at Mar. 31, 2019	$ 10,616.2	$ 882	$ 408.6	$ 1,003.3	$ 10,972.9	$ (345.3)	$ (2,305.3)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash Flows From Operating Activities
Net Income	$ 347.1	$ 381.6
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities
Investment Security Losses, net	0.2	0.2
Amortization and Accretion of Securities and Unearned Income, net	20	35.6
Provision for Credit Losses	0	(3)
Depreciation on Buildings and Equipment	24.9	27.8
Amortization of Computer Software	84.8	83.6
Amortization of Intangibles	4.2	4.5
Pension Plan Contributions	(3)	(71.9)
Change in Receivables	(105.3)	(79.7)
Change in Interest Payable	(3.6)	5.7
Change in Collateral With Derivative Counterparties, net	292.7	(619.8)
Other Operating Activities, net	(368.3)	(242.4)
Net Cash Provided by (Used in) Operating Activities	293.7	(477.8)
Cash Flows From Investing Activities
Net Change in Federal Funds Sold and Securities Purchased under Agreements to Resell	620.5	(211.9)
Change in Interest-Bearing Deposits with Banks	400.6	660.2
Net Change in Federal Reserve and Other Central Bank Deposits	6,738.8	11,533
Purchases of Debt Securities – Held to Maturity	(3,724.4)	(5,511.6)
Proceeds from Maturity and Redemption of Debt Securities – Held to Maturity	5,948.6	4,678.4
Purchases of Debt Securities – Available for Sale	(1,834.1)	(2,725.3)
Proceeds from Sale, Maturity and Redemption of Debt Securities – Available for Sale	1,714.3	2,044.4
Change in Loans and Leases	1,875.1	491.2
Purchases of Buildings and Equipment	(9.1)	(6)
Purchases and Development of Computer Software	(81.9)	(79.8)
Change in Client Security Settlement Receivables	(419.7)	1,058.2
Other Investing Activities, net	378.9	(774.6)
Net Cash Provided by Investing Activities	11,607.6	11,156.2
Cash Flows From Financing Activities
Change in Deposits	(8,838.2)	(7,841.1)
Change in Federal Funds Purchased	(1,942.4)	(1,953.3)
Change in Securities Sold under Agreements to Repurchase	(128.5)	(23.8)
Change in Short-Term Other Borrowings	(158.7)	997.7
Repayments of Senior Notes and Long-Term Debt	0	(1.7)
Treasury Stock Purchased	(257.4)	(263.2)
Net Proceeds from Stock Options	5.5	19.1
Cash Dividends Paid on Common Stock	(120.8)	(95)
Cash Dividends Paid on Preferred Stock	(5.9)	(5.9)
Net Cash Used in Financing Activities	(11,446.4)	(9,167.2)
Effect of Foreign Currency Exchange Rates on Cash	37.6	52.1
Change in Cash and Due from Banks	492.5	1,563.3
Cash and Due from Banks at Beginning of Year	4,581.6	4,518.1
Cash and Due from Banks at End of Year	5,074.1	6,081.4
Supplemental Disclosures Of Cash Flow Information
Interest Paid	244.2	116
Income Taxes Paid	27.2	29.7
Transfers from Loans to OREO	$ 0	$ 1.1

Basis of Presentation

Basis of Presentation	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of Northern Trust Corporation (the Corporation) and its wholly-owned subsidiary, The Northern Trust Company (the Bank), and various other wholly-owned subsidiaries of the Corporation and the Bank. Throughout the notes to the consolidated financial statements, the term “Northern Trust” refers to the Corporation and its subsidiaries. Intercompany balances and transactions have been eliminated in consolidation. The consolidated financial statements, as of and for the periods ended March 31, 2019 and 2018 , have not been audited by the Corporation’s independent registered public accounting firm. In the opinion of management, all accounting entries and adjustments, including normal recurring accruals, necessary for a fair presentation of the financial position and the results of operations for the interim periods have been made. The accounting and financial reporting policies of Northern Trust conform to U.S. generally accepted accounting principles (GAAP) and reporting practices prescribed for the banking industry. The consolidated statements of income include results of acquired subsidiaries from the dates of acquisition. Certain amounts in prior periods have been reclassified to conform with the current year’s presentation. For a description of Northern Trust’s significant accounting policies, refer to Note 1 of the Notes to Consolidated Financial Statements in the Annual Report on Form 10-K for the year ended December 31, 2018 .

Recent Accounting Pronouncement

Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2019
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements On January 1, 2019, Northern Trust adopted ASU No. 2016-02, “Leases (Topic 842)" (ASU 2016-02). ASU 2016-02 introduces a lessee model that brings most leases on the balance sheet, with certain specified scope exceptions. Specifically within the lessee model under ASU 2016-02, a lessee is required to recognize on the balance sheet a liability to make future lease payments, known as the lease liability, and a right-of-use asset (ROU asset) representing its right to use the underlying asset over the lease term. Upon adoption, Northern Trust elected the package of practical expedients available under ASU 2016-02, which allowed Northern Trust to forego a reassessment of (1) whether any expired or existing contracts are or contain leases, (2) lease classification for any expired or existing leases, and (3) the initial direct costs for any existing leases. As a result of adopting ASU 2016-02, Northern Trust recognized operating lease liabilities and ROU assets of approximately $530 million and $480 million , respectively. Northern Trust did not restate comparative periods for the effects of applying ASU 2016-02. There was no significant impact to Northern Trust’s consolidated results of operations. Please refer to “Note 8 - Leases” for further information. On January 1, 2019, Northern Trust adopted ASU No. 2017-08, “Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Securities” (ASU 2017-08). ASU 2017-08 amends the amortization period for certain callable debt securities held at a premium and shortens the amortization period for the premium to the earliest call date. Upon adoption of ASU 2017-08, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations. On January 1, 2019, Northern Trust adopted ASU No. 2018-16, “"Derivatives and Hedging (Topic 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes" (ASU 2018-16). ASU 2018-16 permits use of the OIS rate based on SOFR as a U.S. benchmark interest rate for hedge accounting purposes under Topic 815. Upon adoption of ASU 2018-16, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations.

Fair Value Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair Value Hierarchy. The following describes the hierarchy of valuation inputs (Levels 1, 2, and 3) used to measure fair value and the primary valuation methodologies used by Northern Trust for financial instruments measured at fair value on a recurring basis. Observable inputs reflect market data obtained from sources independent of the reporting entity; unobservable inputs reflect the entity’s own assumptions about how market participants would value an asset or liability based on the best information available. GAAP requires an entity measuring fair value to maximize the use of observable inputs and minimize the use of unobservable inputs and establishes a fair value hierarchy of inputs. Financial instruments are categorized within the hierarchy based on the lowest level input that is significant to their valuation. Northern Trust’s policy is to recognize transfers into and transfers out of fair value levels as of the end of the reporting period in which the transfer occurred. No transfers between fair value levels occurred during the three months ended March 31, 2019 or the year ended December 31, 2018 . Level 1 — Quoted, active market prices for identical assets or liabilities. Northern Trust’s Level 1 assets are comprised of available for sale investments in U.S. treasury securities. Level 2 — Observable inputs other than Level 1 prices, such as quoted active market prices for similar assets or liabilities, quoted prices for identical or similar assets in inactive markets, and model-derived valuations in which all significant inputs are observable in active markets. Northern Trust’s Level 2 assets include available for sale and trading account debt securities, the fair values of which are determined predominantly by external pricing vendors. Prices received from vendors are compared to other vendor and third-party prices. If a security price obtained from a pricing vendor is determined to exceed pre-determined tolerance levels that are assigned based on an asset type’s characteristics, the exception is researched and, if the price is not able to be validated, an alternate pricing vendor is utilized, consistent with Northern Trust’s pricing source hierarchy. As of March 31, 2019 , Northern Trust’s available for sale debt securities portfolio included 1,490 Level 2 debt securities with an aggregate market value of $32.0 billion . All 1,490 debt securities were valued by external pricing vendors. As of December 31, 2018 , Northern Trust’s available for sale debt securities portfolio included 1,479 Level 2 debt securities with an aggregate market value of $31.7 billion . All 1,479 debt securities were valued by external pricing vendors. Trading account debt securities, which totaled $0.3 million as of March 31, 2019 and December 31, 2018 , were all valued using external pricing vendors. Level 2 assets and liabilities also include derivative contracts which are valued internally using widely accepted income-based models that incorporate inputs readily observable in actively quoted markets and reflect the contractual terms of the contracts. Observable inputs include foreign exchange rates and interest rates for foreign exchange contracts; credit spreads, default probabilities, and recovery rates for credit default swap contracts; interest rates for interest rate swap contracts and forward contracts; and interest rates and volatility inputs for interest rate option contracts. Northern Trust evaluates the impact of counterparty credit risk and its own credit risk on the valuation of its derivative instruments. Factors considered include the likelihood of default by Northern Trust and its counterparties, the remaining maturities of the instruments, net exposures after giving effect to master netting arrangements or similar agreements, available collateral, and other credit enhancements in determining the appropriate fair value of derivative instruments. The resulting valuation adjustments have not been considered material. Level 3 — Valuation techniques in which one or more significant inputs are unobservable in the marketplace. Northern Trust’s Level 3 liabilities consist of swaps that Northern Trust entered into with the purchaser of 1.1 million and 1.0 million shares of Visa Inc. Class B common stock (Visa Class B common shares) previously held by Northern Trust and sold in June 2016 and 2015, respectively. Pursuant to the swaps, Northern Trust retains the risks associated with the ultimate conversion of the Visa Class B common shares into shares of Visa Inc. Class A common stock (Visa Class A common shares), such that the counterparty will be compensated for any dilutive adjustments to the conversion ratio and Northern Trust will be compensated for any anti-dilutive adjustments to the ratio. The swaps also require periodic payments from Northern Trust to the counterparty calculated by reference to the market price of Visa Class A common shares and a fixed rate of interest. The fair value of the swaps is determined using a discounted cash flow methodology. The significant unobservable inputs used in the fair value measurement are Northern Trust’s own assumptions about estimated changes in the conversion rate of the Visa Class B common shares into Visa Class A common shares, the date on which such conversion is expected to occur and the estimated growth rate of the Visa Class A common share price. See “Visa Class B Common Shares” under Note 21 – “Contingent Liabilities” for further information. Northern Trust believes its valuation methods for its assets and liabilities carried at fair value are appropriate; however, the use of different methodologies or assumptions, particularly as applied to Level 3 assets and liabilities, could have a material effect on the computation of their estimated fair values. The following table presents the fair values of Northern Trust’s Level 3 liabilities as of March 31, 2019 and December 31, 2018 , as well as the valuation techniques, significant unobservable inputs, and quantitative information used to develop significant unobservable inputs for such assets and liabilities as of such dates. Table 32: Level 3 Significant Unobservable Inputs March 31, 2019 Financial Instrument Fair Value Valuation Technique Unobservable Inputs Range of Inputs Swaps Related to Sale of Certain Visa Class B Common Shares $ 35.0 million Discounted Cash Flow Visa Class A Appreciation 7.0 % — 11.0% Conversion Rate 1.62 x — 1.64x Expected Duration 1.25 — 3.75 years December 31, 2018 Financial Instrument Fair Value Valuation Technique Unobservable Inputs Range of Inputs Swap Related to Sale of Certain Visa Class B Common Shares $ 32.8 million Discounted Cash Flow Visa Class A Appreciation 7.0 % — 11.0% Conversion Rate 1.62 x — 1.64x Expected Duration 1.5 — 4.0 years The following table presents assets and liabilities measured at fair value on a recurring basis as of March 31, 2019 and December 31, 2018 , segregated by fair value hierarchy level. Table 33: Recurring Basis Hierarchy Leveling (In Millions) Level 1 Level 2 Level 3 Netting Assets/Liabilities at Fair Value March 31, 2019 Debt Securities Available for Sale U.S. Government $ 5,022.0 $ — $ — $ — $ 5,022.0 Obligations of States and Political Subdivisions — 764.8 — — 764.8 Government Sponsored Agency — 22,568.6 — — 22,568.6 Non-U.S. Government — 142.7 — — 142.7 Corporate Debt — 2,293.7 — — 2,293.7 Covered Bonds — 837.4 — — 837.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,236.1 — — 2,236.1 Other Asset-Backed — 2,520.2 — — 2,520.2 Commercial Mortgage-Backed — 658.1 — — 658.1 Other — 14.6 — — 14.6 Total Available for Sale 5,022.0 32,036.2 — — 37,058.2 Trading Account — 0.3 — — 0.3 Total Available for Sale and Trading Debt Securities 5,022.0 32,036.5 — — 37,058.5 Other Assets Derivative Assets Foreign Exchange Contracts — 1,642.0 — — 1,642.0 Interest Rate Contracts — 104.6 — — 104.6 Total Derivative Assets — 1,746.6 — (979.9 ) 766.7 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 1,490.5 — — 1,490.5 Interest Rate Contracts — 79.6 — — 79.6 Other Financial Derivatives (1) — 0.9 35.0 — 35.9 Total Derivative Liabilities $ — $ 1,571.0 $ 35.0 $ (1,123.7 ) $ 482.3 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of March 31, 2019 , derivative assets and liabilities shown above also include reductions of $139.2 million and $283.1 million , respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1) This line consists of swaps related to the sale of certain Visa Class B common shares and a total return swap contract. (In Millions) Level 1 Level 2 Level 3 Netting Assets/Liabilities at Fair Value December 31, 2018 Debt Securities Available for Sale U.S. Government $ 5,185.3 $ — $ — $ — $ 5,185.3 Obligations of States and Political Subdivisions — 655.9 — — 655.9 Government Sponsored Agency — 22,424.6 — — 22,424.6 Non-U.S. Government — 142.2 — — 142.2 Corporate Debt — 2,294.7 — — 2,294.7 Covered Bonds — 829.3 — — 829.3 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,096.2 — — 2,096.2 Other Asset-Backed — 2,657.7 — — 2,657.7 Commercial Mortgage-Backed — 587.2 — — 587.2 Other — 15.7 — — 15.7 Total Available for Sale 5,185.3 31,703.5 — — 36,888.8 Trading Account — 0.3 — — 0.3 Total Available for Sale and Trading Debt Securities 5,185.3 31,703.8 — — 36,889.1 Other Assets Derivative Assets Foreign Exchange Contracts — 2,466.1 — — 2,466.1 Interest Rate Contracts — 96.1 — — 96.1 Other Financial Derivatives (1) — 1.3 — — 1.3 Total Derivative Assets — 2,563.5 — (1,357.1 ) 1,206.4 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 2,262.5 — — 2,262.5 Interest Rate Contracts — 93.1 — — 93.1 Other Financial Derivatives (2) — — 32.8 — 32.8 Total Derivative Liabilities $ — $ 2,355.6 $ 32.8 $ (1,796.3 ) $ 592.1 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of December 31, 2018 , derivative assets and liabilities shown above also include reductions of $134.5 million and $573.7 million , respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1) This line consists of a total return swap contract. (2) This line consists of swaps related to the sale of certain Visa Class B common shares. The following table presents the changes in Level 3 liabilities for the three months ended March 31, 2019 and 2018 . Table 34: Changes in Level 3 Liabilities Level 3 Liabilities (In Millions) Swaps Related to Sale of Certain Visa Class B Common Shares Three Months Ended March 31, 2019 2018 Fair Value at January 1 $ 32.8 $ 29.7 Total (Gains) Losses: Included in Earnings (1) 5.1 4.2 Purchases, Issues, Sales, and Settlements Settlements (2.9 ) (2.6 ) Fair Value at March 31 $ 35.0 $ 31.3 (1) (Gains) losses are recorded in other operating income in the consolidated statements of income. During the three months ended March 31, 2019 and 2018 , there were no transfers into or out of Level 3 liabilities. Carrying values of assets and liabilities that are not measured at fair value on a recurring basis may be adjusted to fair value in periods subsequent to their initial recognition, for example, to record an impairment of an asset. GAAP requires entities to separately disclose these subsequent fair value measurements and to classify them under the fair value hierarchy. Assets measured at fair value on a nonrecurring basis at March 31, 2019 and 2018 , all of which were categorized as Level 3 under the fair value hierarchy, were comprised of impaired loans whose values were based on real estate and other available collateral, and of other real estate owned (OREO) properties. Fair values of real estate loan collateral were estimated using a market approach typically supported by third-party valuations and property-specific fees and taxes, and were subject to adjustments to reflect management’s judgment as to realizable value. Other loan collateral, which typically consists of accounts receivable, inventory and equipment, is valued using a market approach adjusted for asset-specific characteristics and in limited instances third-party valuations are used. OREO assets are carried at the lower of cost or fair value less estimated costs to sell, with fair value typically based on third-party appraisals. Collateral-based impaired loans and OREO assets that have been adjusted to fair value totaled $22.3 million and $0.1 million , respectively, at March 31, 2019 , and $9.7 million and $0.4 million , respectively, at March 31, 2018 . Assets measured at fair value on a nonrecurring basis reflect management’s judgment as to realizable value. The following table presents the fair values of Northern Trust’s Level 3 assets that were measured at fair value on a nonrecurring basis as of March 31, 2019 and December 31, 2018 , as well as the valuation technique, significant unobservable inputs and quantitative information used to develop the significant unobservable inputs for such assets as of such dates. Table 35: Level 3 Nonrecurring Basis Significant Unobservable Inputs March 31, 2019 Financial Instrument Fair Value Valuation Technique Unobservable Input Range of Discounts Applied Loans $22.3 million Market Approach Discount to reflect realizable value 15.0 % - 30.0% OREO $0.1 million Market Approach Discount to reflect realizable value 15.0 % - 30.0% December 31, 2018 Financial Instrument Fair Value Valuation Technique Unobservable Input Range of Discounts Applied Loans $24.9 million Market Approach Discount to reflect realizable value 15.0 % - 30.0% OREO $0.4 million Market Approach Discount to reflect realizable value 15.0 % - 30.0% The following table summarizes the fair values of all financial instruments. Table 36: Fair Value of Financial Instruments (In Millions) March 31, 2019 Book Value Total Fair Value Fair Value Level 1 Level 2 Level 3 Assets Cash and Due from Banks $ 5,074.1 $ 5,074.1 $ 5,074.1 $ — $ — Federal Reserve and Other Central Bank Deposits 23,422.2 23,422.2 — 23,422.2 — Interest-Bearing Deposits with Banks 3,861.6 3,861.6 — 3,861.6 — Federal Funds Sold and Securities Purchased under Agreements to Resell 552.2 552.2 — 552.2 — Debt Securities Available for Sale ( Note ) 37,058.2 37,058.2 5,022.0 32,036.2 — Held to Maturity 12,143.0 12,097.7 119.6 11,978.1 — Trading Account 0.3 0.3 — 0.3 — Loans (excluding Leases) Held for Investment 30,417.0 30,481.9 — — 30,481.9 Held for Sale — — — — — Client Security Settlement Receivables 2,067.3 2,067.3 — 2,067.3 — Total Assets Federal Reserve and Federal Home Loan Bank Stock 300.5 300.5 — 300.5 — Community Development Investments 589.5 589.5 — 589.5 — Employee Benefit and Deferred Compensation 200.5 197.5 131.1 66.4 — Liabilities Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 36,648.5 $ 36,648.5 $ 36,648.5 $ — $ — Savings Certificates and Other Time 856.2 866.9 — 866.9 — Non U.S. Offices Interest-Bearing 58,339.5 58,339.5 — 58,339.5 — Federal Funds Purchased 651.8 651.8 — 651.8 — Securities Sold Under Agreements to Repurchase 39.7 39.7 — 39.7 — Other Borrowings 7,749.8 7,754.6 — 7,754.6 — Senior Notes 2,024.1 2,031.0 — 2,031.0 — Long-Term Debt Subordinated Debt 1,125.8 1,133.2 — 1,133.2 — Floating Rate Capital Debt 277.6 256.4 — 256.4 — Other Liabilities Standby Letters of Credit 56.2 56.2 — — 56.2 Loan Commitments 33.0 33.0 — — 33.0 Derivative Instruments Asset/Liability Management Foreign Exchange Contracts Assets $ 80.2 $ 80.2 $ — $ 80.2 $ — Liabilities 16.5 16.5 — 16.5 — Interest Rate Contracts Assets 24.1 24.1 — 24.1 — Liabilities 20.8 20.8 — 20.8 — Other Financial Derivatives Liabilities (1) 35.9 35.9 — 0.9 35.0 Client-Related and Trading Foreign Exchange Contracts Assets 1,561.8 1,561.8 — 1,561.8 — Liabilities 1,474.0 1,474.0 — 1,474.0 — Interest Rate Contracts Assets 80.5 80.5 — 80.5 — Liabilities 58.8 58.8 — 58.8 — Note: Refer to the table located on page 32 for the disaggregation of available for sale debt securities. (1) This line consists of a total return swap contract and swaps related to the sale of certain Visa Class B common shares. (In Millions) December 31, 2018 Book Value Total Fair Value Fair Value Level 1 Level 2 Level 3 Assets Cash and Due from Banks $ 4,581.6 $ 4,581.6 $ 4,581.6 $ — $ — Federal Reserve and Other Central Bank Deposits 30,080.2 30,080.2 — 30,080.2 — Interest-Bearing Deposits with Banks 4,264.2 4,264.2 — 4,264.2 — Federal Funds Sold and Securities Purchased under Agreements to Resell 1,165.2 1,165.2 — 1,165.2 — Debt Securities Available for Sale ( Note ) 36,888.8 36,888.8 5,185.3 31,703.5 — Held to Maturity 14,354.0 14,267.0 101.6 14,165.4 — Trading Account 0.3 0.3 — 0.3 — Loans (excluding Leases) Held for Investment 32,287.0 32,339.2 — — 32,339.2 Held for Sale — — — — — Client Security Settlement Receivables 1,646.1 1,646.1 — 1,646.1 — Total Assets Federal Reserve and Federal Home Loan Bank Stock 300.3 300.3 — 300.3 — Community Development Investments 606.6 606.6 — 606.6 — Employee Benefit and Deferred Compensation 202.3 194.5 125.0 69.5 — Liabilities Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 37,340.1 $ 37,340.1 $ 37,340.1 $ — $ — Savings Certificates and Other Time 688.7 691.8 — 691.8 — Non U.S. Offices Interest-Bearing 66,468.0 66,468.0 — 66,468.0 — Federal Funds Purchased 2,594.2 2,594.2 — 2,594.2 — Securities Sold Under Agreements to Repurchase 168.3 168.3 — 168.3 — Other Borrowings 7,901.7 7,904.1 — 7,904.1 — Senior Notes 2,011.3 1,994.4 — 1,994.4 — Long-Term Debt Subordinated Debt 1,112.4 1,089.7 — 1,089.7 — Floating Rate Capital Debt 277.6 253.5 — 253.5 — Other Liabilities Standby Letters of Credit 30.8 30.8 — — 30.8 Loan Commitments 34.3 34.3 — — 34.3 Derivative Instruments Asset/Liability Management Foreign Exchange Contracts Assets $ 306.7 $ 306.7 $ — $ 306.7 $ — Liabilities 72.5 72.5 — 72.5 — Interest Rate Contracts Assets 30.0 30.0 — 30.0 — Liabilities 24.5 24.5 — 24.5 — Other Financial Derivatives Assets (1) 1.3 1.3 — 1.3 — Liabilities (2) 32.8 32.8 — — 32.8 Client-Related and Trading Foreign Exchange Contracts Assets 2,159.4 2,159.4 — 2,159.4 — Liabilities 2,190.0 2,190.0 — 2,190.0 — Interest Rate Contracts Assets 66.1 66.1 — 66.1 — Liabilities 68.6 68.6 — 68.6 — Note: Refer to the table located on page 33 for the disaggregation of available for sale debt securities. (1) This line consists of a total return swap contract. (2) This line consists of swaps related to the sale of certain Visa Class B common shares.

Securities

Securities	3 Months Ended
	Mar. 31, 2019
Investments, Debt and Equity Securities [Abstract]
Securities	Securities The following tables provide the amortized cost and fair values of debt securities at March 31, 2019 and December 31, 2018 . Table 37: Reconciliation of Amortized Cost to Fair Value of Debt Securities Available for Sale Debt Securities Available for Sale March 31, 2019 Amortized Cost Gross Unrealized Fair Value (In Millions) Gains Losses U.S. Government $ 5,030.0 $ 19.0 $ 27.0 $ 5,022.0 Obligations of States and Political Subdivisions 755.8 10.7 1.7 764.8 Government Sponsored Agency 22,624.9 68.3 124.6 22,568.6 Non-U.S. Government 143.3 — 0.6 142.7 Corporate Debt 2,297.6 10.2 14.1 2,293.7 Covered Bonds 837.4 2.6 2.6 837.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,214.0 24.3 2.2 2,236.1 Other Asset-Backed 2,530.5 3.3 13.6 2,520.2 Commercial Mortgage-Backed 647.6 12.5 2.0 658.1 Other 14.6 — — 14.6 Total $ 37,095.7 $ 150.9 $ 188.4 $ 37,058.2 Debt Securities Available for Sale December 31, 2018 Amortized Cost Gross Unrealized Fair Value (In Millions) Gains Losses U.S. Government $ 5,203.1 $ 21.8 $ 39.6 $ 5,185.3 Obligations of States and Political Subdivisions 657.6 2.0 3.7 655.9 Government Sponsored Agency 22,522.7 52.4 150.5 22,424.6 Non-U.S. Government 143.3 — 1.1 142.2 Corporate Debt 2,312.6 3.2 21.1 2,294.7 Covered Bonds 832.7 1.4 4.8 829.3 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,087.8 11.9 3.5 2,096.2 Other Asset-Backed 2,678.9 1.7 22.9 2,657.7 Commercial Mortgage-Backed 587.4 4.0 4.2 587.2 Other 15.7 — — 15.7 Total $ 37,041.8 $ 98.4 $ 251.4 $ 36,888.8 Table 38: Reconciliation of Amortized Cost to Fair Value of Debt Securities Held to Maturity Debt Securities Held to Maturity March 31, 2019 Amortized Cost Gross Unrealized Fair Value (In Millions) Gains Losses U.S Government $ 119.6 $ — $ — $ 119.6 Obligations of States and Political Subdivisions 16.0 0.6 — 16.6 Government Sponsored Agency 4.3 0.2 — 4.5 Corporate Debt 451.6 0.4 0.3 451.7 Covered Bonds 2,617.8 15.5 4.8 2,628.5 Non-U.S. Government 4,338.1 4.7 5.0 4,337.8 Certificates of Deposit 75.8 — — 75.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,170.2 13.5 4.6 3,179.1 Other Asset-Backed 1,099.6 0.3 1.2 1,098.7 Other 250.0 — 64.6 185.4 Total $ 12,143.0 $ 35.2 $ 80.5 $ 12,097.7 Debt Securities Held to Maturity December 31, 2018 Amortized Cost Gross Unrealized Fair Value (In Millions) Gains Losses U.S Government $ 101.6 $ — $ — $ 101.6 Obligations of States and Political Subdivisions 18.9 0.6 — 19.5 Government Sponsored Agency 4.5 0.2 — 4.7 Corporate Debt 472.9 0.4 1.8 471.5 Covered Bonds 2,877.6 9.6 9.3 2,877.9 Non-U.S. Government 6,488.2 2.1 8.7 6,481.6 Certificates of Deposit 45.1 — — 45.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,966.8 5.8 12.3 2,960.3 Other Asset-Backed 1,146.4 — 4.0 1,142.4 Other 232.0 — 69.6 162.4 Total $ 14,354.0 $ 18.7 $ 105.7 $ 14,267.0 Debt securities held to maturity consist of securities that management intends to, and Northern Trust has the ability to, hold until maturity. During the three months ended March 31, 2019 , no securities were transferred from available for sale to held to maturity. The following table provides the remaining maturity of debt securities as of March 31, 2019 . Table 39: Remaining Maturity of Debt Securities Available for Sale and Held to Maturity March 31, 2019 (In Millions) Amortized Cost Fair Value Available for Sale Due in One Year or Less $ 9,967.0 $ 9,950.6 Due After One Year Through Five Years 19,376.6 19,379.5 Due After Five Years Through Ten Years 6,790.3 6,771.8 Due After Ten Years 961.8 956.3 Total 37,095.7 37,058.2 Held to Maturity Due in One Year or Less 4,820.9 4,820.7 Due After One Year Through Five Years 6,787.3 6,795.4 Due After Five Years Through Ten Years 452.5 440.4 Due After Ten Years 82.3 41.2 Total $ 12,143.0 $ 12,097.7 Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments. Investment Security Gains / Losses. Net investment security losses of $0.2 million were recognized in the three months ended March 31, 2019 . Net investment security losses of $0.2 million were recognized in the three months ended March 31, 2018, which related to the other-than-temporary impairment (OTTI) of certain Community Reinvestment Act (CRA) eligible held to maturity securities. There were $127.5 million sales of securities during the three months ended March 31, 2019 . Gross proceeds from the sale of securities during the three months ended March 31, 2018 were $2.0 million . Debt Securities with Unrealized Losses. The following table provides information regarding debt securities that had been in a continuous unrealized loss position for less than twelve months and for twelve months or longer as of March 31, 2019 and December 31, 2018 . Table 40: Debt Securities with Unrealized Losses Debt Securities with Unrealized Losses as of March 31, 2019 Less than 12 Months 12 Months or Longer Total (In Millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses U.S. Government $ — $ — $ 2,674.5 $ 27.0 $ 2,674.5 $ 27.0 Obligations of States and Political Subdivisions 66.2 1.2 209.8 0.5 276.0 1.7 Government Sponsored Agency 6,933.4 31.9 8,371.6 92.7 15,305.0 124.6 Non-U.S. Government 2,321.8 0.1 1,259.6 5.5 3,581.4 5.6 Corporate Debt 339.3 0.9 1,009.1 13.5 1,348.4 14.4 Covered Bonds 181.0 0.3 1,022.9 7.1 1,203.9 7.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 253.4 0.6 1,501.8 6.2 1,755.2 6.8 Other Asset-Backed 1,436.5 8.7 893.8 6.1 2,330.3 14.8 Commercial Mortgage-Backed 18.7 0.1 193.5 1.9 212.2 2.0 Other 60.7 19.8 125.8 44.8 186.5 64.6 Total $ 11,611.0 $ 63.6 $ 17,262.4 $ 205.3 $ 28,873.4 $ 268.9 Debt Securities with Unrealized Losses as of December 31, 2018 Less than 12 Months 12 Months or Longer Total (In Millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses U.S. Government $ — $ — $ 2,862.0 $ 39.6 $ 2,862.0 $ 39.6 Obligations of States and Political Subdivisions 169.6 2.4 279.6 1.3 449.2 3.7 Government Sponsored Agency 8,368.8 33.5 6,822.4 117.0 15,191.2 150.5 Non-U.S. Government 5,065.2 0.8 1,274.0 9.0 6,339.2 9.8 Corporate Debt 712.7 4.1 1,097.4 18.8 1,810.1 22.9 Covered Bonds 646.4 3.7 696.9 10.4 1,343.3 14.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 1,105.0 4.6 1,189.2 11.2 2,294.2 15.8 Other Asset-Backed 2,507.8 15.9 954.9 11.0 3,462.7 26.9 Commercial Mortgage-Backed 22.8 0.1 274.4 4.1 297.2 4.2 Other 50.5 18.8 112.6 50.8 163.1 69.6 Total $ 18,648.8 $ 83.9 $ 15,563.4 $ 273.2 $ 34,212.2 $ 357.1 As of March 31, 2019 , 1,234 debt securities with a combined fair value of $28.9 billion were in an unrealized loss position, with their unrealized losses totaling $268.9 million . Unrealized losses of $124.6 million and $27.0 million related to government sponsored agency and U.S. Government securities, respectively, are primarily attributable to changes in market interest rates since their purchase. Unrealized losses of $14.4 million within corporate debt securities primarily reflect higher market rates since purchase; 36% of the corporate debt portfolio is backed by guarantees provided by U.S. and non-U.S. governmental entities. The majority of the $64.6 million of unrealized losses in debt securities classified as “other” at March 31, 2019 related to debt securities primarily purchased at a premium or par by Northern Trust to fulfill its obligations under the CRA. Unrealized losses on these CRA-related securities were attributable to yields that were below market rates for the purpose of supporting institutions and programs that benefit low- to moderate- income communities within Northern Trust’s market area. The remaining unrealized losses on Northern Trust’s securities portfolio as of March 31, 2019 were attributable to changes in overall market interest rates, increased credit spreads or reduced market liquidity. As of March 31, 2019 , Northern Trust did not intend to sell any investment in an unrealized loss position and it was more likely than not that Northern Trust would not be required to sell any such investment before the recovery of its amortized cost basis, which may be maturity. Security impairment reviews are conducted quarterly to identify and evaluate securities that have indications of possible OTTI. A determination as to whether a security’s decline in market value is other-than-temporary takes into consideration numerous factors and the relative significance of any single factor can vary by security. Factors Northern Trust considers in determining whether impairment is other-than-temporary include, but are not limited to: the length of time the security has been impaired; the severity of the impairment; the cause of the impairment and the financial condition and near-term prospects of the issuer; activity in the market of the issuer, which may indicate adverse credit conditions; Northern Trust’s intent regarding the sale of the security as of the balance sheet date; and the likelihood that it will not be required to sell the security for a period of time sufficient to allow for the recovery of the security’s amortized cost basis. For each security meeting the requirements of Northern Trust’s internal screening process, an extensive review is conducted to determine if OTTI has occurred. While all securities are considered, the process for identifying credit impairment within CRA-eligible mortgage-backed securities incorporates an expected loss approach using discounted cash flows on the underlying collateral pools. To evaluate whether an unrealized loss on CRA-eligible mortgage-backed securities is other-than-temporary, a calculation of the security’s present value is made using current pool data, the current delinquency pipeline, default rates and loan loss severities based on the historical performance of the mortgage pools, and Northern Trust’s outlook for the housing market and the overall economy. If the present value of the collateral pools were found to be less than the current amortized cost of the security, a credit-related OTTI loss would be recorded in earnings equal to the difference between the two amounts. Impairments of CRA-eligible mortgage-backed securities are influenced by a number of factors, including but not limited to, U.S. economic and housing market performance, pool credit enhancement level, year of origination and estimated credit quality of the collateral. The factors used in estimating losses related to CRA-eligible mortgage-backed securities vary by vintage of loan origination and collateral quality. No OTTI losses were recognized during the three months ended March 31, 2019 related to CRA-eligible mortgage-backed securities. There were $0.2 million OTTI losses recognized during the three months ended March 31, 2018 . Credit Losses on Debt Securities. The table below provides the cumulative credit-related losses recognized in earnings on debt securities other-than-temporarily impaired. Table 41: Cumulative Credit-Related Losses on Debt Securities Three Months Ended March 31, (In Millions) 2019 2018 Cumulative Credit-Related Losses on Debt Securities Held — Beginning of Period $ 4.1 $ 3.6 Plus: Losses on Newly Identified Impairments — 0.2 Additional Losses on Previously Identified Impairments — — Less: Current and Prior Period Losses on Debt Securities Sold During the Period — — Cumulative Credit-Related Losses on Debt Securities Held — End of Period $ 4.1 $ 3.8

Securities Sold Under Agreement

Securities Sold Under Agreements to Repurchase	3 Months Ended
	Mar. 31, 2019
Banking and Thrift [Abstract]
Securities Sold Under Agreements to Repurchase	Securities Sold Under Agreements to Repurchase Securities sold under agreements to repurchase are accounted for as collateralized financings and recorded at the amounts at which the securities were sold plus accrued interest. To minimize any potential credit risk associated with these transactions, the fair value of the securities sold is monitored, limits are set on exposure with counterparties, and the financial condition of counterparties is regularly assessed. Securities sold under agreements to repurchase are held by the counterparty until the repurchase. The following table provides information regarding repurchase agreements that are accounted for as secured borrowings as of March 31, 2019 . Table 42: Repurchase Agreements Accounted for as Secured Borrowings March 31, 2019 (In Millions) Remaining Contractual Maturity of the Agreements Repurchase Agreements Overnight and Continuous U.S. Treasury and Agency Securities $ 39.7 Total Borrowings 39.7 Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 23 39.7 Amounts related to agreements not included in Note 23 —

Loans and Leases

Loans and Leases	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Loans and Leases	Loans and Leases Amounts outstanding for loans and leases, by segment and class, are shown below. Table 43: Loans and Leases (In Millions) March 31, December 31, Commercial Commercial and Institutional $ 8,532.1 $ 8,728.1 Commercial Real Estate 3,185.0 3,228.8 Non-U.S. 1,648.6 2,701.6 Lease Financing, net 89.3 90.7 Other 180.5 426.0 Total Commercial 13,635.5 15,175.2 Personal Private Client 10,669.9 10,733.3 Residential Real Estate 6,286.6 6,514.0 Other 28.6 67.5 Total Personal 16,985.1 17,314.8 Total Loans and Leases $ 30,620.6 $ 32,490.0 Allowance for Credit Losses Assigned to Loans and Leases (114.5 ) (112.6 ) Net Loans and Leases $ 30,506.1 $ 32,377.4 Residential real estate loans consist of traditional first lien mortgages and equity credit lines that generally require a loan-to-collateral value of no more than 65% to 80% at inception. Northern Trust’s equity credit line products generally have draw periods of up to 10 years and a balloon payment of any outstanding balance is due at maturity. Payments are interest only with variable interest rates. Northern Trust does not offer equity credit lines that include an option to convert the outstanding balance to an amortizing payment loan. As of March 31, 2019 and December 31, 2018 , equity credit lines totaled $526.7 million and $655.5 million , respectively, and equity credit lines for which first liens were held by Northern Trust represented 96% and 95% of the total equity credit lines as of March 31, 2019 and December 31, 2018 , respectively. Included within the non-U.S., commercial-other and personal-other classes are short-duration advances primarily related to the processing of custodied client investments that totaled $1.2 billion at March 31, 2019 , and $2.2 billion at December 31, 2018 . Demand deposit overdrafts reclassified as loan balances totaled $88.4 million and $152.5 million at March 31, 2019 and December 31, 2018 , respectively. There were no loans or leases classified as held for sale as of March 31, 2019 and December 31, 2018 , respectively. Credit Quality Indicators. Credit quality indicators are statistics, measurements or other metrics that provide information regarding the relative credit risk of loans and leases. Northern Trust utilizes a variety of credit quality indicators to assess the credit risk of loans and leases at the segment, class and individual credit exposure levels. As part of its credit process, Northern Trust utilizes an internal borrower risk rating system to support identification, approval and monitoring of credit risk. Borrower risk ratings are used in credit underwriting, management reporting and the calculation of credit loss allowances and economic capital. Risk ratings are used for ranking the credit risk of borrowers and the probability of their default. Each borrower is rated using one of a number of ratings models or other subjective assessment methodologies, which consider both quantitative and qualitative factors. The ratings models vary among classes of loans and leases in order to capture the unique risk characteristics inherent within each particular type of credit exposure. Provided below are the more significant performance indicator attributes considered within Northern Trust’s borrower rating models, by loan and lease class. • Commercial and Institutional: leverage, profit margin, liquidity, asset size and capital levels; • Commercial Real Estate: debt service coverage, loan-to-value ratio, leasing status and guarantor support; • Lease Financing and Commercial-Other: leverage, profit margin, liquidity, asset size and capital levels; • Non-U.S.: leverage, profit margin, liquidity, return on assets and capital levels; • Residential Real Estate: payment history, credit bureau scores and loan-to-value ratio; • Private Client: cash-flow-to-debt and net worth ratios, leverage and liquidity; and • Personal-Other: cash-flow-to-debt and net worth ratios. While the criteria vary by model, the objective is for the borrower ratings to be consistent in both the measurement and ranking of risk. Each model is calibrated to a master rating scale to support this consistency. Ratings for borrowers not in default range from “1” for the strongest credits to “7” for the weakest non-defaulted credits. Ratings of “8” or “9” are used for defaulted borrowers. Borrower risk ratings are monitored and are revised when events or circumstances indicate a change is required. Risk ratings are validated at least annually. Loan and lease segment and class balances as of March 31, 2019 and December 31, 2018 are provided below, segregated by borrower ratings into “1 to 3,” “4 to 5” and “6 to 9” (watch list), categories. Table 44: Borrower Ratings March 31, 2019 December 31, 2018 (In Millions) 1 to 3 Category 4 to 5 Category 6 to 9 Category (Watch List) Total 1 to 3 Category 4 to 5 Category 6 to 9 Category (Watch List) Total Commercial Commercial and Institutional $ 5,293.4 $ 3,118.6 $ 120.1 $ 8,532.1 $ 5,477.4 $ 3,159.8 $ 90.9 $ 8,728.1 Commercial Real Estate 1,095.2 2,068.8 21.0 3,185.0 1,209.6 1,992.2 27.0 3,228.8 Non-U.S. 1,021.1 626.3 1.2 1,648.6 1,625.3 1,075.3 1.0 2,701.6 Lease Financing, net 76.9 12.4 — 89.3 78.3 12.4 — 90.7 Other 104.9 75.6 — 180.5 203.3 222.7 — 426.0 Total Commercial 7,591.5 5,901.7 142.3 13,635.5 8,593.9 6,462.4 118.9 15,175.2 Personal Private Client 5,983.0 4,680.2 6.7 10,669.9 6,321.1 4,403.2 9.0 10,733.3 Residential Real Estate 2,535.3 3,496.6 254.7 6,286.6 2,745.0 3,502.3 266.7 6,514.0 Other 16.6 12.0 — 28.6 32.2 35.3 — 67.5 Total Personal 8,534.9 8,188.8 261.4 16,985.1 9,098.3 7,940.8 275.7 17,314.8 Total Loans and Leases $ 16,126.4 $ 14,090.5 $ 403.7 $ 30,620.6 $ 17,692.2 $ 14,403.2 $ 394.6 $ 32,490.0 Loans and leases in the “1 to 3” category are expected to exhibit minimal to modest probabilities of default and are characterized by borrowers having the strongest financial qualities, including above average financial flexibility, cash flows and capital levels. Borrowers assigned these ratings are anticipated to experience very little to moderate financial pressure in adverse down cycle scenarios. As a result of these characteristics, borrowers within this category exhibit a minimal to modest likelihood of loss. Loans and leases in the “4 to 5” category are expected to exhibit moderate to acceptable probabilities of default and are characterized by borrowers with less financial flexibility than those in the “1 to 3” category. Cash flows and capital levels are generally sufficient to allow for borrowers to meet current requirements, but have fewer financial resources to manage through economic downturns. As a result of these characteristics, borrowers within this category exhibit a moderate likelihood of loss. Loans and leases in the watch list category have elevated credit risk profiles that are monitored through internal watch lists, and consist of credits with borrower ratings of “6 to 9.” These credits, which include all nonperforming credits, are expected to exhibit minimally acceptable probabilities of default, elevated risk of default, or are currently in default. Borrowers associated with these risk profiles that are not currently in default have limited financial flexibility. Cash flows and capital levels range from acceptable to potentially insufficient to meet current requirements, particularly in adverse down cycle scenarios. As a result of these characteristics, borrowers in this category exhibit an elevated likelihood of loss. Recognition of Income. Interest income on loans is recorded on an accrual basis unless, in the opinion of management, there is a question as to the ability of the debtor to meet the terms of the loan agreement, or interest or principal is more than 90 days contractually past due and the loan is not well-secured and in the process of collection. Loans meeting such criteria are classified as nonperforming and interest income is recorded on a cash basis. At the time a loan is determined to be nonperforming, interest accrued but not collected is reversed against interest income in the current period. Interest collected on nonperforming loans is applied to principal unless, in the opinion of management, collectability of principal is not in doubt. Management’s assessment of the indicators of loan and lease collectability, and its policies relative to the recognition of interest income, including the suspension and subsequent resumption of income recognition, do not meaningfully vary between loan and lease classes. Nonperforming loans are returned to performing status when factors indicating doubtful collectability no longer exist. Factors considered in returning a loan to performing status are consistent across all classes of loans and leases and, in accordance with regulatory guidance, relate primarily to expected payment performance. Loans are eligible to be returned to performing status when: (i) no principal or interest that is due is unpaid and repayment of the remaining contractual principal and interest is expected or (ii) the loan has otherwise become well-secured (possessing realizable value sufficient to discharge the debt, including accrued interest, in full) and is in the process of collection (through action reasonably expected to result in debt repayment or restoration to a current status in the near future). A loan that has not been brought fully current may be restored to performing status provided there has been a sustained period of repayment performance (generally a minimum of six months) by the borrower in accordance with the contractual terms, and Northern Trust is reasonably assured of repayment within a reasonable period of time. Additionally, a loan that has been formally restructured so as to be reasonably assured of repayment and performance according to its modified terms may be returned to accrual status, provided there was a well-documented credit evaluation of the borrower’s financial condition and prospects of repayment under the revised terms and there has been a sustained period of repayment performance (generally a minimum of six months) under the revised terms. Past due status is based on how long since the contractual due date a principal or interest payment has been past due. For disclosure purposes, loans that are 29 days past due or less are reported as current. The following table provides balances and delinquency status of performing and nonperforming loans and leases by segment and class, as well as the total OREO and nonperforming asset balances, as of March 31, 2019 and December 31, 2018 . Table 45: Delinquency Status March 31, 2019 (In Millions) Current 30-59 Days Past Due 60-89 Days Past Due 90 Days or More Past Due Total Performing Nonperforming Total Loans and Leases Commercial Commercial and Institutional $ 8,499.3 $ 22.1 $ 3.1 $ — $ 8,524.5 $ 7.6 $ 8,532.1 Commercial Real Estate 3,161.4 3.3 8.1 8.0 3,180.8 4.2 3,185.0 Non-U.S. 1,647.6 0.4 — — 1,648.0 0.6 1,648.6 Lease Financing, net 89.3 — — — 89.3 — 89.3 Other 180.5 — — — 180.5 — 180.5 Total Commercial 13,578.1 25.8 11.2 8.0 13,623.1 12.4 13,635.5 Personal Private Client 10,622.5 39.1 7.6 0.5 10,669.7 0.2 10,669.9 Residential Real Estate 6,143.2 28.9 6.5 4.5 6,183.1 103.5 6,286.6 Other 28.6 — — — 28.6 — 28.6 Total Personal 16,794.3 68.0 14.1 5.0 16,881.4 103.7 16,985.1 Total Loans and Leases $ 30,372.4 $ 93.8 $ 25.3 $ 13.0 $ 30,504.5 $ 116.1 $ 30,620.6 Other Real Estate Owned $ 8.0 Total Nonperforming Assets $ 124.1 December 31, 2018 (In Millions) Current 30-59 Days Past Due 60-89 Days Past Due 90 Days or More Past Due Total Performing Nonperforming Total Loans and Leases Commercial Commercial and Institutional $ 8,678.2 $ 37.4 $ 4.5 $ 1.2 $ 8,721.3 $ 6.8 $ 8,728.1 Commercial Real Estate 3,191.5 8.4 15.6 6.4 3,221.9 6.9 3,228.8 Non-U.S. 2,701.2 — — — 2,701.2 0.4 2,701.6 Lease Financing, net 90.7 — — — 90.7 — 90.7 Other 426.0 — — — 426.0 — 426.0 Total Commercial 15,087.6 45.8 20.1 7.6 15,161.1 14.1 15,175.2 Personal Private Client 10,681.1 39.5 12.5 — 10,733.1 0.2 10,733.3 Residential Real Estate 6,376.8 27.2 6.2 8.8 6,419.0 95.0 6,514.0 Other 67.5 — — — 67.5 — 67.5 Total Personal 17,125.4 66.7 18.7 8.8 17,219.6 95.2 17,314.8 Total Loans and Leases $ 32,213.0 $ 112.5 $ 38.8 $ 16.4 $ 32,380.7 $ 109.3 $ 32,490.0 Other Real Estate Owned $ 8.4 Total Nonperforming Assets $ 117.7 Impaired Loans. A loan is considered to be impaired when, based on current information and events, management determines that it is probable that Northern Trust will be unable to collect all amounts due according to the contractual terms of the loan agreement. Impaired loans are identified through ongoing credit management and risk rating processes, including the formal review of past due and watch list credits. Payment performance and delinquency status are critical factors in identifying impairment for all loans and leases, particularly those within the residential real estate, private client and personal-other classes. Other key factors considered in identifying impairment of loans and leases within the commercial and institutional, lease financing, net, non-U.S., and commercial-other classes relate to the borrower’s ability to perform under the terms of the obligation as measured through the assessment of future cash flows, including consideration of collateral value, market value, and other factors. A loan is also considered to be impaired if its terms have been modified as a concession by Northern Trust or a bankruptcy court resulting from the debtor’s financial difficulties, referred to as a troubled debt restructuring (TDR). All TDRs are reported as impaired loans in the calendar year of their restructuring. In subsequent years, a TDR may cease being reported as impaired if the loan was modified at a market rate and has performed according to the modified terms for at least six payment periods. A loan that has been modified at a below market rate will return to performing status if it satisfies the six payment periods performance requirement; however, it will remain reported as impaired. Impairment is measured based upon the present value of expected future cash flows, discounted at the loan's original effective interest rate, the fair value of the collateral if the loan is collateral dependent, or the loan's observable market value. If the loan valuation is less than the recorded value of the loan, based on the certainty of loss, either a specific allowance is established, or a charge-off is recorded, for the difference. Smaller balance (individually less than $1 million ) homogeneous loans are collectively evaluated for impairment and excluded from impaired loan disclosures as allowed under applicable accounting standards. Northern Trust’s accounting policies for material impaired loans is consistent across all classes of loans and leases. The following table provides information related to impaired loans by segment and class. Table 46: Impaired Loans as of the Period End As of March 31, 2019 As of December 31, 2018 (In Millions) Recorded Investment Unpaid Principal Balance Specific Allowance Recorded Investment Unpaid Principal Balance Specific Allowance With No Related Specific Allowance Commercial and Institutional $ 0.1 $ 0.1 $ — $ 0.2 $ 0.4 $ — Commercial Real Estate 2.8 4.7 — 5.8 7.6 — Private Client 1.7 1.7 — 1.7 1.7 — Residential Real Estate 88.7 117.6 — 76.7 104.7 — With a Related Specific Allowance Commercial and Institutional 7.5 8.8 3.7 6.4 7.3 3.0 Commercial Real Estate 1.3 1.4 1.1 2.6 2.8 1.1 Residential Real Estate 21.2 24.8 2.9 22.8 26.1 3.1 Total Commercial 11.7 15.0 4.8 15.0 18.1 4.1 Personal 111.6 144.1 2.9 101.2 132.5 3.1 Total $ 123.3 $ 159.1 $ 7.7 $ 116.2 $ 150.6 $ 7.2 Three Months Ended March 31, 2019 2018 (In Millions) Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized With No Related Specific Allowance Commercial and Institutional $ 0.1 $ — $ 19.6 $ — Commercial Real Estate 3.8 — 6.5 — Private Client 1.7 — 0.6 — Residential Real Estate 89.2 0.6 93.8 0.5 With a Related Specific Allowance Commercial and Institutional 7.1 — — — Commercial Real Estate 1.7 — 1.9 — Residential Real Estate 20.9 — 13.8 — Total Commercial 12.7 — 28.0 — Personal 111.8 0.6 108.2 0.5 Total $ 124.5 $ 0.6 $ 136.2 $ 0.5 Note: Average recorded investment in impaired loans is calculated as the average of the month-end impaired loan balances for the period. Interest income that would have been recorded for nonperforming loans in accordance with their original terms was $1.9 million and $2.2 million , respectively, for the three months ended March 31, 2019 and 2018 . There were $9.0 million and $12.6 million of aggregate undrawn loan commitments and standby letters of credit at March 31, 2019 and December 31, 2018 , respectively, issued to borrowers whose loans were classified as nonperforming or impaired. Troubled Debt Restructurings (TDRs). Included within impaired loans were $70.9 million and $64.6 million of nonperforming TDRs, and $33.2 million and $35.2 million of performing TDRs as of March 31, 2019 and December 31, 2018 , respectively. All TDRs are reported as impaired loans in the calendar year of their restructuring. In subsequent years, a TDR may cease being reported as impaired if the loan was modified at a market rate and has performed according to the modified terms for at least six months. A loan that has been modified at a below market rate will return to performing status if it satisfies the six-month performance requirement; however, it will remain reported as impaired. The following table provides, by segment and class, the number of loans and leases modified in TDRs during the three -month periods ended March 31, 2019 and 2018 , and the recorded investments and unpaid principal balances as of March 31, 2019 and 2018 . Table 47: Modified Troubled Debt Restructurings ($ In Millions) Three Months Ended March 31, 2019 Number of Loans and Leases Recorded Investment Unpaid Principal Balance Commercial Commercial and Institutional 1 $ 7.6 $ 8.8 Commercial Real Estate — — — Total Commercial 1 7.6 8.8 Personal Private Client — — — Residential Real Estate 13 9.8 9.9 Total Personal 13 9.8 9.9 Total Loans and Leases 14 $ 17.4 $ 18.7 Note: Period-end balances reflect all paydowns and charge-offs during the period. ($ In Millions) Three Months Ended March 31, 2018 Number of Loans and Leases Recorded Investment Unpaid Principal Balance Commercial Commercial and Institutional 1 $ 0.3 $ 0.5 Commercial Real Estate — — — Total Commercial 1 0.3 0.5 Personal Private Client 1 — 0.1 Residential Real Estate 14 7.5 8.7 Total Personal 15 7.5 8.8 Total Loans and Leases 16 $ 7.8 $ 9.3 Note: Period-end balances reflect all paydowns and charge-offs during the period. TDR modifications involve extensions of term, deferrals of principal, interest rate concessions, and other modifications. Other modifications typically reflect other nonstandard terms which Northern Trust would not offer in non-troubled situations. During the three months ended March 31, 2019 , the TDR modifications of loans within residential real estate were extension of term, other modifications, and deferred principal. During the three months ended March 31, 2019 , the TDR modification within commercial and institutional was an other modification. During the three months ended March 31, 2018 , the TDR modifications of loans within residential real estate were extension of term and other modifications. During the three months ended March 31, 2018 , there were no TDR modifications within commercial real estate. There were no residential real estate loans modified in a TDR during the twelve months ended December 31, 2018 , which subsequently became nonperforming during the three months ended March 31, 2019 . There were two residential real estate loans modified in TDR during the twelve months ended December 31, 2017 , which subsequently became nonperforming during the three months ended March 31, 2018 . The total recorded investment for these loans was approximately $0.3 million and the unpaid principal balance for these loans was approximately $0.4 million . All loans and leases modified in TDRs are evaluated for impairment. The nature and extent of impairment of TDRs, including those that have experienced a subsequent default, is considered in the determination of an appropriate level of allowance for credit losses. Northern Trust may obtain physical possession of real estate via foreclosure on an in-substance repossession. As of March 31, 2019 , Northern Trust held foreclosed real estate properties with a carrying value of $8.0 million as a result of obtaining physical possession. In addition, as of March 31, 2019 , Northern Trust had loans with a carrying value of $11.8 million for which formal foreclosure proceedings were in process.

Allowance for Credit Losses

Allowance for Credit Losses	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Allowance for Credit Losses	Allowance for Credit Losses The allowance for credit losses, which represents management’s estimate of probable losses related to specific borrower relationships and inherent in the various loan and lease portfolios, undrawn commitments, and standby letters of credit, is determined by management through a disciplined credit review process. Northern Trust’s accounting policies related to the estimation of the allowance for credit losses and the charging off of loans, leases and other extensions of credit deemed uncollectible are consistent across both loan and lease segments. Loans, leases and other extensions of credit deemed uncollectible are charged to the allowance for credit losses. Subsequent recoveries, if any, are credited to the allowance. Determinations as to whether an uncollectible loan is charged-off or a specific allowance is established are based on management’s assessment as to the level of certainty regarding the amount of loss. The following table provides information regarding changes in the total allowance for credit losses by segment during the three months ended March 31, 2019 and 2018 . Table 48: Changes in the Allowance for Credit Losses Three Months Ended March 31, 2019 2018 (In Millions) Commercial Personal Total Commercial Personal Total Balance at Beginning of Period $ 78.7 $ 59.5 $ 138.2 $ 80.8 $ 73.0 $ 153.8 Charge-Offs (0.1 ) (0.9 ) (1.0 ) (0.8 ) (3.5 ) (4.3 ) Recoveries 0.4 1.8 2.2 0.6 0.7 1.3 Net (Charge-Offs) Recoveries 0.3 0.9 1.2 (0.2 ) (2.8 ) (3.0 ) Provision for Credit Losses (0.4 ) 0.4 — (3.5 ) 0.5 (3.0 ) Balance at End of Period $ 78.6 $ 60.8 $ 139.4 $ 77.1 $ 70.7 $ 147.8 The following table provides information regarding the recorded investments in loans and leases and the allowance for credit losses by segment as of March 31, 2019 and December 31, 2018 . Table 49: Recorded Investments in Loans and Leases March 31, 2019 December 31, 2018 (In Millions) Commercial Personal Total Commercial Personal Total Loans and Leases Specifically Evaluated for Impairment $ 11.7 $ 111.6 $ 123.3 $ 15.0 $ 101.2 $ 116.2 Evaluated for Inherent Impairment 13,623.8 16,873.5 30,497.3 15,160.2 17,213.6 32,373.8 Total Loans and Leases 13,635.5 16,985.1 30,620.6 15,175.2 17,314.8 32,490.0 Allowance for Credit Losses on Credit Exposures Specifically Evaluated for Impairment 4.8 2.9 7.7 4.1 3.1 7.2 Evaluated for Inherent Impairment 53.3 53.5 106.8 53.5 51.9 105.4 Allowance Assigned to Loans and Leases 58.1 56.4 114.5 57.6 55.0 112.6 Allowance for Undrawn Exposures Commitments and Standby Letters of Credit 20.5 4.4 24.9 21.1 4.5 25.6 Total Allowance for Credit Losses $ 78.6 $ 60.8 $ 139.4 $ 78.7 $ 59.5 $ 138.2

Lease Commitments

Lease Commitments	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Lease Commitments	Lease Commitments At March 31, 2019 , Northern Trust was obligated under a number of non-cancelable operating leases, primarily for real estate. Certain leases contain rent escalation clauses based on market indices, renewal option clauses calling for increased rentals, and rental payments based on usage. There are no restrictions imposed by any lease agreement regarding the payment of dividends, debt financing or Northern Trust entering into further lease agreements. The following table provides the components of lease cost for the three months ended March 31, 2019 . Table 50: Lease Cost Components (In Millions) Three Months Ended March 31, 2019 Operating Lease Cost $ 25.2 Variable Lease Cost 10.1 Sublease Income (1.5 ) Total Lease Cost $ 33.8 The following table presents a maturity analysis of lease liabilities as of March 31, 2019 . Table 51: Maturity of Lease Liabilities (In Millions) Maturity of Lease Liabilities 2019 (excluding the three months ended March 31, 2019) $ 74.9 2020 96.6 2021 82.0 2022 66.6 2023 57.3 Later Years 207.0 Total Lease Payments 584.4 Less: Imputed Interest (74.7 ) Present Value of Lease Liabilities $ 509.7 As of March 31, 2019 , Northern Trust has additional operating leases that have not yet commenced for office space which are expected to commence in late 2019 and late 2020 with lease terms of 9 and 15 years , respectively. The location and amount of lease right-of-use assets and lease liabilities recorded in the consolidated balance sheet as of March 31, 2019 are presented below. Table 52: Location and Amount of Lease Assets and Liabilities (In Millions) Location of Lease Assets and Liabilities in the Balance Sheet March 31, Assets Operating Lease Right-of-Use Asset Other Assets $ 460.4 Liabilities Operating Lease Liability Other Liabilities $ 509.7 The weighted-average remaining lease term and weighted-average discount rate applied to leases as of March 31, 2019 were as follows: Table 53: Weighted-Average Remaining Lease Term and Discount Rate March 31, Operating Leases Weighted-Average Remaining Lease Term 7.7 years Weighted-Average Discount Rate 3.4% The following table provides supplemental cash flow information related to leases for the three months ended March 31, 2019 . Table 54: Supplemental Cash Flow Information (In Millions) Three Months Ended March 31, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 28.3 Right-of-use assets obtained in exchange for new operating lease liabilities 1.0 Under the provisions of Accounting Standards Code (ASC) Topic 842, Northern Trust has elected not to restate comparative periods in the period of adoption as of March 31, 2019. Therefore, disclosure with respect to minimum annual lease commitments as of December 31, 2018, for all non-cancelable operating leases with a term of one year or more is provided in the table below, as required by ASC Topic 840. Table 55: Minimum Lease Payments as of December 31, 2018 (In Millions) Future Minimum Lease Payments 2019 $ 98.8 2020 97.8 2021 85.9 2022 77.2 2023 67.7 Later Years 335.7 Total Minimum Lease Payments 763.1 Less: Sublease Rentals (23.4 ) Net Minimum Lease Payments $ 739.7 Operating lease rental expense, net of rental income, is recorded in occupancy expense and amounted to $79.0 million in 2018, $76.7 million in 2017, and $76.1 million in 2016.

Pledged Assets

Pledged Assets	3 Months Ended
	Mar. 31, 2019
Transfers and Servicing [Abstract]
Pledged Assets	Pledged Assets Certain of Northern Trust’s subsidiaries, as required or permitted by law, pledge assets to secure public and trust deposits, repurchase agreements and Federal Home Loan Bank borrowings, as well as for other purposes, including support for securities settlement, primarily related to client activities, for potential Federal Reserve Bank discount window borrowings, and for derivative contracts. As of March 31, 2019 , securities and loans totaling $41.5 billion ( $32.4 billion of government-sponsored agency and other securities, $768.8 million of obligations of states and political subdivisions and $8.3 billion of loans) were pledged. This compares to $39.6 billion ( $30.9 billion of government-sponsored agency and other securities, $640.4 million of obligations of states and political subdivisions and $8.1 billion of loans) at December 31, 2018 . Collateral required for these purposes totaled $9.0 billion and $9.3 billion at March 31, 2019 and December 31, 2018 , respectively. Included in the total pledged assets are available for sale debt securities with a total fair value of $29.1 million and $151.5 million , as of March 31, 2019 and December 31, 2018 , respectively, which were pledged as collateral for agreements to repurchase securities sold transactions, and available for sale debt securities with a total fair value of $26.5 million and $29.0 million , as of March 31, 2019 and December 31, 2018 , respectively, which were pledged as collateral for derivative contracts. The secured parties to these transactions have the right to repledge or sell the securities as it relates to $29.2 million and $151.5 million of the pledged collateral as of March 31, 2019 and December 31, 2018 , respectively. Northern Trust is not permitted, by contract or custom, to repledge or sell securities accepted as collateral under certain repurchase agreements. The total fair value of securities accepted as collateral was $300.0 million as of March 31, 2019 and $605.0 million as of December 31, 2018 . Northern Trust has the right to repledge or sell securities accepted as collateral under certain repurchase agreements. The fair value of these securities accepted as collateral was $215.2 million as of March 31, 2019 and $426.2 million as of December 31, 2018 . There was no repledged or sold collateral at March 31, 2019 or December 31, 2018 . Northern Trust has the right to repledge or sell securities accepted as collateral under derivative contracts. The total fair value of securities accepted as collateral was $30.4 million as of March 31, 2019 and $15.3 million as of December 31, 2018 . There was no repledged or sold collateral at March 31, 2019 or December 31, 2018 . Deposits maintained to meet Federal Reserve Bank reserve requirements averaged $1.5 billion for the three months ended March 31, 2019 and $1.8 billion for the three months ended March 31, 2018 .

Goodwill and Other Intangibles

Goodwill and Other Intangibles	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangibles	Goodwill and Other Intangibles The carrying amounts of goodwill and other intangibles assets, reflecting the effect of foreign exchange rates on non-U.S.-dollar-denominated balances, by reporting segment at March 31, 2019 , and December 31, 2018 , were as follows: Table 56: Goodwill by Reporting Segment (In Millions) March 31, December 31, Corporate & Institutional Services $ 611.9 $ 598.2 Wealth Management 71.1 71.1 Total Goodwill $ 683.0 $ 669.3 The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of March 31, 2019 and December 31, 2018 , were as follows: Table 57: Other Intangible Assets (In Millions) March 31, December 31, Gross Carrying Amount $ 206.4 $ 211.1 Less: Accumulated Amortization 74.0 72.5 Net Book Value $ 132.4 $ 138.6 Other intangible assets consist primarily of the value of acquired client relationships and are included within other assets in the consolidated balance sheets. Amortization expense related to other intangible assets totaled $4.2 million and $4.5 million for the three months ended March 31, 2019 and 2018 , respectively. Amortization for the remainder of 2019 and for the years 2020 , 2021 , 2022 , and 2023 is estimated to be $12.5 million , $16.6 million , $14.2 million , $9.6 million , and $9.4 million , respectively. In the first quarter of 2019, Northern Trust completed the purchase accounting related to its acquisition of BEx LLC, a provider of foreign exchange software solutions. The purchase price recorded in connection with the closing of the acquisition totaled $37.9 million . Goodwill and software intangible assets associated with the acquisition totaled $12.5 million and $25.0 million , respectively.

Reporting Segments

Reporting Segments	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Reporting Segments	Reporting Segments Northern Trust is organized around its two client-focused reporting segments: C&IS and Wealth Management. Asset management and related services are provided to C&IS and Wealth Management clients primarily by the Asset Management business. The revenue and expenses of Asset Management and certain other support functions are allocated fully to C&IS and Wealth Management. Reporting segment financial information, presented on an internal management-reporting basis, is determined by accounting systems used to allocate revenue and expense to each segment, and incorporates processes for allocating assets, liabilities, equity and the applicable interest income and expense utilizing a funds transfer pricing (FTP) methodology. Under the methodology, assets and liabilities receive a funding charge or credit that considers interest rate risk, liquidity risk, and other product characteristics on an instrument level. Effective January 1, 2019, Northern Trust implemented several enhancements to its FTP methodology, including the allocation of contingent liquidity charges to C&IS and Wealth Management client instruments and products. These methodology enhancements affect the results of each reporting segment. Due to the lack of historical information, prior-period segment results have not been revised to reflect the methodology enhancements. Also beginning in 2019, all revenues, expenses and average assets are allocated to C&IS and Wealth Management with the exception of non-recurring activities such as certain costs associated with acquisitions, divestitures, litigation, restructuring, and tax adjustments not directly attributable to a specific reporting segment. For reporting periods ended prior to January 1, 2019, income and expense associated with the wholesale funding activities and investment portfolios of the Corporation and its principal subsidiary, The Northern Trust Company (the Bank), as well as certain corporate-based expense, executive level compensation and nonrecurring items, were not allocated to C&IS and Wealth Management, and were reported in Treasury and Other. Reporting segment results are subject to reclassification when organizational changes are made. The results are also subject to refinements in revenue and expense allocation methodologies, which are typically reflected on a prospective basis. The following table reflects the earnings contributions and average assets of Northern Trust’s reporting segments for the three -month periods ended March 31, 2019 and 2018 . Table 58: Results of Reporting Segments Three Months Ended March 31, Corporate & Wealth Treasury and Total ($ In Millions) 2019 2018 2019 2018 2019 2018 2019 2018 Noninterest Income Trust, Investment and Other Servicing Fees $ 535.2 $ 544.3 $ 393.7 $ 393.4 $ — $ — $ 928.9 $ 937.7 Foreign Exchange Trading Income 59.7 62.4 6.5 1.2 — 14.9 66.2 78.5 Other Noninterest Income 43.4 46.6 25.5 25.7 (5.1 ) 3.5 63.8 75.8 Net Interest Income* 234.8 229.4 195.0 198.8 — (35.5 ) 429.8 392.7 Revenue* 873.1 882.7 620.7 619.1 (5.1 ) (17.1 ) 1,488.7 1,484.7 Provision for Credit Losses (1.1 ) (3.9 ) 1.1 0.9 — — — (3.0 ) Noninterest Expense 648.0 585.6 379.9 365.7 0.8 44.0 1,028.7 995.3 Income before Income Taxes* 226.2 301.0 239.7 252.5 (5.9 ) (61.1 ) 460.0 492.4 Provision for Income Taxes* 53.6 66.8 60.8 62.4 (1.5 ) (18.4 ) 112.9 110.8 Net Income $ 172.6 $ 234.2 $ 178.9 $ 190.1 $ (4.4 ) $ (42.7 ) $ 347.1 $ 381.6 Percentage of Consolidated Net Income 50 % 61 % 51 % 50 % (1 )% (11 )% 100 % 100 % Average Assets $ 90,351.7 $ 83,637.0 $ 29,065.0 $ 26,108.0 $ — $ 14,748.3 $ 119,416.7 $ 124,493.3 * Non-GAAP financial measures stated on a fully taxable equivalent basis (FTE). Total consolidated includes FTE adjustments of $7.8 million for 2019 and $8.7 million for 2018 . Further discussion of reporting segment results is provided within the “Reporting Segments” section of Management’s Discussion and Analysis of Financial Condition and Results of Operations.

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock. The Corporation is authorized to issue 10 million shares of preferred stock without par value. The Board of Directors is authorized to fix the particular designations, preferences and relative, participating, optional and other special rights and qualifications, limitations or restrictions for each series of preferred stock issued. As of March 31, 2019 , the Corporation had issued and outstanding 500,000 depositary shares, each representing a 1/100th ownership interest in a share of Series D Non-Cumulative Perpetual Preferred Stock (the “Series D Preferred Stock”) issued in August 2016 . Equity related to Series D Preferred Stock as of March 31, 2019 and December 31, 2018 was $493.5 million . Shares of the Series D Preferred Stock have no par value and a liquidation preference of $100,000 (equivalent to $1,000 per depositary share). Dividends on the Series D Preferred Stock, which are not mandatory, accrue and are payable on the liquidation preference amount, on a non-cumulative basis, at a rate per annum equal to (i) 4.60% from the original issue date of the Series D Preferred Stock to but excluding October 1, 2026 ; and (ii) a floating rate equal to Three-Month LIBOR plus 3.202% from and including October 1, 2026 . Fixed rate dividends are payable in arrears on the 1st day of April and October of each year, through and including October 1, 2026 , and floating rate dividends will be payable in arrears on the 1st day of January, April, July and October of each year, commencing on January 1, 2027 . On January 22, 2019 , the Corporation declared a cash dividend of $2,300 per share of Series D Preferred Stock payable on April 1, 2019 , to stockholders of record as of March 15, 2019 . As of March 31, 2019 , the Corporation also had issued and outstanding 16 million depositary shares, each representing 1/1000th ownership interest in a share of Series C Non-Cumulative Perpetual Preferred Stock (“Series C Preferred Stock”), issued in August 2014. Equity related to Series C Preferred Stock as of March 31, 2019 and December 31, 2018 was $388.5 million . Series C Preferred Stock has no par value and has a liquidation preference of $25,000 (equivalent to $25 per depositary share). Dividends on the Series C Preferred Stock, which are not mandatory, accrue and are payable on the liquidation preference amount, on a non-cumulative basis, quarterly in arrears on the first day of January, April, July and October of each year, at a rate per annum equal to 5.85% . On January 22, 2019 , the Corporation declared a cash dividend of $365.625 per share of Series C Preferred Stock payable on April 1, 2019 , to stockholders of record as of March 15, 2019 . Common Stock. During the three months ended March 31, 2019 , the Corporation repurchased 2,850,152 shares of common stock, including 510,011 shares withheld related to share-based compensation, at a total cost of $257.4 million ( $90.31 average price per share). The Corporation’s current stock repurchase authorization to repurchase up to 25.0 million shares was approved by the Board of Directors in July 2018. Shares are repurchased by the Corporation, to, among other things, manage the Corporation’s capital levels. Repurchased shares are used for general purposes, including the issuance of shares under stock option and other incentive plans. The repurchase authorization approved by the Board of Directors has no expiration date. Under the Corporation’s 2018 Capital Plan, which was reviewed without objection by the Federal Reserve, the Corporation may repurchase up to $272.2 million of common stock after March 31, 2019 through June 30, 2019 .

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) The following tables summarize the components of accumulated other comprehensive income (loss) (AOCI) at March 31, 2019 and 2018 , and changes during the three -month periods then ended. Table 59: Summary of Changes in Accumulated Other Comprehensive Income (Loss) (In Millions) Balance at March 31, 2019 Net Change Balance at December 31, 2018 Net Unrealized Gains (Losses) on Debt Securities Available for Sale* $ (29.3 ) $ 85.6 $ (114.9 ) Net Unrealized Gains (Losses) on Cash Flow Hedges (0.3 ) (4.3 ) 4.0 Net Foreign Currency Adjustments 82.7 14.8 67.9 Net Pension and Other Postretirement Benefit Adjustments (398.4 ) 12.3 (410.7 ) Total $ (345.3 ) $ 108.4 $ (453.7 ) (In Millions) Balance at March 31, 2018 Net Change Reclassification of Certain Tax Effects from AOCI Balance at December 31, 2017 Net Unrealized Gains (Losses) on Debt Securities Available for Sale $ (147.6 ) $ (55.0 ) $ (17.8 ) $ (74.8 ) Net Unrealized Gains (Losses) on Cash Flow Hedges 1.7 (3.7 ) 0.9 4.5 Net Foreign Currency Adjustments 32.6 (13.1 ) 47.5 (1.8 ) Net Pension and Other Postretirement Benefit Adjustments (392.4 ) 5.7 (55.9 ) (342.2 ) Total $ (505.7 ) $ (66.1 ) $ (25.3 ) $ (414.3 ) * Includes net unrealized gains on debt securities transferred from available for sale to held to maturity during the year ended December 31, 2018 . Table 60: Details of Changes in Accumulated Other Comprehensive Income (Loss) Three Months Ended March 31, 2019 2018 (In Millions) Before Tax Tax Effect After Tax Before Tax Tax Effect After Tax Unrealized Gains (Losses) on Debt Securities Available for Sale Unrealized Gains (Losses) on Debt Securities Available for Sale $ 115.3 $ (29.9 ) $ 85.4 $ (75.4 ) $ 20.4 $ (55.0 ) Reclassification Adjustment for (Gains) Losses Included in Net Income 0.2 — 0.2 — — — Net Change $ 115.5 $ (29.9 ) $ 85.6 $ (75.4 ) $ 20.4 $ (55.0 ) Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ 7.2 $ (1.7 ) $ 5.5 $ 13.0 $ (3.2 ) $ 9.8 Interest Rate Contracts 0.6 (0.2 ) 0.4 (1.4 ) 0.4 (1.0 ) Reclassification Adjustment for (Gains) Losses Included in Net Income (13.6 ) 3.4 (10.2 ) (16.6 ) 4.1 (12.5 ) Net Change $ (5.8 ) $ 1.5 $ (4.3 ) $ (5.0 ) $ 1.3 $ (3.7 ) Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (6.5 ) $ 1.6 $ (4.9 ) $ 44.6 $ (2.8 ) $ 41.8 Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) 0.7 (0.2 ) 0.5 1.2 (0.3 ) 0.9 Net Investment Hedge Gains (Losses) 28.6 (9.4 ) 19.2 (74.3 ) 18.5 (55.8 ) Net Change $ 22.8 $ (8.0 ) $ 14.8 $ (28.5 ) $ 15.4 $ (13.1 ) Pension and Other Postretirement Benefit Adjustments Net Actuarial Gain (Loss) $ 11.3 $ (3.1 ) $ 8.2 $ 10.1 $ (2.5 ) $ 7.6 Reclassification Adjustment for (Gains) Losses Included in Net Income 5.4 (1.3 ) 4.1 9.1 (11.0 ) (1.9 ) Net Change $ 16.7 $ (4.4 ) $ 12.3 $ 19.2 $ (13.5 ) $ 5.7 The following table provides the location and before-tax amounts of reclassifications out of AOCI during the three months ended March 31, 2019 . Table 61: Reclassification Adjustment out of Accumulated Other Comprehensive Income (In Millions) Location of Reclassification Adjustments Recognized in Income Amount of Reclassification Adjustments Recognized in Income Three Months Ended March 31, 2019 Debt Securities Available for Sale Realized (Gains) Losses on Debt Securities Available for Sale Investment Security Gains (Losses), net $ 0.2 Realized (Gains) Losses on Cash Flow Hedges Foreign Exchange Contracts Other Operating Income $ 0.6 Interest Income (14.4 ) Interest Rate Contracts Interest Expense 0.2 Total Realized (Gains) on Cash Flow Hedges $ (13.6 ) Pension and Other Postretirement Benefit Adjustments Amortization of Net Actuarial Loss Employee Benefits $ 5.5 Amortization of Prior Service Cost Employee Benefits (0.1 ) Gross Reclassification Adjustment $ 5.4 (In Millions) Location of Reclassification Adjustments Recognized in Income Amount of Reclassification Adjustments Recognized in Income Three Months Ended March 31, 2018 Debt Securities Available for Sale Realized (Gains) Losses on Debt Securities Available for Sale Investment Security Gains (Losses), net $ — Realized (Gains) Losses on Cash Flow Hedges Foreign Exchange Contracts Other Operating Income $ (2.4 ) Interest Income (14.2 ) Interest Rate Contracts Interest Income — Total Realized (Gains) on Cash Flow Hedges $ (16.6 ) Pension and Other Postretirement Benefit Adjustments Amortization of Net Actuarial Loss Employee Benefits $ 9.2 Amortization of Prior Service Cost Employee Benefits (0.1 ) Gross Reclassification Adjustment $ 9.1

Net Income Per Common Share Com

Net Income Per Common Share Computations	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Net Income Per Common Share Computations	Net Income Per Common Share Computations The computations of net income per common share are presented in the following table. Table 62: Net Income per Common Share Three Months Ended March 31, ($ In Millions Except Per Common Share Information) 2019 2018 Basic Net Income Per Common Share Average Number of Common Shares Outstanding 218,236,802 225,681,167 Net Income $ 347.1 $ 381.6 Less: Dividends on Preferred Stock 17.3 17.3 Net Income Applicable to Common Stock $ 329.8 $ 364.3 Less: Earnings Allocated to Participating Securities 4.3 5.2 Earnings Allocated to Common Shares Outstanding $ 325.5 $ 359.1 Basic Net Income Per Common Share $ 1.49 $ 1.59 Diluted Net Income Per Common Share Average Number of Common Shares Outstanding 218,236,802 225,681,167 Plus: Dilutive Effect of Share-based Compensation 1,033,413 1,366,352 Average Common and Potential Common Shares 219,270,215 227,047,519 Earnings Allocated to Common and Potential Common Shares $ 325.4 $ 359.2 Diluted Net Income Per Common Share $ 1.48 $ 1.58 Note: For the three months ended March 31, 2019 , there were no common stock equivalents excluded in the computation of diluted net income per share. There were no common stock equivalents excluded in the computation of diluted net income per share for the three months ended March 31, 2018 .

Revenue from Contracts with Cli

Revenue from Contracts with Clients	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Clients	Revenue from Contracts with Clients Trust, Investment, and Other Servicing Fees. Custody and fund administration income is comprised of revenues received from our core asset servicing business for providing custody, fund administration, and middle-office-related services, primarily to C&IS clients. Investment management and advisory income contains revenue received from providing asset management and related services to Wealth Management and C&IS clients and to Northern Trust sponsored funds. Securities lending income represents revenues generated from securities lending arrangements that Northern Trust enters into as agent, mainly with C&IS clients. Other income largely consists of revenues received from providing employee benefit, investment risk and analytic and other services to C&IS and Wealth Management clients. Other Noninterest Income. Treasury management income represents revenues received from providing cash and liquidity management services to C&IS and Wealth Management clients. The portion of securities commissions and trading income that relates to revenue from contracts with clients is primarily comprised of commissions earned from providing securities brokerage services to Wealth Management and C&IS clients. The portion of other operating income that relates to revenue from contracts with clients is mainly comprised of service fees for banking-related services provided to Wealth Management and C&IS clients. Performance Obligations. Clients are typically charged monthly or quarterly in arrears based on the fee arrangement agreed to with each client; payment terms will vary depending on the client and services offered. Substantially all revenues generated from contracts with clients for asset servicing, asset management, securities lending, treasury management and banking-related services are recognized on an accrual basis, over the period in which services are provided. The nature of Northern Trust’s performance obligations is to provide a series of distinct services in which the customer simultaneously receives and consumes the benefits of the promised services as they are performed. Fee arrangements are mainly comprised of variable amounts based on market value of client assets managed and serviced, transaction volumes, number of accounts, and securities lending volume and spreads. Revenue is recognized using the output method in an amount that reflects the consideration to which Northern Trust expects to be entitled in exchange for providing each month or quarter of service. For contracts with multiple performance obligations, revenue is allocated to each performance obligation based on the price agreed to with the client, representing its relative standalone selling price. Security brokerage revenue is primarily represented by securities commissions received in exchange of providing trade execution related services. Control is transferred at a point in time, on the trade date of the transaction, and fees are typically variable based on transaction volumes and security types. Northern Trust’s contracts with its clients are typically open-ended arrangements. Northern Trust has elected to apply the practical expedient for disclosure requirements allowed in ASU 2014-09 for performance obligations that are included in contracts with an original duration of less than one year. The following table presents revenues disaggregated by major revenue source. Table 63: Revenue Disaggregation Three Months Ended March 31, (In Millions) 2019 2018 Noninterest Income Trust, Investment and Other Servicing Fees Custody and Fund Administration $ 397.5 $ 395.9 Investment Management and Advisory 459.2 465.6 Securities Lending 22.8 26.2 Other 49.4 50.0 Total Trust, Investment and Other Servicing Fees $ 928.9 $ 937.7 Other Noninterest Income Foreign Exchange Income $ 66.2 $ 78.5 Treasury Management 11.7 14.0 Securities Commissions and Trading Income 23.3 27.2 Other Operating Income 29.0 34.8 Investment Security Losses, net (0.2 ) (0.2 ) Total Other Noninterest Income $ 130.0 $ 154.3 Total Noninterest Income $ 1,058.9 $ 1,092.0 Trust, investment and other servicing fees and treasury management fees represent revenue from contracts with clients. For the three months ended March 31, 2019 , revenue from contracts with clients also includes $21.0 million of the $23.3 million total securities commissions and trading income and $9.9 million of the $29.0 million total other operating income. Trust, investment and other servicing fees and treasury management fees represent revenue from contracts with clients. For the three months ended March 31, 2018 , revenue from contracts with clients also includes $24.0 million of the $27.2 million total securities commissions and trading income and $11.3 million of the $34.8 million total other operating income. Receivables Balances. The table below represents receivables balances from contracts with clients, which are included in other assets in the consolidated balance sheets, at March 31, 2019 and December 31, 2018 . Table 64: Client Receivables (In Millions) March 31, December 31, Trust Fees Receivable, net $ 818.4 $ 742.5 Other 91.4 90.1 Total Client Receivables $ 909.8 $ 832.6

Net Interest Income

Net Interest Income	3 Months Ended
	Mar. 31, 2019
Banking and Thrift, Interest [Abstract]
Net Interest Income	Net Interest Income The components of net interest income were as follows: Table 65: Net Interest Income Three Months Ended March 31, (In Millions) 2019 2018 Interest Income Loans and Leases $ 298.2 $ 252.0 Securities — Taxable 277.5 177.8 — Non-Taxable 1.1 2.0 Interest-Bearing Due from and Deposits with Banks (1) 17.9 19.9 Federal Reserve and Other Central Bank Deposits and Other 68.1 54.2 Total Interest Income $ 662.8 $ 505.9 Interest Expense Deposits $ 147.6 $ 63.1 Federal Funds Purchased 13.4 5.3 Securities Sold Under Agreements to Repurchase 1.8 2.7 Other Borrowings 49.9 26.5 Senior Notes 15.9 11.8 Long-Term Debt 10.0 11.0 Floating Rate Capital Debt 2.2 1.5 Total Interest Expense $ 240.8 $ 121.9 Net Interest Income $ 422.0 $ 384.0 (1) Interest-Bearing Due from and Deposits with Banks includes the interest-bearing component of Cash and Due from Banks and Interest-Bearing Deposits with Banks as presented on the consolidated balance sheets.

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Income tax expense for the three months ended March 31, 2019 was $105.1 million , representing an effective tax rate of 23.2% . The prior-year three-month provision for income taxes was $102.1 million , representing an effective tax rate of 21.1% , and included a $22.6 million benefit resulting from a change in accounting method regarding the timing of tax deductions for software development-related expenses, partially offset by a $15.8 million net provision recorded in the prior-year three-month period representing adjustments to the initial estimated impact of the Tax Cuts and Jobs Act enacted in the fourth quarter of 2017.

Pension and Postretirement Heal

Pension and Postretirement Health Care	3 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Pension and Postretirement Health Care	Pension and Postretirement Health Care The following table sets forth the net periodic pension and postretirement benefit expense for Northern Trust’s U.S. and non-U.S. pension plans, supplemental pension plan, and postretirement health care plan for the three months ended March 31, 2019 and 2018 . Table 66: Net Periodic Pension Expense (Benefit) Net Periodic Pension Expense U.S. Plan Three Months Ended March 31, (In Millions) 2019 2018 Service Cost $ 10.4 $ 10.4 Interest Cost 11.8 11.1 Expected Return on Plan Assets (21.7 ) (22.0 ) Amortization Net Actuarial Loss 4.3 7.1 Prior Service Cost (0.1 ) (0.1 ) Net Periodic Pension Expense $ 4.7 $ 6.5 Net Periodic Pension Expense Non-U.S. Plans Three Months Ended March 31, (In Millions) 2019 2018 Service Cost $ 0.5 $ 0.4 Interest Cost 1.0 1.0 Expected Return on Plan Assets (1.0 ) (1.1 ) Settlement Expense — — Net Actuarial Loss Amortization 0.1 0.3 Net Periodic Pension Expense $ 0.6 $ 0.6 Net Periodic Pension Expense Supplemental Plan Three Months Ended March 31, (In Millions) 2019 2018 Service Cost $ 1.0 $ 1.1 Interest Cost 1.5 1.3 Amortization Net Actuarial Loss 1.4 1.8 Prior Service Cost — — Net Periodic Pension Expense $ 3.9 $ 4.2 Net Periodic Postretirement Expense Postretirement Health Care Plan Three Months Ended March 31, (In Millions) 2019 2018 Service Cost $ — $ — Interest Cost 0.3 0.3 Amortization Net Actuarial (Gain) (0.3 ) — Prior Service Cost $ — $ — Net Periodic Postretirement Expense $ — $ 0.3 The components of net periodic pension expense are included in the line item “Employee Benefits” expense in the consolidated statements of income. There were no contributions to the U.S. pension plan during the three months ended March 31, 2019 . There was a $50 million contribution to the U.S. pension plan during the three months ended March 31, 2018 .

Share-Based Compensation Plans

Share-Based Compensation Plans	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-Based Compensation Plans	Share-Based Compensation Plans The Northern Trust Corporation 2017 Long-Term Incentive Plan provides for the grant of non-qualified and incentive stock options; tandem and free-standing stock appreciation rights; stock awards in the form of restricted stock, restricted stock units and other stock awards; and performance awards. Beginning with the grants made on February 21, 2017 under the Corporation’s prior equity incentive plan, restricted stock unit and performance stock unit grants continue to vest in accordance with the original terms of the award if the applicable employee retires after satisfying applicable age and service requirements. For all applicable periods, stock option grants continue to vest in accordance with the original terms of the award if the applicable employee retires after satisfying applicable age and service requirements. The Corporation granted 798,669 stock units awards with a total grant-date fair value of $73.4 million during the three months ended March 31, 2019 , compared to 793,995 stock units awards with a grant-date fair value of $82.6 million during the three months ended March 31, 2018 . Compensation expense for the three months ended March 31, 2019 included $21.2 million attributable to restricted stock units granted to retirement-eligible employees that were expensed in their entirety on the date of grant, compared to $26.9 million in the prior-year quarter. There were no non-qualified stock option grants in the three months ended March 31, 2019 and 2018 . The Corporation granted 211,269 performance stock units with a total grant-date fair value of $19.6 million during the three months ended March 31, 2019 , compared to 242,232 performance stock units with a total grant-date fair value of $25.4 million during the three months ended March 31, 2018 . Compensation expense for the three months ended March 31, 2019 included $9.2 million attributable to performance stock units granted to retirement-eligible employees that were expensed in their entirety on the date of grant as there was no requisite service period associated with the grant. Compensation expense for the three months ended March 31, 2018 included $4.7 million attributable to performance stock units granted to retirement-eligible employees that were expensed from grant date through the requisite service period, which ended on June 30, 2018. Restricted stock unit award compensation expense for the three months ended March 31, 2019 and 2018 included $3.3 million and $2.7 million , respectively, attributable to restricted stock units vested in full and expense in their entirety upon date of grant. Total compensation expense for share-based payment arrangements and the associated tax impacts were as follows for the three months ended March 31, 2019 and 2018 . Table 67: Total Compensation Expense for Share-Based Payment Arrangements Three Months Ended March 31, (In Millions) 2019 2018 Restricted Stock Unit Awards $ 39.2 $ 46.7 Stock Options 0.5 0.8 Performance Stock Units 15.6 9.0 Total Share-Based Compensation Expense 55.3 56.5 Tax Benefits Recognized $ 13.7 $ 14.0

Variable Interest Entities

Variable Interest Entities	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Variable Interest Entities	Variable Interest Entities Variable Interest Entities (VIEs) are defined within GAAP as entities which either have a total equity investment that is insufficient to permit the entity to finance its activities without additional subordinated financial support or whose equity investors lack the characteristics of a controlling financial interest. Investors that finance a VIE through debt or equity interests, or other counterparties that provide other forms of support, such as guarantees, subordinated fee arrangements, or certain types of derivative contracts, are variable interest holders in the entity and the variable interest holder, if any, that has both the power to direct the activities that most significantly impact the entity and a variable interest that could potentially be significant to the entity is deemed to be the VIE’s primary beneficiary and is required to consolidate the VIE. Leveraged Leases. In leveraged leasing transactions, Northern Trust acts as lessor of the underlying asset subject to the lease and typically funds 20 - 30% of the asset’s cost via an equity ownership in a trust with the remaining 70 - 80% provided by third-party non-recourse debt holders. In such transactions, the trusts, which are VIEs, are created to provide the lessee use of the property with substantially all of the rights and obligations of ownership. The lessee’s maintenance and operation of the leased property has a direct effect on the fair value of the underlying property, and the lessee also has the ability to increase the benefits it can receive and limit the losses it can suffer by the manner in which it uses the property. As a result, Northern Trust has determined that it is not the primary beneficiary of the leveraged lease trust VIEs given it lacks the power to direct the activities that most significantly impact the economic performance of the leveraged lease trust VIEs. Northern Trust’s maximum exposure to loss as a result of its involvement with leveraged lease trust VIEs is limited to the carrying amounts of its leveraged lease investments. As of March 31, 2019 and December 31, 2018 , the carrying amounts of these investments, which are included in loans and leases in the consolidated balance sheets, were $56.6 million and $56.8 million , respectively. Northern Trust’s funding requirements relative to the leveraged lease trust VIEs are limited to its invested capital. Northern Trust has no other liquidity arrangements or obligations to purchase assets of the leveraged lease trust VIEs that would expose Northern Trust to a loss. Tax Credit Structures. Northern Trust invests in qualified affordable housing projects and community development entities (collectively, community development projects) that are designed to generate a return primarily through the realization of tax credits. The community development projects are formed as limited partnerships and limited liability companies in which Northern Trust invests as a limited partner/investor member through equity contributions. The economic performance of the community development projects, some of which are VIEs, is subject to the performance of their underlying investment and their ability to operate in compliance with the rules and regulations necessary for the qualification of tax credits generated by equity investments. Northern Trust has determined that it is not the primary beneficiary of any community development project VIEs as it lacks the power to direct the activities that most significantly impact the economic performance of the underlying investments or to affect their ability to operate in compliance with the rules and regulations necessary for the qualification of tax credits generated by equity investments. This power is held by the general partners and managing members who exercise full and exclusive control of the operations of the community development project VIEs. Northern Trust’s maximum exposure to loss as a result of its involvement with community development projects is limited to the carrying amounts of its investments, including any undrawn commitments. As of March 31, 2019 and December 31, 2018 , the carrying amounts of these investments in community development projects that generate tax credits, included in other assets in the consolidated balance sheets, totaled $589.5 million and $602.4 million , respectively, of which $537.8 million and $549.8 million are VIEs as of March 31, 2019 and December 31, 2018 , respectively. As of March 31, 2019 and December 31, 2018 , liabilities related to unfunded commitments on investments in tax credit community development projects, included in other liabilities in the consolidated balance sheets, totaled $302.1 million and $321.0 million , respectively, of which $263.6 million and $279.5 million , related to undrawn commitments on VIEs as of March 31, 2019 and December 31, 2018 , respectively. Northern Trust’s funding requirements are limited to its invested capital and undrawn commitments for future equity contributions. Northern Trust has no exposure to loss from liquidity arrangements and no obligation to purchase assets of the community development projects. Tax credits and other tax benefits attributable to community development projects totaled $16.4 million and $14.7 million for the three months ended March 31, 2019 and 2018 , respectively. Investment Funds. Northern Trust acts as asset manager for various funds in which clients of Northern Trust are investors. As an asset manager of funds, Northern Trust earns a competitively priced fee that is based on assets managed and varies with each fund’s investment objective. Based on its analysis, Northern Trust has determined that it is not the primary beneficiary of these VIEs under GAAP. Periodically, Northern Trust makes seed capital investments to certain funds. As of March 31, 2019 , Northern Trust had $25.0 million of investments valued using net asset value per share and included in other assets and had no unfunded commitments related to seed capital investments. As of December 31, 2018 , Northern Trust had $29.2 million of investments valued using net asset value per share and included in other assets and had no unfunded commitments related to seed capital investments.

Contingent Liabilities

Contingent Liabilities	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Contingent Liabilities	Contingent Liabilities Commitments, Letters of Credit and Indemnifications. Northern Trust, in the normal course of business, enters into various types of commitments and issues letters of credit to meet the liquidity and credit enhancement needs of its clients. Legally binding commitments to extend credit generally have fixed expiration dates or other termination clauses. Since a significant portion of the commitments are expected to expire without being drawn upon, the total commitment amount does not necessarily represent future loans or liquidity requirements. Legally binding commitments to extend credit totaled $25.0 billion as of March 31, 2019 and December 31, 2018 . Standby letters of credit obligate Northern Trust to meet certain financial obligations of its clients, if, under the contractual terms of the agreement, the clients are unable to do so. These instruments are primarily issued to support public and private financial commitments, including commercial paper, bond financing, initial margin requirements on futures exchanges and similar transactions. Northern Trust is obligated to meet the entire financial obligation of these agreements and in certain cases is able to recover the amounts paid through recourse against collateral received or other participants. Standby letters of credit outstanding were $2.5 billion as of March 31, 2019 and December 31, 2018 . As part of its securities custody activities and at the direction of its clients, Northern Trust lends securities owned by clients to borrowers who are reviewed and approved by the Northern Trust Counterparty Risk Management Committee. In connection with these activities, Northern Trust has issued indemnifications to certain clients against certain losses that are a direct result of a borrower’s failure to return securities when due, should the value of such securities exceed the value of the collateral required to be posted. Borrowers are required to collateralize fully securities received with cash or marketable securities. As securities are loaned, collateral is maintained at a minimum of 100% of the fair value of the securities plus accrued interest. The collateral is revalued on a daily basis. The amount of securities loaned as of March 31, 2019 and December 31, 2018 subject to indemnification was $142.6 billion and $128.9 billion , respectively. Because of the credit quality of the borrowers and the requirement to collateralize fully securities borrowed, management believes that the exposure to credit loss from this activity is not significant and no liability was recorded as of March 31, 2019 or December 31, 2018 , related to these indemnifications. Legal Proceedings. In the normal course of business, the Corporation and its subsidiaries are routinely defendants in or parties to pending and threatened legal actions, and are subject to regulatory examinations, information-gathering requests, investigations, and proceedings, both formal and informal. In certain legal actions, claims for substantial monetary damages are asserted. In regulatory matters, claims for disgorgement, restitution, penalties and/or other remedial actions or sanctions may be sought. Based on current knowledge, after consultation with legal counsel and after taking into account current accruals, management does not believe that losses, fines or penalties, if any, arising from pending litigation or threatened legal actions or regulatory matters either individually or in the aggregate, after giving effect to applicable reserves and insurance coverage will have a material adverse effect on the consolidated financial position or liquidity of the Corporation, although such matters could have a material adverse effect on the Corporation’s operating results for a particular period. Under GAAP, (i) an event is “probable” if the “future event or events are likely to occur”; (ii) an event is “reasonably possible” if “the chance of the future event or events occurring is more than remote but less than likely”; and (iii) an event is “remote” if “the chance of the future event or events occurring is slight.” The outcome of litigation and regulatory matters is inherently difficult to predict and/or the range of loss often cannot be reasonably estimated, particularly for matters that (i) will be decided by a jury, (ii) are in early stages, (iii) involve uncertainty as to the likelihood of a class being certified or the ultimate size of the class, (iv) are subject to appeals or motions, (v) involve significant factual issues to be resolved, including with respect to the amount of damages, (vi) do not specify the amount of damages sought or (vii) seek very large damages based on novel and complex damage and liability legal theories. Accordingly, the Corporation cannot reasonably estimate the eventual outcome of these pending matters, the timing of their ultimate resolution or what the eventual loss, fines or penalties, if any, related to each pending matter will be. In accordance with applicable accounting guidance, the Corporation records accruals for litigation and regulatory matters when those matters present loss contingencies that are both probable and reasonably estimable. When loss contingencies are not both probable and reasonably estimable, the Corporation does not record accruals. No material accruals have been recorded for pending litigation or threatened legal actions or regulatory matters. For a limited number of matters for which a loss is reasonably possible in future periods, whether in excess of an accrued liability or where there is no accrued liability, the Corporation is able to estimate a range of possible loss. As of March 31, 2019 , the Corporation has estimated the range of reasonably possible loss for these matters to be from zero to approximately $25 million in the aggregate. The Corporation’s estimate with respect to the aggregate range of reasonably possible loss is based upon currently available information and is subject to significant judgment and a variety of assumptions and known and unknown uncertainties. The matters underlying the estimated range will change from time to time, and actual results may vary significantly from the current estimate. In certain other pending matters, there may be a range of reasonably possible loss (including reasonably possible loss in excess of amounts accrued) that cannot be reasonably estimated for the reasons described above. Such matters are not included in the estimated range of reasonably possible loss discussed above. In 2015 Northern Trust Fiduciary Services (Guernsey) Limited (NTFS), an indirect subsidiary of the Corporation, was charged by a French investigating magistrate judge with complicity in estate tax fraud in connection with the administration of two trusts for which it serves as trustee. Charges also were brought against a number of other persons and entities related to this matter. In 2017 a French court found no estate tax fraud had occurred and NTFS and all other persons and entities charged were acquitted. The Public Prosecutor’s Office of France appealed the court decision and in June 2018 a French appellate court issued its opinion on the matter, acquitting all persons and entities charged, including NTFS. The Public Prosecutor’s Office of France has appealed the appellate court’s decision to the Cour de Cassation, the highest court in France. As trustee, NTFS provided no tax advice and had no involvement in the preparation or filing of the challenged estate tax filings. In the first quarter of 2018, Northern Trust received a document request from the U.S. Commodity Futures Trading Commission (CFTC), Division of Enforcement, seeking the production of documents related to the Bank’s activities as a swap dealer provisionally registered with the CFTC. In addition, the National Futures Association (NFA) provided the Bank with a letter dated April 30, 2018, summarizing certain findings related to the Bank’s swap dealer compliance program identified during a then-recently completed examination. Northern Trust is cooperating with both the NFA and CFTC and working to address and resolve certain findings related to these matters. Visa Class B Common Shares. Northern Trust, as a member of Visa U.S.A. Inc. (Visa U.S.A.) and in connection with the 2007 restructuring of Visa U.S.A. and its affiliates and the 2008 initial public offering of Visa Inc. (Visa), received certain Visa Class B common shares. The Visa Class B common shares are subject to certain selling restrictions until the final resolution of certain litigation related to interchange fees involving Visa (the covered litigation), at which time the shares are convertible into Visa Class A common shares based on a conversion rate dependent upon the ultimate cost of resolving the covered litigation. On June 28, 2018, Visa deposited an additional $600 million into the escrow account previously established with respect to the covered litigation. As a result, the rate at which Visa Class B common shares will convert into Visa Class A common shares was reduced. In September 2018, Visa announced that a proposed class settlement agreement covering damage claims but not injunctive relief claims regarding the covered litigation was reached, with Visa’s share of the proposed settlement amount to be satisfied through funds previously deposited with the court and the $600 million placed into escrow in June 2018. The agreement has been preliminarily approved by the district court, and, if final approval is granted, objecting parties may appeal. Further, individual merchants may opt out of the proposed settlement and pursue claims separately. For these and other reasons, the ultimate resolution of the covered litigation, the timing for removal of the selling restrictions on the Visa Class B common shares and the rate at which such shares will ultimately convert into Visa Class A common shares are uncertain. In June 2016 and 2015, Northern Trust recorded a $123.1 million and $99.9 million net gain on the sale of 1.1 million and 1.0 million of its Visa Class B common shares, respectively. These sales do not affect Northern Trust’s risk related to the impact of the covered litigation on the rate at which such shares will ultimately convert into Visa Class A common shares. Northern Trust continued to hold approximately 4.1 million Visa Class B common shares, which are recorded at their original cost basis of zero , as of March 31, 2019 and December 31, 2018 .

Derivative Financial Instrument

Derivative Financial Instruments	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative Financial Instruments	Derivative Financial Instruments Northern Trust is a party to various derivative financial instruments that are used in the normal course of business to meet the needs of its clients, as part of its trading activity for its own account and as part of its risk management activities. These instruments include foreign exchange contracts, interest rate contracts, total return swap contracts, and swaps related to the sale of certain Visa Class B common shares. Foreign exchange contracts are agreements to exchange specific amounts of currencies at a future date, at a specified rate of exchange. Foreign exchange contracts are entered into primarily to meet the foreign exchange needs of clients. Foreign exchange contracts are also used for trading and risk management purposes. For risk management purposes, Northern Trust uses foreign exchange contracts to reduce its exposure to changes in foreign exchange rates relating to certain forecasted non-functional-currency-denominated revenue and expenditure transactions, foreign-currency-denominated assets and liabilities, including debt securities, and net investments in non-U.S. affiliates. Interest rate contracts include swap and option contracts. Interest rate swap contracts involve the exchange of fixed and floating rate interest payment obligations without the exchange of the underlying principal amounts. Northern Trust enters into interest rate swap contracts with its clients and also may utilize such contracts to reduce or eliminate the exposure to changes in the cash flows or fair value of hedged assets or liabilities due to changes in interest rates. Interest rate option contracts may include caps, floors, collars and swaptions, and provide for the transfer or reduction of interest rate risk, typically in exchange for a fee. Northern Trust enters into option contracts primarily as a seller of interest rate protection to clients. Northern Trust receives a fee at the outset of the agreement for the assumption of the risk of an unfavorable change in interest rates. This assumed interest rate risk is then mitigated by entering into an offsetting position with an outside counterparty. Northern Trust may also purchase or enter into option contracts for risk management purposes including to reduce the exposure to changes in the cash flows of hedged assets due to changes in interest rates. The following table shows the notional and fair values of all derivative financial instruments as of March 31, 2019 and December 31, 2018 . Table 68: Notional and Fair Values of Derivative Financial Instruments March 31, 2019 December 31, 2018 Notional Fair Value Notional Fair Value (In Millions) Asset 1 Liability 2 Asset 1 Liability 2 Derivatives Designated as Hedging under GAAP Interest Rate Contracts Fair Value Hedges $ 4,479.8 $ 23.9 $ 19.9 $ 4,590.4 $ 29.8 $ 23.3 Cash Flow Hedges 600.0 0.2 0.9 600.0 0.2 1.2 Foreign Exchange Contracts Cash Flow Hedges 2,259.1 42.5 10.5 2,648.2 13.8 57.8 Net Investment Hedges 2,509.7 36.5 5.5 3,475.1 292.4 14.5 Total Derivatives Designated as Hedging under GAAP $ 9,848.6 $ 103.1 $ 36.8 $ 11,313.7 $ 336.2 $ 96.8 Derivatives Not Designated as Hedging under GAAP Non-Designated Risk Management Derivatives Foreign Exchange Contracts $ 117.3 $ 1.2 $ 0.5 $ 122.2 $ 0.5 $ 0.2 Other Financial Derivatives 3 559.8 — 35.9 483.4 1.3 32.8 Total Non-Designated Risk Management Derivatives $ 677.1 $ 1.2 $ 36.4 $ 605.6 $ 1.8 $ 33.0 Client-Related and Trading Derivatives Foreign Exchange Contracts $ 286,240.1 $ 1,561.8 $ 1,474.0 $ 281,864.4 $ 2,159.4 $ 2,190.0 Interest Rate Contracts 7,621.5 80.5 58.8 7,711.2 66.1 68.6 Total Client-Related and Trading Derivatives $ 293,861.6 $ 1,642.3 $ 1,532.8 $ 289,575.6 $ 2,225.5 $ 2,258.6 Total Derivatives Not Designated as Hedging under GAAP $ 294,538.7 $ 1,643.5 $ 1,569.2 $ 290,181.2 $ 2,227.3 $ 2,291.6 Total Gross Derivatives $ 304,387.3 $ 1,746.6 $ 1,606.0 $ 301,494.9 $ 2,563.5 $ 2,388.4 Less: Netting 4 979.9 1,123.7 1,357.1 1,796.3 Total Derivative Financial Instruments $ 766.7 $ 482.3 $ 1,206.4 $ 592.1 (1) Derivative assets are reported in other assets on the consolidated balance sheets. (2) Derivative liabilities are reported in other liabilities on the consolidated balance sheets. (3) This line includes swaps related to sales of certain Visa Class B common shares and total return swap contracts. (4) See further detail in Note 23 - Offsetting of Assets and Liabilities. Notional amounts of derivative financial instruments do not represent credit risk, and are not recorded in the consolidated balance sheets. They are used merely to express the volume of this activity. Northern Trust’s credit-related risk of loss is limited to the positive fair value of the derivative instrument, net of any collateral received, which is significantly less than the notional amount. All derivative financial instruments, whether designated as hedges or not, are recorded on the consolidated balance sheets at fair value within other assets or other liabilities. Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. Hedging Derivative Instruments Designated under GAAP. Northern Trust uses derivative instruments to hedge its exposure to foreign currency, interest rate, and equity price. Certain hedging relationships are formally designated and qualify for hedge accounting under GAAP as fair value, cash flow or net investment hedges. Other derivatives that are entered into for risk management purposes as economic hedges are not formally designated as hedges and changes in fair value are recognized currently in other operating income (see below section “Derivative Instruments Not Designated as Hedging under GAAP”). In order to qualify for hedge accounting, a formal assessment is performed on a calendar-quarter basis to verify that derivatives used in designated hedging transactions continue to be highly effective in offsetting the changes in fair value or cash flows of the hedged item. If a derivative ceases to be highly effective, matures, is sold or is terminated, or if a hedged forecasted transaction is no longer probable of occurring, hedge accounting is terminated and the derivative is treated as if it were a trading instrument. Fair Value Hedges. Derivatives are designated as fair value hedges to limit Northern Trust’s exposure to changes in the fair value of assets and liabilities due to movements in interest rates. Northern Trust enters into interest rate swaps to hedge changes in fair value of available for sale debt securities and long-term subordinated debt and senior notes. Northern Trust applied the “shortcut” method of accounting, available under GAAP, which assumes there is perfect effectiveness in a hedge, for all of its fair value hedges during the three months ended March 31, 2019 and 2018 . Changes in the fair value of the derivative instrument and changes in the fair value of the hedged asset or liability attributable to the hedged risk are recognized currently in earnings within the same income statement line item. Cash Flow Hedges. Derivatives are also d esignated as cash flow hedges in order to minimize the variability in cash flows of earning assets or forecasted transactions caused by movements in interest or foreign exchange rates. Northern Trust enters into foreign exchange contracts to hedge changes in cash flows due to movements in foreign exchange rates of forecasted foreign- currency-denominated transactions and foreign-currency-denominated debt securities. Northern Trust also enters into interest rate contracts to hedge changes in cash flows due to movements in interest rates of available for sale debt securities. The change in fair value of cash flow hedging derivative instruments are recorded in AOCI and reclassified to earnings when the hedged forecasted transaction impacts earnings within the same income statement line item. There were no material gains or losses reclassified into earnings during the three months ended March 31, 2019 and 2018 , as a result of the discontinuance of forecasted transactions that were no longer probable of occurring. It is estimated that net losses of $0.2 million and net gains of $0.3 million will be reclassified into net income within the next twelve months relating to cash flow hedges of foreign-currency-denominated transactions and cash flow hedges of foreign-currency-denominated debt securities, respectively. It is estimated that a net loss of $0.8 million will be reclassified into net income upon the receipt of interest payments on earning assets within the next twelve months relating to cash flow hedges of available for sale debt securities. As of March 31, 2019 , 23 months was the maximum length of time over which the exposure to variability in future cash flows of forecasted foreign-currency-denominated transactions was being hedged. There was no ineffectiveness recognized in earnings for cash flow hedges during the three months ended March 31, 2018 . The following tables provide fair value and cash flow hedge derivative gains and losses recognized in income during the three months ended March 31, 2019 and 2018 . Table 69: Location and Amount of Fair Value and Cash Flow Hedge Derivative Gains and Losses Recorded in Income Location and Amount of Derivative Gain/(Loss) Recognized in Income (In Millions) Interest Income Interest Expense Other Operating Income Three Months Ended March 31, 2019 2018 2019 2018 2019 2018 Total amounts on the consolidated statements of income $ 662.8 $ 505.9 $ 240.8 $ 121.9 $ 29.0 $ 34.8 Gains/(Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives (35.4 ) 54.3 28.5 (21.9 ) — — Recognized on hedged items 35.4 (54.3 ) (28.5 ) 21.9 — — Amounts related to interest settlements on derivatives 5.5 (3.7 ) (1.6 ) 1.5 — — Total gain/(loss) recognized on fair value hedges $ 5.5 $ (3.7 ) $ (1.6 ) $ 1.5 $ — $ — Gains/(Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gain/(loss) reclassified from AOCI to net income $ 14.4 $ 14.2 $ — $ — $ (0.6 ) $ 2.4 Interest Rate Contracts Net gain/(loss) reclassified from AOCI to net income (0.2 ) — — — — — Total gain/(loss) reclassified from AOCI to net income on cash flow hedges $ 14.2 $ 14.2 $ — $ — $ (0.6 ) $ 2.4 The following table provides the impact of fair value hedge accounting on the carrying value of the designated hedged items as of March 31, 2019 . Table 70: Hedged Items in Fair Value Hedges March 31, 2019 December 31, 2018 (In Millions) Carrying Value of the Hedged Items Cumulative Hedge Accounting Basis Adjustment (1) Carrying Value of the Hedged Items Cumulative Hedge Accounting Basis Adjustment (1) Available for Sale Debt Securities (2) $ 3,759.5 $ 60.5 $ 3,831.6 $ 99.4 Senior Notes and Long-Term Subordinated Debt 1,248.9 55.1 1,248.8 29.3 Total $ 5,008.4 $ 115.6 $ 5,080.4 $ 128.7 (1) There are no amounts related to discontinued hedging relationships. (2) Carrying value represents amortized cost. Net Investment Hedges. Certain foreign exchange contracts are designated as net investment hedges to minimize Northern Trust’s exposure to variability in the foreign currency translation of net investments in non-U.S. branches and subsidiaries. For net investment hedges, there was no ineffectiveness recorded during the three months ended March 31, 2018 . Net investment hedge gains of $28.6 million and losses of $74.3 million were recognized in AOCI related to foreign exchange contracts for the three months ended March 31, 2019 and 2018 , respectively. Derivative Instruments Not Designated as Hedging under GAAP. Northern Trust’s derivative instruments that are not designated as hedging under GAAP include derivatives for purposes of client-related and trading activities, as well as other risk management purposes. These activities consist principally of providing foreign exchange services to clients in connection with Northern Trust’s global custody business. However, in the normal course of business, Northern Trust also engages in trading of currencies for its own account. Non-designated risk management derivatives include foreign exchange contracts entered into to manage the foreign currency risk of non-U.S.-dollar-denominated assets and liabilities, the net investment in certain non-U.S. affiliates, commercial loans and forecasted foreign-currency-denominated transactions. Swaps related to sales of certain Visa Class B common shares were entered into pursuant to which Northern Trust retains the risks associated with the ultimate conversion of the Visa Class B common shares into Visa Class A common shares. Total return swaps are entered into to manage the equity price risk associated with certain investments. Changes in the fair value of derivative instruments not designated as hedges under GAAP are recognized currently in income. The following table provides the location and amount of gains and losses recorded in the consolidated statements of income for the three months ended March 31, 2019 and 2018 . Table 71: Location and Amount of Gains and Losses Recorded in Income for Derivatives Not Designated as Hedging Under GAAP (In Millions) Location of Amount of Derivative Gain / (Loss) Three Months Ended March 31, 2019 2018 Non-designated risk management derivatives Foreign Exchange Contracts Other Operating Income $ 0.9 $ 4.0 Other Financial Derivatives (1) Other Operating Income (7.3 ) (4.0 ) Gains/(Losses) from non-designated risk management derivatives $ (6.4 ) $ — Client-related and trading derivatives Foreign Exchange Contracts Foreign Exchange Trading Income $ 66.2 $ 78.5 Interest Rate Contracts Security Commissions and Trading Income 1.5 1.7 Gains/(Losses) from client-related and trading derivatives $ 67.7 $ 80.2 Total gains/(losses) from derivatives not designated as hedging under GAAP $ 61.3 $ 80.2 (1) This line includes swaps related to sales of certain Visa Class B common shares and total return swap contracts.

Offsetting of Assets and Liabil

Offsetting of Assets and Liabilities	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Offsetting of Assets and Liabilities	Offsetting of Assets and Liabilities Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. The following table provides information regarding the offsetting of derivative assets and securities purchased under agreements to resell within the consolidated balance sheets as of March 31, 2019 and December 31, 2018 . Table 72: Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell March 31, 2019 (In Millions) Gross Recognized Assets Gross Amounts Offset in the Balance Sheet (2) Net Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net Amount (4) Derivative Assets (1) Foreign Exchange Contracts Over the Counter (OTC) $ 1,127.8 $ 926.8 $ 201.0 $ 30.4 $ 170.6 Interest Rate Swaps OTC 60.5 12.3 48.2 — 48.2 Interest Rate Swaps Exchange Cleared 44.2 40.8 3.4 — 3.4 Total Derivatives Subject to a Master Netting Arrangement 1,232.5 979.9 252.6 30.4 222.2 Total Derivatives Not Subject to a Master Netting Arrangement 514.1 — 514.1 — 514.1 Total Derivatives 1,746.6 979.9 766.7 30.4 736.3 Securities Purchased under Agreements to Resell (2) $ 515.2 $ — $ 515.2 $ 515.2 $ — December 31, 2018 (In Millions) Gross Recognized Assets Gross Amounts Offset in the Balance Sheet (2) Net Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net Amount (4) Derivative Assets (1) Foreign Exchange Contracts OTC $ 1,902.3 $ 1,308.8 $ 593.5 $ 12.7 $ 580.8 Interest Rate Swaps OTC 71.6 22.6 49.0 — 49.0 Interest Rate Swaps Exchange Cleared 24.5 24.4 0.1 — 0.1 Other Financial Derivatives 1.3 1.3 — — — Total Derivatives Subject to a Master Netting Arrangement 1,999.7 1,357.1 642.6 12.7 629.9 Total Derivatives Not Subject to a Master Netting Arrangement 563.8 — 563.8 2.7 561.1 Total Derivatives 2,563.5 1,357.1 1,206.4 15.4 1,191.0 Securities Purchased under Agreements to Resell (3) $ 1,031.2 $ — $ 1,031.2 $ 1,031.2 $ — (1) Derivative assets are reported in other assets in the consolidated balance sheets. Other assets (excluding derivative assets) totaled $5.3 billion and $4.6 billion as of March 31, 2019 and December 31, 2018 , respectively. (2) Including cash collateral received from counterparties. (3) Securities purchased under agreements to resell are reported in federal funds sold and securities purchased under agreements to resell in the consolidated balance sheets. Federal funds sold totaled $37.0 million and $134.0 million as of March 31, 2019 and December 31, 2018 , respectively. (4) Northern Trust did not possess any cash collateral that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2019 and December 31, 2018 . The following table provides information regarding the offsetting of derivative liabilities and securities sold under agreements to repurchase within the consolidated balance sheets as of March 31, 2019 and December 31, 2018 . Table 73: Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase March 31, 2019 (In Millions) Gross Recognized Liabilities Gross Amounts Offset in the Balance Sheet (2) Net Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net Amount (3) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 1,169.5 $ 1,054.9 $ 114.6 $ 0.1 $ 114.5 Interest Rate Swaps OTC 38.8 27.8 11.0 — 11.0 Interest Rate Swaps Exchange Cleared 40.8 40.8 — — — Other Financial Derivatives 35.9 0.2 35.7 — 35.7 Total Derivatives Subject to a Master Netting Arrangement 1,285.0 1,123.7 161.3 0.1 161.2 Total Derivatives Not Subject to a Master Netting Arrangement 321.0 — 321.0 — 321.0 Total Derivatives 1,606.0 1,123.7 482.3 0.1 482.2 Securities Sold under Agreements to Repurchase $ 39.7 $ — $ 39.7 $ 39.7 $ — December 31, 2018 (In Millions) Gross Recognized Liabilities Gross Amounts Offset in the Balance Sheet (2) Net Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net Amount (3) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 1,821.0 $ 1,751.7 $ 69.3 $ — $ 69.3 Interest Rate Swaps OTC 68.8 19.0 49.8 — 49.8 Interest Rate Swaps Exchange Cleared 24.4 24.4 — — — Other Financial Derivatives 32.8 1.2 31.6 — 31.6 Total Derivatives Subject to a Master Netting Arrangement 1,947.0 1,796.3 150.7 — 150.7 Total Derivatives Not Subject to a Master Netting Arrangement 441.4 — 441.4 — 441.4 Total Derivatives 2,388.4 1,796.3 592.1 — 592.1 Securities Sold under Agreements to Repurchase $ 168.3 $ — $ 168.3 $ 168.3 $ — (1) Derivative liabilities are reported in other liabilities in the consolidated balance sheets. Other liabilities (excluding derivative liabilities) totaled $3.1 billion and $2.5 billion as of March 31, 2019 and December 31, 2018 , respectively. (2) Including cash collateral deposited with counterparties. (3) Northern Trust did not place any cash collateral with counterparties that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2019 and December 31, 2018 . All of Northern Trust’s securities sold under agreements to repurchase (repurchase agreements) and securities purchased under agreements to resell (reverse repurchase agreements) involve the transfer of financial assets in exchange for cash subject to a right and obligation to repurchase those assets for an agreed upon amount. In the event of a repurchase failure, the cash or financial assets are available for offset. All of Northern Trust’s repurchase agreements and reverse repurchase agreements are subject to a master netting arrangement, which sets forth the rights and obligations for repurchase and offset. Under the master netting arrangement, Northern Trust is entitled to offset receivables from and collateral placed with a single counterparty against obligations owed to that counterparty. In addition, collateral held by Northern Trust can be offset against receivables from that counterparty. However, Northern Trust’s repurchase agreements and reverse repurchase agreements do not meet the requirements to net. Derivative asset and liability positions with a single counterparty can be offset against each other in cases where legally enforceable master netting arrangements or similar agreements exist. Derivative assets and liabilities can be further offset by cash collateral received from, and deposited with, the transacting counterparty. The basis for this view is that, upon termination of transactions subject to a master netting arrangement or similar agreement, the individual derivative receivables do not represent resources to which general creditors have rights and individual derivative payables do not represent claims that are equivalent to the claims of general creditors. Credit risk associated with derivative instruments relates to the failure of the counterparty and the failure of Northern Trust to pay based on the contractual terms of the agreement, and is generally limited to the unrealized fair value gains and losses on these instruments, net of any collateral received or deposited. The amount of credit risk will increase or decrease during the lives of the instruments as interest rates, foreign exchange rates, equity prices or other underlying exposures fluctuate. Northern Trust’s risk is controlled by limiting such activity to an approved list of counterparties and by subjecting such activity to the same credit and quality controls as are followed in lending and investment activities. Credit Support Annexes and other similar agreements are currently in place with a number of Northern Trust’s counterparties which mitigate the aforementioned credit risk associated with derivative activity conducted with those counterparties by requiring that significant net unrealized fair value gains be supported by collateral placed with Northern Trust. Additional cash collateral received from and deposited with derivative counterparties totaling $69.0 million and $67.9 million , respectively, as of March 31, 2019 , and $27.6 million and $91.5 million , respectively, as of December 31, 2018 , was not offset against derivative assets and liabilities in the consolidated balance sheets as the amounts exceeded the net derivative positions with those counterparties. Certain master netting arrangements Northern Trust enters into with derivative counterparties contain credit-risk-related contingent features in which the counterparty has the option to declare Northern Trust in default and accelerate cash settlement of net derivative liabilities with the counterparty in the event Northern Trust’s credit rating falls below specified levels. The aggregate fair value of all derivative instruments with credit-risk-related contingent features that were in a liability position was $130.2 million and $324.1 million at March 31, 2019 and December 31, 2018 , respectively. Cash collateral amounts deposited with derivative counterparties on those dates included $124.2 million and $316.5 million , respectively, posted against these liabilities, resulting in a net maximum amount of termination payments that could have been required at March 31, 2019 and December 31, 2018 , of $6.0 million and $7.6 million , respectively. Accelerated settlement of these liabilities would not have a material effect on the consolidated financial position or liquidity of Northern Trust.

Recent Accounting Pronounceme_2

Recent Accounting Pronouncements (Policies)	3 Months Ended
	Mar. 31, 2019
Accounting Changes and Error Corrections [Abstract]
Recent Accounting Pronouncements	On January 1, 2019, Northern Trust adopted ASU No. 2016-02, “Leases (Topic 842)" (ASU 2016-02). ASU 2016-02 introduces a lessee model that brings most leases on the balance sheet, with certain specified scope exceptions. Specifically within the lessee model under ASU 2016-02, a lessee is required to recognize on the balance sheet a liability to make future lease payments, known as the lease liability, and a right-of-use asset (ROU asset) representing its right to use the underlying asset over the lease term. Upon adoption, Northern Trust elected the package of practical expedients available under ASU 2016-02, which allowed Northern Trust to forego a reassessment of (1) whether any expired or existing contracts are or contain leases, (2) lease classification for any expired or existing leases, and (3) the initial direct costs for any existing leases. As a result of adopting ASU 2016-02, Northern Trust recognized operating lease liabilities and ROU assets of approximately $530 million and $480 million , respectively. Northern Trust did not restate comparative periods for the effects of applying ASU 2016-02. There was no significant impact to Northern Trust’s consolidated results of operations. Please refer to “Note 8 - Leases” for further information. On January 1, 2019, Northern Trust adopted ASU No. 2017-08, “Receivables-Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization on Purchased Callable Securities” (ASU 2017-08). ASU 2017-08 amends the amortization period for certain callable debt securities held at a premium and shortens the amortization period for the premium to the earliest call date. Upon adoption of ASU 2017-08, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations. On January 1, 2019, Northern Trust adopted ASU No. 2018-16, “"Derivatives and Hedging (Topic 815): Inclusion of the Secured Overnight Financing Rate (SOFR) Overnight Index Swap (OIS) Rate as a Benchmark Interest Rate for Hedge Accounting Purposes" (ASU 2018-16). ASU 2018-16 permits use of the OIS rate based on SOFR as a U.S. benchmark interest rate for hedge accounting purposes under Topic 815. Upon adoption of ASU 2018-16, there was no significant impact to Northern Trust’s consolidated financial condition or results of operations.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Recurring Basis Hierarchy Leveling	The following table presents assets and liabilities measured at fair value on a recurring basis as of March 31, 2019 and December 31, 2018 , segregated by fair value hierarchy level. Table 33: Recurring Basis Hierarchy Leveling (In Millions) Level 1 Level 2 Level 3 Netting Assets/Liabilities at Fair Value March 31, 2019 Debt Securities Available for Sale U.S. Government $ 5,022.0 $ — $ — $ — $ 5,022.0 Obligations of States and Political Subdivisions — 764.8 — — 764.8 Government Sponsored Agency — 22,568.6 — — 22,568.6 Non-U.S. Government — 142.7 — — 142.7 Corporate Debt — 2,293.7 — — 2,293.7 Covered Bonds — 837.4 — — 837.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,236.1 — — 2,236.1 Other Asset-Backed — 2,520.2 — — 2,520.2 Commercial Mortgage-Backed — 658.1 — — 658.1 Other — 14.6 — — 14.6 Total Available for Sale 5,022.0 32,036.2 — — 37,058.2 Trading Account — 0.3 — — 0.3 Total Available for Sale and Trading Debt Securities 5,022.0 32,036.5 — — 37,058.5 Other Assets Derivative Assets Foreign Exchange Contracts — 1,642.0 — — 1,642.0 Interest Rate Contracts — 104.6 — — 104.6 Total Derivative Assets — 1,746.6 — (979.9 ) 766.7 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 1,490.5 — — 1,490.5 Interest Rate Contracts — 79.6 — — 79.6 Other Financial Derivatives (1) — 0.9 35.0 — 35.9 Total Derivative Liabilities $ — $ 1,571.0 $ 35.0 $ (1,123.7 ) $ 482.3 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of March 31, 2019 , derivative assets and liabilities shown above also include reductions of $139.2 million and $283.1 million , respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1) This line consists of swaps related to the sale of certain Visa Class B common shares and a total return swap contract. (In Millions) Level 1 Level 2 Level 3 Netting Assets/Liabilities at Fair Value December 31, 2018 Debt Securities Available for Sale U.S. Government $ 5,185.3 $ — $ — $ — $ 5,185.3 Obligations of States and Political Subdivisions — 655.9 — — 655.9 Government Sponsored Agency — 22,424.6 — — 22,424.6 Non-U.S. Government — 142.2 — — 142.2 Corporate Debt — 2,294.7 — — 2,294.7 Covered Bonds — 829.3 — — 829.3 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds — 2,096.2 — — 2,096.2 Other Asset-Backed — 2,657.7 — — 2,657.7 Commercial Mortgage-Backed — 587.2 — — 587.2 Other — 15.7 — — 15.7 Total Available for Sale 5,185.3 31,703.5 — — 36,888.8 Trading Account — 0.3 — — 0.3 Total Available for Sale and Trading Debt Securities 5,185.3 31,703.8 — — 36,889.1 Other Assets Derivative Assets Foreign Exchange Contracts — 2,466.1 — — 2,466.1 Interest Rate Contracts — 96.1 — — 96.1 Other Financial Derivatives (1) — 1.3 — — 1.3 Total Derivative Assets — 2,563.5 — (1,357.1 ) 1,206.4 Other Liabilities Derivative Liabilities Foreign Exchange Contracts — 2,262.5 — — 2,262.5 Interest Rate Contracts — 93.1 — — 93.1 Other Financial Derivatives (2) — — 32.8 — 32.8 Total Derivative Liabilities $ — $ 2,355.6 $ 32.8 $ (1,796.3 ) $ 592.1 Note: Northern Trust has elected to net derivative assets and liabilities when legally enforceable master netting arrangements or similar agreements exist between Northern Trust and the counterparty. As of December 31, 2018 , derivative assets and liabilities shown above also include reductions of $134.5 million and $573.7 million , respectively, as a result of cash collateral received from and deposited with derivative counterparties. (1) This line consists of a total return swap contract. (2) This line consists of swaps related to the sale of certain Visa Class B common shares.
Changes in Level 3 Liabilities	The following table presents the changes in Level 3 liabilities for the three months ended March 31, 2019 and 2018 . Table 34: Changes in Level 3 Liabilities Level 3 Liabilities (In Millions) Swaps Related to Sale of Certain Visa Class B Common Shares Three Months Ended March 31, 2019 2018 Fair Value at January 1 $ 32.8 $ 29.7 Total (Gains) Losses: Included in Earnings (1) 5.1 4.2 Purchases, Issues, Sales, and Settlements Settlements (2.9 ) (2.6 ) Fair Value at March 31 $ 35.0 $ 31.3 (1) (Gains) losses are recorded in other operating income in the consolidated statements of income.
Fair Value of Financial Instruments	The following table summarizes the fair values of all financial instruments. Table 36: Fair Value of Financial Instruments (In Millions) March 31, 2019 Book Value Total Fair Value Fair Value Level 1 Level 2 Level 3 Assets Cash and Due from Banks $ 5,074.1 $ 5,074.1 $ 5,074.1 $ — $ — Federal Reserve and Other Central Bank Deposits 23,422.2 23,422.2 — 23,422.2 — Interest-Bearing Deposits with Banks 3,861.6 3,861.6 — 3,861.6 — Federal Funds Sold and Securities Purchased under Agreements to Resell 552.2 552.2 — 552.2 — Debt Securities Available for Sale ( Note ) 37,058.2 37,058.2 5,022.0 32,036.2 — Held to Maturity 12,143.0 12,097.7 119.6 11,978.1 — Trading Account 0.3 0.3 — 0.3 — Loans (excluding Leases) Held for Investment 30,417.0 30,481.9 — — 30,481.9 Held for Sale — — — — — Client Security Settlement Receivables 2,067.3 2,067.3 — 2,067.3 — Total Assets Federal Reserve and Federal Home Loan Bank Stock 300.5 300.5 — 300.5 — Community Development Investments 589.5 589.5 — 589.5 — Employee Benefit and Deferred Compensation 200.5 197.5 131.1 66.4 — Liabilities Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 36,648.5 $ 36,648.5 $ 36,648.5 $ — $ — Savings Certificates and Other Time 856.2 866.9 — 866.9 — Non U.S. Offices Interest-Bearing 58,339.5 58,339.5 — 58,339.5 — Federal Funds Purchased 651.8 651.8 — 651.8 — Securities Sold Under Agreements to Repurchase 39.7 39.7 — 39.7 — Other Borrowings 7,749.8 7,754.6 — 7,754.6 — Senior Notes 2,024.1 2,031.0 — 2,031.0 — Long-Term Debt Subordinated Debt 1,125.8 1,133.2 — 1,133.2 — Floating Rate Capital Debt 277.6 256.4 — 256.4 — Other Liabilities Standby Letters of Credit 56.2 56.2 — — 56.2 Loan Commitments 33.0 33.0 — — 33.0 Derivative Instruments Asset/Liability Management Foreign Exchange Contracts Assets $ 80.2 $ 80.2 $ — $ 80.2 $ — Liabilities 16.5 16.5 — 16.5 — Interest Rate Contracts Assets 24.1 24.1 — 24.1 — Liabilities 20.8 20.8 — 20.8 — Other Financial Derivatives Liabilities (1) 35.9 35.9 — 0.9 35.0 Client-Related and Trading Foreign Exchange Contracts Assets 1,561.8 1,561.8 — 1,561.8 — Liabilities 1,474.0 1,474.0 — 1,474.0 — Interest Rate Contracts Assets 80.5 80.5 — 80.5 — Liabilities 58.8 58.8 — 58.8 — Note: Refer to the table located on page 32 for the disaggregation of available for sale debt securities. (1) This line consists of a total return swap contract and swaps related to the sale of certain Visa Class B common shares. (In Millions) December 31, 2018 Book Value Total Fair Value Fair Value Level 1 Level 2 Level 3 Assets Cash and Due from Banks $ 4,581.6 $ 4,581.6 $ 4,581.6 $ — $ — Federal Reserve and Other Central Bank Deposits 30,080.2 30,080.2 — 30,080.2 — Interest-Bearing Deposits with Banks 4,264.2 4,264.2 — 4,264.2 — Federal Funds Sold and Securities Purchased under Agreements to Resell 1,165.2 1,165.2 — 1,165.2 — Debt Securities Available for Sale ( Note ) 36,888.8 36,888.8 5,185.3 31,703.5 — Held to Maturity 14,354.0 14,267.0 101.6 14,165.4 — Trading Account 0.3 0.3 — 0.3 — Loans (excluding Leases) Held for Investment 32,287.0 32,339.2 — — 32,339.2 Held for Sale — — — — — Client Security Settlement Receivables 1,646.1 1,646.1 — 1,646.1 — Total Assets Federal Reserve and Federal Home Loan Bank Stock 300.3 300.3 — 300.3 — Community Development Investments 606.6 606.6 — 606.6 — Employee Benefit and Deferred Compensation 202.3 194.5 125.0 69.5 — Liabilities Deposits Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing $ 37,340.1 $ 37,340.1 $ 37,340.1 $ — $ — Savings Certificates and Other Time 688.7 691.8 — 691.8 — Non U.S. Offices Interest-Bearing 66,468.0 66,468.0 — 66,468.0 — Federal Funds Purchased 2,594.2 2,594.2 — 2,594.2 — Securities Sold Under Agreements to Repurchase 168.3 168.3 — 168.3 — Other Borrowings 7,901.7 7,904.1 — 7,904.1 — Senior Notes 2,011.3 1,994.4 — 1,994.4 — Long-Term Debt Subordinated Debt 1,112.4 1,089.7 — 1,089.7 — Floating Rate Capital Debt 277.6 253.5 — 253.5 — Other Liabilities Standby Letters of Credit 30.8 30.8 — — 30.8 Loan Commitments 34.3 34.3 — — 34.3 Derivative Instruments Asset/Liability Management Foreign Exchange Contracts Assets $ 306.7 $ 306.7 $ — $ 306.7 $ — Liabilities 72.5 72.5 — 72.5 — Interest Rate Contracts Assets 30.0 30.0 — 30.0 — Liabilities 24.5 24.5 — 24.5 — Other Financial Derivatives Assets (1) 1.3 1.3 — 1.3 — Liabilities (2) 32.8 32.8 — — 32.8 Client-Related and Trading Foreign Exchange Contracts Assets 2,159.4 2,159.4 — 2,159.4 — Liabilities 2,190.0 2,190.0 — 2,190.0 — Interest Rate Contracts Assets 66.1 66.1 — 66.1 — Liabilities 68.6 68.6 — 68.6 — Note: Refer to the table located on page 33 for the disaggregation of available for sale debt securities. (1) This line consists of a total return swap contract. (2) This line consists of swaps related to the sale of certain Visa Class B common shares.
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assets and Liabilities, Measured on Recurring and Nonrecurring Basis, Valuation Techniques, Unobservable Inputs and Quantitative Information	The following table presents the fair values of Northern Trust’s Level 3 liabilities as of March 31, 2019 and December 31, 2018 , as well as the valuation techniques, significant unobservable inputs, and quantitative information used to develop significant unobservable inputs for such assets and liabilities as of such dates. Table 32: Level 3 Significant Unobservable Inputs March 31, 2019 Financial Instrument Fair Value Valuation Technique Unobservable Inputs Range of Inputs Swaps Related to Sale of Certain Visa Class B Common Shares $ 35.0 million Discounted Cash Flow Visa Class A Appreciation 7.0 % — 11.0% Conversion Rate 1.62 x — 1.64x Expected Duration 1.25 — 3.75 years December 31, 2018 Financial Instrument Fair Value Valuation Technique Unobservable Inputs Range of Inputs Swap Related to Sale of Certain Visa Class B Common Shares $ 32.8 million Discounted Cash Flow Visa Class A Appreciation 7.0 % — 11.0% Conversion Rate 1.62 x — 1.64x Expected Duration 1.5 — 4.0 years
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value Assets and Liabilities, Measured on Recurring and Nonrecurring Basis, Valuation Techniques, Unobservable Inputs and Quantitative Information	The following table presents the fair values of Northern Trust’s Level 3 assets that were measured at fair value on a nonrecurring basis as of March 31, 2019 and December 31, 2018 , as well as the valuation technique, significant unobservable inputs and quantitative information used to develop the significant unobservable inputs for such assets as of such dates. Table 35: Level 3 Nonrecurring Basis Significant Unobservable Inputs March 31, 2019 Financial Instrument Fair Value Valuation Technique Unobservable Input Range of Discounts Applied Loans $22.3 million Market Approach Discount to reflect realizable value 15.0 % - 30.0% OREO $0.1 million Market Approach Discount to reflect realizable value 15.0 % - 30.0% December 31, 2018 Financial Instrument Fair Value Valuation Technique Unobservable Input Range of Discounts Applied Loans $24.9 million Market Approach Discount to reflect realizable value 15.0 % - 30.0% OREO $0.4 million Market Approach Discount to reflect realizable value 15.0 % - 30.0%

Securities (Tables)

Securities (Tables)	3 Months Ended
	Mar. 31, 2019
Debt and Equity Securities, FV-NI [Line Items]
Reconciliation of Amortized Cost to Fair Value of Securities Available for Sale	The following tables provide the amortized cost and fair values of debt securities at March 31, 2019 and December 31, 2018 . Table 37: Reconciliation of Amortized Cost to Fair Value of Debt Securities Available for Sale Debt Securities Available for Sale March 31, 2019 Amortized Cost Gross Unrealized Fair Value (In Millions) Gains Losses U.S. Government $ 5,030.0 $ 19.0 $ 27.0 $ 5,022.0 Obligations of States and Political Subdivisions 755.8 10.7 1.7 764.8 Government Sponsored Agency 22,624.9 68.3 124.6 22,568.6 Non-U.S. Government 143.3 — 0.6 142.7 Corporate Debt 2,297.6 10.2 14.1 2,293.7 Covered Bonds 837.4 2.6 2.6 837.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,214.0 24.3 2.2 2,236.1 Other Asset-Backed 2,530.5 3.3 13.6 2,520.2 Commercial Mortgage-Backed 647.6 12.5 2.0 658.1 Other 14.6 — — 14.6 Total $ 37,095.7 $ 150.9 $ 188.4 $ 37,058.2 Debt Securities Available for Sale December 31, 2018 Amortized Cost Gross Unrealized Fair Value (In Millions) Gains Losses U.S. Government $ 5,203.1 $ 21.8 $ 39.6 $ 5,185.3 Obligations of States and Political Subdivisions 657.6 2.0 3.7 655.9 Government Sponsored Agency 22,522.7 52.4 150.5 22,424.6 Non-U.S. Government 143.3 — 1.1 142.2 Corporate Debt 2,312.6 3.2 21.1 2,294.7 Covered Bonds 832.7 1.4 4.8 829.3 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,087.8 11.9 3.5 2,096.2 Other Asset-Backed 2,678.9 1.7 22.9 2,657.7 Commercial Mortgage-Backed 587.4 4.0 4.2 587.2 Other 15.7 — — 15.7 Total $ 37,041.8 $ 98.4 $ 251.4 $ 36,888.8
Reconciliation of Amortized Cost to Fair Values of Securities Held to Maturity	Table 38: Reconciliation of Amortized Cost to Fair Value of Debt Securities Held to Maturity Debt Securities Held to Maturity March 31, 2019 Amortized Cost Gross Unrealized Fair Value (In Millions) Gains Losses U.S Government $ 119.6 $ — $ — $ 119.6 Obligations of States and Political Subdivisions 16.0 0.6 — 16.6 Government Sponsored Agency 4.3 0.2 — 4.5 Corporate Debt 451.6 0.4 0.3 451.7 Covered Bonds 2,617.8 15.5 4.8 2,628.5 Non-U.S. Government 4,338.1 4.7 5.0 4,337.8 Certificates of Deposit 75.8 — — 75.8 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 3,170.2 13.5 4.6 3,179.1 Other Asset-Backed 1,099.6 0.3 1.2 1,098.7 Other 250.0 — 64.6 185.4 Total $ 12,143.0 $ 35.2 $ 80.5 $ 12,097.7 Debt Securities Held to Maturity December 31, 2018 Amortized Cost Gross Unrealized Fair Value (In Millions) Gains Losses U.S Government $ 101.6 $ — $ — $ 101.6 Obligations of States and Political Subdivisions 18.9 0.6 — 19.5 Government Sponsored Agency 4.5 0.2 — 4.7 Corporate Debt 472.9 0.4 1.8 471.5 Covered Bonds 2,877.6 9.6 9.3 2,877.9 Non-U.S. Government 6,488.2 2.1 8.7 6,481.6 Certificates of Deposit 45.1 — — 45.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 2,966.8 5.8 12.3 2,960.3 Other Asset-Backed 1,146.4 — 4.0 1,142.4 Other 232.0 — 69.6 162.4 Total $ 14,354.0 $ 18.7 $ 105.7 $ 14,267.0
Debt Securities with Unrealized Losses	The following table provides information regarding debt securities that had been in a continuous unrealized loss position for less than twelve months and for twelve months or longer as of March 31, 2019 and December 31, 2018 . Table 40: Debt Securities with Unrealized Losses Debt Securities with Unrealized Losses as of March 31, 2019 Less than 12 Months 12 Months or Longer Total (In Millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses U.S. Government $ — $ — $ 2,674.5 $ 27.0 $ 2,674.5 $ 27.0 Obligations of States and Political Subdivisions 66.2 1.2 209.8 0.5 276.0 1.7 Government Sponsored Agency 6,933.4 31.9 8,371.6 92.7 15,305.0 124.6 Non-U.S. Government 2,321.8 0.1 1,259.6 5.5 3,581.4 5.6 Corporate Debt 339.3 0.9 1,009.1 13.5 1,348.4 14.4 Covered Bonds 181.0 0.3 1,022.9 7.1 1,203.9 7.4 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 253.4 0.6 1,501.8 6.2 1,755.2 6.8 Other Asset-Backed 1,436.5 8.7 893.8 6.1 2,330.3 14.8 Commercial Mortgage-Backed 18.7 0.1 193.5 1.9 212.2 2.0 Other 60.7 19.8 125.8 44.8 186.5 64.6 Total $ 11,611.0 $ 63.6 $ 17,262.4 $ 205.3 $ 28,873.4 $ 268.9 Debt Securities with Unrealized Losses as of December 31, 2018 Less than 12 Months 12 Months or Longer Total (In Millions) Fair Value Unrealized Losses Fair Value Unrealized Losses Fair Value Unrealized Losses U.S. Government $ — $ — $ 2,862.0 $ 39.6 $ 2,862.0 $ 39.6 Obligations of States and Political Subdivisions 169.6 2.4 279.6 1.3 449.2 3.7 Government Sponsored Agency 8,368.8 33.5 6,822.4 117.0 15,191.2 150.5 Non-U.S. Government 5,065.2 0.8 1,274.0 9.0 6,339.2 9.8 Corporate Debt 712.7 4.1 1,097.4 18.8 1,810.1 22.9 Covered Bonds 646.4 3.7 696.9 10.4 1,343.3 14.1 Sub-Sovereign, Supranational and Non-U.S. Agency Bonds 1,105.0 4.6 1,189.2 11.2 2,294.2 15.8 Other Asset-Backed 2,507.8 15.9 954.9 11.0 3,462.7 26.9 Commercial Mortgage-Backed 22.8 0.1 274.4 4.1 297.2 4.2 Other 50.5 18.8 112.6 50.8 163.1 69.6 Total $ 18,648.8 $ 83.9 $ 15,563.4 $ 273.2 $ 34,212.2 $ 357.1
Cumulative Credit-Related Losses on Debt Securities	The table below provides the cumulative credit-related losses recognized in earnings on debt securities other-than-temporarily impaired. Table 41: Cumulative Credit-Related Losses on Debt Securities Three Months Ended March 31, (In Millions) 2019 2018 Cumulative Credit-Related Losses on Debt Securities Held — Beginning of Period $ 4.1 $ 3.6 Plus: Losses on Newly Identified Impairments — 0.2 Additional Losses on Previously Identified Impairments — — Less: Current and Prior Period Losses on Debt Securities Sold During the Period — — Cumulative Credit-Related Losses on Debt Securities Held — End of Period $ 4.1 $ 3.8
Available for Sale Debt Securities
Debt and Equity Securities, FV-NI [Line Items]
Remaining Maturity of Securities Available for Sale and Held to Maturity	The following table provides the remaining maturity of debt securities as of March 31, 2019 . Table 39: Remaining Maturity of Debt Securities Available for Sale and Held to Maturity March 31, 2019 (In Millions) Amortized Cost Fair Value Available for Sale Due in One Year or Less $ 9,967.0 $ 9,950.6 Due After One Year Through Five Years 19,376.6 19,379.5 Due After Five Years Through Ten Years 6,790.3 6,771.8 Due After Ten Years 961.8 956.3 Total 37,095.7 37,058.2 Held to Maturity Due in One Year or Less 4,820.9 4,820.7 Due After One Year Through Five Years 6,787.3 6,795.4 Due After Five Years Through Ten Years 452.5 440.4 Due After Ten Years 82.3 41.2 Total $ 12,143.0 $ 12,097.7 Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments.

Securities Sold Under Agreeme_2

Securities Sold Under Agreements to Repurchase (Tables)	3 Months Ended
	Mar. 31, 2019
Banking and Thrift [Abstract]
Repurchase Agreements Accounted for as Secured Borrowings	The following table provides information regarding repurchase agreements that are accounted for as secured borrowings as of March 31, 2019 . Table 42: Repurchase Agreements Accounted for as Secured Borrowings March 31, 2019 (In Millions) Remaining Contractual Maturity of the Agreements Repurchase Agreements Overnight and Continuous U.S. Treasury and Agency Securities $ 39.7 Total Borrowings 39.7 Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 23 39.7 Amounts related to agreements not included in Note 23 —

Loans and Leases (Tables)

Loans and Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Loans and Leases	Amounts outstanding for loans and leases, by segment and class, are shown below. Table 43: Loans and Leases (In Millions) March 31, December 31, Commercial Commercial and Institutional $ 8,532.1 $ 8,728.1 Commercial Real Estate 3,185.0 3,228.8 Non-U.S. 1,648.6 2,701.6 Lease Financing, net 89.3 90.7 Other 180.5 426.0 Total Commercial 13,635.5 15,175.2 Personal Private Client 10,669.9 10,733.3 Residential Real Estate 6,286.6 6,514.0 Other 28.6 67.5 Total Personal 16,985.1 17,314.8 Total Loans and Leases $ 30,620.6 $ 32,490.0 Allowance for Credit Losses Assigned to Loans and Leases (114.5 ) (112.6 ) Net Loans and Leases $ 30,506.1 $ 32,377.4
Borrower Ratings	Loan and lease segment and class balances as of March 31, 2019 and December 31, 2018 are provided below, segregated by borrower ratings into “1 to 3,” “4 to 5” and “6 to 9” (watch list), categories. Table 44: Borrower Ratings March 31, 2019 December 31, 2018 (In Millions) 1 to 3 Category 4 to 5 Category 6 to 9 Category (Watch List) Total 1 to 3 Category 4 to 5 Category 6 to 9 Category (Watch List) Total Commercial Commercial and Institutional $ 5,293.4 $ 3,118.6 $ 120.1 $ 8,532.1 $ 5,477.4 $ 3,159.8 $ 90.9 $ 8,728.1 Commercial Real Estate 1,095.2 2,068.8 21.0 3,185.0 1,209.6 1,992.2 27.0 3,228.8 Non-U.S. 1,021.1 626.3 1.2 1,648.6 1,625.3 1,075.3 1.0 2,701.6 Lease Financing, net 76.9 12.4 — 89.3 78.3 12.4 — 90.7 Other 104.9 75.6 — 180.5 203.3 222.7 — 426.0 Total Commercial 7,591.5 5,901.7 142.3 13,635.5 8,593.9 6,462.4 118.9 15,175.2 Personal Private Client 5,983.0 4,680.2 6.7 10,669.9 6,321.1 4,403.2 9.0 10,733.3 Residential Real Estate 2,535.3 3,496.6 254.7 6,286.6 2,745.0 3,502.3 266.7 6,514.0 Other 16.6 12.0 — 28.6 32.2 35.3 — 67.5 Total Personal 8,534.9 8,188.8 261.4 16,985.1 9,098.3 7,940.8 275.7 17,314.8 Total Loans and Leases $ 16,126.4 $ 14,090.5 $ 403.7 $ 30,620.6 $ 17,692.2 $ 14,403.2 $ 394.6 $ 32,490.0
Delinquency Status	The following table provides balances and delinquency status of performing and nonperforming loans and leases by segment and class, as well as the total OREO and nonperforming asset balances, as of March 31, 2019 and December 31, 2018 . Table 45: Delinquency Status March 31, 2019 (In Millions) Current 30-59 Days Past Due 60-89 Days Past Due 90 Days or More Past Due Total Performing Nonperforming Total Loans and Leases Commercial Commercial and Institutional $ 8,499.3 $ 22.1 $ 3.1 $ — $ 8,524.5 $ 7.6 $ 8,532.1 Commercial Real Estate 3,161.4 3.3 8.1 8.0 3,180.8 4.2 3,185.0 Non-U.S. 1,647.6 0.4 — — 1,648.0 0.6 1,648.6 Lease Financing, net 89.3 — — — 89.3 — 89.3 Other 180.5 — — — 180.5 — 180.5 Total Commercial 13,578.1 25.8 11.2 8.0 13,623.1 12.4 13,635.5 Personal Private Client 10,622.5 39.1 7.6 0.5 10,669.7 0.2 10,669.9 Residential Real Estate 6,143.2 28.9 6.5 4.5 6,183.1 103.5 6,286.6 Other 28.6 — — — 28.6 — 28.6 Total Personal 16,794.3 68.0 14.1 5.0 16,881.4 103.7 16,985.1 Total Loans and Leases $ 30,372.4 $ 93.8 $ 25.3 $ 13.0 $ 30,504.5 $ 116.1 $ 30,620.6 Other Real Estate Owned $ 8.0 Total Nonperforming Assets $ 124.1 December 31, 2018 (In Millions) Current 30-59 Days Past Due 60-89 Days Past Due 90 Days or More Past Due Total Performing Nonperforming Total Loans and Leases Commercial Commercial and Institutional $ 8,678.2 $ 37.4 $ 4.5 $ 1.2 $ 8,721.3 $ 6.8 $ 8,728.1 Commercial Real Estate 3,191.5 8.4 15.6 6.4 3,221.9 6.9 3,228.8 Non-U.S. 2,701.2 — — — 2,701.2 0.4 2,701.6 Lease Financing, net 90.7 — — — 90.7 — 90.7 Other 426.0 — — — 426.0 — 426.0 Total Commercial 15,087.6 45.8 20.1 7.6 15,161.1 14.1 15,175.2 Personal Private Client 10,681.1 39.5 12.5 — 10,733.1 0.2 10,733.3 Residential Real Estate 6,376.8 27.2 6.2 8.8 6,419.0 95.0 6,514.0 Other 67.5 — — — 67.5 — 67.5 Total Personal 17,125.4 66.7 18.7 8.8 17,219.6 95.2 17,314.8 Total Loans and Leases $ 32,213.0 $ 112.5 $ 38.8 $ 16.4 $ 32,380.7 $ 109.3 $ 32,490.0 Other Real Estate Owned $ 8.4 Total Nonperforming Assets $ 117.7
Impaired Loans as of the Period End	d leases. The following table provides information related to impaired loans by segment and class. Table 46: Impaired Loans as of the Period End As of March 31, 2019 As of December 31, 2018 (In Millions) Recorded Investment Unpaid Principal Balance Specific Allowance Recorded Investment Unpaid Principal Balance Specific Allowance With No Related Specific Allowance Commercial and Institutional $ 0.1 $ 0.1 $ — $ 0.2 $ 0.4 $ — Commercial Real Estate 2.8 4.7 — 5.8 7.6 — Private Client 1.7 1.7 — 1.7 1.7 — Residential Real Estate 88.7 117.6 — 76.7 104.7 — With a Related Specific Allowance Commercial and Institutional 7.5 8.8 3.7 6.4 7.3 3.0 Commercial Real Estate 1.3 1.4 1.1 2.6 2.8 1.1 Residential Real Estate 21.2 24.8 2.9 22.8 26.1 3.1 Total Commercial 11.7 15.0 4.8 15.0 18.1 4.1 Personal 111.6 144.1 2.9 101.2 132.5 3.1 Total $ 123.3 $ 159.1 $ 7.7 $ 116.2 $ 150.6 $ 7.2 Three Months Ended March 31, 2019 2018 (In Millions) Average Recorded Investment Interest Income Recognized Average Recorded Investment Interest Income Recognized With No Related Specific Allowance Commercial and Institutional $ 0.1 $ — $ 19.6 $ — Commercial Real Estate 3.8 — 6.5 — Private Client 1.7 — 0.6 — Residential Real Estate 89.2 0.6 93.8 0.5 With a Related Specific Allowance Commercial and Institutional 7.1 — — — Commercial Real Estate 1.7 — 1.9 — Residential Real Estate 20.9 — 13.8 — Total Commercial 12.7 — 28.0 — Personal 111.8 0.6 108.2 0.5 Total $ 124.5 $ 0.6 $ 136.2 $ 0.5 Note: Average recorded investment in impaired loans is calculated as the average of the month-end impaired loan balances for the period.
Modified Troubled Debt Restructurings	The following table provides, by segment and class, the number of loans and leases modified in TDRs during the three -month periods ended March 31, 2019 and 2018 , and the recorded investments and unpaid principal balances as of March 31, 2019 and 2018 . Table 47: Modified Troubled Debt Restructurings ($ In Millions) Three Months Ended March 31, 2019 Number of Loans and Leases Recorded Investment Unpaid Principal Balance Commercial Commercial and Institutional 1 $ 7.6 $ 8.8 Commercial Real Estate — — — Total Commercial 1 7.6 8.8 Personal Private Client — — — Residential Real Estate 13 9.8 9.9 Total Personal 13 9.8 9.9 Total Loans and Leases 14 $ 17.4 $ 18.7 Note: Period-end balances reflect all paydowns and charge-offs during the period. ($ In Millions) Three Months Ended March 31, 2018 Number of Loans and Leases Recorded Investment Unpaid Principal Balance Commercial Commercial and Institutional 1 $ 0.3 $ 0.5 Commercial Real Estate — — — Total Commercial 1 0.3 0.5 Personal Private Client 1 — 0.1 Residential Real Estate 14 7.5 8.7 Total Personal 15 7.5 8.8 Total Loans and Leases 16 $ 7.8 $ 9.3 Note: Period-end balances reflect all paydowns and charge-offs during the period.

Allowance for Credit Losses (Ta

Allowance for Credit Losses (Tables)	3 Months Ended
	Mar. 31, 2019
Receivables [Abstract]
Changes in Allowance for Credit Losses	The following table provides information regarding changes in the total allowance for credit losses by segment during the three months ended March 31, 2019 and 2018 . Table 48: Changes in the Allowance for Credit Losses Three Months Ended March 31, 2019 2018 (In Millions) Commercial Personal Total Commercial Personal Total Balance at Beginning of Period $ 78.7 $ 59.5 $ 138.2 $ 80.8 $ 73.0 $ 153.8 Charge-Offs (0.1 ) (0.9 ) (1.0 ) (0.8 ) (3.5 ) (4.3 ) Recoveries 0.4 1.8 2.2 0.6 0.7 1.3 Net (Charge-Offs) Recoveries 0.3 0.9 1.2 (0.2 ) (2.8 ) (3.0 ) Provision for Credit Losses (0.4 ) 0.4 — (3.5 ) 0.5 (3.0 ) Balance at End of Period $ 78.6 $ 60.8 $ 139.4 $ 77.1 $ 70.7 $ 147.8
Recorded Investments in Loans and Leases	The following table provides information regarding the recorded investments in loans and leases and the allowance for credit losses by segment as of March 31, 2019 and December 31, 2018 . Table 49: Recorded Investments in Loans and Leases March 31, 2019 December 31, 2018 (In Millions) Commercial Personal Total Commercial Personal Total Loans and Leases Specifically Evaluated for Impairment $ 11.7 $ 111.6 $ 123.3 $ 15.0 $ 101.2 $ 116.2 Evaluated for Inherent Impairment 13,623.8 16,873.5 30,497.3 15,160.2 17,213.6 32,373.8 Total Loans and Leases 13,635.5 16,985.1 30,620.6 15,175.2 17,314.8 32,490.0 Allowance for Credit Losses on Credit Exposures Specifically Evaluated for Impairment 4.8 2.9 7.7 4.1 3.1 7.2 Evaluated for Inherent Impairment 53.3 53.5 106.8 53.5 51.9 105.4 Allowance Assigned to Loans and Leases 58.1 56.4 114.5 57.6 55.0 112.6 Allowance for Undrawn Exposures Commitments and Standby Letters of Credit 20.5 4.4 24.9 21.1 4.5 25.6 Total Allowance for Credit Losses $ 78.6 $ 60.8 $ 139.4 $ 78.7 $ 59.5 $ 138.2

Lease Commitments (Tables)

Lease Commitments (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Lease Cost Components	The following table provides the components of lease cost for the three months ended March 31, 2019 . Table 50: Lease Cost Components (In Millions) Three Months Ended March 31, 2019 Operating Lease Cost $ 25.2 Variable Lease Cost 10.1 Sublease Income (1.5 ) Total Lease Cost $ 33.8
Maturity of Lease Liability	The following table presents a maturity analysis of lease liabilities as of March 31, 2019 . Table 51: Maturity of Lease Liabilities (In Millions) Maturity of Lease Liabilities 2019 (excluding the three months ended March 31, 2019) $ 74.9 2020 96.6 2021 82.0 2022 66.6 2023 57.3 Later Years 207.0 Total Lease Payments 584.4 Less: Imputed Interest (74.7 ) Present Value of Lease Liabilities $ 509.7
Leases	The location and amount of lease right-of-use assets and lease liabilities recorded in the consolidated balance sheet as of March 31, 2019 are presented below. Table 52: Location and Amount of Lease Assets and Liabilities (In Millions) Location of Lease Assets and Liabilities in the Balance Sheet March 31, Assets Operating Lease Right-of-Use Asset Other Assets $ 460.4 Liabilities Operating Lease Liability Other Liabilities $ 509.7
Weighted-Average Remaining Lease Term and Discount Rate	The weighted-average remaining lease term and weighted-average discount rate applied to leases as of March 31, 2019 were as follows: Table 53: Weighted-Average Remaining Lease Term and Discount Rate March 31, Operating Leases Weighted-Average Remaining Lease Term 7.7 years Weighted-Average Discount Rate 3.4%
Supplemental Cash Flow Information	The following table provides supplemental cash flow information related to leases for the three months ended March 31, 2019 . Table 54: Supplemental Cash Flow Information (In Millions) Three Months Ended March 31, 2019 Cash paid for amounts included in the measurement of lease liabilities Operating cash flows for operating leases $ 28.3 Right-of-use assets obtained in exchange for new operating lease liabilities 1.0
Minimum Annual Lease Commitments	Table 55: Minimum Lease Payments as of December 31, 2018 (In Millions) Future Minimum Lease Payments 2019 $ 98.8 2020 97.8 2021 85.9 2022 77.2 2023 67.7 Later Years 335.7 Total Minimum Lease Payments 763.1 Less: Sublease Rentals (23.4 ) Net Minimum Lease Payments $ 739.7

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	3 Months Ended
	Mar. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill by Reporting Segment	The carrying amounts of goodwill and other intangibles assets, reflecting the effect of foreign exchange rates on non-U.S.-dollar-denominated balances, by reporting segment at March 31, 2019 , and December 31, 2018 , were as follows: Table 56: Goodwill by Reporting Segment (In Millions) March 31, December 31, Corporate & Institutional Services $ 611.9 $ 598.2 Wealth Management 71.1 71.1 Total Goodwill $ 683.0 $ 669.3
Other Intangible Assets	The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of March 31, 2019 and December 31, 2018 , were as follows: Table 57: Other Intangible Assets (In Millions) March 31, December 31, Gross Carrying Amount $ 206.4 $ 211.1 Less: Accumulated Amortization 74.0 72.5 Net Book Value $ 132.4 $ 138.6

Reporting Segments (Tables)

Reporting Segments (Tables)	3 Months Ended
	Mar. 31, 2019
Segment Reporting [Abstract]
Results of Reporting Segments	The following table reflects the earnings contributions and average assets of Northern Trust’s reporting segments for the three -month periods ended March 31, 2019 and 2018 . Table 58: Results of Reporting Segments Three Months Ended March 31, Corporate & Wealth Treasury and Total ($ In Millions) 2019 2018 2019 2018 2019 2018 2019 2018 Noninterest Income Trust, Investment and Other Servicing Fees $ 535.2 $ 544.3 $ 393.7 $ 393.4 $ — $ — $ 928.9 $ 937.7 Foreign Exchange Trading Income 59.7 62.4 6.5 1.2 — 14.9 66.2 78.5 Other Noninterest Income 43.4 46.6 25.5 25.7 (5.1 ) 3.5 63.8 75.8 Net Interest Income* 234.8 229.4 195.0 198.8 — (35.5 ) 429.8 392.7 Revenue* 873.1 882.7 620.7 619.1 (5.1 ) (17.1 ) 1,488.7 1,484.7 Provision for Credit Losses (1.1 ) (3.9 ) 1.1 0.9 — — — (3.0 ) Noninterest Expense 648.0 585.6 379.9 365.7 0.8 44.0 1,028.7 995.3 Income before Income Taxes* 226.2 301.0 239.7 252.5 (5.9 ) (61.1 ) 460.0 492.4 Provision for Income Taxes* 53.6 66.8 60.8 62.4 (1.5 ) (18.4 ) 112.9 110.8 Net Income $ 172.6 $ 234.2 $ 178.9 $ 190.1 $ (4.4 ) $ (42.7 ) $ 347.1 $ 381.6 Percentage of Consolidated Net Income 50 % 61 % 51 % 50 % (1 )% (11 )% 100 % 100 % Average Assets $ 90,351.7 $ 83,637.0 $ 29,065.0 $ 26,108.0 $ — $ 14,748.3 $ 119,416.7 $ 124,493.3 * Non-GAAP financial measures stated on a fully taxable equivalent basis (FTE). Total consolidated includes FTE adjustments of $7.8 million for 2019 and $8.7 million for 2018 .

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2019
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive Income (Loss)	The following tables summarize the components of accumulated other comprehensive income (loss) (AOCI) at March 31, 2019 and 2018 , and changes during the three -month periods then ended. Table 59: Summary of Changes in Accumulated Other Comprehensive Income (Loss) (In Millions) Balance at March 31, 2019 Net Change Balance at December 31, 2018 Net Unrealized Gains (Losses) on Debt Securities Available for Sale* $ (29.3 ) $ 85.6 $ (114.9 ) Net Unrealized Gains (Losses) on Cash Flow Hedges (0.3 ) (4.3 ) 4.0 Net Foreign Currency Adjustments 82.7 14.8 67.9 Net Pension and Other Postretirement Benefit Adjustments (398.4 ) 12.3 (410.7 ) Total $ (345.3 ) $ 108.4 $ (453.7 ) (In Millions) Balance at March 31, 2018 Net Change Reclassification of Certain Tax Effects from AOCI Balance at December 31, 2017 Net Unrealized Gains (Losses) on Debt Securities Available for Sale $ (147.6 ) $ (55.0 ) $ (17.8 ) $ (74.8 ) Net Unrealized Gains (Losses) on Cash Flow Hedges 1.7 (3.7 ) 0.9 4.5 Net Foreign Currency Adjustments 32.6 (13.1 ) 47.5 (1.8 ) Net Pension and Other Postretirement Benefit Adjustments (392.4 ) 5.7 (55.9 ) (342.2 ) Total $ (505.7 ) $ (66.1 ) $ (25.3 ) $ (414.3 ) * Includes net unrealized gains on debt securities transferred from available for sale to held to maturity during the year ended December 31, 2018 .
Details of Changes in Accumulated Other Comprehensive Income (Loss)	Table 60: Details of Changes in Accumulated Other Comprehensive Income (Loss) Three Months Ended March 31, 2019 2018 (In Millions) Before Tax Tax Effect After Tax Before Tax Tax Effect After Tax Unrealized Gains (Losses) on Debt Securities Available for Sale Unrealized Gains (Losses) on Debt Securities Available for Sale $ 115.3 $ (29.9 ) $ 85.4 $ (75.4 ) $ 20.4 $ (55.0 ) Reclassification Adjustment for (Gains) Losses Included in Net Income 0.2 — 0.2 — — — Net Change $ 115.5 $ (29.9 ) $ 85.6 $ (75.4 ) $ 20.4 $ (55.0 ) Unrealized Gains (Losses) on Cash Flow Hedges Foreign Exchange Contracts $ 7.2 $ (1.7 ) $ 5.5 $ 13.0 $ (3.2 ) $ 9.8 Interest Rate Contracts 0.6 (0.2 ) 0.4 (1.4 ) 0.4 (1.0 ) Reclassification Adjustment for (Gains) Losses Included in Net Income (13.6 ) 3.4 (10.2 ) (16.6 ) 4.1 (12.5 ) Net Change $ (5.8 ) $ 1.5 $ (4.3 ) $ (5.0 ) $ 1.3 $ (3.7 ) Foreign Currency Adjustments Foreign Currency Translation Adjustments $ (6.5 ) $ 1.6 $ (4.9 ) $ 44.6 $ (2.8 ) $ 41.8 Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses) 0.7 (0.2 ) 0.5 1.2 (0.3 ) 0.9 Net Investment Hedge Gains (Losses) 28.6 (9.4 ) 19.2 (74.3 ) 18.5 (55.8 ) Net Change $ 22.8 $ (8.0 ) $ 14.8 $ (28.5 ) $ 15.4 $ (13.1 ) Pension and Other Postretirement Benefit Adjustments Net Actuarial Gain (Loss) $ 11.3 $ (3.1 ) $ 8.2 $ 10.1 $ (2.5 ) $ 7.6 Reclassification Adjustment for (Gains) Losses Included in Net Income 5.4 (1.3 ) 4.1 9.1 (11.0 ) (1.9 ) Net Change $ 16.7 $ (4.4 ) $ 12.3 $ 19.2 $ (13.5 ) $ 5.7
Reclassification Adjustment out of Accumulated Other Comprehensive Income	The following table provides the location and before-tax amounts of reclassifications out of AOCI during the three months ended March 31, 2019 . Table 61: Reclassification Adjustment out of Accumulated Other Comprehensive Income (In Millions) Location of Reclassification Adjustments Recognized in Income Amount of Reclassification Adjustments Recognized in Income Three Months Ended March 31, 2019 Debt Securities Available for Sale Realized (Gains) Losses on Debt Securities Available for Sale Investment Security Gains (Losses), net $ 0.2 Realized (Gains) Losses on Cash Flow Hedges Foreign Exchange Contracts Other Operating Income $ 0.6 Interest Income (14.4 ) Interest Rate Contracts Interest Expense 0.2 Total Realized (Gains) on Cash Flow Hedges $ (13.6 ) Pension and Other Postretirement Benefit Adjustments Amortization of Net Actuarial Loss Employee Benefits $ 5.5 Amortization of Prior Service Cost Employee Benefits (0.1 ) Gross Reclassification Adjustment $ 5.4 (In Millions) Location of Reclassification Adjustments Recognized in Income Amount of Reclassification Adjustments Recognized in Income Three Months Ended March 31, 2018 Debt Securities Available for Sale Realized (Gains) Losses on Debt Securities Available for Sale Investment Security Gains (Losses), net $ — Realized (Gains) Losses on Cash Flow Hedges Foreign Exchange Contracts Other Operating Income $ (2.4 ) Interest Income (14.2 ) Interest Rate Contracts Interest Income — Total Realized (Gains) on Cash Flow Hedges $ (16.6 ) Pension and Other Postretirement Benefit Adjustments Amortization of Net Actuarial Loss Employee Benefits $ 9.2 Amortization of Prior Service Cost Employee Benefits (0.1 ) Gross Reclassification Adjustment $ 9.1

Net Income Per Common Share C_2

Net Income Per Common Share Computations (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Net Income per Common Share	The computations of net income per common share are presented in the following table. Table 62: Net Income per Common Share Three Months Ended March 31, ($ In Millions Except Per Common Share Information) 2019 2018 Basic Net Income Per Common Share Average Number of Common Shares Outstanding 218,236,802 225,681,167 Net Income $ 347.1 $ 381.6 Less: Dividends on Preferred Stock 17.3 17.3 Net Income Applicable to Common Stock $ 329.8 $ 364.3 Less: Earnings Allocated to Participating Securities 4.3 5.2 Earnings Allocated to Common Shares Outstanding $ 325.5 $ 359.1 Basic Net Income Per Common Share $ 1.49 $ 1.59 Diluted Net Income Per Common Share Average Number of Common Shares Outstanding 218,236,802 225,681,167 Plus: Dilutive Effect of Share-based Compensation 1,033,413 1,366,352 Average Common and Potential Common Shares 219,270,215 227,047,519 Earnings Allocated to Common and Potential Common Shares $ 325.4 $ 359.2 Diluted Net Income Per Common Share $ 1.48 $ 1.58 Note: For the three months ended March 31, 2019 , there were no common stock equivalents excluded in the computation of diluted net income per share. There were no common stock equivalents excluded in the computation of diluted net income per share for the three months ended March 31, 2018 .

Revenue from Contracts with C_2

Revenue from Contracts with Clients (Tables)	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue Disaggregation	The following table presents revenues disaggregated by major revenue source. Table 63: Revenue Disaggregation Three Months Ended March 31, (In Millions) 2019 2018 Noninterest Income Trust, Investment and Other Servicing Fees Custody and Fund Administration $ 397.5 $ 395.9 Investment Management and Advisory 459.2 465.6 Securities Lending 22.8 26.2 Other 49.4 50.0 Total Trust, Investment and Other Servicing Fees $ 928.9 $ 937.7 Other Noninterest Income Foreign Exchange Income $ 66.2 $ 78.5 Treasury Management 11.7 14.0 Securities Commissions and Trading Income 23.3 27.2 Other Operating Income 29.0 34.8 Investment Security Losses, net (0.2 ) (0.2 ) Total Other Noninterest Income $ 130.0 $ 154.3 Total Noninterest Income $ 1,058.9 $ 1,092.0
Contract Balances	The table below represents receivables balances from contracts with clients, which are included in other assets in the consolidated balance sheets, at March 31, 2019 and December 31, 2018 . Table 64: Client Receivables (In Millions) March 31, December 31, Trust Fees Receivable, net $ 818.4 $ 742.5 Other 91.4 90.1 Total Client Receivables $ 909.8 $ 832.6

Net Interest Income (Tables)

Net Interest Income (Tables)	3 Months Ended
	Mar. 31, 2019
Banking and Thrift, Interest [Abstract]
Net Interest Income	The components of net interest income were as follows: Table 65: Net Interest Income Three Months Ended March 31, (In Millions) 2019 2018 Interest Income Loans and Leases $ 298.2 $ 252.0 Securities — Taxable 277.5 177.8 — Non-Taxable 1.1 2.0 Interest-Bearing Due from and Deposits with Banks (1) 17.9 19.9 Federal Reserve and Other Central Bank Deposits and Other 68.1 54.2 Total Interest Income $ 662.8 $ 505.9 Interest Expense Deposits $ 147.6 $ 63.1 Federal Funds Purchased 13.4 5.3 Securities Sold Under Agreements to Repurchase 1.8 2.7 Other Borrowings 49.9 26.5 Senior Notes 15.9 11.8 Long-Term Debt 10.0 11.0 Floating Rate Capital Debt 2.2 1.5 Total Interest Expense $ 240.8 $ 121.9 Net Interest Income $ 422.0 $ 384.0 (1) Interest-Bearing Due from and Deposits with Banks includes the interest-bearing component of Cash and Due from Banks and Interest-Bearing Deposits with Banks as presented on the consolidated balance sheets.

Pension and Postretirement He_2

Pension and Postretirement Health Care (Tables)	3 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Net Periodic Pension Expense (Benefit)	The following table sets forth the net periodic pension and postretirement benefit expense for Northern Trust’s U.S. and non-U.S. pension plans, supplemental pension plan, and postretirement health care plan for the three months ended March 31, 2019 and 2018 . Table 66: Net Periodic Pension Expense (Benefit) Net Periodic Pension Expense U.S. Plan Three Months Ended March 31, (In Millions) 2019 2018 Service Cost $ 10.4 $ 10.4 Interest Cost 11.8 11.1 Expected Return on Plan Assets (21.7 ) (22.0 ) Amortization Net Actuarial Loss 4.3 7.1 Prior Service Cost (0.1 ) (0.1 ) Net Periodic Pension Expense $ 4.7 $ 6.5 Net Periodic Pension Expense Non-U.S. Plans Three Months Ended March 31, (In Millions) 2019 2018 Service Cost $ 0.5 $ 0.4 Interest Cost 1.0 1.0 Expected Return on Plan Assets (1.0 ) (1.1 ) Settlement Expense — — Net Actuarial Loss Amortization 0.1 0.3 Net Periodic Pension Expense $ 0.6 $ 0.6 Net Periodic Pension Expense Supplemental Plan Three Months Ended March 31, (In Millions) 2019 2018 Service Cost $ 1.0 $ 1.1 Interest Cost 1.5 1.3 Amortization Net Actuarial Loss 1.4 1.8 Prior Service Cost — — Net Periodic Pension Expense $ 3.9 $ 4.2 Net Periodic Postretirement Expense Postretirement Health Care Plan Three Months Ended March 31, (In Millions) 2019 2018 Service Cost $ — $ — Interest Cost 0.3 0.3 Amortization Net Actuarial (Gain) (0.3 ) — Prior Service Cost $ — $ — Net Periodic Postretirement Expense $ — $ 0.3

Share-Based Compensation Plans

Share-Based Compensation Plans (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Total Compensation Expense for Share-Based Payment Arrangements	Total compensation expense for share-based payment arrangements and the associated tax impacts were as follows for the three months ended March 31, 2019 and 2018 . Table 67: Total Compensation Expense for Share-Based Payment Arrangements Three Months Ended March 31, (In Millions) 2019 2018 Restricted Stock Unit Awards $ 39.2 $ 46.7 Stock Options 0.5 0.8 Performance Stock Units 15.6 9.0 Total Share-Based Compensation Expense 55.3 56.5 Tax Benefits Recognized $ 13.7 $ 14.0

Derivative Financial Instrume_2

Derivative Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Notional and Fair Value Amounts of Client-related and Trading Derivative Financial Instruments	The following table shows the notional and fair values of all derivative financial instruments as of March 31, 2019 and December 31, 2018 . Table 68: Notional and Fair Values of Derivative Financial Instruments March 31, 2019 December 31, 2018 Notional Fair Value Notional Fair Value (In Millions) Asset 1 Liability 2 Asset 1 Liability 2 Derivatives Designated as Hedging under GAAP Interest Rate Contracts Fair Value Hedges $ 4,479.8 $ 23.9 $ 19.9 $ 4,590.4 $ 29.8 $ 23.3 Cash Flow Hedges 600.0 0.2 0.9 600.0 0.2 1.2 Foreign Exchange Contracts Cash Flow Hedges 2,259.1 42.5 10.5 2,648.2 13.8 57.8 Net Investment Hedges 2,509.7 36.5 5.5 3,475.1 292.4 14.5 Total Derivatives Designated as Hedging under GAAP $ 9,848.6 $ 103.1 $ 36.8 $ 11,313.7 $ 336.2 $ 96.8 Derivatives Not Designated as Hedging under GAAP Non-Designated Risk Management Derivatives Foreign Exchange Contracts $ 117.3 $ 1.2 $ 0.5 $ 122.2 $ 0.5 $ 0.2 Other Financial Derivatives 3 559.8 — 35.9 483.4 1.3 32.8 Total Non-Designated Risk Management Derivatives $ 677.1 $ 1.2 $ 36.4 $ 605.6 $ 1.8 $ 33.0 Client-Related and Trading Derivatives Foreign Exchange Contracts $ 286,240.1 $ 1,561.8 $ 1,474.0 $ 281,864.4 $ 2,159.4 $ 2,190.0 Interest Rate Contracts 7,621.5 80.5 58.8 7,711.2 66.1 68.6 Total Client-Related and Trading Derivatives $ 293,861.6 $ 1,642.3 $ 1,532.8 $ 289,575.6 $ 2,225.5 $ 2,258.6 Total Derivatives Not Designated as Hedging under GAAP $ 294,538.7 $ 1,643.5 $ 1,569.2 $ 290,181.2 $ 2,227.3 $ 2,291.6 Total Gross Derivatives $ 304,387.3 $ 1,746.6 $ 1,606.0 $ 301,494.9 $ 2,563.5 $ 2,388.4 Less: Netting 4 979.9 1,123.7 1,357.1 1,796.3 Total Derivative Financial Instruments $ 766.7 $ 482.3 $ 1,206.4 $ 592.1 (1) Derivative assets are reported in other assets on the consolidated balance sheets. (2) Derivative liabilities are reported in other liabilities on the consolidated balance sheets. (3) This line includes swaps related to sales of certain Visa Class B common shares and total return swap contracts. (4) See further detail in Note 23 - Offsetting of Assets and Liabilities.
Cash Flow Hedge Derivative Gains and Losses Recognized in AOCI and Reclassified to Income	The following tables provide fair value and cash flow hedge derivative gains and losses recognized in income during the three months ended March 31, 2019 and 2018 . Table 69: Location and Amount of Fair Value and Cash Flow Hedge Derivative Gains and Losses Recorded in Income Location and Amount of Derivative Gain/(Loss) Recognized in Income (In Millions) Interest Income Interest Expense Other Operating Income Three Months Ended March 31, 2019 2018 2019 2018 2019 2018 Total amounts on the consolidated statements of income $ 662.8 $ 505.9 $ 240.8 $ 121.9 $ 29.0 $ 34.8 Gains/(Losses) on fair value hedges recognized on Interest Rate Contracts Recognized on derivatives (35.4 ) 54.3 28.5 (21.9 ) — — Recognized on hedged items 35.4 (54.3 ) (28.5 ) 21.9 — — Amounts related to interest settlements on derivatives 5.5 (3.7 ) (1.6 ) 1.5 — — Total gain/(loss) recognized on fair value hedges $ 5.5 $ (3.7 ) $ (1.6 ) $ 1.5 $ — $ — Gains/(Losses) on cash flow hedges recognized on Foreign Exchange Contracts Net gain/(loss) reclassified from AOCI to net income $ 14.4 $ 14.2 $ — $ — $ (0.6 ) $ 2.4 Interest Rate Contracts Net gain/(loss) reclassified from AOCI to net income (0.2 ) — — — — — Total gain/(loss) reclassified from AOCI to net income on cash flow hedges $ 14.2 $ 14.2 $ — $ — $ (0.6 ) $ 2.4
Location and Amount of Fair Value Hedge Derivative Gains and Losses Recorded in Income	The following table provides the impact of fair value hedge accounting on the carrying value of the designated hedged items as of March 31, 2019 . Table 70: Hedged Items in Fair Value Hedges March 31, 2019 December 31, 2018 (In Millions) Carrying Value of the Hedged Items Cumulative Hedge Accounting Basis Adjustment (1) Carrying Value of the Hedged Items Cumulative Hedge Accounting Basis Adjustment (1) Available for Sale Debt Securities (2) $ 3,759.5 $ 60.5 $ 3,831.6 $ 99.4 Senior Notes and Long-Term Subordinated Debt 1,248.9 55.1 1,248.8 29.3 Total $ 5,008.4 $ 115.6 $ 5,080.4 $ 128.7 (1) There are no amounts related to discontinued hedging relationships. (2) Carrying value represents amortized cost.
Location and Amount of Gains and Losses Recorded in Income for Non-Designated Risk Management Derivative Instruments	The following table provides the location and amount of gains and losses recorded in the consolidated statements of income for the three months ended March 31, 2019 and 2018 . Table 71: Location and Amount of Gains and Losses Recorded in Income for Derivatives Not Designated as Hedging Under GAAP (In Millions) Location of Amount of Derivative Gain / (Loss) Three Months Ended March 31, 2019 2018 Non-designated risk management derivatives Foreign Exchange Contracts Other Operating Income $ 0.9 $ 4.0 Other Financial Derivatives (1) Other Operating Income (7.3 ) (4.0 ) Gains/(Losses) from non-designated risk management derivatives $ (6.4 ) $ — Client-related and trading derivatives Foreign Exchange Contracts Foreign Exchange Trading Income $ 66.2 $ 78.5 Interest Rate Contracts Security Commissions and Trading Income 1.5 1.7 Gains/(Losses) from client-related and trading derivatives $ 67.7 $ 80.2 Total gains/(losses) from derivatives not designated as hedging under GAAP $ 61.3 $ 80.2 (1) This line includes swaps related to sales of certain Visa Class B common shares and total return swap contracts.

Offsetting of Assets and Liab_2

Offsetting of Assets and Liabilities (Tables)	3 Months Ended
	Mar. 31, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell	The following table provides information regarding the offsetting of derivative assets and securities purchased under agreements to resell within the consolidated balance sheets as of March 31, 2019 and December 31, 2018 . Table 72: Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell March 31, 2019 (In Millions) Gross Recognized Assets Gross Amounts Offset in the Balance Sheet (2) Net Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net Amount (4) Derivative Assets (1) Foreign Exchange Contracts Over the Counter (OTC) $ 1,127.8 $ 926.8 $ 201.0 $ 30.4 $ 170.6 Interest Rate Swaps OTC 60.5 12.3 48.2 — 48.2 Interest Rate Swaps Exchange Cleared 44.2 40.8 3.4 — 3.4 Total Derivatives Subject to a Master Netting Arrangement 1,232.5 979.9 252.6 30.4 222.2 Total Derivatives Not Subject to a Master Netting Arrangement 514.1 — 514.1 — 514.1 Total Derivatives 1,746.6 979.9 766.7 30.4 736.3 Securities Purchased under Agreements to Resell (2) $ 515.2 $ — $ 515.2 $ 515.2 $ — December 31, 2018 (In Millions) Gross Recognized Assets Gross Amounts Offset in the Balance Sheet (2) Net Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net Amount (4) Derivative Assets (1) Foreign Exchange Contracts OTC $ 1,902.3 $ 1,308.8 $ 593.5 $ 12.7 $ 580.8 Interest Rate Swaps OTC 71.6 22.6 49.0 — 49.0 Interest Rate Swaps Exchange Cleared 24.5 24.4 0.1 — 0.1 Other Financial Derivatives 1.3 1.3 — — — Total Derivatives Subject to a Master Netting Arrangement 1,999.7 1,357.1 642.6 12.7 629.9 Total Derivatives Not Subject to a Master Netting Arrangement 563.8 — 563.8 2.7 561.1 Total Derivatives 2,563.5 1,357.1 1,206.4 15.4 1,191.0 Securities Purchased under Agreements to Resell (3) $ 1,031.2 $ — $ 1,031.2 $ 1,031.2 $ — (1) Derivative assets are reported in other assets in the consolidated balance sheets. Other assets (excluding derivative assets) totaled $5.3 billion and $4.6 billion as of March 31, 2019 and December 31, 2018 , respectively. (2) Including cash collateral received from counterparties. (3) Securities purchased under agreements to resell are reported in federal funds sold and securities purchased under agreements to resell in the consolidated balance sheets. Federal funds sold totaled $37.0 million and $134.0 million as of March 31, 2019 and December 31, 2018 , respectively. (4) Northern Trust did not possess any cash collateral that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2019 and December 31, 2018 .
Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase	The following table provides information regarding the offsetting of derivative liabilities and securities sold under agreements to repurchase within the consolidated balance sheets as of March 31, 2019 and December 31, 2018 . Table 73: Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase March 31, 2019 (In Millions) Gross Recognized Liabilities Gross Amounts Offset in the Balance Sheet (2) Net Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net Amount (3) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 1,169.5 $ 1,054.9 $ 114.6 $ 0.1 $ 114.5 Interest Rate Swaps OTC 38.8 27.8 11.0 — 11.0 Interest Rate Swaps Exchange Cleared 40.8 40.8 — — — Other Financial Derivatives 35.9 0.2 35.7 — 35.7 Total Derivatives Subject to a Master Netting Arrangement 1,285.0 1,123.7 161.3 0.1 161.2 Total Derivatives Not Subject to a Master Netting Arrangement 321.0 — 321.0 — 321.0 Total Derivatives 1,606.0 1,123.7 482.3 0.1 482.2 Securities Sold under Agreements to Repurchase $ 39.7 $ — $ 39.7 $ 39.7 $ — December 31, 2018 (In Millions) Gross Recognized Liabilities Gross Amounts Offset in the Balance Sheet (2) Net Amounts Presented in the Balance Sheet Gross Amounts Not Offset in the Balance Sheet Net Amount (3) Derivative Liabilities (1) Foreign Exchange Contracts OTC $ 1,821.0 $ 1,751.7 $ 69.3 $ — $ 69.3 Interest Rate Swaps OTC 68.8 19.0 49.8 — 49.8 Interest Rate Swaps Exchange Cleared 24.4 24.4 — — — Other Financial Derivatives 32.8 1.2 31.6 — 31.6 Total Derivatives Subject to a Master Netting Arrangement 1,947.0 1,796.3 150.7 — 150.7 Total Derivatives Not Subject to a Master Netting Arrangement 441.4 — 441.4 — 441.4 Total Derivatives 2,388.4 1,796.3 592.1 — 592.1 Securities Sold under Agreements to Repurchase $ 168.3 $ — $ 168.3 $ 168.3 $ — (1) Derivative liabilities are reported in other liabilities in the consolidated balance sheets. Other liabilities (excluding derivative liabilities) totaled $3.1 billion and $2.5 billion as of March 31, 2019 and December 31, 2018 , respectively. (2) Including cash collateral deposited with counterparties. (3) Northern Trust did not place any cash collateral with counterparties that was not offset in the consolidated balance sheets that could have been used to offset the net amounts presented in the consolidated balance sheets as of March 31, 2019 and December 31, 2018 .

Recent Accounting Pronounceme_3

Recent Accounting Pronouncements (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Present value of lease liabilities	$ 509.7
Operating lease right-of-use asset	$ 460.4
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Present value of lease liabilities		$ 530
Operating lease right-of-use asset		$ 480

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) shares in Millions, $ in Millions	Mar. 31, 2019USD ($)security	Dec. 31, 2018USD ($)security	Jun. 30, 2016shares	Jun. 30, 2015shares
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available for Sale	$ 37,058.2	$ 36,888.8
Trading account securities	$ 0.3	$ 0.3
Visa Class B
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Shares issued (in shares) | shares			1.1	1
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of available for sale securities portfolio | security	1,490	1,479
Available for Sale	$ 32,000	$ 31,700
Level 2 | External Pricing
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Number of available for sale securities portfolio | security	1,490	1,479
Trading account securities	$ 0.3	$ 0.3
Level 3 | Fair Value, Measurements, Nonrecurring | Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	22.3	9.7
Level 3 | Fair Value, Measurements, Nonrecurring | OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 0.1	$ 0.4

Fair Value Measurements (Level

Fair Value Measurements (Level 3 Significant Unobservable Inputs) (Details) - Fair Value, Measurements, Recurring - Level 3 - Swaps Related to Sale of Certain Visa Class B Common Shares - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 35	$ 32.8
Group One
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable Inputs	Visa Class A Appreciation	Visa Class A Appreciation
Group Two
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable Inputs	Conversion Rate	Conversion Rate
Group Three
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unobservable Inputs	Expected Duration	Expected Duration
Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instrument visa class A appreciation (as percent)	7.00%	7.00%
Financial instrument conversion rate (as percent)	1.62%	1.62%
Financial instrument expected duration (in years)	1 year 3 months	1 year 6 months
Upper Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instrument visa class A appreciation (as percent)	11.00%	11.00%
Financial instrument conversion rate (as percent)	1.64%	1.64%
Financial instrument expected duration (in years)	3 years 9 months	4 years

Fair Value Measurements (Recurr

Fair Value Measurements (Recurring Basis Hierarchy Leveling) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	$ 37,058.2	$ 36,888.8
Derivative Assets	1,746.6	2,563.5
Netting	(979.9)	(1,357.1)
Derivative Asset	766.7	1,206.4
Derivative Liabilities	1,606	2,388.4
Netting	(1,123.7)	(1,796.3)
Derivative Liabilities	482.3	592.1
Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Netting		(1.3)
Netting	(0.2)	(1.2)
Cross Product Collateral Adjustment
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Netting	(139.2)	(134.5)
Netting	(283.1)	(573.7)
U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	5,022	5,185.3
Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	764.8	655.9
Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	22,568.6	22,424.6
Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	142.7	142.2
Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,293.7	2,294.7
Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	837.4	829.3
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,236.1	2,096.2
Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,520.2	2,657.7
Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	658.1	587.2
Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	14.6	15.7
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	32,000	31,700
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	37,058.2	36,888.8
Trading Account	0.3	0.3
Total Available for Sale and Trading Debt Securities	37,058.5	36,889.1
Fair Value, Measurements, Recurring | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	5,022	5,185.3
Fair Value, Measurements, Recurring | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	764.8	655.9
Fair Value, Measurements, Recurring | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	22,568.6	22,424.6
Fair Value, Measurements, Recurring | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	142.7	142.2
Fair Value, Measurements, Recurring | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,293.7	2,294.7
Fair Value, Measurements, Recurring | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	837.4	829.3
Fair Value, Measurements, Recurring | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,236.1	2,096.2
Fair Value, Measurements, Recurring | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,520.2	2,657.7
Fair Value, Measurements, Recurring | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	658.1	587.2
Fair Value, Measurements, Recurring | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	14.6	15.7
Fair Value, Measurements, Recurring | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Netting	(979.9)	(1,357.1)
Derivative Asset	766.7	1,206.4
Fair Value, Measurements, Recurring | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset	1,642	2,466.1
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset	104.6	96.1
Fair Value, Measurements, Recurring | Other Assets | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Asset		1.3
Fair Value, Measurements, Recurring | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Netting	(1,123.7)	(1,796.3)
Derivative Liabilities	482.3	592.1
Fair Value, Measurements, Recurring | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	1,490.5	2,262.5
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	79.6	93.1
Fair Value, Measurements, Recurring | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	35.9	32.8
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	5,022	5,185.3
Trading Account	0	0
Total Available for Sale and Trading Debt Securities	5,022	5,185.3
Fair Value, Measurements, Recurring | Level 1 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	5,022	5,185.3
Fair Value, Measurements, Recurring | Level 1 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 1 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 1 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 1 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 1 | Other Assets | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets		0
Fair Value, Measurements, Recurring | Level 1 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | Level 1 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | Level 1 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | Level 1 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	32,036.2	31,703.5
Trading Account	0.3	0.3
Total Available for Sale and Trading Debt Securities	32,036.5	31,703.8
Fair Value, Measurements, Recurring | Level 2 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 2 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	764.8	655.9
Fair Value, Measurements, Recurring | Level 2 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	22,568.6	22,424.6
Fair Value, Measurements, Recurring | Level 2 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	142.7	142.2
Fair Value, Measurements, Recurring | Level 2 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,293.7	2,294.7
Fair Value, Measurements, Recurring | Level 2 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	837.4	829.3
Fair Value, Measurements, Recurring | Level 2 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,236.1	2,096.2
Fair Value, Measurements, Recurring | Level 2 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	2,520.2	2,657.7
Fair Value, Measurements, Recurring | Level 2 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	658.1	587.2
Fair Value, Measurements, Recurring | Level 2 | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	14.6	15.7
Fair Value, Measurements, Recurring | Level 2 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	1,746.6	2,563.5
Fair Value, Measurements, Recurring | Level 2 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	1,642	2,466.1
Fair Value, Measurements, Recurring | Level 2 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	104.6	96.1
Fair Value, Measurements, Recurring | Level 2 | Other Assets | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets		1.3
Fair Value, Measurements, Recurring | Level 2 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	1,571	2,355.6
Fair Value, Measurements, Recurring | Level 2 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	1,490.5	2,262.5
Fair Value, Measurements, Recurring | Level 2 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	79.6	93.1
Fair Value, Measurements, Recurring | Level 2 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0.9	0
Fair Value, Measurements, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Trading Account	0	0
Total Available for Sale and Trading Debt Securities	0	0
Fair Value, Measurements, Recurring | Level 3 | U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Obligations of States and Political Subdivisions
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Government Sponsored Agency
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Non-U.S. Government
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Corporate Debt
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Covered Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Other Asset-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Commercial Mortgage-Backed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for Sale	0	0
Fair Value, Measurements, Recurring | Level 3 | Other Assets
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 3 | Other Assets | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 3 | Other Assets | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets	0	0
Fair Value, Measurements, Recurring | Level 3 | Other Assets | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Assets		0
Fair Value, Measurements, Recurring | Level 3 | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	35	32.8
Fair Value, Measurements, Recurring | Level 3 | Other Liabilities | Foreign Exchange Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | Level 3 | Other Liabilities | Interest Rate Contracts
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring | Level 3 | Other Liabilities | Other Financial Derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Derivative Liabilities	$ 35	$ 32.8

Fair Value Measurements (Change

Fair Value Measurements (Changes in Level 3 Liabilities) (Details) - Swaps Related to Sale of Certain Visa Class B Common Shares - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value liabilities beginning balance	$ 32.8	$ 29.7
Total (Gains) Losses:
Included in Earnings	5.1	4.2
Purchases, Issues, Sales, and Settlements
Settlements	(2.9)	(2.6)
Fair value liabilities ending balance	$ 35	$ 31.3

Fair Value Measurements (Nonrec

Fair Value Measurements (Nonrecurring Basis Significant Unobservable Inputs) (Details) - Fair Value, Measurements, Nonrecurring - Level 3 $ in Millions	Mar. 31, 2019USD ($)	Dec. 31, 2018USD ($)
Loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 22.3	$ 9.7
OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 0.1	$ 0.4
Measurement Input, Discount Rate | Lower Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, Range of Discounts Applied	0.150	0.150
OREO, Range of Discounts Applied	0.150	0.150
Measurement Input, Discount Rate | Upper Limit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Loans, Range of Discounts Applied	0.300	0.300
OREO, Range of Discounts Applied	0.300	0.300
Loans | Measurement Input, Discount Rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 22.3	$ 24.9
OREO
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	$ 0.1	$ 0.4

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Assets
Cash and Due from Banks	$ 5,074.1	$ 4,581.6	$ 6,081.4	$ 4,518.1
Federal Reserve and Other Central Bank Deposits	23,422.2	30,080.2
Interest-Bearing Deposits with Banks	3,861.6	4,264.2
Federal Funds Sold and Securities Purchased under Agreements to Resell	552.2	1,165.2
Debt Securities
Available for Sale (Note)	37,058.2	36,888.8
Held to Maturity	12,143	14,354
Loans (excluding Leases)
Client Security Settlement Receivables	2,067.3	1,646.1
Deposits
Savings Certificates and Other Time	856.2	688.7
Non U.S. Offices Interest-Bearing	58,339.5	66,468
Federal Funds Purchased	651.8	2,594.2
Securities Sold Under Agreements to Repurchase	39.7	168.3
Other Borrowings	7,749.8	7,901.7
Senior Notes	2,024.1	2,011.3
Long-Term Debt
Floating Rate Capital Debt	277.6	277.6
Derivative Instruments
Fair value asset	1,232.5	1,999.7
Fair value liability	1,285	1,947
Other Financial Derivatives
Derivative Instruments
Fair value asset		1.3
Fair value liability	35.9	32.8
Level 2
Debt Securities
Available for Sale (Note)	32,000	31,700
Book Value
Assets
Cash and Due from Banks	5,074.1	4,581.6
Federal Reserve and Other Central Bank Deposits	23,422.2	30,080.2
Interest-Bearing Deposits with Banks	3,861.6	4,264.2
Federal Funds Sold and Securities Purchased under Agreements to Resell	552.2	1,165.2
Debt Securities
Available for Sale (Note)	37,058.2	36,888.8
Held to Maturity	12,143	14,354
Trading Account	0.3	0.3
Loans (excluding Leases)
Held for Investment	30,417	32,287
Held for Sale	0	0
Client Security Settlement Receivables	2,067.3	1,646.1
Total Assets
Federal Reserve and Federal Home Loan Bank Stock	300.5	300.3
Community Development Investments	589.5	606.6
Employee Benefit and Deferred Compensation	200.5	202.3
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	36,648.5	37,340.1
Savings Certificates and Other Time	856.2	688.7
Non U.S. Offices Interest-Bearing	58,339.5	66,468
Federal Funds Purchased	651.8	2,594.2
Securities Sold Under Agreements to Repurchase	39.7	168.3
Other Borrowings	7,749.8	7,901.7
Senior Notes	2,024.1	2,011.3
Long-Term Debt
Subordinated Debt	1,125.8	1,112.4
Floating Rate Capital Debt	277.6	277.6
Other Liabilities
Standby Letters of Credit	56.2	30.8
Loan Commitments	33	34.3
Book Value | Asset And Liability Management | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	80.2	306.7
Fair value liability	16.5	72.5
Book Value | Asset And Liability Management | Interest Rate Contracts
Derivative Instruments
Fair value asset	24.1	30
Fair value liability	20.8	24.5
Book Value | Asset And Liability Management | Other Financial Derivatives
Derivative Instruments
Fair value asset		1.3
Fair value liability	35.9	32.8
Book Value | Client Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	1,561.8	2,159.4
Fair value liability	1,474	2,190
Book Value | Client Related and Trading | Interest Rate Contracts
Derivative Instruments
Fair value asset	80.5	66.1
Fair value liability	58.8	68.6
Total Fair Value
Assets
Cash and Due from Banks	5,074.1	4,581.6
Federal Reserve and Other Central Bank Deposits	23,422.2	30,080.2
Interest-Bearing Deposits with Banks	3,861.6	4,264.2
Federal Funds Sold and Securities Purchased under Agreements to Resell	552.2	1,165.2
Debt Securities
Available for Sale (Note)	37,058.2	36,888.8
Held to Maturity	12,097.7	14,267
Trading Account	0.3	0.3
Loans (excluding Leases)
Held for Investment	30,481.9	32,339.2
Held for Sale	0	0
Client Security Settlement Receivables	2,067.3	1,646.1
Total Assets
Federal Reserve and Federal Home Loan Bank Stock	300.5	300.3
Community Development Investments	589.5	606.6
Employee Benefit and Deferred Compensation	197.5	194.5
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	36,648.5	37,340.1
Savings Certificates and Other Time	866.9	691.8
Non U.S. Offices Interest-Bearing	58,339.5	66,468
Federal Funds Purchased	651.8	2,594.2
Securities Sold Under Agreements to Repurchase	39.7	168.3
Other Borrowings	7,754.6	7,904.1
Senior Notes	2,031	1,994.4
Long-Term Debt
Subordinated Debt	1,133.2	1,089.7
Floating Rate Capital Debt	256.4	253.5
Other Liabilities
Standby Letters of Credit	56.2	30.8
Loan Commitments	33	34.3
Total Fair Value | Asset And Liability Management | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	80.2	306.7
Fair value liability	16.5	72.5
Total Fair Value | Asset And Liability Management | Interest Rate Contracts
Derivative Instruments
Fair value asset	24.1	30
Fair value liability	20.8	24.5
Total Fair Value | Asset And Liability Management | Other Financial Derivatives
Derivative Instruments
Fair value asset		1.3
Fair value liability	35.9	32.8
Total Fair Value | Client Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	1,561.8	2,159.4
Fair value liability	1,474	2,190
Total Fair Value | Client Related and Trading | Interest Rate Contracts
Derivative Instruments
Fair value asset	80.5	66.1
Fair value liability	58.8	68.6
Total Fair Value | Level 1
Assets
Cash and Due from Banks	5,074.1	4,581.6
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Federal Funds Sold and Securities Purchased under Agreements to Resell	0	0
Debt Securities
Available for Sale (Note)	5,022	5,185.3
Held to Maturity	119.6	101.6
Trading Account	0	0
Loans (excluding Leases)
Held for Investment	0	0
Held for Sale	0	0
Client Security Settlement Receivables	0	0
Total Assets
Federal Reserve and Federal Home Loan Bank Stock	0	0
Community Development Investments	0	0
Employee Benefit and Deferred Compensation	131.1	125
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	36,648.5	37,340.1
Savings Certificates and Other Time	0	0
Non U.S. Offices Interest-Bearing	0	0
Federal Funds Purchased	0	0
Securities Sold Under Agreements to Repurchase	0	0
Other Borrowings	0	0
Senior Notes	0	0
Long-Term Debt
Subordinated Debt	0	0
Floating Rate Capital Debt	0	0
Other Liabilities
Standby Letters of Credit	0	0
Loan Commitments	0	0
Total Fair Value | Level 1 | Asset And Liability Management | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	0	0
Fair value liability	0	0
Total Fair Value | Level 1 | Asset And Liability Management | Interest Rate Contracts
Derivative Instruments
Fair value asset	0	0
Fair value liability	0	0
Total Fair Value | Level 1 | Asset And Liability Management | Other Financial Derivatives
Derivative Instruments
Fair value asset		0
Fair value liability	0	0
Total Fair Value | Level 1 | Client Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	0	0
Fair value liability	0	0
Total Fair Value | Level 1 | Client Related and Trading | Interest Rate Contracts
Derivative Instruments
Fair value asset	0	0
Fair value liability	0	0
Total Fair Value | Level 2
Assets
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	23,422.2	30,080.2
Interest-Bearing Deposits with Banks	3,861.6	4,264.2
Federal Funds Sold and Securities Purchased under Agreements to Resell	552.2	1,165.2
Debt Securities
Available for Sale (Note)	32,036.2	31,703.5
Held to Maturity	11,978.1	14,165.4
Trading Account	0.3	0.3
Loans (excluding Leases)
Held for Investment	0	0
Held for Sale	0	0
Client Security Settlement Receivables	2,067.3	1,646.1
Total Assets
Federal Reserve and Federal Home Loan Bank Stock	300.5	300.3
Community Development Investments	589.5	606.6
Employee Benefit and Deferred Compensation	66.4	69.5
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0	0
Savings Certificates and Other Time	866.9	691.8
Non U.S. Offices Interest-Bearing	58,339.5	66,468
Federal Funds Purchased	651.8	2,594.2
Securities Sold Under Agreements to Repurchase	39.7	168.3
Other Borrowings	7,754.6	7,904.1
Senior Notes	2,031	1,994.4
Long-Term Debt
Subordinated Debt	1,133.2	1,089.7
Floating Rate Capital Debt	256.4	253.5
Other Liabilities
Standby Letters of Credit	0	0
Loan Commitments	0	0
Total Fair Value | Level 2 | Asset And Liability Management | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	80.2	306.7
Fair value liability	16.5	72.5
Total Fair Value | Level 2 | Asset And Liability Management | Interest Rate Contracts
Derivative Instruments
Fair value asset	24.1	30
Fair value liability	20.8	24.5
Total Fair Value | Level 2 | Asset And Liability Management | Other Financial Derivatives
Derivative Instruments
Fair value asset		1.3
Fair value liability	0.9	0
Total Fair Value | Level 2 | Client Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	1,561.8	2,159.4
Fair value liability	1,474	2,190
Total Fair Value | Level 2 | Client Related and Trading | Interest Rate Contracts
Derivative Instruments
Fair value asset	80.5	66.1
Fair value liability	58.8	68.6
Total Fair Value | Level 3
Assets
Cash and Due from Banks	0	0
Federal Reserve and Other Central Bank Deposits	0	0
Interest-Bearing Deposits with Banks	0	0
Federal Funds Sold and Securities Purchased under Agreements to Resell	0	0
Debt Securities
Available for Sale (Note)	0	0
Held to Maturity	0	0
Trading Account	0	0
Loans (excluding Leases)
Held for Investment	30,481.9	32,339.2
Held for Sale	0	0
Client Security Settlement Receivables	0	0
Total Assets
Federal Reserve and Federal Home Loan Bank Stock	0	0
Community Development Investments	0	0
Employee Benefit and Deferred Compensation	0	0
Deposits
Demand, Noninterest-Bearing, Savings, Money Market and Other Interest-Bearing	0	0
Savings Certificates and Other Time	0	0
Non U.S. Offices Interest-Bearing	0	0
Federal Funds Purchased	0	0
Securities Sold Under Agreements to Repurchase	0	0
Other Borrowings	0	0
Senior Notes	0	0
Long-Term Debt
Subordinated Debt	0	0
Floating Rate Capital Debt	0	0
Other Liabilities
Standby Letters of Credit	56.2	30.8
Loan Commitments	33	34.3
Total Fair Value | Level 3 | Asset And Liability Management | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	0	0
Fair value liability	0	0
Total Fair Value | Level 3 | Asset And Liability Management | Interest Rate Contracts
Derivative Instruments
Fair value asset	0	0
Fair value liability	0	0
Total Fair Value | Level 3 | Asset And Liability Management | Other Financial Derivatives
Derivative Instruments
Fair value asset		0
Fair value liability	35	32.8
Total Fair Value | Level 3 | Client Related and Trading | Foreign Exchange Contracts
Derivative Instruments
Fair value asset	0	0
Fair value liability	0	0
Total Fair Value | Level 3 | Client Related and Trading | Interest Rate Contracts
Derivative Instruments
Fair value asset	0	0
Fair value liability	$ 0	$ 0

Securities (Narrative) (Details

Securities (Narrative) (Details)	3 Months Ended
	Mar. 31, 2019USD ($)Investment	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)
Debt and Equity Securities, FV-NI [Line Items]
Held to maturity securities, transferred from available for sale	$ 0
Investment Security Losses, net	(200,000)	$ (200,000)
Gross proceeds from sale of securities	$ 127,500,000	2,000,000
Number of securities in an unrealized loss position | Investment	1,234
Total fair value	$ 28,900,000,000
Total unrealized losses	268,900,000
Debt securities, unrealized losses	268,900,000		$ 357,100,000
OTTI losses	0	$ 200,000
CRA Eligible, Mortgage Backed Securities
Debt and Equity Securities, FV-NI [Line Items]
OTTI losses	0
Government Sponsored Agency
Debt and Equity Securities, FV-NI [Line Items]
Total unrealized losses	124,600,000
Debt securities, unrealized losses	124,600,000		150,500,000
Corporate Debt
Debt and Equity Securities, FV-NI [Line Items]
Total unrealized losses	14,400,000
Debt securities, unrealized losses	$ 14,400,000		22,900,000
Percent of corporate debt portfolio	36.00%
Other
Debt and Equity Securities, FV-NI [Line Items]
Total unrealized losses	$ 64,600,000
Debt securities, unrealized losses	$ 64,600,000		$ 69,600,000

Securities (Reconciliation of A

Securities (Reconciliation of Amortized Cost to Fair Value of Securities Available for Sale) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Investment Holdings [Line Items]
Total	$ 37,095.7	$ 37,041.8
Gross Unrealized Gains	150.9	98.4
Gross Unrealized Losses	188.4	251.4
Fair Value	37,058.2	36,888.8
U.S. Government
Investment Holdings [Line Items]
Total	5,030	5,203.1
Gross Unrealized Gains	19	21.8
Gross Unrealized Losses	27	39.6
Fair Value	5,022	5,185.3
Obligations of States and Political Subdivisions
Investment Holdings [Line Items]
Total	755.8	657.6
Gross Unrealized Gains	10.7	2
Gross Unrealized Losses	1.7	3.7
Fair Value	764.8	655.9
Government Sponsored Agency
Investment Holdings [Line Items]
Total	22,624.9	22,522.7
Gross Unrealized Gains	68.3	52.4
Gross Unrealized Losses	124.6	150.5
Fair Value	22,568.6	22,424.6
Non-U.S. Government
Investment Holdings [Line Items]
Total	143.3	143.3
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0.6	1.1
Fair Value	142.7	142.2
Corporate Debt
Investment Holdings [Line Items]
Total	2,297.6	2,312.6
Gross Unrealized Gains	10.2	3.2
Gross Unrealized Losses	14.1	21.1
Fair Value	2,293.7	2,294.7
Covered Bonds
Investment Holdings [Line Items]
Total	837.4	832.7
Gross Unrealized Gains	2.6	1.4
Gross Unrealized Losses	2.6	4.8
Fair Value	837.4	829.3
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Investment Holdings [Line Items]
Total	2,214	2,087.8
Gross Unrealized Gains	24.3	11.9
Gross Unrealized Losses	2.2	3.5
Fair Value	2,236.1	2,096.2
Other Asset-Backed
Investment Holdings [Line Items]
Total	2,530.5	2,678.9
Gross Unrealized Gains	3.3	1.7
Gross Unrealized Losses	13.6	22.9
Fair Value	2,520.2	2,657.7
Commercial Mortgage-Backed
Investment Holdings [Line Items]
Total	647.6	587.4
Gross Unrealized Gains	12.5	4
Gross Unrealized Losses	2	4.2
Fair Value	658.1	587.2
Other
Investment Holdings [Line Items]
Total	14.6	15.7
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	$ 14.6	$ 15.7

Securities (Reconciliation of_2

Securities (Reconciliation of Amortized Cost to Fair Value of Securities Held to Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Schedule of Held-to-maturity Securities [Line Items]
Total	$ 12,143	$ 14,354
Gross Unrealized Gains	35.2	18.7
Gross Unrealized Losses	80.5	105.7
Fair Value	12,097.7	14,267
U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Total	119.6	101.6
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	119.6	101.6
Obligations of States and Political Subdivisions
Schedule of Held-to-maturity Securities [Line Items]
Total	16	18.9
Gross Unrealized Gains	0.6	0.6
Gross Unrealized Losses	0	0
Fair Value	16.6	19.5
Government Sponsored Agency
Schedule of Held-to-maturity Securities [Line Items]
Total	4.3	4.5
Gross Unrealized Gains	0.2	0.2
Gross Unrealized Losses	0	0
Fair Value	4.5	4.7
Corporate Debt
Schedule of Held-to-maturity Securities [Line Items]
Total	451.6	472.9
Gross Unrealized Gains	0.4	0.4
Gross Unrealized Losses	0.3	1.8
Fair Value	451.7	471.5
Covered Bonds
Schedule of Held-to-maturity Securities [Line Items]
Total	2,617.8	2,877.6
Gross Unrealized Gains	15.5	9.6
Gross Unrealized Losses	4.8	9.3
Fair Value	2,628.5	2,877.9
Non-U.S. Government
Schedule of Held-to-maturity Securities [Line Items]
Total	4,338.1	6,488.2
Gross Unrealized Gains	4.7	2.1
Gross Unrealized Losses	5	8.7
Fair Value	4,337.8	6,481.6
Certificates of Deposit
Schedule of Held-to-maturity Securities [Line Items]
Total	75.8	45.1
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	75.8	45.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Schedule of Held-to-maturity Securities [Line Items]
Total	3,170.2	2,966.8
Gross Unrealized Gains	13.5	5.8
Gross Unrealized Losses	4.6	12.3
Fair Value	3,179.1	2,960.3
Other Asset-Backed
Schedule of Held-to-maturity Securities [Line Items]
Total	1,099.6	1,146.4
Gross Unrealized Gains	0.3	0
Gross Unrealized Losses	1.2	4
Fair Value	1,098.7	1,142.4
Other
Schedule of Held-to-maturity Securities [Line Items]
Total	250	232
Gross Unrealized Gains	0	0
Gross Unrealized Losses	64.6	69.6
Fair Value	$ 185.4	$ 162.4

Securities (Remaining Maturity

Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Available for Sale - Cost
Due in One Year or Less	$ 9,967
Due After One Year Through Five Years	19,376.6
Due After Five Years Through Ten Years	6,790.3
Due After Ten Years	961.8
Total	37,095.7	$ 37,041.8
Held to Maturity - Amortized Cost
Due in One Year or Less	4,820.9
Due After One Year Through Five Years	6,787.3
Due After Five Years Through Ten Years	452.5
Due After Ten Years	82.3
Total	12,143	14,354
Available for Sale - Value
Due in One Year or Less	9,950.6
Due After One Year Through Five Years	19,379.5
Due After Five Years Through Ten Years	6,771.8
Due After Ten Years	956.3
Total	37,058.2	36,888.8
Held to Maturity - Fair Value
Due in One Year or Less	4,820.7
Due After One Year Through Five Years	6,795.4
Due After Five Years Through Ten Years	440.4
Due After Ten Years	41.2
Total	$ 12,097.7	$ 14,267

Securities (Securities with Unr

Securities (Securities with Unrealized Losses) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value
Less than 12 months, fair value	$ 11,611	$ 18,648.8
12 months or longer fair value	17,262.4	15,563.4
Total fair value	28,873.4	34,212.2
Unrealized Losses
Less than 12 months, unrealized losses	63.6	83.9
12 months or longer unrealized losses	205.3	273.2
Total unrealized losses	268.9	357.1
U.S. Government
Fair Value
Less than 12 months, fair value	0	0
12 months or longer fair value	2,674.5	2,862
Total fair value	2,674.5	2,862
Unrealized Losses
Less than 12 months, unrealized losses	0	0
12 months or longer unrealized losses	27	39.6
Total unrealized losses	27	39.6
Obligations of States and Political Subdivisions
Fair Value
Less than 12 months, fair value	66.2	169.6
12 months or longer fair value	209.8	279.6
Total fair value	276	449.2
Unrealized Losses
Less than 12 months, unrealized losses	1.2	2.4
12 months or longer unrealized losses	0.5	1.3
Total unrealized losses	1.7	3.7
Government Sponsored Agency
Fair Value
Less than 12 months, fair value	6,933.4	8,368.8
12 months or longer fair value	8,371.6	6,822.4
Total fair value	15,305	15,191.2
Unrealized Losses
Less than 12 months, unrealized losses	31.9	33.5
12 months or longer unrealized losses	92.7	117
Total unrealized losses	124.6	150.5
Non-U.S. Government
Fair Value
Less than 12 months, fair value	2,321.8	5,065.2
12 months or longer fair value	1,259.6	1,274
Total fair value	3,581.4	6,339.2
Unrealized Losses
Less than 12 months, unrealized losses	0.1	0.8
12 months or longer unrealized losses	5.5	9
Total unrealized losses	5.6	9.8
Corporate Debt
Fair Value
Less than 12 months, fair value	339.3	712.7
12 months or longer fair value	1,009.1	1,097.4
Total fair value	1,348.4	1,810.1
Unrealized Losses
Less than 12 months, unrealized losses	0.9	4.1
12 months or longer unrealized losses	13.5	18.8
Total unrealized losses	14.4	22.9
Covered Bonds
Fair Value
Less than 12 months, fair value	181	646.4
12 months or longer fair value	1,022.9	696.9
Total fair value	1,203.9	1,343.3
Unrealized Losses
Less than 12 months, unrealized losses	0.3	3.7
12 months or longer unrealized losses	7.1	10.4
Total unrealized losses	7.4	14.1
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Fair Value
Less than 12 months, fair value	253.4	1,105
12 months or longer fair value	1,501.8	1,189.2
Total fair value	1,755.2	2,294.2
Unrealized Losses
Less than 12 months, unrealized losses	0.6	4.6
12 months or longer unrealized losses	6.2	11.2
Total unrealized losses	6.8	15.8
Other Asset-Backed
Fair Value
Less than 12 months, fair value	1,436.5	2,507.8
12 months or longer fair value	893.8	954.9
Total fair value	2,330.3	3,462.7
Unrealized Losses
Less than 12 months, unrealized losses	8.7	15.9
12 months or longer unrealized losses	6.1	11
Total unrealized losses	14.8	26.9
Commercial Mortgage-Backed
Fair Value
Less than 12 months, fair value	18.7	22.8
12 months or longer fair value	193.5	274.4
Total fair value	212.2	297.2
Unrealized Losses
Less than 12 months, unrealized losses	0.1	0.1
12 months or longer unrealized losses	1.9	4.1
Total unrealized losses	2	4.2
Other
Fair Value
Less than 12 months, fair value	60.7	50.5
12 months or longer fair value	125.8	112.6
Total fair value	186.5	163.1
Unrealized Losses
Less than 12 months, unrealized losses	19.8	18.8
12 months or longer unrealized losses	44.8	50.8
Total unrealized losses	$ 64.6	$ 69.6

Securities (Cumulative Credit-R

Securities (Cumulative Credit-Related Losses on Securities) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Cumulative Credit-Related Losses on Securities Held — Beginning of Period	$ 4.1	$ 3.6
Plus: Losses on Newly Identified Impairments	0	0.2
Additional Losses on Previously Identified Impairments	0	0
Less: Current and Prior Period Losses on Debt Securities Sold During the Period	0	0
Cumulative Credit-Related Losses on Securities Held — End of Period	$ 4.1	$ 3.8

Securities Sold Under Agreeme_3

Securities Sold Under Agreements to Repurchase (Repurchase Agreements Accounted for as Secured Borrowings) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 23	$ 161.2	$ 150.7
Overnight and Continuous
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	39.7
Gross Amount of Recognized Liabilities for Repurchase Agreements in Note 23	39.7
Amounts related to agreements not included in Note 23	0
Overnight and Continuous | U.S. Treasury and Agency Securities
Transfer of Certain Financial Assets Accounted for as Secured Borrowings [Line Items]
Borrowings	$ 39.7

Loans and Leases (Narrative) (D

Loans and Leases (Narrative) (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2019USD ($)payment_period	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)Loan	Dec. 31, 2017USD ($)Loan
Accounts, Notes, Loans and Financing Receivable [Line Items]
Collateral required on Residential real estate loan, lower limit	65.00%
Collateral required on Residential real estate loan, upper limit	80.00%
Draw period for credit line products	10 years
Other U.S. loans and non-U.S. loans, short duration advances	$ 1,200,000,000		$ 2,200,000,000
Demand deposits	88,400,000		152,500,000
Loans classified as held for sale	0
Leases classified as held for sale			0
Interest income that would have been recorded for nonperforming loans	1,900,000	$ 2,200,000
Undrawn loan commitments and standby letters of credit	9,000,000		12,600,000
Total loans and leases	$ 30,620,600,000		32,490,000,000
Performing status, minimum period of time	6 months
Recorded investment		$ 400,000		$ 300,000
Consumer loans with carrying value collateralized by residential real estate property	$ 11,800,000
Nonperforming Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	70,900,000		64,600,000
Performing Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total loans and leases	$ 33,200,000		$ 35,200,000
Re-Defaulted | Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of loans and leases | Loan			0	2
Lower Limit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Days contractually past due for interest and principal and the loan is not well-secured and in the process of collection	90 days
Lower Limit | Performing Financing Receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Period for which troubled debt restructurings with modified terms is performing before ceasing to be classified as impaired loan	6 months
Upper Limit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of payment periods | payment_period	6
Limit of individual homogeneous loans collective evaluation for impairment and excluded from impaired loan disclosures (less than)	$ 1,000,000
Equity
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equity credit lines	$ 526,700,000		$ 655,500,000
Percentage of total equity credit lines	96.00%		95.00%

Loans and Leases (Loans and Lea

Loans and Leases (Loans and Leases) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 30,620.6	$ 32,490
Allowance for Credit Losses Assigned to Loans and Leases	(114.5)	(112.6)
Net Loans and Leases	30,506.1	32,377.4
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	13,635.5	15,175.2
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,532.1	8,728.1
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,185	3,228.8
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,648.6	2,701.6
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	89.3	90.7
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	180.5	426
Personal
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	16,985.1	17,314.8
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6,286.6	6,514
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	10,669.9	10,733.3
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 28.6	$ 67.5

Loans and Leases (Borrower Rati

Loans and Leases (Borrower Ratings) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 30,620.6	$ 32,490
1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	16,126.4	17,692.2
4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	14,090.5	14,403.2
6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	403.7	394.6
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	13,635.5	15,175.2
Commercial | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	7,591.5	8,593.9
Commercial | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,901.7	6,462.4
Commercial | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	142.3	118.9
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,532.1	8,728.1
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,293.4	5,477.4
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,118.6	3,159.8
Commercial | Commercial and Institutional | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	120.1	90.9
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,185	3,228.8
Commercial | Real Estate | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,095.2	1,209.6
Commercial | Real Estate | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,068.8	1,992.2
Commercial | Real Estate | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	21	27
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,648.6	2,701.6
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,021.1	1,625.3
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	626.3	1,075.3
Commercial | Non-U.S. | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1.2	1
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	89.3	90.7
Commercial | Lease Financing, net | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	76.9	78.3
Commercial | Lease Financing, net | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	12.4	12.4
Commercial | Lease Financing, net | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	0	0
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	180.5	426
Commercial | Other | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	104.9	203.3
Commercial | Other | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	75.6	222.7
Commercial | Other | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	0	0
Personal
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	16,985.1	17,314.8
Personal | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,534.9	9,098.3
Personal | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,188.8	7,940.8
Personal | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	261.4	275.7
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6,286.6	6,514
Personal | Real Estate | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,535.3	2,745
Personal | Real Estate | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,496.6	3,502.3
Personal | Real Estate | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	254.7	266.7
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	10,669.9	10,733.3
Personal | Private Client | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,983	6,321.1
Personal | Private Client | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	4,680.2	4,403.2
Personal | Private Client | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6.7	9
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	28.6	67.5
Personal | Other | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	16.6	32.2
Personal | Other | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	12	35.3
Personal | Other | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 0	$ 0

Loans and Leases (Delinquency S

Loans and Leases (Delinquency Status) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 30,620.6	$ 32,490
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	13,635.5	15,175.2
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8,532.1	8,728.1
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,185	3,228.8
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,648.6	2,701.6
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	89.3	90.7
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	180.5	426
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	16,985.1	17,314.8
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,286.6	6,514
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	10,669.9	10,733.3
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	28.6	67.5
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Current	30,372.4	32,213
Total Loans and Leases	30,504.5	32,380.7
Performing Financing Receivable | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	93.8	112.5
Performing Financing Receivable | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	25.3	38.8
Performing Financing Receivable | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	13	16.4
Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	13,578.1	15,087.6
Total Loans and Leases	13,623.1	15,161.1
Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Current	8,499.3	8,678.2
Total Loans and Leases	8,524.5	8,721.3
Performing Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	3,161.4	3,191.5
Total Loans and Leases	3,180.8	3,221.9
Performing Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Current	1,647.6	2,701.2
Total Loans and Leases	1,648	2,701.2
Performing Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Current	89.3	90.7
Total Loans and Leases	89.3	90.7
Performing Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Current	180.5	426
Total Loans and Leases	180.5	426
Performing Financing Receivable | Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	25.8	45.8
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	22.1	37.4
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.3	8.4
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.4	0
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	11.2	20.1
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.1	4.5
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	8.1	15.6
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	8	7.6
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	1.2
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	8	6.4
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Current	16,794.3	17,125.4
Total Loans and Leases	16,881.4	17,219.6
Performing Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	6,143.2	6,376.8
Total Loans and Leases	6,183.1	6,419
Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Current	10,622.5	10,681.1
Total Loans and Leases	10,669.7	10,733.1
Performing Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Current	28.6	67.5
Total Loans and Leases	28.6	67.5
Performing Financing Receivable | Personal | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	68	66.7
Performing Financing Receivable | Personal | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	28.9	27.2
Performing Financing Receivable | Personal | 30-59 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	39.1	39.5
Performing Financing Receivable | Personal | 30-59 Days Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Personal | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	14.1	18.7
Performing Financing Receivable | Personal | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	6.5	6.2
Performing Financing Receivable | Personal | 60-89 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	7.6	12.5
Performing Financing Receivable | Personal | 60-89 Days Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Performing Financing Receivable | Personal | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	5	8.8
Performing Financing Receivable | Personal | 90 Days or More Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	4.5	8.8
Performing Financing Receivable | Personal | 90 Days or More Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.5	0
Performing Financing Receivable | Personal | 90 Days or More Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0	0
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	116.1	109.3
Other Real Estate Owned	8	8.4
Total Nonperforming Assets	124.1	117.7
Nonperforming Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	12.4	14.1
Nonperforming Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	7.6	6.8
Nonperforming Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	4.2	6.9
Nonperforming Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.6	0.4
Nonperforming Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0	0
Nonperforming Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0	0
Nonperforming Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	103.7	95.2
Nonperforming Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	103.5	95
Nonperforming Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.2	0.2
Nonperforming Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 0	$ 0

Loans and Leases (Impaired Loan

Loans and Leases (Impaired Loans as of the Period End) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Recorded investment	$ 123.3		$ 116.2
Unpaid principal balance	159.1		150.6
Specific allowance	7.7		7.2
Average recorded investment	124.5	$ 136.2
Interest income recognized	0.6	0.5
Commercial
Financing Receivable, Impaired [Line Items]
Recorded investment	11.7		15
Unpaid principal balance	15		18.1
Specific allowance	4.8		4.1
Average recorded investment	12.7	28
Interest income recognized	0	0
Commercial | Commercial and Institutional
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	0.1		0.2
With a related specific reserve, recorded investment	7.5		6.4
With no related specific reserve, unpaid principal balance	0.1		0.4
With a related specific reserve, unpaid principal balance	8.8		7.3
Specific allowance	3.7		3
With no related specific reserve, average recorded investment	0.1	19.6
With a related specific reserve, average recorded investment	7.1	0
With no related specific reserve, interest income recognized	0	0
With a related specific reserve, interest income recognized	0	0
Commercial | Real Estate
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	2.8		5.8
With a related specific reserve, recorded investment	1.3		2.6
With no related specific reserve, unpaid principal balance	4.7		7.6
With a related specific reserve, unpaid principal balance	1.4		2.8
Specific allowance	1.1		1.1
With no related specific reserve, average recorded investment	3.8	6.5
With a related specific reserve, average recorded investment	1.7	1.9
With no related specific reserve, interest income recognized	0	0
With a related specific reserve, interest income recognized	0	0
Personal
Financing Receivable, Impaired [Line Items]
Recorded investment	111.6		101.2
Unpaid principal balance	144.1		132.5
Specific allowance	2.9		3.1
Average recorded investment	111.8	108.2
Interest income recognized	0.6	0.5
Personal | Real Estate
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	88.7		76.7
With a related specific reserve, recorded investment	21.2		22.8
With no related specific reserve, unpaid principal balance	117.6		104.7
With a related specific reserve, unpaid principal balance	24.8		26.1
Specific allowance	2.9		3.1
With no related specific reserve, average recorded investment	89.2	93.8
With a related specific reserve, average recorded investment	20.9	13.8
With no related specific reserve, interest income recognized	0.6	0.5
With a related specific reserve, interest income recognized	0	0
Personal | Private Client
Financing Receivable, Impaired [Line Items]
With no related specific reserve, recorded investment	1.7		1.7
With no related specific reserve, unpaid principal balance	1.7		$ 1.7
With no related specific reserve, average recorded investment	1.7	0.6
With no related specific reserve, interest income recognized	$ 0	$ 0

Loans and Leases (Troubled Debt

Loans and Leases (Troubled Debt Restructurings) (Details) - Lease Financing, net $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)Contract	Mar. 31, 2018USD ($)Contract
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | Contract	14	16
Recorded Investment	$ 17.4	$ 7.8
Unpaid Principal Balance	$ 18.7	$ 9.3
Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | Contract	1	1
Recorded Investment	$ 7.6	$ 0.3
Unpaid Principal Balance	$ 8.8	$ 0.5
Commercial | Commercial and Institutional
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | Contract	1	1
Recorded Investment	$ 7.6	$ 0.3
Unpaid Principal Balance	$ 8.8	$ 0.5
Commercial | Real Estate
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | Contract	0	0
Recorded Investment	$ 0	$ 0
Unpaid Principal Balance	$ 0	$ 0
Personal
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | Contract	13	15
Recorded Investment	$ 9.8	$ 7.5
Unpaid Principal Balance	$ 9.9	$ 8.8
Personal | Real Estate
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | Contract	13	14
Recorded Investment	$ 9.8	$ 7.5
Unpaid Principal Balance	$ 9.9	$ 8.7
Personal | Private Client
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases | Contract	0	1
Recorded Investment	$ 0	$ 0
Unpaid Principal Balance	$ 0	$ 0.1

Allowance for Credit Losses (Ch

Allowance for Credit Losses (Changes in Allowance for Credit Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 138.2	$ 153.8
Charge-Offs	(1)	(4.3)
Recoveries	2.2	1.3
Net (Charge-Offs) Recoveries	1.2	(3)
Provision for Credit Losses	0	(3)
Balance at end of period	139.4	147.8
Commercial
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	78.7	80.8
Charge-Offs	(0.1)	(0.8)
Recoveries	0.4	0.6
Net (Charge-Offs) Recoveries	0.3	(0.2)
Provision for Credit Losses	(0.4)	(3.5)
Balance at end of period	78.6	77.1
Personal
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	59.5	73
Charge-Offs	(0.9)	(3.5)
Recoveries	1.8	0.7
Net (Charge-Offs) Recoveries	0.9	(2.8)
Provision for Credit Losses	0.4	0.5
Balance at end of period	$ 60.8	$ 70.7

Allowance for Credit Losses (Re

Allowance for Credit Losses (Recorded Investments in Loans and Leases) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Loans and Leases
Specifically Evaluated for Impairment	$ 123.3	$ 116.2
Evaluated for Inherent Impairment	30,497.3	32,373.8
Total Loans and Leases	30,620.6	32,490
Allowance for Credit Losses on Credit Exposures
Specifically Evaluated for Impairment	7.7	7.2
Evaluated for Inherent Impairment	106.8	105.4
Allowance Assigned to Loans and Leases	114.5	112.6
Allowance for Undrawn Exposures
Commitments and Standby Letters of Credit	24.9	25.6
Total Allowance for Credit Losses	139.4	138.2	$ 147.8	$ 153.8
Commercial
Loans and Leases
Specifically Evaluated for Impairment		15
Evaluated for Inherent Impairment	13,623.8	15,160.2
Total Loans and Leases	13,635.5	15,175.2
Allowance for Credit Losses on Credit Exposures
Specifically Evaluated for Impairment	4.8	4.1
Evaluated for Inherent Impairment	53.3	53.5
Allowance Assigned to Loans and Leases	58.1	57.6
Allowance for Undrawn Exposures
Commitments and Standby Letters of Credit	20.5	21.1
Total Allowance for Credit Losses	78.6	78.7	77.1	80.8
Personal
Loans and Leases
Specifically Evaluated for Impairment		101.2
Evaluated for Inherent Impairment	16,873.5	17,213.6
Total Loans and Leases	16,985.1	17,314.8
Allowance for Credit Losses on Credit Exposures
Specifically Evaluated for Impairment	2.9	3.1
Evaluated for Inherent Impairment	53.5	51.9
Allowance Assigned to Loans and Leases	56.4	55
Allowance for Undrawn Exposures
Commitments and Standby Letters of Credit	4.4	4.5
Total Allowance for Credit Losses	$ 60.8	$ 59.5	$ 70.7	$ 73

Lease Commitments (Lease Cost C

Lease Commitments (Lease Cost Components) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Operating Lease Cost	$ 25.2
Variable Lease Cost	10.1
Sublease Income	(1.5)
Total Lease Cost	$ 33.8

Lease Commitments (Maturity of

Lease Commitments (Maturity of Lease Liability) (Details) $ in Millions	Mar. 31, 2019USD ($)
Leases [Abstract]
2019 (excluding the three months ended Mar 31, 2019)	$ 74.9
2020	96.6
2021	82
2022	66.6
2023	57.3
Later Years	207
Total Lease Payments	584.4
Less: Imputed Interest	(74.7)
Present Value of Lease Liabilities	$ 509.7

Lease Commitments (Leases) (Det

Lease Commitments (Leases) (Details) $ in Millions	Mar. 31, 2019USD ($)
Assets
Operating lease right-of-use asset	$ 460.4
Liabilities
Present Value of Lease Liabilities	$ 509.7

Lease Commitments (Weighted-Ave

Lease Commitments (Weighted-Average Remaining Lease Term and Discount Rate) (Details)	Mar. 31, 2019
Operating Leases
Weighted-Average Remaining Lease Term	7 years 8 months 12 days
Weighted-Average Discount Rate	3.40%

Lease Commitments (Supplemental

Lease Commitments (Supplemental Cash Flow Information) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows for operating leases	$ 28.3
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 1

Lease Commitments (Narrative) (

Lease Commitments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2019
Lessee, Lease, Description [Line Items]
Operating lease rental expense, net	$ 79	$ 76.7	$ 76.1
Lower Limit
Lessee, Lease, Description [Line Items]
Lease terms (in years)				9 years
Upper Limit
Lessee, Lease, Description [Line Items]
Lease terms (in years)				15 years

Lease Commitments (Minimum Annu

Lease Commitments (Minimum Annual Lease Commitments) (Details) $ in Millions	Dec. 31, 2018USD ($)
Leases [Abstract]
2019	$ 98.8
2020	97.8
2021	85.9
2022	77.2
2023	67.7
Later Years	335.7
Total Minimum Lease Payments	763.1
Less: Sublease Rentals	(23.4)
Net Minimum Lease Payments	$ 739.7

Pledged Assets (Narrative) (Det

Pledged Assets (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 41,500,000,000		$ 39,600,000,000
Securities eligible to be repledged or sold	29,200,000		151,500,000
Fair value of accepted collateral	215,200,000		426,200,000
Amount of securities re pledged or sold collateral	0		0
Average deposits maintained to meet Federal Reserve Bank reserve requirements	1,500,000,000	$ 1,800,000,000
US Government Agencies Debt Securities And Other Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	32,400,000,000		30,900,000,000
Obligations of States and Political Subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	768,800,000		640,400,000
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	8,300,000,000		8,100,000,000
Collateral Requirements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	9,000,000,000		9,300,000,000
Available for Sale Debt Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	29,100,000		151,500,000
Repurchase Agreements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	26,500,000		29,000,000
Fair value of accepted collateral	300,000,000		605,000,000
Derivative contract
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fair value of accepted collateral	30,400,000		15,300,000
Amount of securities re pledged or sold collateral	$ 0		$ 0

Goodwill and Other Intangible_2

Goodwill and Other Intangibles (Goodwill by Reporting Segment) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Goodwill [Line Items]
Goodwill	$ 683	$ 669.3
Corporate & Institutional Services
Goodwill [Line Items]
Goodwill	611.9	598.2
Wealth Management
Goodwill [Line Items]
Goodwill	$ 71.1	$ 71.1

Goodwill and Other Intangible_3

Goodwill and Other Intangibles (Other Intangible Assets) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Gross Carrying Amount	$ 206.4	$ 211.1
Less: Accumulated Amortization	74	72.5
Net Book Value	$ 132.4	$ 138.6

Goodwill and Other Intangible_4

Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense related to other intangible assets	$ 4.2	$ 4.5
Other Intangible Assets
Acquired Finite-Lived Intangible Assets [Line Items]
Amortization expense related to other intangible assets	4.2	$ 4.5
Estimated future amortization expense for 2019	12.5
Estimated future amortization expense for 2020	16.6
Estimated future amortization expense for 2021	14.2
Estimated future amortization expense for 2022	9.6
Estimated future amortization expense for 2023	9.4
BEx LLC
Acquired Finite-Lived Intangible Assets [Line Items]
Consideration transferred	37.9
Goodwill acquired	12.5
Software intangible assets acquired	$ 25

Reporting Segments (Results of

Reporting Segments (Results of Reporting Segments) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019USD ($)Segment	Mar. 31, 2018USD ($)
Segment Reporting Information [Line Items]
Number of reporting segments | Segment	2
Trust, Investment and Other Servicing Fees	$ 928.9	$ 937.7
Foreign Exchange Trading Income	66.2	78.5
Other Noninterest Income	63.8	75.8
Net Interest Income	429.8	392.7
Revenue	1,488.7	1,484.7
Provision for Credit Losses	0	(3)
Noninterest Expense	1,028.7	995.3
Income before Income Taxes	460	492.4
Provision for Income Taxes	112.9	110.8
Net Income	$ 347.1	$ 381.6
Percentage of Consolidated Net Income	100.00%	100.00%
Average Assets	$ 119,416.7	$ 124,493.3
FTE adjustments	7.8	8.7
Corporate & Institutional Services
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	535.2	544.3
Foreign Exchange Trading Income	59.7	62.4
Other Noninterest Income	43.4	46.6
Net Interest Income	234.8	229.4
Revenue	873.1	882.7
Provision for Credit Losses	(1.1)	(3.9)
Noninterest Expense	648	585.6
Income before Income Taxes	226.2	301
Provision for Income Taxes	53.6	66.8
Net Income	$ 172.6	$ 234.2
Percentage of Consolidated Net Income	50.00%	61.00%
Average Assets	$ 90,351.7	$ 83,637
Wealth Management
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	393.7	393.4
Foreign Exchange Trading Income	6.5	1.2
Other Noninterest Income	25.5	25.7
Net Interest Income	195	198.8
Revenue	620.7	619.1
Provision for Credit Losses	1.1	0.9
Noninterest Expense	379.9	365.7
Income before Income Taxes	239.7	252.5
Provision for Income Taxes	60.8	62.4
Net Income	$ 178.9	$ 190.1
Percentage of Consolidated Net Income	51.00%	50.00%
Average Assets	$ 29,065	$ 26,108
Treasury and Other
Segment Reporting Information [Line Items]
Trust, Investment and Other Servicing Fees	0	0
Foreign Exchange Trading Income	0	14.9
Other Noninterest Income	(5.1)	3.5
Net Interest Income	0	(35.5)
Revenue	(5.1)	(17.1)
Provision for Credit Losses	0	0
Noninterest Expense	0.8	44
Income before Income Taxes	(5.9)	(61.1)
Provision for Income Taxes	(1.5)	(18.4)
Net Income	$ (4.4)	$ (42.7)
Percentage of Consolidated Net Income	(1.00%)	(11.00%)
Average Assets	$ 0	$ 14,748.3

Stockholders' Equity (Narrative

Stockholders' Equity (Narrative) (Details) - USD ($)	Jan. 22, 2019	Mar. 31, 2019	Dec. 31, 2018	Jul. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)		10,000,000	10,000,000
Preferred stock, without par value (in dollars per share)		$ 0	$ 0
Equity related to preferred stock		$ 10,616,200,000	$ 10,508,300,000		$ 10,226,000,000
Stock repurchase, shares (in shares)		2,850,152
Stock repurchase, share-based compensation plan (in shares)		510,011
Stock repurchase, aggregate cost		$ 257,400,000
Average price paid per share for common stock repurchased (in usd per share)		$ 90.31
Stock repurchase program, number of shares authorized to be repurchased (in shares)				25,000,000
Upper Limit
Class of Stock [Line Items]
Stock repurchase authorized amount		$ 272,156,972
Series D Preferred Stock, Depositary Shares
Class of Stock [Line Items]
Shares issued (in shares)		500,000
Preferred stock, outstanding (in shares)		500,000
Per share ownership interest, percentage		1.00%
Preferred stock, without par value (in dollars per share)		$ 0
Preferred stock, liquidation preference		$ 100,000
Depository shares, liquidation preference per share (in dollars per share)		$ 1,000
Series D Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		5,000	5,000
Preferred stock		$ 493,500,000	$ 493,500,000
Preferred stock, annual dividend rate		4.60%
Preferred stock, dividend payment rate, variable rate		3.202%
Preferred stock, dividends per share, declared (in dollars per share)	$ 2,300
Equity related to preferred stock			$ 493,500,000
Series C Preferred Stock, Depositary Shares
Class of Stock [Line Items]
Shares issued (in shares)		16,000,000
Preferred stock, outstanding (in shares)		16,000,000
Per share ownership interest, percentage		0.10%
Preferred stock, without par value (in dollars per share)		$ 0
Preferred stock, liquidation preference		$ 25,000
Depository shares, liquidation preference per share (in dollars per share)		$ 25
Series C Preferred Stock
Class of Stock [Line Items]
Preferred stock, outstanding (in shares)		16,000	16,000
Preferred stock		$ 388,500,000	$ 388,500,000
Preferred stock, annual dividend rate		5.85%
Preferred stock, dividends per share, declared (in dollars per share)	$ 365.625
Dividends payable, date to be paid	Apr. 1, 2019
Dividends payable, date of record	Mar. 15, 2019
Preferred Stock
Class of Stock [Line Items]
Equity related to preferred stock		$ 882,000,000	$ 882,000,000		$ 882,000,000	$ 882,000,000
Preferred Stock | Series C Preferred Stock
Class of Stock [Line Items]
Equity related to preferred stock		$ 388,500,000

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) (Summary of Changes in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	$ 10,508.3
Net Change	108.4	$ (66.1)
Ending balance	10,616.2	10,226
Net Unrealized Gains (Losses) on Debt Securities Available for Sale
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(114.9)	(74.8)
Net Change	85.6	(55)
Reclassification of Certain Tax Effects from AOCI		(17.8)
Ending balance	(29.3)	(147.6)
Net Unrealized Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	4	4.5
Net Change	(4.3)	(3.7)
Reclassification of Certain Tax Effects from AOCI		0.9
Ending balance	(0.3)	1.7
Net Foreign Currency Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	67.9	(1.8)
Net Change	14.8	(13.1)
Reclassification of Certain Tax Effects from AOCI		47.5
Ending balance	82.7	32.6
Net Pension and Other Postretirement Benefit Adjustments
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(410.7)	(342.2)
Net Change	12.3	5.7
Reclassification of Certain Tax Effects from AOCI		(55.9)
Ending balance	(398.4)	(392.4)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Beginning balance	(453.7)	(414.3)
Net Change	108.4	(66.1)
Reclassification of Certain Tax Effects from AOCI	0	(25.3)
Ending balance	$ (345.3)	$ (505.7)

Accumulated Other Comprehensi_4

Accumulated Other Comprehensive Income (Loss) (Details of Changes In Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
After Tax
Other Comprehensive Income	$ 108.4	$ (66.1)
Net Unrealized Gains (Losses) on Debt Securities Available for Sale
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	115.3	(75.4)
Reclassification adjustment, before tax	0.2	0
Net Change	115.5	(75.4)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(29.9)	20.4
Reclassification adjustment, tax	0	0
Net Change	(29.9)	20.4
After Tax
Other comprehensive income (loss), before reclassification, after tax	85.4	(55)
Reclassification adjustment, after tax	0.2	0
Other Comprehensive Income	85.6	(55)
Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Reclassification adjustment, before tax	(13.6)	(16.6)
Net Change	(5.8)	(5)
Tax Effect
Reclassification adjustment, tax	3.4	4.1
Net Change	1.5	1.3
After Tax
Reclassification adjustment, after tax	(10.2)	(12.5)
Other Comprehensive Income	(4.3)	(3.7)
Net Foreign Currency Adjustments
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	(6.5)	44.6
Net Change	22.8	(28.5)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	1.6	(2.8)
Net Change	(8)	15.4
After Tax
Other comprehensive income (loss), before reclassification, after tax	(4.9)	41.8
Other Comprehensive Income	14.8	(13.1)
Long-Term Intra-Entity Foreign Currency Transaction Gains (Losses)
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	0.7	1.2
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(0.2)	(0.3)
After Tax
Other comprehensive income (loss), before reclassification, after tax	0.5	0.9
Net Investment Hedge Gains (Losses)
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	28.6	(74.3)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(9.4)	18.5
After Tax
Other comprehensive income (loss), before reclassification, after tax	19.2	(55.8)
Net Pension and Other Postretirement Benefit Adjustments
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	11.3	10.1
Reclassification adjustment, before tax	5.4	9.1
Net Change	16.7	19.2
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(3.1)	(2.5)
Reclassification adjustment, tax	(1.3)	(11)
Net Change	(4.4)	(13.5)
After Tax
Other comprehensive income (loss), before reclassification, after tax	8.2	7.6
Reclassification adjustment, after tax	4.1	(1.9)
Other Comprehensive Income	12.3	5.7
Foreign Exchange Contracts | Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	7.2	13
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(1.7)	(3.2)
After Tax
Other comprehensive income (loss), before reclassification, after tax	5.5	9.8
Interest Rate Contracts | Net Unrealized Gains (Losses) on Cash Flow Hedges
Before Tax
Other comprehensive income (loss), before reclassifications, before tax	0.6	(1.4)
Tax Effect
Other comprehensive income (loss), before reclassifications, tax	(0.2)	0.4
After Tax
Other comprehensive income (loss), before reclassification, after tax	$ 0.4	$ (1)

Accumulated Other Comprehensi_5

Accumulated Other Comprehensive Income (Loss) (Reclassification Adjustment Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment Security Gains (Losses), net	$ 0.2	$ 0.2
Other Operating Income	(29)	(34.8)
Interest Income	(662.8)	(505.9)
Employee Benefits	85.7	91.7
Net Income	(347.1)	(381.6)
Net Unrealized Gains (Losses) on Debt Securities Available for Sale | Net Gain/(Loss) Reclassified from AOCI to Net Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Investment Security Gains (Losses), net	0.2	0
Net Unrealized Gains (Losses) on Cash Flow Hedges | Net Gain/(Loss) Reclassified from AOCI to Net Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income	(13.6)	16.6
Amortization of Net Actuarial Loss | Net Gain/(Loss) Reclassified from AOCI to Net Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Employee Benefits	5.5	9.2
Amortization of Prior Service Cost | Net Gain/(Loss) Reclassified from AOCI to Net Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Employee Benefits	(0.1)	(0.1)
Net Pension and Other Postretirement Benefit Adjustments | Net Gain/(Loss) Reclassified from AOCI to Net Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income	5.4	9.1
Foreign Exchange Contracts | Net Unrealized Gains (Losses) on Cash Flow Hedges | Net Gain/(Loss) Reclassified from AOCI to Net Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Operating Income	0.6	(2.4)
Interest Income	(14.4)	(14.2)
Interest Rate Contracts | Net Unrealized Gains (Losses) on Cash Flow Hedges | Net Gain/(Loss) Reclassified from AOCI to Net Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest Income	$ 0.2	$ 0

Net Income Per Common Share C_3

Net Income Per Common Share Computations (Net Income Per Common Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Basic Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	218,236,802	225,681,167
Net Income	$ 347.1	$ 381.6
Less: Dividends on Preferred Stock	17.3	17.3
Net Income Applicable to Common Stock	329.8	364.3
Less: Earnings Allocated to Participating Securities	4.3	5.2
Earnings Allocated to Common Shares Outstanding	$ 325.5	$ 359.1
Basic Earnings per Share (in dollars per share)	$ 1.49	$ 1.59
Diluted Net Income Per Common Share
Average Number of Common Shares Outstanding (in shares)	218,236,802	225,681,167
Plus: Dilutive Effect of Share-based Compensation (in shares)	1,033,413	1,366,352
Diluted (in shares)	219,270,215	227,047,519
Earnings Allocated to Common and Potential Common Shares	$ 325.4	$ 359.2
Diluted Earnings per Share (in dollars per share)	$ 1.48	$ 1.58
Common stock equivalents not included in the computation of diluted earnings per share because their inclusion would have been antidilutive (in shares)	0	0

Revenue from Contracts with C_3

Revenue from Contracts with Clients (Revenue Disaggregation) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Foreign Exchange Trading Income	$ 66.2	$ 78.5
Treasury Management Fees	11.7	14
Security Commissions and Trading Income	23.3	27.2
Other Operating Income	29	34.8
Investment Security Losses, net	(0.2)	(0.2)
Total Other Noninterest Income	130	154.3
Total Noninterest Income	1,058.9	1,092
Custody and Fund Administration
Disaggregation of Revenue [Line Items]
Revenue from contract with client	397.5	395.9
Investment Management and Advisory
Disaggregation of Revenue [Line Items]
Revenue from contract with client	459.2	465.6
Securities Lending
Disaggregation of Revenue [Line Items]
Revenue from contract with client	22.8	26.2
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with client	49.4	50
Total Trust, Investment and Other Servicing Fees
Disaggregation of Revenue [Line Items]
Revenue from contract with client	928.9	937.7
Other Operating Income
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 9.9	$ 11.3

Revenue from Contracts with C_4

Revenue from Contracts with Clients (Contract Receivables) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Total Client Receivables	$ 909.8	$ 832.6
Trust Fees Receivable, net
Disaggregation of Revenue [Line Items]
Total Client Receivables	818.4	742.5
Other
Disaggregation of Revenue [Line Items]
Total Client Receivables	$ 91.4	$ 90.1

Revenue from Contracts with C_5

Revenue from Contracts with Clients (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Security commissions and trading income	$ 23.3	$ 27.2
Other operating income	29	34.8
Securities Commissions and Trading Income
Disaggregation of Revenue [Line Items]
Revenue from contract with client	21	24
Other Operating Income
Disaggregation of Revenue [Line Items]
Revenue from contract with client	$ 9.9	$ 11.3

Net Interest Income (Net Intere

Net Interest Income (Net Interest Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Interest Income
Loans and Leases	$ 298.2	$ 252
Securities — Taxable	277.5	177.8
Securities - Non-Taxable	1.1	2
Interest-Bearing Due from and Deposits with Banks	17.9	19.9
Federal Reserve and Other Central Bank Deposits and Other	68.1	54.2
Total Interest Income	662.8	505.9
Interest Expense
Deposits	147.6	63.1
Federal Funds Purchased	13.4	5.3
Securities Sold Under Agreements to Repurchase	1.8	2.7
Other Borrowings	49.9	26.5
Senior Notes	15.9	11.8
Long-Term Debt	10	11
Floating Rate Capital Debt	2.2	1.5
Total Interest Expense	240.8	121.9
Net Interest Income	$ 422	$ 384

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Operating Loss Carryforwards [Line Items]
Provision for income taxes	$ 105.1	$ 102.1
Effective tax rate (percentage)	23.20%	21.10%
Provision for income taxes, adjustments to initial estimate impact of TCJA		$ 15.8
Tax Year 2013 through 2016
Operating Loss Carryforwards [Line Items]
Provision for income taxes		$ (22.6)

Pension and Postretirement He_3

Pension and Postretirement Health Care (Net Periodic Pension Expense (Benefit)) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Pension Plan
Amortization
Contribution to pension plan	$ 0	$ 50,000,000
Supplemental Plan
Defined Benefit plan Net periodic benefit cost
Service Cost	1,000,000	1,100,000
Interest Cost	1,500,000	1,300,000
Amortization
Net Actuarial Loss (Gain)	1,400,000	1,800,000
Prior Service Cost	0	0
Net Periodic Pension Expense	3,900,000	4,200,000
Postretirement Health Care Plan
Defined Benefit plan Net periodic benefit cost
Service Cost	0	0
Interest Cost	300,000	300,000
Amortization
Net Actuarial Loss (Gain)	(300,000)	0
Prior Service Cost	0	0
Net Periodic Pension Expense	0	300,000
U.S. Plan | Pension Plan
Defined Benefit plan Net periodic benefit cost
Service Cost	10,400,000	10,400,000
Interest Cost	11,800,000	11,100,000
Expected Return on Plan Assets	(21,700,000)	(22,000,000)
Amortization
Net Actuarial Loss (Gain)	4,300,000	7,100,000
Prior Service Cost	(100,000)	(100,000)
Net Periodic Pension Expense	4,700,000	6,500,000
Non U.S. Plans | Pension Plan
Defined Benefit plan Net periodic benefit cost
Service Cost	500,000	400,000
Interest Cost	1,000,000	1,000,000
Expected Return on Plan Assets	(1,000,000)	(1,100,000)
Settlement Expense	0	0
Amortization
Net Actuarial Loss (Gain)	100,000	300,000
Net Periodic Pension Expense	$ 600,000	$ 600,000

Share-Based Compensation Plan_2

Share-Based Compensation Plans (Compensation Expense for Share-Based Arrangements and Tax Impacts) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 55.3	$ 56.5
Tax Benefits Recognized	13.7	14
Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	39.2	46.7
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	0.5	0.8
Performance Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 15.6	$ 9

Share-Based Compensation Plan_3

Share-Based Compensation Plans (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock unit awards granted (in shares)	798,669	793,995
Stock unit awards grant-date fair value	$ 73.4	$ 82.6
Share-based compensation expense	55.3	56.5
Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	39.2	46.7
Retirement Eligible Employees | Restricted Stock Unit Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	21.2	26.9
Retirement Eligible Employees | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 9.2	$ 4.7
Performance stock units granted (in shares)	211,269	242,232
Performance stock awards grant-date fair value	$ 19.6	$ 25.4
Retirement Eligible Employees | RSU's Vested And Expensed Upon Issuance
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation expense	$ 3.3	$ 2.7

Variable Interest Entities (Nar

Variable Interest Entities (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Variable Interest Entity [Line Items]
Exposure to loss from liquidity arrangements and obligations to purchase assets	$ 0
Affordable housing tax credits and other tax benefits	16,400,000	$ 14,700,000
Fair value, investments, entities that calculate net asset value per Share, unfunded commitments	0		$ 0
Leveraged Leasing Transactions
Variable Interest Entity [Line Items]
VIE carrying amounts	56,600,000		56,800,000
Exposure to loss from liquidity arrangements and obligations to purchase assets	$ 0
Leveraged Leasing Transactions | Lower Limit
Variable Interest Entity [Line Items]
Funding of assets cost via equity interest	20.00%
Funding of asset's cost via third party non recourse debt holders	70.00%
Leveraged Leasing Transactions | Upper Limit
Variable Interest Entity [Line Items]
Funding of assets cost via equity interest	30.00%
Funding of asset's cost via third party non recourse debt holders	80.00%
Other Assets
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, assets	$ 589,500,000		602,400,000
Alternative investment	25,000,000		29,200,000
Other Assets | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
VIE carrying amounts	537,800,000		549,800,000
Other Liabilities
Variable Interest Entity [Line Items]
Investments in community development projects, carrying amount, liabilities	302,100,000		321,000,000
Other Liabilities | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Variable interest entity, nonconsolidated, carrying amount, liabilities	$ 263,600,000		$ 279,500,000

Contingent Liabilities (Narrati

Contingent Liabilities (Narrative) (Details) shares in Millions	Jun. 28, 2018USD ($)	Jun. 30, 2016USD ($)shares	Jun. 30, 2015USD ($)shares	Dec. 31, 2015trust	Mar. 31, 2019USD ($)shares	Dec. 31, 2018USD ($)shares
Loss Contingencies [Line Items]
Commitments and letters of credit					$ 25,000,000,000	$ 25,000,000,000
Standby letters of credit outstanding					$ 2,500,000,000	$ 2,500,000,000
Minimum securities lending related collateral percentage					100.00%
Loss contingency accrual					$ 0
Visa Class B
Loss Contingencies [Line Items]
Visa redemption gain		$ 123,100,000	$ 99,900,000
Shares issued (in shares) | shares		1.1	1
Remaining Visa shares held by Northern Trust (in shares) | shares					4.1	4.1
Remaining Visa shares held by Northern Trust, original cost basis					$ 0	$ 0
Northern Trust Fiduciary Services (Guernsey) Limited | Subsidiaries
Loss Contingencies [Line Items]
Number of administrated trusts serving as trustee on | trust				2
Indemnification Agreement
Loss Contingencies [Line Items]
Collateralized securities loaned, subject to indemnification					142,600,000,000	128,900,000,000
Credit loss liability					0	$ 0
Lower Limit
Loss Contingencies [Line Items]
Possible loss in future periods in excess of accrual					0
Upper Limit
Loss Contingencies [Line Items]
Possible loss in future periods in excess of accrual					$ 25,000,000
Visa Inc. | Visa Class B Litigation Case
Loss Contingencies [Line Items]
Escrow deposit	$ 600,000,000

Derivative Financial Instrume_3

Derivative Financial Instruments (Narrative) (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative [Line Items]
Gains or losses reclassified into earnings	$ 0	$ 0
Maximum length of time over which exposure was being hedged	23 months
Net investment gains (losses) recognized in AOCI	$ 28,600,000	(74,300,000)
Foreign Currency Denominate
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges	200,000
Foreign Currency Denominated Debt Securities
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges	(300,000)
Available for Sale Debt Securities
Derivative [Line Items]
Estimated net gain (loss) to be reclassified into net income within the next twelve months relating to cash flow hedges	$ 800,000
Cash Flow Hedges
Derivative [Line Items]
Derivative instruments, gain (loss) recognized in income, ineffective portion and amount excluded from effectiveness testing, net		$ 0

Derivative Financial Instrume_4

Derivative Financial Instruments (Notional and Fair Values of Client-Related and Trading Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Notional Value	$ 304,387.3	$ 301,494.9
Fair value asset	1,232.5	1,999.7
Total Gross Derivatives, asset	1,746.6	2,563.5
Less: Netting	979.9	1,357.1
Derivative Asset	766.7	1,206.4
Fair value liability	1,285	1,947
Derivative Liabilities	1,606	2,388.4
Less: Netting	1,123.7	1,796.3
Derivative Liabilities	482.3	592.1
Derivatives Designated as Hedging under GAAP
Derivative [Line Items]
Notional Value	9,848.6	11,313.7
Fair value asset	103.1	336.2
Fair value liability	36.8	96.8
Fair Value Hedges | Derivatives Designated as Hedging under GAAP | Interest Rate Contracts
Derivative [Line Items]
Notional Value	4,479.8	4,590.4
Fair value asset	23.9	29.8
Fair value liability	19.9	23.3
Fair Value Hedges | Derivatives Not Designated as Hedging under GAAP
Derivative [Line Items]
Notional Value	294,538.7	290,181.2
Fair value asset	1,643.5	2,227.3
Fair value liability	1,569.2	2,291.6
Fair Value Hedges | Non-Designated Risk Management Derivatives
Derivative [Line Items]
Notional Value	677.1	605.6
Fair value asset	1.2	1.8
Fair value liability	36.4	33
Fair Value Hedges | Non-Designated Risk Management Derivatives | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	117.3	122.2
Fair value asset	1.2	0.5
Fair value liability	0.5	0.2
Fair Value Hedges | Non-Designated Risk Management Derivatives | Other Financial Derivatives
Derivative [Line Items]
Notional Value	559.8	483.4
Fair value asset	0	1.3
Fair value liability	35.9	32.8
Fair Value Hedges | Client-Related and Trading Derivatives
Derivative [Line Items]
Notional Value	293,861.6	289,575.6
Fair value asset	1,642.3	2,225.5
Fair value liability	1,532.8	2,258.6
Fair Value Hedges | Client-Related and Trading Derivatives | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	286,240.1	281,864.4
Fair value asset	1,561.8	2,159.4
Fair value liability	1,474	2,190
Fair Value Hedges | Client-Related and Trading Derivatives | Interest Rate Contracts
Derivative [Line Items]
Notional Value	7,621.5	7,711.2
Fair value asset	80.5	66.1
Fair value liability	58.8	68.6
Cash Flow Hedges | Derivatives Designated as Hedging under GAAP | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	2,259.1	2,648.2
Fair value asset	42.5	13.8
Fair value liability	10.5	57.8
Cash Flow Hedges | Derivatives Designated as Hedging under GAAP | Interest Rate Contracts
Derivative [Line Items]
Notional Value	600	600
Fair value asset	0.2	0.2
Fair value liability	0.9	1.2
Net Investment Hedges | Derivatives Designated as Hedging under GAAP | Foreign Exchange Contracts
Derivative [Line Items]
Notional Value	2,509.7	3,475.1
Fair value asset	36.5	292.4
Fair value liability	$ 5.5	$ 14.5

Derivative Financial Instrume_5

Derivative Financial Instruments (Location and Amount of Gains and Losses Recorded in Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Interest Income	$ 662.8	$ 505.9
Interest Expense	240.8	121.9
Other Operating Income	29	34.8
Other Operating Expense	72.7	69
Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	5.5	(3.7)
Gains/(Losses) on cash flow hedges recognized on	14.2	14.2
Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	(1.6)	1.5
Gains/(Losses) on cash flow hedges recognized on	0	0
Other Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Total gain/(loss) recognized on fair value hedges	0	0
Gains/(Losses) on cash flow hedges recognized on	(0.6)	2.4
Foreign Exchange Contracts | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	14.4	14.2
Foreign Exchange Contracts | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	0	0
Foreign Exchange Contracts | Other Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains/(Losses) on cash flow hedges recognized on	(0.6)	2.4
Interest Rate Contracts | Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	(35.4)	54.3
Recognized on hedged items	35.4	(54.3)
Amounts related to interest settlements on derivatives	5.5	(3.7)
Gains/(Losses) on cash flow hedges recognized on	(0.2)	0
Interest Rate Contracts | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	28.5	(21.9)
Recognized on hedged items	(28.5)	21.9
Amounts related to interest settlements on derivatives	(1.6)	1.5
Gains/(Losses) on cash flow hedges recognized on	0	0
Interest Rate Contracts | Other Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Recognized on derivatives	0	0
Recognized on hedged items	0	0
Amounts related to interest settlements on derivatives	0	0
Gains/(Losses) on cash flow hedges recognized on	$ 0	$ 0

Derivative Financial Instrume_6

Derivative Financial Instruments (Location and Amount of Gains and Losses Recorded in Income for Non-Designated Risk Management Derivative Instruments) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Derivatives Not Designated as Hedging under GAAP
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain / (Loss) Recognized in Income	$ 61.3	$ 80.2
Non-Designated Risk Management Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain / (Loss) Recognized in Income	(6.4)	0
Non-Designated Risk Management Derivatives | Foreign Exchange Contracts | Others Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain / (Loss) Recognized in Income	0.9	4
Non-Designated Risk Management Derivatives | Other Financial Derivatives | Others Operating Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain / (Loss) Recognized in Income	(7.3)	(4)
Client-Related and Trading Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain / (Loss) Recognized in Income	67.7	80.2
Client-Related and Trading Derivatives | Foreign Exchange Contracts | Foreign Exchange Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain / (Loss) Recognized in Income	66.2	78.5
Client-Related and Trading Derivatives | Interest Rate Contracts | Security Commissions and Trading Income
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Derivative Gain / (Loss) Recognized in Income	$ 1.5	$ 1.7

Derivative Financial Instrume_7

Derivative Financial Instruments (Fair Value of Hedged Items) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Carrying value of the hedged items, available for sale debt securities	$ 3,759.5	$ 3,831.6
Cumulative hedge accounting basis adjustment, available for sale debt securities	60.5	99.4
Carrying value of the hedged items, senior notes and long-term subordinated debt	1,248.9	1,248.8
Cumulative hedge accounting basis adjustment, senior notes and long-term subordinated debt	55.1	29.3
Carrying Value of the Hedged Items	5,008.4	5,080.4
Cumulative Hedge Accounting Basis Adjustment	$ 115.6	$ 128.7

Offsetting of Assets and Liab_3

Offsetting of Assets and Liabilities (Offsetting of Derivative Assets and Securities Purchased Under Agreements to Resell) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Assets	$ 1,232.5	$ 1,999.7
Gross Amounts Offset in the Balance Sheet	979.9	1,357.1
Net Amounts Presented in the Balance Sheet	252.6	642.6
Gross Amounts Not Offset in the Balance Sheet	30.4	12.7
Net Amount	222.2	629.9
Total Derivatives Not Subject to a Master Netting Arrangement
Gross Recognized Assets	514.1	563.8
Gross Amounts Not Offset in the Balance Sheet	0	2.7
Net Amount	514.1	561.1
Total Derivatives
Gross Recognized Assets	1,746.6	2,563.5
Derivative Asset	766.7	1,206.4
Gross Amounts Not Offset in the Balance Sheet	30.4	15.4
Net Amount	736.3	1,191
Securities Purchased under Agreements to Resell
Gross Recognized Assets	515.2	1,031.2
Net Amounts Presented in the Balance Sheet	515.2	1,031.2
Gross Amounts Not Offset in the Balance Sheet	515.2	1,031.2
Other assets excluding derivatives and non financial instruments	5,300	4,600
Federal funds sold	37	134
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Assets	1,127.8	1,902.3
Gross Amounts Offset in the Balance Sheet	926.8	1,308.8
Net Amounts Presented in the Balance Sheet	201	593.5
Gross Amounts Not Offset in the Balance Sheet	30.4	12.7
Net Amount	170.6	580.8
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Assets	60.5	71.6
Gross Amounts Offset in the Balance Sheet	12.3	22.6
Net Amounts Presented in the Balance Sheet	48.2	49
Net Amount	48.2	49
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Assets	44.2	24.5
Gross Amounts Offset in the Balance Sheet	40.8	24.4
Net Amounts Presented in the Balance Sheet	3.4	0.1
Net Amount	$ 3.4	0.1
Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Assets		1.3
Gross Amounts Offset in the Balance Sheet		1.3
Net Amounts Presented in the Balance Sheet		0
Net Amount		$ 0

Offsetting of Assets and Liab_4

Offsetting of Assets and Liabilities (Offsetting of Derivative Liabilities and Securities Sold Under Agreements to Repurchase) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Liabilities	$ 1,285	$ 1,947
Gross Amounts Offset in the Balance Sheet	1,123.7	1,796.3
Net Amounts Presented in the Balance Sheet	161.3	150.7
Gross Amounts Not Offset in the Balance Sheet	0.1
Net Amount	161.2	150.7
Total Derivatives Not Subject to a Master Netting Arrangement
Gross Recognized Liabilities	321	441.4
Gross Amounts Not Offset in the Balance Sheet	0
Net Amount	321	441.4
Offsetting Derivative Liabilities [Abstract]
Gross Recognized Liabilities	1,606	2,388.4
Derivative Liabilities	482.3	592.1
Gross Amounts Not Offset in the Balance Sheet	0.1
Net Amount	482.2	592.1
Securities Sold under Agreements to Repurchase
Gross Recognized Liabilities	39.7	168.3
Net Amounts Presented in the Balance Sheet	39.7	168.3
Gross Amounts Not Offset in the Balance Sheet	39.7	168.3
Other liabilities	3,100	2,500
Foreign Exchange Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Liabilities	1,169.5	1,821
Gross Amounts Offset in the Balance Sheet	1,054.9	1,751.7
Net Amounts Presented in the Balance Sheet	114.6	69.3
Gross Amounts Not Offset in the Balance Sheet	0.1
Net Amount	114.5	69.3
Interest Rate Swap Contracts | Over the Counter Derivative
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Liabilities	38.8	68.8
Gross Amounts Offset in the Balance Sheet	27.8	19
Net Amounts Presented in the Balance Sheet	11	49.8
Net Amount	11	49.8
Interest Rate Swap Contracts | Interest Rate Swaps Exchange Cleared
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Liabilities	40.8	24.4
Gross Amounts Offset in the Balance Sheet	40.8	24.4
Net Amounts Presented in the Balance Sheet	0	0
Net Amount	0	0
Other Financial Derivatives
Total Derivatives Subject to a Master Netting Arrangement
Gross Recognized Liabilities	35.9	32.8
Gross Amounts Offset in the Balance Sheet	0.2	1.2
Net Amounts Presented in the Balance Sheet	35.7	31.6
Net Amount	$ 35.7	$ 31.6

Offsetting of Assets and Liab_5

Offsetting of Assets and Liabilities (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Offsetting Assets and Liabilities [Line Items]
Collateral received	$ 30.4	$ 12.7
Gross amounts not offset in the balance sheet	0.1
Aggregate fair value of all derivative instruments with credit-risk-related contingent features that are in a liability position	130.2	324.1
Collateral deposited with derivative counterparties for derivatives instruments with credit-risk-related contingent features that are in a liability position	124.2	316.5
Net maximum amount of termination payments that could have been required	6	7.6
Net Investment Hedges
Offsetting Assets and Liabilities [Line Items]
Collateral received	69
Gross amounts not offset in the balance sheet	$ 67.9
Cash collateral received from derivative counterparties and not offset against derivative assets		27.6
Cash collateral deposited with derivative counterparties not offset against derivative liabilities		$ 91.5

Uncategorized Items - ntrs-2019

Label	Element	Value
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (4,500,000)
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 0