Northern Trust (NTRS) 10-Q 31 Oct 14 2014 Q3 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	9 Months Ended
	Sep. 30, 2014
Document Information [Line Items]	'
Document Type	'10-Q
Amendment Flag	'false
Document Period End Date	30-Sep-14
Document Fiscal Year Focus	'2014
Document Fiscal Period Focus	'Q3
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 Common Stock, Shares Outstanding	235,505,008

Consolidated_Balance_Sheet

Consolidated Balance Sheet (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Assets	'	'
Cash and Due from Banks	$2,918.90	$3,162.40
Federal Funds Sold and Securities Purchased under Agreements to Resell	1,010	529.6
Interest-Bearing Deposits with Banks	15,334.50	19,397.40
Federal Reserve Deposits	21,328	12,911.50
Securities	'	'
Available for Sale	28,107.70	28,392.80
Held to Maturity (Fair value of $4,195.1 and $2,321.4)	4,196.70	2,325.80
Trading Account	4.3	1.7
Total Securities	32,308.70	30,720.30
Loans and Leases	'	'
Commercial	13,868.60	12,620
Personal	16,851.30	16,765.50
Total Loans and Leases	30,719.90	29,385.50
Allowance for Credit Losses Assigned to Loans and Leases	-269.4	-278.1
Buildings and Equipment	436.6	458.8
Client Security Settlement Receivables	1,538.60	1,355.20
Goodwill	538.1	540.7
Other Assets	5,289.80	4,764
Total Assets	111,153.70	102,947.30
Deposits	'	'
Demand and Other Noninterest-Bearing	21,609.60	16,888.70
Savings and Money Market	14,525.10	14,991.50
Savings Certificates and Other Time	1,869	1,874.40
Non U.S. Offices - Noninterest-Bearing	3,132.70	1,881.80
- Interest-Bearing	50,586.10	48,461.70
Total Deposits	91,722.50	84,098.10
Federal Funds Purchased	786.4	965.1
Securities Sold under Agreements to Repurchase	866.8	917.3
Other Borrowings	1,758.30	1,558.60
Senior Notes	1,496.90	1,996.60
Long-Term Debt	1,598.70	1,709.20
Floating Rate Capital Debt	277.2	277.1
Other Liabilities	4,104.30	3,513.30
Total Liabilities	102,611.10	95,035.30
Stockholders' Equity	'	'
Preferred Stock, No Par Value; Authorized 10,000,000 shares: Series C, outstanding shares of 16,000 and 0	388.5	'
Common Stock, $1.66 2/3 Par Value; Authorized 560,000,000 shares; Outstanding shares of 235,505,008 and 237,322,035	408.6	408.6
Additional Paid-In Capital	1,055.50	1,035.70
Retained Earnings	7,469.40	7,134.80
Accumulated Other Comprehensive Loss	-218.4	-244.3
Treasury Stock (9,666,516 and 7,849,489 shares, at cost)	-561	-422.8
Total Stockholders' Equity	8,542.60	7,912
Total Liabilities and Stockholders' Equity	$111,153.70	$102,947.30

Consolidated_Balance_Sheet_Par

Consolidated Balance Sheet (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, except Share data, unless otherwise specified
Held to Maturity, Fair value	$4,195.10	$2,321.40
Total Loans and Leases, unearned income	$299.20	$286.20
Preferred Stock, Par Value	'	'
Preferred Stock, Authorized	10,000,000	'
Preferred Stock, Outstanding	16,000	'
Common Stock, Par Value	$1.67	$1.67
Common Stock, Authorized	560,000,000	560,000,000
Common Stock, Outstanding	235,505,008	237,322,035
Treasury Stock, shares	9,666,516	7,849,489

Consolidated_Statement_of_Inco

Consolidated Statement of Income (USD $)	3 Months Ended				9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Noninterest Income	'		'		'		'
Trust, Investment and Other Servicing Fees	$718.20		$648		$2,104.60		$1,936
Foreign Exchange Trading Income	46.4		62.8		149.4		193.6
Treasury Management Fees	16.4		17.6		49.8		51.5
Security Commissions and Trading Income	14.2		16.8		46.7		53.4
Other Operating Income	34.1		67.2		112.3		128.3
Investment Security Gains (Losses), net	0.3	[1]	-2.2	[1]	-3.3	[1]	-1.9	[1]
Total Noninterest Income	829.6		810.2		2,459.50		2,360.90
Net Interest Income	'		'		'		'
Interest Income	293.8		291.1		883		853.1
Interest Expense	44.5		54.1		141.4		169.9
Net Interest Income	249.3		237		741.6		683.2
Provision for Credit Losses	'		5		3		15
Net Interest Income after Provision for Credit Losses	249.3		232		738.6		668.2
Noninterest Expense	'		'		'		'
Compensation	348		324.6		1,062.20		971.8
Employee Benefits	70.6		63.5		206		191
Outside Services	142.4		145.9		431.4		412
Equipment and Software	100.5		95.5		317.9		279
Occupancy	43.8		43.3		135.2		130
Other Operating Expense	69.4		67.9		201		215.5
Total Noninterest Expense	774.7		740.7		2,353.70		2,199.30
Income before Income Taxes	304.2		301.5		844.4		829.8
Provision for Income Taxes	99.7		95		276.6		268.2
Net Income	204.5		206.5		567.8		561.6
Net Income Applicable to Common Stock	$204.50		$206.50		$567.80		$561.60
Per Common Share	'		'		'		'
Net Income - Basic	$0.85		$0.85		$2.36		$2.31
Net Income - Diluted	$0.84		$0.84		$2.34		$2.29
Average Number of Common Shares Outstanding - Basic	235,701,076		239,930,074		236,301,789		239,614,868
Average Number of Common Shares Outstanding - Diluted	237,737,129		241,330,652		238,175,696		240,857,697
[1]	Changes in Other-Than-Temporary-Impairment (OTTI) Losses $ - $ - $ (4.6 ) $ - Noncredit-related OTTI Losses Recorded in/(Reclassified from) OCI - - 0.7 - Other Security Gains (Losses), net 0.3 (2.2 ) 0.6 (1.9 ) Investment Security Gains (Losses), net $ 0.3 $ (2.2 ) $ (3.3 ) $ (1.9 )

Consolidated_Statement_of_Comp

Consolidated Statement of Comprehensive Income (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Net Income	$204.50	$206.50	$567.80	$561.60
Other Comprehensive Income (Net of Tax and Reclassifications)	'	'	'	'
Net Unrealized Gains (Losses) on Securities Available for Sale	-5.7	5.8	32.3	-74.4
Net Unrealized Gains (Losses) on Cash Flow Hedges	-7.4	4.3	-6.4	1.2
Foreign Currency Translation Adjustments	-3.6	-4.4	-10.5	-2.8
Pension and Other Postretirement Benefit Adjustments	3.5	7.1	10.5	21.1
Other Comprehensive Income (Loss)	-13.2	12.8	25.9	-54.9
Comprehensive Income	$191.30	$219.30	$593.70	$506.70

Consolidated_Statement_of_Inco1

Consolidated Statement of Income (Parenthetical) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Changes in Other-Than-Temporary-Impairment (OTTI) Losses	'		'		($4.60)	[1]	'
Noncredit-related OTTI Losses Recorded in/(Reclassified from) OCI	'		'		0.7	[2]	'
Other Security Gains (Losses), net	0.3		-2.2		0.6		-1.9
Investment Security Gains (Losses), net	$0.30	[3]	($2.20)	[3]	($3.30)	[3]	($1.90)	[3]
[1]	For initial other-than-temporary impairments in the respective period, the balance includes the excess of the amortized cost over the fair value of the impaired securities. For subsequent impairments of the same security, the balance includes any additional changes in fair value of the security subsequent to its most recently recorded OTTI.
[2]	For initial other-than-temporary impairments in the respective period, the balance includes the portion of the excess of amortized cost over the fair value of the impaired securities that was recorded in OCI. For subsequent impairments of the same security, the balance includes additional changes in OCI for that security subsequent to its most recently recorded OTTI.
[3]	Changes in Other-Than-Temporary-Impairment (OTTI) Losses $ - $ - $ (4.6 ) $ - Noncredit-related OTTI Losses Recorded in/(Reclassified from) OCI - - 0.7 - Other Security Gains (Losses), net 0.3 (2.2 ) 0.6 (1.9 ) Investment Security Gains (Losses), net $ 0.3 $ (2.2 ) $ (3.3 ) $ (1.9 )

Consolidated_Statement_of_Chan

Consolidated Statement of Changes in Stockholders' Equity (USD $)	Total	Preferred Stock	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
In Millions
Balance at Dec. 31, 2012	'	'	$408.60	$1,012.70	$6,702.70	($283)	($314)
Net Unrealized Gains (Losses) on Securities Available for Sale	-74.4	'	'	'	'	-74.4	'
Stock Options and Awards	'	'	'	-41.2	'	'	175.6
Net Income	561.6	'	'	'	561.6	'	'
Net Unrealized Gains (Losses) on Cash Flow Hedges	1.2	'	'	'	'	1.2	'
Stock Options and Awards - Amortization	'	'	'	57.4	'	'	'
Dividends Declared - Common Stock	'	'	'	'	-224.2	'	'
Stock Purchased	'	'	'	'	'	'	-187.1
Foreign Currency Translation Adjustments	-2.8	'	'	'	'	-2.8	'
Stock Options and Awards - Tax Benefits	'	'	'	2.9	'	'	'
Pension and Other Postretirement Benefit Adjustments	21.1	'	'	'	'	21.1	'
Balance at Sep. 30, 2013	7,817.10	'	408.6	1,031.80	7,040.10	-337.9	-325.5
Balance at Dec. 31, 2013	7,912	'	408.6	1,035.70	7,134.80	-244.3	-422.8
Net Unrealized Gains (Losses) on Securities Available for Sale	32.3	'	'	'	'	32.3	'
Stock Options and Awards	'	'	'	-55	'	'	177
Net Income	567.8	'	'	'	567.8	'	'
Issuance of Preferred Stock, Series C	'	388.5	'	'	'	'	'
Net Unrealized Gains (Losses) on Cash Flow Hedges	-6.4	'	'	'	'	-6.4	'
Stock Options and Awards - Amortization	'	'	'	60.4	'	'	'
Dividends Declared - Common Stock	'	'	'	'	-233.2	'	'
Stock Purchased	'	'	'	'	'	'	-315.2
Foreign Currency Translation Adjustments	-10.5	'	'	'	'	-10.5	'
Stock Options and Awards - Tax Benefits	'	'	'	14.4	'	'	'
Pension and Other Postretirement Benefit Adjustments	10.5	'	'	'	'	10.5	'
Balance at Sep. 30, 2014	$8,542.60	$388.50	$408.60	$1,055.50	$7,469.40	($218.40)	($561)

Consolidated_Statement_of_Cash

Consolidated Statement of Cash Flows (USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013
Cash Flows from Operating Activities:	'		'
Net Income	$567.80		$561.60
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:	'		'
Investment Security Losses (Gains), net	3.3	[1]	1.9	[1]
Amortization and Accretion of Securities and Unearned Income, net	30.1		25.8
Provision for Credit Losses	3		15
Depreciation on Buildings and Equipment	68		69.5
(Gains) Losses on Sale of Buildings and Equipment	'		-32.6
Computer Software Write-Offs	9.5		'
Pension Plan Contributions	-13.9		-16.4
Change in Receivables	42.1		-27.9
Change in Interest Payable	-2.9		-14.7
Change in Collateral With Derivative Counterparties, net	163.1		111
Other Operating Activities, net	220.8		99.7
Net Cash Provided by Operating Activities	1,273.50		960.9
Cash Flows from Investing Activities:	'		'
Net Change in Federal Funds Sold and Securities Purchased under Agreements to Resell	-480.4		-223.8
Change in Interest-Bearing Deposits with Banks	3,498.10		1,150.70
Net Change in Federal Reserve Deposits	-8,416.50		-833.2
Purchases of Securities - Held to Maturity	-5,596.90		-5,068.80
Proceeds from Maturity and Redemption of Securities - Held to Maturity	3,505.40		4,515.80
Purchases of Securities - Available for Sale	-8,969.20		-5,333.40
Proceeds from Sale, Maturity and Redemption of Securities - Available for Sale	9,254.90		6,359.20
Change in Loans and Leases	-1,352		387.6
Purchases of Buildings and Equipment	-51		-43.8
Proceeds from Sale of Buildings	'		38.8
Purchases and Development of Computer Software	-235.2		-203.8
Change in Client Security Settlement Receivables	-181.8		416.7
Other Investing Activities, net	-41.3		-652
Net Cash (Used in) Provided by Investing Activities	-9,065.90		510
Cash Flows from Financing Activities:	'		'
Change in Deposits	8,556.60		-2,845.70
Change in Federal Funds Purchased	-178.7		273.4
Change in Securities Sold under Agreements to Repurchase	-50.5		-230.8
Change in Short-Term Other Borrowings	33.4		1,382.40
Repayments of Senior Notes and Long-Term Debt	-638.7		-803.2
Contingent Consideration Liability Payment	-55.3		'
Proceeds from Issuance of Preferred Stock - Series C	388.5		'
Treasury Stock Purchased	-315.2		-186.8
Net Proceeds from Stock Options	122		134.1
Cash Dividends Paid on Common Stock	-225.4		-146.3
Other Financing Activities, net	-145.6		-2.9
Net Cash Provided by (Used in) Financing Activities	7,491.10		-2,425.80
Effect of Foreign Currency Exchange Rates on Cash	57.8		-107.1
Decrease in Cash and Due from Banks	-243.5		-1,062
Cash and Due from Banks at Beginning of Year	3,162.40		3,752.70
Cash and Due from Banks at End of Period	2,918.90		2,690.70
Supplemental Disclosures of Cash Flow Information:	'		'
Interest Paid	146.4		185
Income Taxes Paid	159.7		184.2
Transfers from Loans to OREO	10		16.4
Computer Software	'		'
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:	'		'
Amortization of Intangibles	167.9		152.5
Other Intangible Assets	'		'
Adjustments to Reconcile Net Income to Net Cash Provided by Operating Activities:	'		'
Amortization of Intangibles	$14.70		$15.50
[1]	Changes in Other-Than-Temporary-Impairment (OTTI) Losses $ - $ - $ (4.6 ) $ - Noncredit-related OTTI Losses Recorded in/(Reclassified from) OCI - - 0.7 - Other Security Gains (Losses), net 0.3 (2.2 ) 0.6 (1.9 ) Investment Security Gains (Losses), net $ 0.3 $ (2.2 ) $ (3.3 ) $ (1.9 )

Basis_of_Presentation

Basis of Presentation	9 Months Ended
	Sep. 30, 2014
Basis of Presentation	'
	1. Basis of Presentation — The consolidated financial statements include the accounts of Northern Trust Corporation (Corporation) and its subsidiaries (collectively, Northern Trust). Significant intercompany balances and transactions have been eliminated. The consolidated financial statements, as of and for the periods ended September 30, 2014, and 2013, 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. For a description of Northern Trust’s significant accounting policies, refer to Note 1 of the Notes to Consolidated Financial Statements in the 2013 Annual Report to Shareholders.

Recent_Accounting_Pronouncemen

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2014
Recent Accounting Pronouncements	'
	2. Recent Accounting Pronouncements — In May 2014, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2014-09, “Revenue from Contracts with Customers (Topic 606).” The ASU is a converged standard between the FASB and the International Accounting Standards Board (IASB) that provides a single comprehensive revenue recognition model for all contracts with customers across transactions and industries. The primary objective of the ASU is revenue recognition that represents the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The ASU is effective for interim and annual reporting periods beginning after December 15, 2016. Northern Trust is currently assessing the impact of adoption of ASU 2014-09.
	In August 2014, the FASB issued ASU No. 2014-14, “Receivables — Troubled Debt Restructurings by Creditors (Subtopic 310-40): Classification of Certain Government-Guaranteed Mortgage Loans upon Foreclosure (a consensus of the FASB Emerging Issues Task Force).” This ASU requires that a mortgage loan be derecognized and a separate receivable, measured based on the amount of the loan balance expected to be recovered from the guarantor, be recognized upon foreclosure if certain conditions are met. This ASU is effective for interim and annual reporting periods beginning after December 15, 2014. The adoption of this ASU is not expected to significantly impact Northern Trust’s consolidated financial position or results of operations.

Fair_Value_Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2014
Fair Value Measurements	'
	3. 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 nine months ended September 30, 2014, or the year ended December 31, 2013.
	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 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 September 30, 2014, Northern Trust’s available for sale securities portfolio included 843 Level 2 securities with an aggregate market value of $24.6 billion. Of those, 842 securities, with an aggregate market value of $24.5 billion, were valued by external pricing vendors. The remaining security, with an aggregate market value of $88.0 million, was valued consistent with prices of similar securities as there were no vended prices available for that security. As of December 31, 2013, Northern Trust’s available for sale securities portfolio included 831 Level 2 securities with an aggregate market value of $26.4 billion. Of those, 829 securities, with an aggregate market value of $26.3 billion, were valued by external pricing vendors. The remaining 2 securities, with an aggregate market value of $57.4 million, were valued consistent with prices of similar securities as there were no vended prices available for these securities. Trading account securities, which totaled $4.3 million and $1.7 million as of September 30, 2014, and December 31, 2013, respectively, were all valued using external pricing vendors.
	Northern Trust has established processes and procedures to assess the suitability of valuation methodologies used by external pricing vendors, including reviews of valuation techniques and assumptions used for selected securities. On a daily basis, periodic quality control reviews of prices received from vendors are conducted which include comparisons to prices on similar security types received from multiple pricing vendors and to the previous day’s reported prices for each security. Predetermined tolerance level exceptions are researched and may result in additional validation through available market information or the use of an alternate pricing vendor. Quarterly, Northern Trust reviews documentation from third-party pricing vendors regarding the valuation processes and assumptions used in their valuations and assesses whether the fair value levels assigned by Northern Trust to each security classification are appropriate. Annually, valuation inputs used within third-party pricing vendor valuations are reviewed for propriety on a sample basis through a comparison of inputs used to comparable market data, including security classifications that are less actively traded and security classifications comprising significant portions of the portfolio.
	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 assets consist of auction rate securities purchased in 2008 from Northern Trust clients. To estimate the fair value of auction rate securities, for which trading is limited and market prices are generally unavailable, Northern Trust developed and maintains a pricing model that discounts estimated cash flows over their estimated remaining lives. Significant inputs to the model include the contractual terms of the securities, credit risk ratings, discount rates, forward interest rates, credit/liquidity spreads, and Northern Trust’s own assumptions about the estimated remaining lives of the securities. The significant unobservable inputs used in the fair value measurement are Northern Trust’s own assumptions about the estimated remaining lives of the securities and the applicable discount rates. Significant increases (decreases) in the estimated remaining lives or the discount rates in isolation would result in a significantly lower (higher) fair value measurement. Level 3 liabilities at December 31, 2013, consisted of acquisition-related contingent consideration liabilities, the fair value of which was determined using an income-based (discounted cash flow) model that incorporated
	Northern Trust’s own assumptions about business growth rates and applicable discount rates, which represented unobservable inputs to the model. In April 2014, Northern Trust made a payment of $55.3 million to extinguish the contingent consideration liability at the value agreed by the parties.
	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.
	Management of various businesses and departments of Northern Trust (including Corporate Market Risk, Credit Policy, Corporate Financial Management, and relevant business unit personnel) determine the valuation policies and procedures for Level 3 assets and liabilities. Each business and department represents a component of Northern Trust’s business units, and reports to management of their respective business units. Generally, valuation policies are reviewed by management of each business or department. Fair value measurements are performed upon acquisitions of an asset or liability. As necessary, the valuation models are reviewed by management of the appropriate business or department, and adjusted for changes in inputs. Management of each business or department reviews the inputs in order to substantiate the unobservable inputs used in each fair value measurement. When appropriate, management reviews forecasts used in the valuation process in light of other relevant financial projections to understand any variances between current and previous fair value measurements. In certain circumstances, third party information is used to support the fair value measurements. If certain third party information seems inconsistent with consensus views, a review of the information is performed by management of the respective business or department to conclude as to the appropriate fair value of the asset or liability.
	The following presents the fair values of, and the valuation techniques, significant unobservable inputs, and quantitative information used to develop significant unobservable inputs for, Northern Trust’s Level 3 assets as of September 30, 2014.
	Financial Instrument		Fair Value			Valuation		Unobservable Inputs	Range of Lives
						Technique			and Rates
	Auction Rate Securities		$	85.2 million		Discounted Cash		Remaining lives	1.7 — 8.6 years
						Flow
								Discount rates	0.2% — 7.9%
	The following tables present assets and liabilities measured at fair value on a recurring basis as of September 30, 2014, and December 31, 2013, segregated by fair value hierarchy level.
	(In Millions)		Level 1			Level 2			Level 3		Netting			Assets/Liabilities
														at Fair Value
	September 30, 2014
	Securities
	Available for Sale
	U.S. Government		$	3,409.60		$	—		$	—	$	—		$	3,409.60
	Obligations of States and Political Subdivisions			—			4.6			—		—			4.6
	Government Sponsored Agency			—			16,174.40			—		—			16,174.40
	Non-U.S. Government			—			310.5			—		—			310.5
	Corporate Debt			—			3,364.80			—		—			3,364.80
	Covered Bonds			—			1,978.90			—		—			1,978.90
	Supranational and Non-U.S. Agency Bonds			—			360.2			—		—			360.2
	Residential Mortgage-Backed			—			17.6			—		—			17.6
	Other Asset-Backed			—			2,233.10			—		—			2,233.10
	Auction Rate			—			—			85.2		—			85.2
	Other			—			168.8			—		—			168.8
	Total Available for Sale			3,409.60			24,612.90			85.2		—			28,107.70
	Trading Account			—			4.3			—		—			4.3
	Total Available for Sale and Trading Securities			3,409.60			24,617.20			85.2		—			28,112.00
	Other Assets
	Derivative Assets
	Foreign Exchange Contracts			—			4,203.80			—		—			4,203.80
	Interest Rate Contracts			—			213.5			—		—			213.5
	Total Derivative Assets			—			4,417.30			—		(2,358.4	)		2,058.90
	Other Liabilities
	Derivative Liabilities
	Foreign Exchange Contracts			—			4,141.60			—		—			4,141.60
	Interest Rate Swaps			—			123.5			—		—			123.5
	Total Derivative Liabilities		$	—		$	4,265.10		$	—	$	(2,752.3	)	$	1,512.80
	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 September 30, 2014, derivative assets and liabilities shown above also include reductions of $207.4 million and $601.3 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties.
	(In Millions)		Level 1			Level 2			Level 3		Netting			Assets/Liabilities
														at Fair Value
	December 31, 2013
	Securities
	Available for Sale
	U.S. Government		$	1,917.90		$	—		$	—	$	—		$	1,917.90
	Obligations of States and Political Subdivisions			—			4.6			—		—			4.6
	Government Sponsored Agency			—			17,528.00			—		—			17,528.00
	Non-U.S. Government			—			310.6			—		—			310.6
	Corporate Debt			—			3,524.50			—		—			3,524.50
	Covered Bonds			—			1,943.90			—		—			1,943.90
	Supranational and Non-U.S. Agency Bonds			—			410			—		—			410
	Residential Mortgage-Backed			—			48.1			—		—			48.1
	Other Asset-Backed			—			2,391.80			—		—			2,391.80
Auction Rate			—			—			98.9		—			98.9
Other			—			214.5			—		—			214.5
Total Available for Sale			1,917.90			26,376.00			98.9		—			28,392.80
Trading Account			—			1.7			—		—			1.7
Total Available for Sale and Trading Securities			1,917.90			26,377.70			98.9		—			28,394.50
Other Assets
Derivative Assets
Foreign Exchange Contracts			—			2,865.70			—		—			2,865.70
Interest Rate Contracts			—			237.9			—		—			237.9
Total Derivative Assets			—			3,103.60			—		(1,369.0	)		1,734.60
Other Liabilities
Derivative Liabilities
Foreign Exchange Contracts			—			2,905.70			—		—			2,905.70
Interest Rate Swaps			—			195.2			—		—			195.2
Total Derivative Liabilities			—			3,100.90			—		(1,926.0	)		1,174.90
Contingent Consideration		$	—		$	—		$	55.4	$	—		$	55.4
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, 2013, derivative assets and liabilities shown above also include reductions of $210.7 million and $767.7 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties.
The following tables present the changes in Level 3 assets and liabilities for the three and nine months ended September 30, 2014, and 2013.
Level 3 Assets (In Millions)		Auction Rate Securities
Three Months Ended September 30,		2014			2013
Fair Value at July 1		$	98.8		$	99.1
Total Gains (Losses):
Included in Earnings			0.7			—
Included in Other Comprehensive Income (2)			0.1			0.3
Purchases, Issues, Sales, and Settlements:
Sales			(14.4	)		—
Fair Value at September 30		$	85.2		$	98.7
Nine Months Ended September 30,		2014			2013
Fair Value at January 1		$	98.9		$	97.8
Total Gains (Losses):
Included in Earnings (1)			0.7			0.1
Included in Other Comprehensive Income (2)			0.4			3
Purchases, Issues, Sales, and Settlements:
Sales			(14.4	)		—
Settlements			(0.4	)		(2.2	)
Fair Value at September 30		$	85.2		$	98.7
-1	Realized gains for the three and nine months ended September 30, 2014, of $0.7 million, represent gains from sales of securities. Realized gains for the nine month period ended September 30, 2013, of $0.1 million, represent gains from redemptions by issuers. Gains on sales are recorded in investment security gains (losses) and gains on redemptions are recorded in interest income, within the consolidated statement of income.
-2	Unrealized gains (losses) are included in net unrealized gains (losses) on securities available for sale within the consolidated statement of comprehensive income.
Level 3 Liabilities (In Millions)		Contingent Consideration
Three Months Ended September 30,		2014			2013
Fair Value at July 1		$	—		$	52.7
Total (Gains) Losses:
Included in Earnings (1)			—			1.3
Included in Other Comprehensive Income			—			—
Purchases, Issues, Sales, and Settlements			—			—
Fair Value at September 30		$	—		$	54
Unrealized (Gains) Losses Included in Earnings Related to Financial Instruments Held at September 30 (1)		$	—		$	1.3
Nine Months Ended September 30,		2014			2013
Fair Value at January 1		$	55.4		$	50.1
Total (Gains) Losses:
Included in Earnings (1)			(0.1	)		3.9
Included in Other Comprehensive Income			—			—
Purchases, Issues, Sales, and Settlements:
Settlements			(55.3	)		—
Fair Value at September 30		$	—		$	54
Unrealized (Gains) Losses Included in Earnings Related to Financial Instruments Held at September 30 (1)		$	—		$	3.9
-1	(Gains) losses are recorded in other operating income (expense) within the consolidated statement of income.
During the nine months ended September 30, 2014, and 2013, there were no transfers into or out of Level 3 assets or 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 disclose separately these subsequent fair value measurements and to classify them under the fair value hierarchy.
Assets measured at fair value on a nonrecurring basis at September 30, 2014, and 2013, 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. 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 $26.6 million and $1.5 million, respectively, at September 30, 2014, and $38.1 million and $1.6 million, respectively, at September 30, 2013. Assets measured at fair value on a nonrecurring basis reflect management’s judgment as to realizable value.
The following table provides the fair value of, and the valuation technique, significant unobservable inputs, and quantitative information used to develop the significant unobservable inputs for, Northern Trust’s Level 3 assets that were measured at fair value on a nonrecurring basis as of September 30, 2014.
Financial Instrument		Fair Value		Valuation	Unobservable Input		Range of Discounts
				Technique			Applied
Loans		$26.6 million		Market Approach	Discount to reflect realizable value		15% — 25%
OREO		$1.5 million		Market Approach	Discount to reflect realizable value		15% — 20%
Fair Value of Financial Instruments. GAAP requires disclosure of the estimated fair value of certain financial instruments and the methods and significant assumptions used to estimate fair value. It excludes from this requirement nonfinancial assets and liabilities, as well as a wide range of franchise, relationship, and intangible values that add value to Northern Trust. Accordingly, the required fair value disclosures provide only a partial estimate of the fair value of Northern Trust. Financial instruments recorded at fair value on Northern Trust’s consolidated balance sheet are discussed above. The following methods and assumptions were used in estimating the fair values of financial instruments that are not carried at fair value.
Held to Maturity Securities. The fair values of held to maturity securities were modeled by external pricing vendors, or in limited cases internally, using widely accepted models which are based on an income approach (discounted cash flow) that incorporates current market yield curves.
Loans (excluding lease receivables). The fair value of the loan portfolio was estimated using an income approach (discounted cash flow) that incorporates current market rates offered by Northern Trust as of the date of the consolidated financial statements. The fair values of all loans were adjusted to reflect current assessments of loan collectability.
Federal Reserve and Federal Home Loan Bank Stock. The fair values of Federal Reserve and Federal Home Loan Bank stock are equal to their carrying values which represent redemption value.
Community Development Investments. The fair values of these instruments were estimated using an income approach (discounted cash flow) that incorporates current market rates.
Employee Benefit and Deferred Compensation. These assets include U.S. treasury securities and investments in mutual and collective trust funds held to fund certain supplemental employee benefit obligations and deferred compensation plans. Fair values of U.S. treasury securities were determined using quoted, active market prices for identical securities. The fair values of investments in mutual and collective trust funds were valued at the funds’ net asset values based on a market approach.
Savings Certificates and Other Time Deposits. The fair values of these instruments were estimated using an income approach (discounted cash flow) that incorporates market interest rates currently offered by Northern Trust for deposits with similar maturities.
Senior Notes, Subordinated Debt, and Floating Rate Capital Debt. Fair values were determined using a market approach based on quoted market prices, when available. If quoted market prices were not available, fair values were based on quoted market prices for comparable instruments.
Federal Home Loan Bank Borrowings. The fair values of these instruments were estimated using an income approach (discounted cash flow) that incorporates market interest rates.
Loan Commitments. The fair values of loan commitments represent the estimated costs to terminate or otherwise settle the obligations with a third party adjusted for any related allowance for credit losses.
Standby Letters of Credit. The fair values of standby letters of credit are measured as the amount of unamortized fees on these instruments, inclusive of the related allowance for credit losses. Fees are determined by applying basis points to the principal amounts of the letters of credit.
Financial Instruments Valued at Carrying Value. Due to their short maturity, the carrying values of certain financial instruments approximated their fair values. These financial instruments include cash and due from banks; federal funds sold and securities purchased under agreements to resell, interest-bearing deposits with banks, Federal Reserve deposits; client security settlement receivables; non-U.S. offices interest-bearing deposits; federal funds purchased; securities sold under agreements to repurchase; and other borrowings (includes term federal funds purchased, and other short-term borrowings). As required by GAAP, the fair values required to be disclosed for demand, noninterest-bearing, savings, and money market deposits must equal the amounts disclosed in the consolidated balance sheet, even though such deposits are typically priced at a premium in banking industry consolidations.
The following tables summarize the fair values of all financial instruments.
(In Millions)		September 30, 2014
		Book			Total			Fair Value
		Value			Fair Value			Level 1		Level 2			Level 3
Assets
Cash and Due from Banks		$	2,918.90		$	2,918.90		$	2,918.90	$	—		$	—
Federal Funds Sold and Resell Agreements			1,010.00			1,010.00			—		1,010.00			—
Interest-Bearing Deposits with Banks			15,334.50			15,334.50			—		15,334.50			—
Federal Reserve Deposits			21,328.00			21,328.00			—		21,328.00			—
Securities
Available for Sale (1)			28,107.70			28,107.70			3,409.60		24,612.90			85.2
Held to Maturity			4,196.70			4,195.10			—		4,195.10			—
Trading Account			4.3			4.3			—		4.3			—
Loans (excluding Leases)
Held for Investment			29,499.60			29,522.70			—		—			29,522.70
Held for Sale			2.1			2.1			—		—			2.1
Client Security Settlement Receivables			1,538.60			1,538.60			—		1,538.60			—
Other Assets
Federal Reserve and Federal Home Loan Bank Stock			207.5			207.5			—		207.5			—
Community Development Investments			225.1			223.8			—		223.8			—
Employee Benefit and Deferred Compensation			145.2			147.4			97.4		50			—
Liabilities
Deposits
Demand, Noninterest-Bearing, Savings and Money Market		$	39,267.40		$	39,267.40		$	39,267.40	$	—		$	—
Savings Certificates and Other Time			1,869.00			1,869.50			—		1,869.50			—
Non U.S. Offices Interest-Bearing			50,586.10			50,586.10			—		50,586.10			—
Federal Funds Purchased			786.4			786.4			—		786.4			—
Securities Sold under Agreements to Repurchase			866.8			866.8			—		866.8			—
Other Borrowings			1,758.30			1,758.90			—		1,758.90			—
Senior Notes			1,496.90			1,526.80			—		1,526.80			—
Long Term Debt (excluding Leases)
Subordinated Debt			1,565.50			1,595.50			—		1,595.50			—
Federal Home Loan Bank Borrowings			—			—			—		—			—
Floating Rate Capital Debt			277.2			242.8			—		242.8			—
Other Liabilities
Standby Letters of Credit			57			57			—		—			57
Loan Commitments			28.7			28.7			—		—			28.7
Derivative Instruments
Asset/Liability Management
Foreign Exchange Contracts
Assets		$	71		$	71		$	—	$	71		$	—
Liabilities			16.1			16.1			—		16.1			—
Interest Rate Contracts
Assets			113.3			113.3			—		113.3			—
Liabilities			27.6			27.6			—		27.6			—
Client-Related and Trading
Foreign Exchange Contracts
Assets			4,132.80			4,132.80			—		4,132.80			—
Liabilities			4,125.50			4,125.50			—		4,125.50			—
Interest Rate Contracts
Assets			100.2			100.2			—		100.2			—
Liabilities			95.9			95.9			—		95.9			—
-1	Refer to the table located on page 36 for the disaggregation of available for sale securities.
(In Millions)		December 31, 2013
		Book			Total			Fair Value
		Value			Fair Value			Level 1		Level 2			Level 3
Assets
Cash and Due from Banks		$	3,162.40		$	3,162.40		$	3,162.40	$	—		$	—
Federal Funds Sold and Resell Agreements			529.6			529.6			—		529.6			—
Interest-Bearing Deposits with Banks			19,397.40			19,397.40			—		19,397.40			—
Federal Reserve Deposits and Other Interest-Bearing			12,911.50			12,911.50			—		12,911.50			—
Securities
Available for Sale (1)			28,392.80			28,392.80			1,917.90		26,376.00			98.9
Held to Maturity			2,325.80			2,321.40			—		2,321.40			—
Trading Account			1.7			1.7			—		1.7			—
Loans (excluding Leases)
Held for Investment			28,136.50			28,147.20			—		—			28,147.20
Held for Sale			—			—			—		—			—
Client Security Settlement Receivables			1,355.20			1,355.20			—		1,355.20			—
Other Assets
Federal Reserve and Federal Home Loan Bank Stock			194.7			194.7			—		194.7			—
Community Development Investments			228.1			227.8			—		227.8			—
Employee Benefit and Deferred Compensation			132.7			126.9			79.3		47.6			—
Liabilities
Deposits
Demand, Noninterest-Bearing, Savings and Money Market		$	33,762.00		$	33,762.00		$	33,762.00	$	—		$	—
Savings Certificates and Other Time			1,874.40			1,877.10			—		1,877.10			—
Non U.S. Offices Interest-Bearing			48,461.70			48,461.70			—		48,461.70			—
Federal Funds Purchased			965.1			965.1			—		965.1			—
Securities Sold under Agreements to Repurchase			917.3			917.3			—		917.3			—
Other Borrowings			1,558.60			1,558.60			—		1,558.60			—
Senior Notes			1,996.60			1,989.30			—		1,989.30			—
Long Term Debt (excluding Leases)
Subordinated Debt			1,537.30			1,563.50			—		1,563.50			—
Federal Home Loan Bank Borrowings			135			137.2			—		137.2			—
Floating Rate Capital Debt			277.1			230.2			—		230.2			—
Other Liabilities
Standby Letters of Credit			59.6			59.6			—		—			59.6
Contingent Consideration			55.4			55.4			—		—			55.4
Loan Commitments			35.7			35.7			—		—			35.7
Derivative Instruments
Asset/Liability Management
Foreign Exchange Contracts
Assets		$	21		$	21		$	—	$	21		$	—
Liabilities			59.5			59.5			—		59.5			—
Interest Rate Swaps
Assets			115.1			115.1			—		115.1			—
Liabilities			78.2			78.2			—		78.2			—
Client-Related and Trading
Foreign Exchange Contracts
Assets			2,844.70			2,844.70			—		2,844.70			—
Liabilities			2,846.20			2,846.20			—		2,846.20			—
Interest Rate Contracts
Assets			122.8			122.8			—		122.8			—
Liabilities			117			117			—		117			—
-1	Refer to the table located on page 37 for the disaggregation of available for sale securities.

Securities

Securities	9 Months Ended
	Sep. 30, 2014
Securities	'
	4. Securities — The following tables provide the amortized cost and fair values of securities at September 30, 2014, and December 31, 2013.
	Securities Available for Sale		September 30, 2014
			Amortized			Gross Unrealized						Fair
	(In Millions)		Cost			Gains			Losses			Value
	U.S. Government		$	3,395.10		$	16		$	1.5		$	3,409.60
	Obligations of States and Political Subdivisions			4.5			0.1			—			4.6
	Government Sponsored Agency			16,114.20			85.4			25.2			16,174.40
	Non-U.S. Government			309.3			1.2			—			310.5
	Corporate Debt			3,393.50			4.7			33.4			3,364.80
	Covered Bonds			1,966.90			12.2			0.2			1,978.90
	Supranational and Non-U.S. Agency Bonds			360			1.4			1.2			360.2
	Residential Mortgage-Backed			18.8			0.1			1.3			17.6
	Other Asset-Backed			2,232.00			1.3			0.2			2,233.10
	Auction Rate			83.4			2.3			0.5			85.2
	Other			168.5			0.3			—			168.8
	Total		$	28,046.20		$	125		$	63.5		$	28,107.70
	Securities Held to Maturity		September 30, 2014
			Amortized			Gross Unrealized						Fair
	(In Millions)		Cost			Gains			Losses			Value
	Obligations of States and Political Subdivisions		$	138.8		$	8.5		$	—		$	147.3
	Government Sponsored Agency			22.8			1.1			—			23.9
	Non-U.S. Government			1,094.10			3.7			0.7			1,097.10
	Certificates of Deposit			1,479.50			0.2			0.1			1,479.60
	Supranational and Non-U.S. Agency Bonds			1,393.90			3.9			1.9			1,395.90
	Other			67.6			—			16.3			51.3
	Total		$	4,196.70		$	17.4		$	19		$	4,195.10
	Securities Available for Sale		31-Dec-13
			Amortized			Gross Unrealized						Fair
	(In Millions)		Cost			Gains			Losses			Value
	U.S. Government		$	1,896.70		$	22.6		$	1.4		$	1,917.90
	Obligations of States and Political Subdivisions			4.5			0.1			—			4.6
	Government Sponsored Agency			17,495.20			80.7			47.9			17,528.00
	Non-U.S. Government			307			3.6			—			310.6
	Corporate Debt			3,615.20			10.5			101.2			3,524.50
	Covered Bonds			1,898.90			50.9			5.9			1,943.90
	Supranational and Non-U.S. Agency Bonds			410			1.7			1.7			410
	Residential Mortgage-Backed			52.4			0.1			4.4			48.1
	Other Asset-Backed			2,390.80			1.4			0.4			2,391.80
	Auction Rate			97.5			2.2			0.8			98.9
	Other			214.1			0.4			—			214.5
	Total		$	28,382.30		$	174.2		$	163.7		$	28,392.80
	Securities Held to Maturity		December 31, 2013
			Amortized			Gross Unrealized						Fair
	(In Millions)		Cost			Gains			Losses			Value
	Obligations of States and Political Subdivisions		$	225.2		$	10.3		$	—		$	235.5
	Government Sponsored Agency			35.9			1.1			—			37
	Non-U.S. Government			722			0.8			1.1			721.7
	Certificates of Deposit			698.1			—			0.2			697.9
	Supranational and Non-U.S. Agency Bonds			584.7			—			3.2			581.5
	Other			59.9			0.1			12.2			47.8
	Total		$	2,325.80		$	12.3		$	16.7		$	2,321.40
	Securities held to maturity consist of debt securities that management intends to, and Northern Trust has the ability to, hold until maturity.
	The following table provides the remaining maturity of securities as of September 30, 2014.
	Remaining Maturity of Securities
	(In Millions)		Amortized			Fair
			Cost			Value
	Available for Sale
	Due in One Year or Less		$	7,195.00		$	7,210.60
	Due After One Year Through Five Years			16,637.90			16,677.90
	Due After Five Years Through Ten Years			3,116.80			3,138.10
	Due After Ten Years			1,096.50			1,081.10
	Total			28,046.20			28,107.70
	Held to Maturity
Due in One Year or Less			1,914.10			1,915.30
Due After One Year Through Five Years			2,222.20			2,230.50
Due After Five Years Through Ten Years			23.3			24.1
Due After Ten Years			37.1			25.2
Total		$	4,196.70		$	4,195.10
Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments.
Investment Security Gains and Losses. Net investment security gains of $0.3 million were recognized in the three months ended September 30, 2014, representing net realized gains from the sale of securities. Net investment security losses of $2.2 million were recognized in the three months ended September 30, 2013, representing realized losses from the sale of securities. For the three months ended September 30, 2014, proceeds of $337.3 million were received from the sale of securities, representing gross realized gains and losses of $1.0 million and $0.7 million, respectively. For the three months ended September 30, 2013, proceeds of $316.4 million were received from the sale of securities, representing gross realized gains and losses of $0.1 million and $2.3 million, respectively.
Net investment security losses of $3.3 million were recognized in the nine months ended September 30, 2014, and include $3.9 million of charges related to the other-than-temporary impairment of certain Community Reinvestment Act (CRA) eligible held to maturity securities. Net investment security losses of $1.9 million were recognized in the nine months ended September 30, 2013, representing net realized losses from the sale of securities. For the nine months ended September 30, 2014, proceeds of $801.2 million were received from the sale of securities, representing gross realized gains and losses totaling $1.7 million and $1.1 million, respectively. For the nine months ended September 30, 2013, proceeds of $398.1 million were received from the sale of securities, representing gross realized gains and losses totaling $0.4 million and $2.3 million, respectively.
Securities with Unrealized Losses. The following tables provide information regarding securities that had been in a continuous unrealized loss position for less than 12 months and for 12 months or longer as of September 30, 2014, and December 31, 2013.
Securities with Unrealized Losses as of		Less than 12 Months						12 Months or Longer						Total
September 30, 2014
(In Millions)		Fair Value			Unrealized			Fair Value			Unrealized			Fair Value			Unrealized
					Losses						Losses						Losses
U.S. Government		$	1,596.00		$	1.5		$	—		$	—		$	1,596.00		$	1.5
Government Sponsored Agency			2,099.20			8.3			1,773.50			16.9			3,872.70			25.2
Non-U.S. Government			235.4			0.1			80.3			0.6			315.7			0.7
Corporate Debt			862.3			2.8			1,258.00			30.6			2,120.30			33.4
Covered Bonds			77			0.1			9.9			0.1			86.9			0.2
Supranational and Non-U.S. Agency Bonds			438.2			0.7			300.8			2.4			739			3.1
Residential Mortgage-Backed			—			—			15			1.3			15			1.3
Other Asset-Backed			485.2			0.1			7.1			0.1			492.3			0.2
Certificates of Deposit			552			0.1			—			—			552			0.1
Auction Rate			1.1			0.1			5.1			0.4			6.2			0.5
Other			13			8.5			43.4			7.8			56.4			16.3
Total		$	6,359.40		$	22.3		$	3,493.10		$	60.2		$	9,852.50		$	82.5
Securities with Unrealized Losses as of		Less than 12 Months						12 Months or Longer						Total
December 31, 2013
(In Millions)		Fair Value			Unrealized			Fair			Unrealized			Fair Value			Unrealized
					Losses			Value			Losses						Losses
U.S. Government		$	896.4		$	1.4		$	—		$	—		$	896.4		$	1.4
Government Sponsored Agency			4,340.80			42.6			413.7			5.3			4,754.50			47.9
Non-U.S. Government			176.7			1.1			—			—			176.7			1.1
Corporate Debt			1,759.50			85.4			267			15.8			2,026.50			101.2
Covered Bonds			278.8			5.7			9.9			0.2			288.7			5.9
Supranational and Non-U.S. Agency Bonds			612.7			4.9			—			—			612.7			4.9
Residential Mortgage-Backed			—			—			42			4.4			42			4.4
Other Asset-Backed			677			0.4			—			—			677			0.4
Certificates of Deposit			684.2			0.2			—			—			684.2			0.2
Auction Rate			22.1			0.1			14			0.7			36.1			0.8
Other			25.7			4			29.5			8.2			55.2			12.2
Total		$	9,473.90		$	145.8		$	776.1		$	34.6		$	10,250.00		$	180.4
As of September 30, 2014, 471 securities with a combined fair value of $9.9 billion were in an unrealized loss position, with their combined unrealized losses totaling $82.5 million. Unrealized losses of $33.4 million within corporate debt securities primarily reflect higher market rates since purchase; 40% of the corporate debt portfolio is backed by guarantees provided by U.S. and non-U.S. governmental entities. Unrealized losses of $25.2 million related to government sponsored agency securities are primarily attributable to changes in market rates since their purchase.
Unrealized losses on residential mortgage-backed securities totaling $1.3 million reflect the impact of wider credit and liquidity spreads on the valuations of two residential mortgage-backed securities since purchase, with both having been in an unrealized loss position for more than 12 months. Securities classified as “other asset-backed” had average lives less than 5 years, and 100% were rated triple-A.
The majority of the $16.3 million of unrealized losses in securities classified as “other” at September 30, 2014, relate to securities primarily purchased at a premium or par by Northern Trust for compliance with CRA. Unrealized losses on these CRA related securities are attributable to yields that are below market rates for the purpose of supporting institutions and programs that benefit low to moderate income communities within Northern Trust’s market area. Unrealized losses of $0.5 million related to auction rate securities primarily reflect reduced market liquidity as a majority of auctions continue to fail preventing holders from liquidating their investments at par. The remaining unrealized losses on Northern Trust’s securities portfolio as of September 30, 2014, are attributable to changes in overall market interest rates, increased credit spreads, or reduced market liquidity. As of September 30, 2014, Northern Trust does not intend to sell any investment in an unrealized loss position and it is not more likely than not that Northern Trust will 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 following describes Northern Trust’s process for identifying credit impairment within non-agency residential mortgage-backed securities, the security type for which Northern Trust has previously recognized the majority of its OTTI. To determine if an unrealized loss on a non-agency residential mortgage-backed security is other-than-temporary, economic models are used to perform cash flow analyses by developing multiple scenarios in order to create reasonable forecasts of the security’s future performance using available data including servicers’ loan charge off patterns, prepayment speeds, annualized default rates, each security’s current delinquency pipeline, the delinquency pipeline’s growth rate, the roll rate from delinquency to default, loan loss severities and historical performance of like collateral, along with Northern Trust’s outlook for the housing market and the overall economy. If the present value of future cash flows projected as a result of this analysis is less than the current amortized cost of the security, a credit-related OTTI loss is recorded in earnings equal to the difference between the two amounts.
Impairments of non-agency residential mortgage-backed securities are influenced by a number of factors, including but not limited to, U.S. economic and housing market performance, security credit enhancement level, insurance coverage, year of origination, and type of collateral. The factors used in estimating losses on non-agency residential mortgage-backed securities vary by year of origination and type of collateral.
As of September 30, 2014, loss estimates for subprime, Alt-A, prime and 2nd lien collateral portfolios were developed using default roll rates, determined primarily by the stage of delinquency of the underlying instrument, that generally assumed ultimate default rates approximating 5% to 30% for current loans; 30% for loans 30 to 60 days delinquent; 80% for loans 60 to 90 days delinquent; 90% for loans delinquent greater than 90 days; and 100% for OREO properties and loans that are in foreclosure. Amortized cost, weighted average ultimate default rates, and impairment severity rates for the non-agency residential mortgage-backed securities portfolio, by security type as of September 30, 2014, are provided in the following table.
($ In Millions)		September 30, 2014
		Amortized			Weighted Average			Loss Severity Rates
Security Type		Cost			Ultimate Default Rates			Low			High			Weighted
														Average
Prime		$	2			5.4	%		32.1	%		32.1	%		32.1	%
Alt-A			11.2			40			62.8			62.8			62.8
2nd Lien			5.6			32.7			98.7			99			99
Total Non-Agency Residential Mortgage-Backed Securities		$	18.8			33.1	%		32.1	%		99	%		70.3	%
Northern Trust’s processes for identifying credit impairment within auction rate securities are largely consistent with the processes utilized for non-agency residential mortgage-backed securities and include analyses of expected loss severities and default rates adjusted for the type of underlying loan and the presence of government guarantees, as applicable.
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 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 like collateral, and Northern Trust’s outlook for the housing market and the overall economy. If the present value of the collateral pools was 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 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 mortgage-backed securities vary by vintage of loan origination and collateral quality.
There were no OTTI losses recognized in the three months ended September 30, 2014, or in the three or nine months ended September 30, 2013. There were $3.9 million of OTTI losses recognized during the nine months ended September 30, 2014, related to CRA eligible mortgage-backed securities.
Credit Losses on Debt Securities. The table below provides information regarding total other-than-temporarily impaired securities, including noncredit-related amounts recognized in other comprehensive income and net impairment losses recognized in earnings, for the three and nine months ended September 30, 2014, and 2013.
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
(In Millions)		2014			2013			2014			2013
Changes in OTTI Losses*		$	—		$	—		$	(4.6	)	$	—
Noncredit-related Losses Recorded in / (Reclassified from) OCI**			—			—			0.7			—
Net Impairment Losses Recognized in Earnings		$	—		$	—		$	(3.9	)	$	—
*	For initial other-than-temporary impairments in the respective period, the balance includes the excess of the amortized cost over the fair value of the impaired securities. For subsequent impairments of the same security, the balance includes any additional changes in fair value of the security subsequent to its most recently recorded OTTI.
**	For initial other-than-temporary impairments in the respective period, the balance includes the portion of the excess of amortized cost over the fair value of the impaired securities that was recorded in OCI. For subsequent impairments of the same security, the balance includes additional changes in OCI for that security subsequent to its most recently recorded OTTI.
Provided in the table below are the cumulative credit-related losses recognized in earnings on debt securities other-than-temporarily impaired.
		Three Months Ended						Nine Months Ended
		September 30,						September 30,
(In Millions)		2014			2013			2014			2013
Cumulative Credit-Related Losses on Securities Held — Beginning of Period		$	12.7		$	8.8		$	8.8		$	42.3
Plus: Losses on Newly Identified Impairments			—			—			1.8			—
Additional Losses on Previously Identified Impairments			—			—			2.1			—
Less: Current and Prior Period Losses on Securities Sold During the Period			(1.8	)		—			(1.8	)		(33.5	)
Cumulative Credit-Related Losses on Securities Held — End of Period		$	10.9		$	8.8		$	10.9		$	8.8

Loans_and_Leases

Loans and Leases	9 Months Ended
	Sep. 30, 2014
Loans and Leases	'
	5. Loans and Leases — Amounts outstanding for loans and leases, by segment and class, are shown below.
	(In Millions)		September 30,			December 31,
			2014			2013
	Commercial
	Commercial and Institutional		$	8,212.10		$	7,375.80
	Commercial Real Estate			3,107.70			2,955.80
	Lease Financing, net			952.5			975.1
	Non-U.S.			1,408.40			954.7
	Other			187.9			358.6
	Total Commercial			13,868.60			12,620.00
	Personal
	Residential Real Estate			9,872.70			10,271.30
	Private Client			6,953.10			6,445.60
	Other			25.5			48.6
	Total Personal			16,851.30			16,765.50
	Total Loans and Leases			30,719.90			29,385.50
	Allowance for Credit Losses Assigned to Loans and Leases			(269.4	)		(278.1	)
	Net Loans and Leases		$	30,450.50		$	29,107.40
	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 September 30, 2014, and December 31, 2013, equity credit lines totaled $1.8 billion and $2.0 billion, respectively, and equity credit lines for which first liens were held by Northern Trust represented 88% and 87%, respectively, of the total equity credit lines as of those dates.
	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 $1.4 billion at September 30, 2014, and $1.3 billion at December 31, 2013. Demand deposits reclassified as loan balances totaled $109.0 million and $104.1 million at September 30, 2014, and December 31, 2013, respectively. Loans classified as held for sale totaled $2.1 million at September 30, 2014. There were no loans classified as held for sale at December 31, 2013.
	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, 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, return on assets, asset size, and capital levels;
		•		Commercial Real Estate: debt service coverage and leasing status for income-producing properties; loan-to-value and loan-to-cost ratios, leasing status, and guarantor support for loans associated with construction and development properties;
		•		Lease Financing and Commercial-Other: leverage and profit margin levels;
		•		Non-U.S.: entity type, liquidity, size, and leverage;
		•		Residential Real Estate: payment history, credit bureau scores, and cash flow-to-debt and net worth ratios;
		•		Private Client: cash flow-to-debt and net worth ratios, leverage, and profit margin levels; 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 September 30, 2014, and December 31, 2013, are provided below, segregated by borrower ratings into “1 to 3”, “4 to 5” and “6 to 9” (watch list), categories.
			September 30, 2014										December 31, 2013
	(In Millions)		1 to 3			4 to 5			6 to 9		Total		1 to 3		4 to 5		6 to 9		Total
			Category			Category			Category				Category		Category		Category
									(Watch List)								(Watch List)
	Commercial
	Commercial and Institutional		$	5,115.40		$	2,983.60		$	113.1	$	8,212.10	$	4,432.50	$	2,801.50	$	141.8	$	7,375.80
	Commercial Real Estate			1,263.60			1,718.20			125.9		3,107.70		1,053.70		1,748.70		153.4		2,955.80
	Lease Financing, net			572.2			376.1			4.2		952.5		685.7		285		4.4		975.1
	Non-U.S.			643.7			763.8			0.9		1,408.40		442.8		511.9		—		954.7
	Other			137.4			50.5			—		187.9		157.7		200.9		—		358.6
	Total Commercial			7,732.30			5,892.20			244.1		13,868.60		6,772.40		5,548.00		299.6		12,620.00
	Personal
	Residential Real Estate			2,995.70			6,439.90			437.1		9,872.70		3,204.60		6,563.60		503.1		10,271.30
	Private Client			4,461.80			2,479.90			11.4		6,953.10		3,957.60		2,481.20		6.8		6,445.60
	Other			18.6			6.9			—		25.5		21.2		27.4		—		48.6
	Total Personal			7,476.10			8,926.70			448.5		16,851.30		7,183.40		9,072.20		509.9		16,765.50
	Total Loans and Leases		$	15,208.40		$	14,818.90		$	692.6	$	30,719.90	$	13,955.80	$	14,620.20	$	809.5	$	29,385.50
	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 reduced cushion in adverse down cycle scenarios. 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 to probable 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. At the time a loan is determined to be nonperforming, interest accrued but not collected is reversed against interest income of the current period and the loan is classified as nonperforming. 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 tables provide balances and delinquency status of performing and nonperforming loans and leases by segment and class, as well as the total other real estate owned and nonperforming asset balances, as of September 30, 2014, and December 31, 2013.
	September 30, 2014
	(In Millions)		Current			30-59 Days			60-89 Days		90 Days or		Total		Nonperforming		Total Loans
						Past Due			Past Due		More Past		Performing				and Leases
											Due
	Commercial
	Commercial and Institutional		$	8,153.80		$	10.2		$	13.3	$	3.1	$	8,180.40	$	31.7	$	8,212.10
	Commercial Real Estate			3,044.40			7.8			5.2		10.4		3,067.80		39.9		3,107.70
Lease Financing, net			952.5			—			—		—		952.5		—		952.5
Non-U.S.			1,408.40			—			—		—		1,408.40		—		1,408.40
Other			187.9			—			—		—		187.9		—		187.9
Total Commercial			13,747.00			18			18.5		13.5		13,797.00		71.6		13,868.60
Personal
Residential Real Estate			9,702.10			7.9			9		6.4		9,725.40		147.3		9,872.70
Private Client			6,917.80			21.1			7.4		5.2		6,951.50		1.6		6,953.10
Other			25.5			—			—		—		25.5		—		25.5
Total Personal			16,645.40			29			16.4		11.6		16,702.40		148.9		16,851.30
Total Loans and Leases		$	30,392.40		$	47		$	34.9	$	25.1	$	30,499.40	$	220.5	$	30,719.90
											Other Real Estate Owned				10.7
											Total Nonperforming Assets			$	231.2
December 31, 2013
(In Millions)		Current			30-59 Days			60-89 Days		90 Days or		Total		Nonperforming		Total Loans
					Past Due			Past Due		More Past		Performing				and Leases
										Due
Commercial
Commercial and Institutional		$	7,332.30		$	5		$	12.1	$	3.3	$	7,352.70	$	23.1	$	7,375.80
Commercial Real Estate			2,881.10			4.1			14.6		6.8		2,906.60		49.2		2,955.80
Lease Financing, net			975.1			—			—		—		975.1		—		975.1
Non-U.S.			954.7			—			—		—		954.7		—		954.7
Other			358.6			—			—		—		358.6		—		358.6
Total Commercial			12,501.80			9.1			26.7		10.1		12,547.70		72.3		12,620.00
Personal
Residential Real Estate			9,934.40			129.3			15.6		2.9		10,082.20		189.1		10,271.30
Private Client			6,404.20			29.1			7.5		3.4		6,444.20		1.4		6,445.60
Other			48.6			—			—		—		48.6		—		48.6
Total Personal			16,387.20			158.4			23.1		6.3		16,575.00		190.5		16,765.50
Total Loans and Leases		$	28,889.00		$	167.5		$	49.8	$	16.4	$	29,122.70	$	262.8	$	29,385.50
											Other Real Estate Owned				11.9
											Total Nonperforming Assets			$	274.7
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. A loan is also considered to be impaired if its terms have been modified as a concession resulting from the debtor’s financial difficulties, referred to as a troubled debt restructuring (TDR) and discussed in further detail below. Impairment is measured based upon the loan’s market price, the present value of expected future cash flows, discounted at the loan’s effective interest rate, or the fair value of the collateral if the loan is collateral dependent. 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 $250,000) 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 impaired loans is consistent across all classes of loans and leases.
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, non-U.S., lease financing, 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.
The following tables provide information related to impaired loans by segment and class.
		As of September 30, 2014								As of December 31, 2013
(In Millions)		Recorded			Unpaid			Specific		Recorded		Unpaid		Specific
		Investment			Principal			Allowance		Investment		Principal		Allowance
					Balance							Balance
With No Related Specific Allowance
Commercial and Institutional		$	11.6		$	14.6		$	—	$	12.2	$	18.1	$	—
Commercial Real Estate			49.2			54.9			—		46.6		57.1		—
Lease Financing, net			4.2			4.2			—		4.4		4.4		—
Residential Real Estate			170.2			214.5			—		185		227.8		—
Private Client			0.1			0.4			—		0.8		0.8		—
With a Related Specific Allowance
Commercial and Institutional			20.5			20.5			5.1		9.6		12.1		3.6
Commercial Real Estate			12.4			18.4			3.5		26.7		31.5		4.5
Residential Real Estate			1.3			1.5			0.4		8.1		8.7		2.3
Private Client			0.9			0.9			0.5		—		—		—
Total
Commercial			97.9			112.6			8.6		99.5		123.2		8.1
Personal			172.5			217.3			0.9		193.9		237.3		2.3
Total		$	270.4		$	329.9		$	9.5	$	293.4	$	360.5	$	10.4
		Three Months Ended September 30,										Nine Months Ended September 30,
		2014						2013				2014				2013
(In Millions)		Average			Interest			Average		Interest		Average		Interest		Average		Interest
		Recorded			Income			Recorded		Income		Recorded		Income		Recorded		Income
		Investment			Recognized			Investment		Recognized		Investment		Recognized		Investment		Recognized
With No Related Specific Allowance
Commercial and Institutional		$	12.6		$	0.1		$	10.7	$	—	$	11.5	$	0.1	$	11.3	$	0.1
Commercial Real Estate			48.5			0.2			42		0.2		46		0.7		40.6		0.6
Lease Financing, net			4.3			0.1			4.5		0.1		4.3		0.2		4.6		0.2
Residential Real Estate			172			0.8			168.1		0.3		180.8		2.1		155.2		1.4
Private Client			0.3			—			13.3		0.2		0.6		—		12		0.5
With a Related Specific Allowance
Commercial and Institutional			11.9			—			14.1		—		10.6		—		12.5		—
Commercial Real Estate			13.7			—			31.2		—		20.9		—		31.6		—
Residential Real Estate			1.3			—			10		—		4.1		—		9.4		—
Private Client			0.9			—			0.8		—		0.5		—		1.1		—
Total
Commercial			91			0.4			102.5		0.3		93.3		1		100.6		0.9
Personal			174.5			0.8			192.2		0.5		186		2.1		177.7		1.9
Total		$	265.5		$	1.2		$	294.7	$	0.8	$	279.3	$	3.1	$	278.3	$	2.8
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 $2.2 million and $2.8 million, respectively, for the three months ended September 30, 2014, and 2013, and $7.1 million and $8.0 million, respectively, for the nine months ended September 30, 2014, and 2013.
There were $3.5 million and $3.4 million of aggregate undrawn loan commitments and standby letters of credit at September 30, 2014, and December 31, 2013, respectively, issued to borrowers whose loans were classified as nonperforming or impaired.
Troubled Debt Restructurings (TDRs). Included within impaired loans were $58.6 million and $72.7 million of nonperforming TDRs, and $96.9 million and $89.8 million of performing TDRs as of September 30, 2014, and December 31, 2013, respectively. All TDRs are reported as impaired loans in the calendar year of their restructuring. In subsequent years, a TDR may cease being reported as impaired if the loan was modified at a market rate and has performed according to the modified terms for at least six months. A loan that has been modified at a below market rate will return to performing status if it satisfies the six month performance requirement; however, it will remain reported as impaired.
The following tables provide, by segment and class, the number of loans and leases modified in TDRs during the three and nine month periods ended September 30, 2014, and 2013, and the recorded investments and unpaid principal balances as of September 30, 2014, and 2013.
($ In Millions)		Three Months Ended								Nine Months Ended
		September 30, 2014								September 30, 2014
		Number of			Recorded			Unpaid Principal		Number of		Recorded		Unpaid Principal
		Loans and Leases			Investment			Balance		Loans and Leases		Investment		Balance
Commercial
Commercial and Institutional			1		$	0.4		$	0.4		3	$	0.7	$	0.8
Commercial Real Estate			5			2.9			3.4		6		3.5		4.1
Total Commercial			6			3.3			3.8		9		4.2		4.9
Personal
Residential Real Estate			28			18			18.7		96		25.3		27.1
Private Client			—			—			—		3		—		0.3
Total Personal			28			18			18.7		99		25.3		27.4
Total Loans and Leases			34		$	21.3		$	22.5		108	$	29.5	$	32.3
Note: Period end balances reflect all paydowns and charge-offs during the period.
($ In Millions)		Three Months Ended								Nine Months Ended
		September 30, 2013								September 30, 2013
		Number of			Recorded			Unpaid Principal		Number of		Recorded		Unpaid Principal
		Loans and Leases			Investment			Balance		Loans and Leases		Investment		Balance
Commercial
Commercial and Institutional			—		$	—		$	—		7	$	0.5	$	1
Commercial Real Estate			7			22.8			25		11		27.4		31.9
Total Commercial			7			22.8			25		18		27.9		32.9
Personal
Residential Real Estate			38			6.7			11.4		122		51.2		59.8
Private Client			—			—			—		6		12.8		12.8
Total Personal			38			6.7			11.4		128		64		72.6
Total Loans and Leases			45		$	29.5		$	36.4		146	$	91.9	$	105.5
Note: Period end balances reflect all paydowns and charge-offs during the period.
TDR modifications involve interest rate concessions, extensions of term, deferrals of principal, and other modifications. Other modifications typically reflect other nonstandard terms which Northern Trust would not offer in non-troubled situations.
During the three and nine months ended September 30, 2014, the majority of TDR modifications of loans within the commercial real estate, residential real estate, and private client classes were extensions of term and/or other modifications. During the three and nine months ended September 30, 2013, TDR modifications of loans within the commercial and institutional, commercial real estate, and private client classes were primarily deferrals of principal; extensions of term, and other modifications, and modifications of loans within the residential real estate class were primarily deferrals of principal, interest rate concessions, extensions of term, and other modifications.
There were no loans or leases modified in TDRs in the 12 months ended June 30, 2014 or 2013, which subsequently became nonperforming during the three or nine months ended September 30, 2014 or 2013 respectively.
All loans and leases modified in troubled debt restructurings 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.

Allowance_for_Credit_Losses

Allowance for Credit Losses	9 Months Ended
	Sep. 30, 2014
Allowance for Credit Losses	'
	6. 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.
	In establishing the inherent portion of the allowance for credit losses, Northern Trust’s Loan Loss Allowance Committee assesses a common set of qualitative factors applicable to both the commercial and personal loan segments. The risk characteristics underlying these qualitative factors, and management’s assessments as to the relative importance of a qualitative factor, can vary between loan segments and between classes within loan segments. Factors evaluated include those related to external matters, such as economic conditions and changes in collateral value, and those related to internal matters, such as changes in asset quality metrics and loan review activities. In addition to the factors noted above, risk characteristics such as portfolio delinquencies, percentage of portfolio on the watch list and on nonperforming status, and average borrower ratings are assessed in the determination of the inherent allowance.
	Loan-to-value levels are considered for collateral-secured loans and leases in both the personal and commercial segments. Borrower debt service coverage is evaluated in the personal segment, and cash flow coverage is analyzed in the commercial segment.
	Similar risk characteristics by type of exposure are analyzed when determining the allowance for undrawn commitments and standby letters of credit. These qualitative factors, together with historical loss rates, serve as the basis for the allowance for credit losses.
	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 tables provide information regarding changes in the total allowance for credit losses by segment during the three and nine months ended September 30, 2014, and 2013.
		Three Months Ended September 30,
		2014									2013
	(In Millions)	Commercial			Personal			Total			Commercial			Personal			Total
	Balance at Beginning of Period	$	168.7		$	134.8		$	303.5		$	184.1		$	136.6		$	320.7
	Charge-Offs		(2.5	)		(6.1	)		(8.6	)		(1.7	)		(9.9	)		(11.6	)
	Recoveries		1.9			1.5			3.4			1.7			1.6			3.3
	Net (Charge-Offs) Recoveries		(0.6	)		(4.6	)		(5.2	)		—			(8.3	)		(8.3	)
	Provision for Credit Losses		1			(1.0	)		—			(4.6	)		9.6			5
	Effect of Foreign Exchange Rates		—			—			—			0.1			—			0.1
	Balance at End of Period	$	169.1		$	129.2		$	298.3		$	179.6		$	137.9		$	317.5
		Nine Months Ended September 30,
		2014									2013
	(In Millions)	Commercial			Personal			Total			Commercial			Personal			Total
	Balance at Beginning of Period	$	168		$	139.9		$	307.9		$	194.2		$	133.4		$	327.6
	Charge-Offs		(8.8	)		(19.1	)		(27.9	)		(6.9	)		(32.9	)		(39.8	)
	Recoveries		10.7			4.6			15.3			8.1			6.6			14.7
	Net (Charge-Offs) Recoveries		1.9			(14.5	)		(12.6	)		1.2			(26.3	)		(25.1	)
	Provision for Credit Losses		(0.8	)		3.8			3			(15.8	)		30.8			15
	Effect of Foreign Exchange Rates		—			—			—			—			—			—
	Balance at End of Period	$	169.1		$	129.2		$	298.3		$	179.6		$	137.9		$	317.5
	The following table provides information regarding the balances of the recorded investments in loans and leases and the allowance for credit losses by segment as of September 30, 2014, and December 31, 2013.
		September 30, 2014									December 31, 2013
	(In Millions)	Commercial			Personal			Total			Commercial			Personal			Total
	Loans and Leases
	Specifically Evaluated for Impairment	$	97.9		$	172.5		$	270.4		$	99.5		$	193.9		$	293.4
	Evaluated for Inherent Impairment		13,770.70			16,678.80			30,449.50			12,520.50			16,571.60			29,092.10
	Total Loans and Leases		13,868.60			16,851.30			30,719.90			12,620.00			16,765.50			29,385.50
	Allowance for Loans and Leases
	Specifically Evaluated for Impairment		8.6			0.9			9.5			8.1			2.3			10.4
	Evaluated for Inherent Impairment		134.5			125.4			259.9			132.8			134.9			267.7
	Allowance Assigned to Loans and Leases		143.1			126.3			269.4			140.9			137.2			278.1
	Allowance for Unfunded Exposures
	Commitments and Standby Letters of Credit		26			2.9			28.9			27.1			2.7			29.8
	Total Allowance for Credit Losses	$	169.1		$	129.2		$	298.3		$	168		$	139.9		$	307.9

Pledged_Assets

Pledged Assets	9 Months Ended
	Sep. 30, 2014
Pledged Assets	'
	7. Pledged Assets — Certain of Northern Trust’s subsidiaries, as required or permitted by law, pledge assets to secure public and trust deposits; repurchase agreements; Federal Home Loan Bank borrowings; and for other purposes, including support for securities settlement, primarily related to client activities, and for potential Federal Reserve Bank discount window borrowings. At September 30, 2014, securities and loans totaling $32.4 billion ($23.5 billion of government sponsored agency and other securities, $137.0 million of obligations of states and political subdivisions, and $8.8 billion of loans) were pledged. This compares to $32.4 billion ($22.6 billion of government sponsored agency and other securities, $222.7 million of obligations of states and political subdivisions, and $9.6 billion of loans) at December 31, 2013. Collateral required for these purposes totaled $3.5 billion and $5.0 billion at September 30, 2014, and December 31, 2013, respectively. Included in the total pledged assets at September 30, 2014, and December 31, 2013 were available for sale securities with a total fair value of $865.5 million and $915.3 million, respectively, which were pledged as collateral for agreements to repurchase securities sold transactions. The secured parties to these transactions have the right to repledge or sell these securities.
	Northern Trust is not permitted, by contract or custom, to repledge or sell collateral from agreements to resell securities purchased transactions. The total fair value of accepted collateral as of September 30, 2014, and December 31, 2013, was $1.0 billion and $500.0 million, respectively. There was no repledged or sold collateral at September 30, 2014, or December 31, 2013. Deposits maintained to meet Federal Reserve Bank reserve requirements averaged $1.3 billion for the three and nine months ended September 30, 2014, and $0.9 billion for both the three and nine months ended September 30, 2013.

Goodwill_and_Other_Intangibles

Goodwill and Other Intangibles	9 Months Ended
	Sep. 30, 2014
Goodwill and Other Intangibles	'
	8. Goodwill and Other Intangibles — The carrying amounts of goodwill, reflecting the effect of foreign exchange rates on non-U.S. dollar denominated balances, by business unit at September 30, 2014, and December 31, 2013, were as follows:
	(In Millions)	September 30,		December 31,
		2014		2013
	Corporate & Institutional Services	$	466.6	$	469.2
	Wealth Management		71.5		71.5
	Total Goodwill	$	538.1	$	540.7
	The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of September 30, 2014, and December 31, 2013, were as follows:
	(In Millions)	September 30,		December 31,
		2014		2013
	Gross Carrying Amount	$	193.4	$	198.2
	Less: Accumulated Amortization		127.6		115.2
	Net Book Value	$	65.8	$	83
	Other intangible assets consist primarily of the value of acquired client relationships and are included within other assets on the consolidated balance sheet. Amortization expense related to other intangible assets totaled $4.8 million and $14.7 million for the three and nine months ended September 30, 2014, respectively, and $5.2 million and $15.5 million for the three and nine months ended September 30, 2013, respectively. Amortization for the remainder of 2014 and for the years 2015, 2016, 2017, and 2018 is estimated to be $4.8 million, $11.5 million, $9.0 million, $8.9 million and $8.2 million, respectively.

Issuance_of_Preferred_Stock

Issuance of Preferred Stock	9 Months Ended
	Sep. 30, 2014
Issuance of Preferred Stock	'
	9. Issuance of Preferred Stock — Northern Trust is authorized to issue 10 million shares of preferred stock, without par value.
	On August 5, 2014, Northern Trust issued 16 million depositary shares, each representing 1/1000 ownership interest in a share of Northern Trust’s Series C Non-Cumulative Perpetual Preferred Stock (“Series C Preferred Stock”), without par value, with a liquidation preference of $25,000 ($25 per depositary share). The aggregate proceeds from the public offering of the depositary shares, net of underwriting discounts, commissions and offering expenses, were $388.5 million.
	Dividends on the Series C Preferred Stock, which are not mandatory, will accrue and be 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, commencing on January 1, 2015, at a rate per annum equal to 5.85%. On October 21, 2014, Northern Trust declared a cash dividend of $593.125 per share of Series C Preferred Stock payable on January 1, 2015 to stockholders of record on December 15, 2014.
	The Series C Preferred Stock has no maturity date. Shares of the Series C Preferred Stock rank senior to Northern Trust’s common stock, and will rank at least equally with any other series of preferred stock we may issue (except for any senior series that may be issued with the requisite consent of the holders of the Series C Preferred Stock) and all other parity stock, with respect to the payment of dividends and distributions upon liquidation, dissolution or winding up.
	The Series C Preferred Stock is redeemable at Northern Trust’s option, in whole or in part, on any dividend payment date on or after October 1, 2019. The Series C Preferred stock is redeemable at the Company’s option, in whole, but not in part, prior to October 1, 2019 within 90 days of a regulatory capital treatment event, as described in the Series C Preferred Stock Certificate of Designation.

Business_Units

Business Units	9 Months Ended
	Sep. 30, 2014
Business Units	'
	10. Business Units — The following tables show the earnings contributions of Northern Trust’s business units for the three and nine month periods ended September 30, 2014, and 2013.
	Three Months Ended		Corporate &						Wealth						Treasury and						Total
	September 30,		Institutional Services						Management						Other						Consolidated
	($ In Millions)		2014			2013			2014			2013			2014			2013			2014			2013
	Noninterest Income
	Trust, Investment and Other Servicing Fees		$	399.9		$	359.8		$	318.3		$	288.2		$	—		$	—		$	718.2		$	648
	Foreign Exchange Trading Income			44.4			61.8			2			1			—			—			46.4			62.8
	Other Noninterest Income			42.8			44.3			20.9			54.3			1.3			0.8			65			99.4
	Net Interest Income*			78.4			70.1			131.2			136.3			46.6			38.4			256.2			244.8
	Revenue*			565.5			536			472.4			479.8			47.9			39.2			1,085.80			1,055.00
	Provision for Credit Losses			0.9			0.4			(0.9	)		4.6			—			—			—			5
	Noninterest Expense			429.6			412			312.1			297.3			33			31.4			774.7			740.7
	Income before Income Taxes*			135			123.6			161.2			177.9			14.9			7.8			311.1			309.3
	Provision (Benefit) for Income Taxes*			42.4			38.8			60.7			67			3.5			(3.0	)		106.6			102.8
	Net Income		$	92.6		$	84.8		$	100.5		$	110.9		$	11.4		$	10.8		$	204.5		$	206.5
	Percentage of Consolidated Net Income			45	%		41	%		49	%		54	%		6	%		5	%		100	%		100	%
	Average Assets		$	59,907.10		$	53,653.50		$	26,061.80		$	22,923.60		$	19,275.80		$	18,635.40		$	105,244.70		$	95,212.50
	*	Stated on a fully taxable equivalent basis (FTE). Total consolidated includes FTE adjustments of $6.9 million for 2014 and $7.8 million for 2013.
	Nine Months Ended		Corporate &						Wealth						Treasury and						Total
	September 30,		Institutional Services						Management						Other						Consolidated
	($ In Millions)		2014			2013			2014			2013			2014			2013			2014			2013
	Noninterest Income
	Trust, Investment and Other Servicing Fees		$	1,174.50		$	1,072.70		$	930.1		$	863.3		$	—		$	—		$	2,104.60		$	1,936.00
	Foreign Exchange Trading Income			143.2			189.8			6.2			3.8			—			—			149.4			193.6
	Other Noninterest Income			134.3			130.1			66.7			95.8			4.5			5.4			205.5			231.3
	Net Interest Income*			228.8			200.2			398.8			425.3			136.4			81			764			706.5
	Revenue*			1,680.80			1,592.80			1,401.80			1,388.20			140.9			86.4			3,223.50			3,067.40
	Provision for Credit Losses			4.5			(1.1	)		(1.5	)		16.1			—			—			3			15
	Noninterest Expense			1,299.50			1,206.70			960.3			900.9			93.9			91.7			2,353.70			2,199.30
	Income (loss) before Income Taxes*			376.8			387.2			443			471.2			47			(5.3	)		866.8			853.1
	Provision (Benefit) for Income Taxes*			113.3			123			166.9			177.8			18.8			(9.3	)		299			291.5
	Net Income		$	263.5		$	264.2		$	276.1		$	293.4		$	28.2		$	4		$	567.8		$	561.6
	Percentage of Consolidated Net Income			46	%		47	%		49	%		52	%		5	%		1	%		100	%		100	%
	Average Assets		$	59,061.30		$	52,323.80		$	23,613.40		$	22,863.10		$	20,281.10		$	18,036.60		$	102,955.80		$	93,223.50
	*	Stated on a fully taxable equivalent basis (FTE). Total consolidated includes FTE adjustments of $22.4 million for 2014 and $23.3 million for 2013.
	Further discussion of business unit results is provided within the “Business Unit Reporting” section of Management’s Discussion and Analysis of Financial Condition and Results of Operations.

Accumulated_Other_Comprehensiv

Accumulated Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss)	'
	11. Accumulated Other Comprehensive Income (Loss) — The following tables summarize the components of accumulated other comprehensive income (loss) at September 30, 2014, and 2013, and changes during the three and nine month periods then ended.
	(In Millions)	Balance at				Net Change				Balance at
		December 31,								September 30,
		2013								2014
	Net Unrealized Gains (Losses) on Securities Available for Sale	$	6			$	32.3			$	38.3
	Net Unrealized Gains (Losses) on Cash Flow Hedges		2.9				(6.4	)			(3.5	)
	Net Foreign Currency Adjustments		7.1				(10.5	)			(3.4	)
	Net Pension and Other Postretirement Benefit Adjustments		(260.3	)			10.5				(249.8	)
	Total	$	(244.3	)		$	25.9			$	(218.4	)
	(In Millions)	Balance at				Net Change				Balance at
		December 31,								September 30,
		2012								2013
	Net Unrealized Gains (Losses) on Securities Available for Sale	$	101			$	(74.4	)		$	26.6
	Net Unrealized Gains (Losses) on Cash Flow Hedges		(1.4	)			1.2				(0.2	)
	Net Foreign Currency Adjustments		10.5				(2.8	)			7.7
	Net Pension and Other Postretirement Benefit Adjustments		(393.1	)			21.1				(372.0	)
	Total	$	(283.0	)		$	(54.9	)		$	(337.9	)
		Three Months Ended September 30,
		2014											2013
	(In Millions)	Before Tax				Tax Effect				After Tax			Before Tax			Tax Effect			After Tax
	Unrealized Gains (Losses) on Securities Available for Sale
	Noncredit-Related Unrealized Gains (Losses) on Securities OTTI	$	5.5			$	(2.1	)		$	3.4		$	—		$	—		$	—
	Other Unrealized Gains (Losses) on Securities Available for Sale		(14.2	)			5.4				(8.8	)		7.3			(2.8	)		4.5
	Reclassification Adjustment for (Gains) Losses Included in Net Income		(0.3	)			—				(0.3	)		2.1			(0.8	)		1.3
	Net Change		(9.0	)			3.3				(5.7	)		9.4			(3.6	)		5.8
	Unrealized Gains (Losses) on Cash Flow Hedges
	Unrealized Gains (Losses) on Cash Flow Hedges		(7.6	)			2.5				(5.1	)		5.3			(1.7	)		3.6
	Reclassification Adjustment for (Gains) Losses Included in Net Income		(3.7	)			1.4				(2.3	)		1.1			(0.4	)		0.7
	Net Change		(11.3	)			3.9				(7.4	)		6.4			(2.1	)		4.3
	Foreign Currency Adjustments
	Foreign Currency Translation Adjustments		(77.1	)			6.6				(70.5	)		55			(4.0	)		51
	Long-Term Intra-Entity Foreign Currency Transaction Losses		(7.4	)			—				(7.4	)		—			—			—
	Net Investment Hedge Gains (Losses)		119.9				(45.6	)			74.3			(88.8	)		33.4			(55.4	)
	Reclassification Adjustment for (Gains) Losses Included in Net Income		—				—				—			—			—			—
	Net Change		35.4				(39.0	)			(3.6	)		(33.8	)		29.4			(4.4	)
	Pension and Other Postretirement Benefit Adjustments
	Net Actuarial Gain (Loss)		—				—				—			—			—			—
	Reclassification Adjustment for (Gains) Losses Included in Net Income		6.5				(3.0	)			3.5			11.3			(4.2	)		7.1
	Net Change	$	6.5			$	(3.0	)		$	3.5		$	11.3		$	(4.2	)	$	7.1
		Nine Months Ended September 30,
		2014											2013
	(In Millions)	Before Tax				Tax Effect				After Tax			Before Tax			Tax Effect			After Tax
	Unrealized Gains (Losses) on Securities Available for Sale
	Noncredit-Related Unrealized Gains (Losses) on Securities OTTI	$	3.7			$	(1.4	)		$	2.3		$	2.1		$	(0.8	)	$	1.3
	Other Unrealized Gains (Losses) on Securities Available for Sale		48.8				(18.2	)			30.6			(123.2	)		46.3			(76.9	)
	Reclassification Adjustment for (Gains) Losses Included in Net Income		(0.6	)			—				(0.6	)		1.9			(0.7	)		1.2
	Net Change		51.9				(19.6	)			32.3			(119.2	)		44.8			(74.4	)
	Unrealized Gains (Losses) on Cash Flow Hedges
	Unrealized Gains (Losses) on Cash Flow Hedges		(6.5	)			2.2				(4.3	)		(4.0	)		1.6			(2.4	)
	Reclassification Adjustment for (Gains) Losses Included in Net Income		(3.3	)			1.2				(2.1	)		5.7			(2.1	)		3.6
	Net Change		(9.8	)			3.4				(6.4	)		1.7			(0.5	)		1.2
	Foreign Currency Adjustments
	Foreign Currency Translation Adjustments		(57.2	)			6				(51.2	)		5.3			(2.3	)		3
	Long-Term Intra-Entity Foreign Currency Transaction Losses		(9.0	)			—				(9.0	)		—			—			—
	Net Investment Hedge Gains (Losses)		79.7				(30.0	)			49.7			(9.3	)		3.5			(5.8	)
	Reclassification Adjustment for (Gains) Losses Included in Net Income		—				—				—			—			—			—
	Net Change		13.5				(24.0	)			(10.5	)		(4.0	)		1.2			(2.8	)
	Pension and Other Postretirement Benefit Adjustments
	Net Actuarial Gain (Loss)		—				—				—			—			—			—
	Reclassification Adjustment for (Gains) Losses Included in Net Income		19				(8.5	)			10.5			33.7			(12.6	)		21.1
	Net Change	$	19			$	(8.5	)		$	10.5		$	33.7		$	(12.6	)	$	21.1
	The following table provides the location and before-tax amounts of reclassifications out of accumulated other comprehensive income (loss) during the three and nine months ended September 30, 2014.
	(In Millions)	Location of		Amount of Reclassification
Reclassification Adjustments		Adjustments Recognized
Recognized in Income		in Income
			Three Months Ended				Nine Months Ended
			30-Sep-14
Securities Available for Sale
Realized (Gains) Losses on Securities Available for Sale	Investment Security Gains (Losses), net		$	(0.3	)		$	(0.6	)
Realized (Gains) Losses on Cash Flow Hedges
Foreign Exchange Contracts	Other Operating Income/Expense			(3.7	)			(3.3	)
Pension and Other Postretirement Benefit Adjustments
Amortization of Net Actuarial (Gain) Loss	Employee Benefits			(0.3	)			(1.1	)
Amortization of Prior Service Cost	Employee Benefits			6.8				20.1
Gross Reclassification Adjustment			$	6.5			$	19

Net_Income_Per_Common_Share_Co

Net Income Per Common Share Computations	9 Months Ended
	Sep. 30, 2014
Net Income Per Common Share Computations	'
	12. Net Income Per Common Share Computations — The computations of net income per common share are presented in the following table.
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	($ In Millions Except Per Common Share Information)	2014		2013		2014		2013
	Basic Net Income Per Common Share
	Average Number of Common Shares Outstanding		235,701,076		239,930,074		236,301,789		239,614,868
	Net Income	$	204.5	$	206.5	$	567.8	$	561.6
	Less: Dividends on Preferred Stock		—		—		—		—
	Net Income Applicable to Common Stock		204.5		206.5		567.8		561.6
	Less: Earnings Allocated to Participating Securities		3.5		3.5		9.5		9.1
	Earnings Allocated to Common Shares Outstanding		201		203		558.3		552.5
	Basic Net Income Per Common Share	$	0.85	$	0.85	$	2.36	$	2.31
	Diluted Net Income Per Common Share
	Average Number of Common Shares Outstanding		235,701,076		239,930,074		236,301,789		239,614,868
	Plus: Dilutive Effect of Share-based Compensation		2,036,053		1,400,578		1,873,907		1,242,829
	Average Common and Potential Common Shares		237,737,129		241,330,652		238,175,696		240,857,697
	Earnings Allocated to Common and Potential
	Common Shares	$	201	$	203	$	558.4	$	552.5
	Diluted Net Income Per Common Share		0.84		0.84		2.34		2.29
	Note: Common stock equivalents totaling 1,071,654 and 1,671,849 for the three and nine months ended September 30, 2014, respectively, and 3,371,680 and 3,783,018 for the three and nine months ended September 30, 2013, respectively, were not included in the computation of diluted net income per common share because their inclusion would have been antidilutive.

Net_Interest_Income

Net Interest Income	9 Months Ended
	Sep. 30, 2014
Net Interest Income	'
	13. Net Interest Income — The components of net interest income were as follows:
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	(In Millions)	2014		2013		2014		2013
	Interest Income
	Loans and Leases	$	184.8	$	185.4	$	553.5	$	558.5
	Securities — Taxable		65.1		60.9		198		167.6
	— Non-Taxable		1.6		2.7		5.7		9
	Interest-Bearing Deposits with Banks		30.9		36.3		96.6		105.8
	Federal Reserve Deposits and Other		11.4		5.8		29.2		12.2
	Total Interest Income		293.8		291.1		883		853.1
	Interest Expense
	Deposits		21.6		25.8		64.1		79.9
	Federal Funds Purchased		0.5		0.4		1.1		1
	Securities Sold Under Agreements to Repurchase		0.1		0.1		0.3		0.3
	Other Borrowings		0.9		0.8		2.4		2.5
	Senior Notes		11.6		18.4		42.8		56.9
	Long-Term Debt		9.2		8		29		27.5
	Floating Rate Capital Debt		0.6		0.6		1.7		1.8
	Total Interest Expense		44.5		54.1		141.4		169.9
	Net Interest Income	$	249.3	$	237	$	741.6	$	683.2

Income_Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2014
Income Taxes	'
	14. Income Taxes – Income tax expense for the three and nine months ended September 30, 2014, of $99.7 million and $276.6 million, respectively, was recorded, each representing an effective tax rate of 32.8%. The prior year three and nine month provisions for income taxes were $95.0 million and $268.2 million, representing effective tax rates of 31.5% and 32.3%, respectively.

Pension_and_Other_Postretireme

Pension and Other Postretirement Plans	9 Months Ended
	Sep. 30, 2014
Pension and Other Postretirement Plans	'
	15. Pension and Other Postretirement Plans — The following tables set 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 other postretirement plan for the three and nine months ended September 30, 2014, and 2013.
	Net Periodic Pension Expense	Three Months Ended						Nine Months Ended
	U.S. Plan	September 30,						September 30,
	(In Millions)	2014			2013			2014			2013
	Service Cost	$	8.2		$	7.5		$	24.6		$	22.7
	Interest Cost		11.1			10.5			33.3			31.6
	Expected Return on Plan Assets		(24.4	)		(23.1	)		(73.3	)		(69.2	)
	Amortization
	Net Actuarial Loss		(0.1	)		10.3			(0.3	)		30.9
	Prior Service Cost		5.4			(0.1	)		16.1			(0.3	)
	Net Periodic Pension Expense	$	0.2		$	5.1		$	0.4		$	15.7
	Net Periodic Pension Expense (Benefit)	Three Months Ended						Nine Months Ended
	Non U.S. Plans	September 30,						September 30,
	(In Millions)	2014			2013			2014			2013
	Interest Cost	$	1.8		$	1.6		$	5.3		$	4.9
	Expected Return on Plan Assets		(1.8	)		(1.5	)		(5.3	)		(4.6	)
	Net Actuarial Loss Amortization		(0.4	)		0.2			(1.2	)		0.7
	Net Periodic Pension Expense (Benefit)	$	(0.4	)	$	0.3		$	(1.2	)	$	1
	Net Periodic Pension Expense	Three Months Ended						Nine Months Ended
	Supplemental Plan	September 30,						September 30,
	(In Millions)	2014			2013			2014			2013
	Service Cost	$	0.8		$	0.4		$	2.3		$	1.2
	Interest Cost		1.2			1.1			3.6			3.3
	Amortization
	Net Actuarial Loss		0.2			1.7			0.4			5.1
	Prior Service Cost		1.5			0.2			4.4			0.4
	Net Periodic Pension Expense	$	3.7		$	3.4		$	10.7		$	10
	Net Periodic Postretirement Expense (Benefit)	Three Months Ended						Nine Months Ended
	Other Postretirement Plan	September 30,						September 30,
	(In Millions)	2014			2013			2014			2013
	Service Cost	$	—		$	—		$	0.1		$	0.1
	Interest Cost		0.4			0.3			1.1			0.9
	Amortization
	Net Actuarial Gain		—			(0.3	)		—			(0.9	)
	Prior Service Cost		(0.1	)		(0.7	)		(0.4	)		(2.2	)
	Net Periodic Postretirement Expense (Benefit)	$	0.3		$	(0.7	)	$	0.8		$	(2.1	)

ShareBased_Compensation_Plans

Share-Based Compensation Plans	9 Months Ended
	Sep. 30, 2014
Share-Based Compensation Plans	'
	16. Share-Based Compensation Plans — The Northern Trust Corporation 2012 Stock Plan provides for the grant of nonqualified stock options, incentive stock options, stock appreciation rights, stock awards, restricted stock units, and performance stock units.
	Total compensation expense for share-based payment arrangements and the associated tax impacts were as follows for the three and nine months ended September 30, 2014, and 2013.
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	(In Millions)	2014		2013		2014		2013
	Restricted Stock Unit Awards	$	12.7	$	12.1	$	41.7	$	36.4
	Stock Options		2.2		3.7		10.7		14.9
	Performance Stock Units		3.1		2.1		8.9		5.4
	Total Share-Based Compensation Expense		18		17.9		61.3		56.7
	Tax Benefits Recognized	$	6.8	$	6.8	$	23	$	21.3

Variable_Interest_Entities

Variable Interest Entities	9 Months Ended
	Sep. 30, 2014
Variable Interest Entities	'
	17. Variable Interest Entities — Variable Interest Entities (VIEs) are defined within GAAP as entities that 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. 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 these VIEs given it lacks the power to direct the activities that most significantly impact the economic performance of the VIEs.
	Northern Trust’s maximum exposure to loss as a result of its involvement with the leveraged lease trust VIEs is limited to the carrying amounts of its leveraged lease investments. As of September 30, 2014, and December 31, 2013, the carrying amounts of these investments, which are included in loans and leases in the consolidated balance sheet, were $579.1 million and $671.2 million, respectively. Northern Trust’s funding requirements relative to the VIEs are limited to its invested capital. Northern Trust has no other liquidity arrangements or obligations to purchase assets of the 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. These community development projects are formed as limited partnerships and LLCs in which Northern Trust invests as a limited partner/investor member through equity contributions. The economic performance of the community development projects, which are VIEs, is subject to the performance of their underlying investments 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 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 VIEs.
	Northern Trust’s maximum exposure to loss as a result of its involvement with community development projects is limited to the carrying amount of its investments, including any unfunded commitments. As of September 30, 2014, and December 31, 2013, the carrying amount of investments in community development projects that generate tax credits, included in other assets in the consolidated balance sheet, totaled $224.1 million and $222.3 million, respectively. As of September 30, 2014, and December 31, 2013, liabilities related to unfunded commitments on investments in tax credit community development projects, included in other liabilities in the consolidated balance sheet, totaled $27.4 million and $19.8 million, respectively. Northern Trust’s funding requirements are limited to its invested capital and unfunded 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.
	Affordable housing tax credits and other tax benefits attributable to community development projects totaled $14.5 million and $43.2 million for the three and nine months ended September 30, 2014.
	Trust Preferred Securities. In 1997, Northern Trust issued Floating Rate Capital Securities, Series A and Series B, through NTC Capital I and NTC Capital II, respectively, statutory business trusts wholly-owned by the Corporation. The sole assets of the trusts are Subordinated Debentures of the Corporation that have the same interest rates and maturity dates as the corresponding distribution rates and redemption dates of the Floating Rate Capital Securities. NTC Capital I and NTC Capital II are considered VIEs; however, as the sole asset of each trust is a receivable from the Corporation and proceeds to the Corporation from the receivable exceed the Corporation’s investment in the VIEs’ equity shares, the Corporation is not permitted to consolidate the trusts, even though the Corporation owns all of the voting equity shares of the trusts, has fully guaranteed the trusts’ obligations, and has the right to redeem the preferred securities in certain circumstances. Northern Trust recognizes the subordinated debentures on its consolidated balance sheet as long-term liabilities.
	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, the Corporation 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.

Contingent_Liabilities

Contingent Liabilities	9 Months Ended
	Sep. 30, 2014
Contingent Liabilities	'
	18. Contingent Liabilities — Standby Letters of Credit and Indemnifications. 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 $4.3 billion at September 30, 2014, and $4.5 billion at December 31, 2013.
	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 Senior Credit 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 subject to indemnification was $99.9 billion at September 30, 2014, and $82.7 billion at December 31, 2013. 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 at September 30, 2014, or December 31, 2013, related to these indemnifications.
	Legal Proceedings. In the normal course of business, the Corporation and its subsidiaries are routinely defendants in or parties to a number of pending and threatened legal actions, including, but not limited to, actions brought on behalf of various claimants or classes of claimants, regulatory matters, employment matters, and challenges from tax authorities regarding the amount of taxes due. In certain of these actions and proceedings, claims for substantial monetary damages or adjustments to recorded tax liabilities are asserted.
	Based on current knowledge, after consultation with legal counsel and after taking into account current accruals, management does not believe that losses, if any, arising from pending litigation or threatened legal actions or regulatory matters 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”. Thus, references to the upper end of the range of reasonably possible loss for matters in which the Corporation is able to estimate a range of reasonably possible loss mean the upper end of the range of loss for matters for which the Corporation believes the risk of loss is more than remote but less than likely.
	For the reasons set out in this paragraph, the outcome of some matters is inherently difficult to predict and/or the range of loss cannot be reasonably estimated. This may be the case in 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 the 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 September 30, 2014, the Corporation has estimated the upper end of the range of reasonably possible losses for these matters to be approximately $130 million in the aggregate. This aggregate amount 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 will vary significantly from the current estimate.
	In certain other pending matters, there may be a range of reasonably possible losses (including reasonably possible losses in excess of amounts accrued) that cannot be reasonably estimated for the reasons described above. Such matters are not included in the estimate of reasonably possible losses identified above.
	As previously disclosed, a number of participants in our securities lending program, which is associated with the Corporation’s asset servicing business, have commenced either individual lawsuits or purported class actions in which they claim, among other things, that we failed to exercise prudence in the investment management of the collateral received from the borrowers of the securities, resulting in losses that they seek to recover. The cases assert various contractual, statutory and common law claims, including claims for breach of fiduciary duty under common law and under the Employee Retirement Income Security Act (ERISA). In the fourth quarter of 2013, Northern Trust recorded a $19.2 million pre-tax charge in connection with an agreement to resolve claims related to two of these lawsuits. The settlement is not final as it requires further documentation, signed agreements and court approval. Other lawsuits related to securities lending are not part of the proposed settlement, and remain pending.
	In April 2014 Northern Trust received a subpoena from the U.S. Securities and Exchange Commission (SEC) seeking documents related to Northern Trust’s securities lending activities. Northern Trust is cooperating with the SEC in this investigation.
	Visa Membership. Northern Trust, as a member of Visa U.S.A. Inc. and in connection with the 2007 initial public offering of Visa Inc. (Visa), received shares of restricted stock in Visa. As of September 30, 2014, the Visa shares held by Northern Trust are recorded at their original cost basis of zero and have restrictions as to their sale or transfer.
	Northern Trust is obligated to indemnify Visa for losses resulting from certain indemnified litigation relating to interchange fees and has been required to recognize, at its estimated fair value in accordance with GAAP, a guarantee liability arising from such litigation that has not yet settled. During 2007, Northern Trust recorded liabilities relating to Visa indemnified litigation. Subsequently, Visa established an escrow account to cover the settlements of, or judgments in, indemnified litigation. The fundings by Visa of its escrow account resulted in reductions of Northern Trust’s indemnification liability. Northern Trust’s indemnification liability was fully eliminated as of December 31, 2011. On October 19, 2012, Visa signed a settlement agreement with plaintiff representatives for binding settlement of the indemnified litigation. On January 14, 2014, the trial court entered a final judgment order approving the settlement with the class plaintiffs, which is subject to appeal. A number of objectors have appealed from that order and more than 30 opt-out cases have been filed by merchants in various federal district courts.
	While the ultimate resolution of the indemnified litigation and the timing for removal of selling restrictions on the Visa shares are highly uncertain, Northern Trust anticipates that the value of its Visa shares will be adequate to offset any remaining indemnification obligations related to Visa litigation.
	Contingent Purchase Consideration. In connection with an acquisition consummated in 2011, contingent consideration was recorded relating to certain performance-related purchase price adjustments. The fair value of the contingent consideration was $55.4 million at December 31, 2013. In April 2014 Northern Trust made a payment of $55.3 million to extinguish the contingent consideration liability at the value agreed by the parties.

Derivative_Financial_Instrumen

Derivative Financial Instruments	9 Months Ended
	Sep. 30, 2014
Derivative Financial Instruments	'
	19. 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, and credit default swap contracts.
	Northern Trust’s primary risks associated with these instruments is the possibility that interest rates, foreign exchange rates, or credit spreads could change in an unanticipated manner, resulting in higher costs or a loss in the underlying value of the instrument. These risks are mitigated by establishing limits, monitoring the level of actual positions taken against such established limits, and monitoring the level of any interest rate sensitivity gaps created by such positions. When establishing position limits, market liquidity and volatility, as well as experience in each market, are taken into account.
	Credit risk associated with derivative instruments relates to the failure of the counterparty to pay based on the contractual terms of the agreement, and is generally limited to the unrealized fair value gains on these instruments, net of any cash 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, or credit spreads 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.
	All derivative financial instruments, whether designated as hedges or not, are recorded in the consolidated balance sheet at fair value within other assets or other liabilities. As noted in the discussions below, the manner in which changes in the fair value of a derivative is accounted for in the consolidated statement of income depends on whether the contract has been designated as a hedge and qualifies for hedge accounting under GAAP. 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. Derivative assets and liabilities recorded in the consolidated balance sheet were each reduced by $2.2 billion as of September 30, 2014, and by $1.2 billion as of December 31, 2013, as a result of master netting arrangements and similar agreements in place. Derivative assets and liabilities recorded at September 30, 2014, also reflect reductions of $207.4 million and $601.3 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties, respectively.
	This compares with reductions of derivative assets and liabilities of $210.7 million and $767.7 million, respectively, at December 31, 2013. Additional cash collateral received from and deposited with derivative counterparties totaling $42.0 million and $51.3 million, respectively, as of September 30, 2014, and $36.4 million and $39.3 million, respectively, as of December 31, 2013, were not offset against derivative assets and liabilities on the consolidated balance sheet as the amounts exceeded the net derivative positions with those counterparties. Northern Trust centrally clears interest rate derivative instruments that are addressed under Title VII of the Dodd-Frank Wall Street Reform and Consumer Protection Act. Securities posted as collateral for these transactions totaled $27.5 million and $27.6 million at September 30, 2014, and December 31, 2013, respectively, are not offset against derivative assets and liabilities on the consolidated balance sheet, and the counterparty receiving the securities as collateral does not have the right to repledge or sell the securities.
	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 $113.4 million and $257.3 million at September 30, 2014, and December 31, 2013, respectively. Cash collateral amounts deposited with derivative counterparties on those dates included $41.5 million and $197.0 million, respectively, posted against these liabilities, resulting in a net maximum amount of termination payments that could have been required at September 30, 2014, and December 31, 2013 of $71.9 million and $60.3 million, respectively. Accelerated settlement of these liabilities would not have a material effect on the consolidated financial position or liquidity of Northern Trust.
	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 purposes and risk management. 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, 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 on behalf of 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.
	Credit default swap contracts are agreements to transfer credit default risk from one party to another in exchange for a fee. Northern Trust enters into credit default swaps with outside counterparties where the counterparty agrees to assume the underlying credit exposure of a specific Northern Trust commercial loan or loan commitment.
	Client-Related and Trading Derivative Instruments. Approximately 97% of Northern Trust’s derivatives outstanding at September 30, 2014, and December 31, 2013, measured on a notional value basis, relate to client-related and trading activities. 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.
	The following table shows the notional and fair values of client-related and trading derivative financial instruments. Notional amounts of derivative financial instruments do not represent credit risk, and are not recorded in the consolidated balance sheet. 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, which is significantly less than the notional amount.
		September 30, 2014												December 31, 2013
		Notional				Fair Value								Notional				Fair Value
	(In Millions)	Value				Asset				Liability				Value				Asset			Liability
	Foreign Exchange Contracts	$	270,022.40			$	4,132.80			$	4,125.50			$	243,135.00			$	2,844.70		$	2,846.20
	Interest Rate Contracts		5,048.90				100.2				95.9				5,001.70				122.8			117
	Total	$	275,071.30			$	4,233.00			$	4,221.40			$	248,136.70			$	2,967.50		$	2,963.20
	Changes in the fair value of client-related and trading derivative instruments are recognized currently in income. The following table shows the location and amount of gains and losses recorded in the consolidated statement of income for the three and nine months ended September 30, 2014, and 2013.
		Location of Derivative Gain/(Loss)		Amount of Derivative Gain/(Loss) Recognized in Income
		Recognized in Income		Three Months Ended								Nine Months Ended
				September 30,								September 30,
	(In Millions)			2014				2013				2014				2013
	Foreign Exchange Contracts	Foreign Exchange Trading Income		$	46.4			$	62.8			$	149.4			$	193.6
	Interest Rate Contracts	Security Commissions and Trading Income			0.6				4.4				4.6				11.4
	Total			$	47			$	67.2			$	154			$	205
	Risk Management Instruments. Northern Trust uses derivative instruments to hedge its exposure to foreign currency, interest rate, and credit risk. 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.
	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.
	The following table identifies the types and classifications of derivative instruments formally designated as hedges under GAAP and used by Northern Trust to manage risk, their notional and fair values, and the respective risks addressed.
						September 30, 2014												December 31, 2013
	(In Millions)	Derivative		Risk		Notional				Fair Value								Notional			Fair Value
		Instrument		Classification		Value				Asset				Liability				Value			Asset		Liability
	Fair Value Hedges
	Available for Sale Investment Securities	Interest Rate Swap Contracts		Interest		$	2,939.70			$	20.8			$	24.9			$	3,296.90		$	31.5	$	44.8
				Rate
	Senior Notes and Long-Term Subordinated Debt	Interest Rate Swap Contracts		Interest			1,250.00				92.4				2				1,250.00			83.6		33.4
				Rate
	Cash Flow Hedges
	Forecasted Foreign Currency Denominated Transactions	Foreign Exchange Contracts		Foreign			341				5.2				9.5				314			10.2		5.5
				Currency
	Available for Sale Investment Securities	Interest Rate Swap Contracts		Interest			10				—				—				—			—		—
				Rate
	Available for Sale Investment Securities	Interest Rate Option Contracts		Interest			375				0.1				0.7				—			—		—
				Rate
	Net Investment Hedges
	Net Investments in Non-U.S. Affiliates	Foreign Exchange Contracts		Foreign			1,753.60				65.5				3.1				1,684.90			9.8		52.8
				Currency
	Total					$	6,669.30			$	184			$	40.2			$	6,545.80		$	135.1	$	136.5
	In addition to the above, Sterling denominated debt, totaling $250.4 million and $259.1 million at September 30, 2014, and December 31, 2013, respectively, was designated as a hedge of the foreign exchange risk associated with the net investment in certain non-U.S. affiliates.
	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. For a fair value hedge, 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 recorded currently in income. The following table shows the location and amount of derivative gains and losses recorded in the consolidated statement of income related to fair value hedges for the three and nine months ended September 30, 2014, and 2013.
	(In Millions)	Derivative		Location of		Amount of Derivative
		Instrument		Derivative		Gain/(Loss) Recognized in Income
				Gain/(Loss)
				Recognized in		Three Months Ended								Nine Months Ended
				Income		September 30,								September 30,
						2014				2013				2014				2013
	Available for Sale Investment Securities	Interest Rate Swap Contracts		Interest		$	5.1			$	(16.4	)		$	(21.9	)		$	21.6
				Income
	Senior Notes and Long-Term Subordinated Debt	Interest Rate Swap Contracts		Interest			5.8				(3.6	)			66				(16.1	)
				Expense
	Total					$	10.9			$	(20.0	)		$	44.1			$	5.5
	Northern Trust applies the “shortcut” method of accounting, available under GAAP, to substantially all of its fair value hedges, which assumes there is no ineffectiveness in a hedge. As a result, changes recorded in the fair value of the hedged item are equal to the offsetting gain or loss on the derivative and are reflected in the same line item as the gain or loss. For fair value hedges that do not qualify for the “shortcut” method of accounting, Northern Trust utilizes regression analysis, a “long-haul” method of accounting, in assessing whether the hedging relationships are highly effective at inception and on an ongoing basis. There was no ineffectiveness or changes in the fair value of hedged items recognized in earnings for fair value hedges during the three and nine months ended September 30, 2014. There were losses of $0.3 million and $0.9 million recorded within the fair values of hedged items for such “long-haul” hedges during the three and nine months ended September 30, 2013, respectively. There were losses of $0.3 million and $0.8 million from ineffectiveness recorded during the three and nine months ended September 30, 2013, respectively, in connection with the hedging of available for sale investment securities, senior notes, and subordinated debt. Ineffectiveness resulting from fair value hedges is recorded in either interest income or interest expense.
	Derivatives are also designated 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. The effective portion of changes in the fair value of such derivatives is recognized in AOCI, a component of stockholders’ equity, and there is no change in the accounting for the hedged item. When the hedged forecasted transaction impacts earnings, balances in AOCI are reclassified to earnings. Northern Trust applies the “shortcut” method of accounting for cash flow hedges of certain available for sale investment securities. For cash flow hedges of certain available for sale investment securities and forecasted foreign currency denominated revenue and expenditure transactions, Northern Trust closely matches all terms of the hedged item and the hedging derivative at inception and on an ongoing basis which limits hedge ineffectiveness. For cash flow hedges of available for sale investment securities, to the extent all terms are not perfectly matched, effectiveness is assessed using regression analysis and any ineffectiveness is measured using the hypothetical derivative method.
For cash flow hedges of forecasted foreign currency denominated revenue and expenditure transactions, to the extent all terms are not perfectly matched, effectiveness is assessed using the dollar-offset method and any ineffectiveness is measured using the hypothetical derivative method. There was no ineffectiveness recognized in earnings for cash flow hedges during the three and nine months ended September 30, 2014, and 2013. As of September 30, 2014, 23 months is the maximum length of time over which the exposure to variability in future cash flows of forecasted foreign currency denominated transactions is being hedged.
The following tables provide cash flow hedge derivative gains and losses recognized in AOCI and the amounts reclassified to earnings during the three and nine months ended September 30, 2014, and 2013.
(In Millions)	Foreign Exchange								Interest Rate Swap								Interest Rate Option
	Contracts (Before Tax)								Contracts (Before Tax)								Contracts (Before Tax)
Three Months Ended September 30,	2014				2013				2014				2013				2014			2013
Net Gain/(Loss) Recognized in AOCI	$	(6.9	)		$	5.3			$	—			$	—			$	(0.7	)	$	—
Net Gain/(Loss) Reclassified from AOCI to Earnings
Other Operating Income		0.7				—				—				—				—			—
Interest Income		—				—				—				—				0.1			—
Other Operating Expense		—				(1.1	)			—				—				—			—
Total	$	0.7			$	(1.1	)		$	—			$	—			$	0.1		$	—
(In Millions)	Foreign Exchange								Interest Rate Swap								Interest Rate Option
	Contracts (Before Tax)								Contracts (Before Tax)								Contracts (Before Tax)
Nine Months Ended September 30,	2014				2013				2014				2013				2014			2013
Net Gain/(Loss) Recognized in AOCI	$	(5.8	)		$	(4.0	)		$	—			$	—			$	(0.7	)	$	—
Net Gain/(Loss) Reclassified from AOCI to Earnings
Other Operating Income		3.4				(1.8	)			—				—				—			—
Interest Income		—				—				—				—				0.1			—
Other Operating Expense		(0.2	)			(3.9	)			—				—				—			—
Total	$	3.2			$	(5.7	)		$	—			$	—			$	0.1		$	—
During the three and nine months ended September 30, 2014, and 2013, there were no transactions discontinued due to the original forecasted transactions no longer being probable of occurring. It is estimated that a net loss of $1.8 million will be reclassified into earnings within the next twelve months relating to cash flow hedges of foreign currency denominated transactions. It is estimated that a net gain of $2.2 million will be reclassified into earnings upon the receipt of interest payments on earning assets within the next twelve months relating to cash flow hedges of available for sale investment securities.
Certain foreign exchange contracts and qualifying nonderivative instruments 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. The effective portion of changes in the fair value of the hedging instrument is recognized in AOCI consistent with the related translation gains and losses of the hedged net investment. For net investment hedges, all critical terms of the hedged item and the hedging instrument are matched at inception and on an ongoing basis to minimize the risk of hedge ineffectiveness. To the extent all terms are not perfectly matched, any ineffectiveness is measured using the hypothetical derivative method. Ineffectiveness resulting from net investment hedges is recorded in other operating income. There was no ineffectiveness recorded during the three and nine months ended September 30, 2014, and 2013. Amounts recorded in AOCI are reclassified to earnings only upon the sale or liquidation of an investment in a non-U.S. branch or subsidiary.
The following table provides net investment hedge gains and losses recognized in AOCI during the three and nine months ended September 30, 2014, and 2013.
	Hedging Gain/(Loss)
	Recognized in OCI (Before Tax)
	Three Months Ended September 30,								Nine Months Ended September 30,
(In Millions)	2014				2013				2014				2013
Foreign Exchange Contracts	$	106.2			$	(73.8	)		$	74.3			$	(9.5	)
Sterling Denominated Subordinated Debt		13.7				(15.0	)			5.4				0.2
Total	$	119.9			$	(88.8	)		$	79.7			$	(9.3	)
Derivatives that are not formally designated as hedges under GAAP are entered into for risk management purposes. Foreign exchange contracts are 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. Credit default swaps are entered into to manage the credit risk associated with certain loans and loan commitments. The following table identifies the types of risk management derivative instruments not formally designated as hedges and their notional amounts and fair values.
(In Millions)	September 30, 2014												December 31, 2013
	Notional				Fair Value								Notional				Fair Value
	Value				Asset				Liability				Value				Asset			Liability
Foreign Exchange Contracts	$	192.3			$	0.3			$	3.5			$	168.8			$	1		$	1.2
Changes in the fair value of derivative instruments not formally designated as hedges are recognized currently in income. The following table provides the location and amount of gains and losses recorded in the consolidated statement of income for the three and nine months ended September 30, 2014, and 2013.
(In Millions)	Location of		Amount of Derivative Gain/(Loss)
	Derivative Gain/		Recognized in Income
	(Loss) Recognized		Three Months Ended								Nine Months Ended
	in Income		September 30,								September 30,
			2014				2013				2014				2013
Credit Default Swap Contracts	Other Operating Income		$	—			$	—			$	—			$	(0.1	)
Foreign Exchange Contracts	Other Operating Income			(10.1	)			6.7				(9.3	)			(4.3	)
Total			$	(10.1	)		$	6.7			$	(9.3	)		$	(4.4	)

Offsetting_of_Assets_and_Liabi

Offsetting of Assets and Liabilities	9 Months Ended
	Sep. 30, 2014
Offsetting of Assets and Liabilities	'
	20. Offsetting of Assets and Liabilities
	The following tables provide information regarding the offsetting of derivative assets and securities purchased under agreements to resell within the consolidated balance sheet as of September 30, 2014, and December 31, 2013.
	September 30, 2014
	(In Millions)		Gross		Gross		Net		Gross		Net
			Recognized		Amounts		Amounts		Amounts		Amount (3)
			Assets		Offset		Presented		Not Offset
	Derivative Assets (1)
	Foreign Exchange Contracts Over the Counter (OTC)		$	3,265.00	$	2,085.00	$	1,180.00	$	—	$	1,180.00
	Interest Rate Swaps OTC			183.7		31.5		152.2		—		152.2
	Interest Rate Swaps Exchange Cleared			29.8		7.4		22.4		—		22.4
	Cross Product Netting Adjustment			—		27.1		—		—		—
	Cross Product Collateral Adjustment			—		207.4		—		—		—
	Total Derivatives Subject to a Master Netting Arrangement			3,478.50		2,358.40		1,120.10		—		1,120.10
	Total Derivatives Not Subject to a Master Netting Arrangement			938.8		—		938.8		—		938.8
	Total Derivatives			4,417.30		2,358.40		2,058.90		—		2,058.90
	Securities Purchased under Agreements to Resell (2)		$	1,000.00	$	—	$	1,000.00	$	1,000.00	$	—
	December 31, 2013
	(In Millions)		Gross		Gross		Net		Gross		Net
			Recognized		Amounts		Amounts		Amounts		Amount (3)
			Assets		Offset		Presented		Not Offset
	Derivative Assets (1)
	Foreign Exchange Contracts OTC		$	2,612.50	$	1,073.30	$	1,539.20	$	—	$	1,539.20
	Interest Rate Swaps OTC			228.8		47.5		181.3		—		181.3
	Interest Rate Swaps Exchange Cleared			9.1		9.1		—		—		—
	Cross Product Netting Adjustment			—		28.4		—		—		—
	Cross Product Collateral Adjustment			—		210.7		—		—		—
	Total Derivatives Subject to a Master Netting Arrangement			2,850.40		1,369.00		1,481.40		—		1,481.40
	Total Derivatives Not Subject to a Master Netting Arrangement			253.2		—		253.2		—		253.2
	Total Derivatives			3,103.60		1,369.00		1,734.60		—		1,734.60
	Securities Purchased under Agreements to Resell (2)		$	500	$	—	$	500	$	500	$	—
	-1	Derivative assets are reported in other assets in the consolidated balance sheet. Other assets (excluding derivative assets) totaled $3,230.9 million and $3,029.4 million as of September 30, 2014, and December 31, 2013, respectively.
	-2	Securities purchased under agreements to resell are reported in federal funds sold and securities purchased under agreements to resell in the consolidated balance sheet. Federal funds sold totaled $10.0 million and $29.6 million as of September 30, 2014, and December 31, 2013, respectively.
	-3	Northern Trust did not possess any cash collateral that was not offset in the consolidated balance sheet that could have been used to offset the net amounts presented in the consolidated balance sheet as of September 30, 2014, and December 31, 2013.
	The following tables provide information regarding the offsetting of derivative liabilities and securities sold under agreements to repurchase within the consolidated balance sheet as of September 30, 2014, and December 31, 2013.
	September 30, 2014
	(In Millions)		Gross		Gross		Net		Gross		Net
			Recognized		Amounts		Amounts		Amounts		Amount (2)
			Liabilities		Offset		Presented		Not
									Offset
	Derivative Liabilities (1)
	Foreign Exchange Contracts OTC		$	3,404.30	$	2,085.00	$	1,319.30	$	—	$	1,319.30
	Interest Rate Swaps OTC			116.1		31.5		84.6		—		84.6
	Interest Rate Swaps Exchange Cleared			7.4		7.4		—		—		—
	Cross Product Netting Adjustment			—		27.1		—		—		—
	Cross Product Collateral Adjustment			—		601.3		—		—		—
	Total Derivatives Subject to a Master Netting Arrangement			3,527.80		2,752.30		775.5		—		775.5
	Total Derivatives Not Subject to a Master Netting Arrangement			737.3		—		737.3		—		737.3
	Total Derivatives			4,265.10		2,752.30		1,512.80		—		1,512.80
	Securities Sold under Agreements to Repurchase		$	866.8	$	—	$	866.8	$	866.8	$	—
	December 31, 2013
	(In Millions)		Gross		Gross		Net		Gross		Net
			Recognized		Amounts		Amounts		Amounts		Amount (2)
			Liabilities		Offset		Presented		Not
									Offset
	Derivative Liabilities (1)
	Foreign Exchange Contracts OTC		$	2,039.00	$	1,073.30	$	965.7	$	—	$	965.7
	Interest Rate Swaps OTC			163.7		47.5		116.2		—		116.2
	Interest Rate Swaps Exchange Cleared			31.5		9.1		22.4		—		22.4
	Cross Product Netting Adjustment			—		28.4		—		—		—
	Cross Product Collateral Adjustment			—		767.7		—		—		—
	Total Derivatives Subject to a Master Netting Arrangement			2,234.20		1,926.00		308.2		—		308.2
	Total Derivatives Not Subject to a Master Netting Arrangement			866.7		—		866.7				866.7
	Total Derivatives			3,100.90		1,926.00		1,174.90		—		1,174.90
Securities Sold under Agreements to Repurchase		$	917.3	$	—	$	917.3	$	917.3	$	—
-1	Derivative liabilities are reported in other liabilities in the consolidated balance sheet. Other liabilities (excluding derivative liabilities) totaled $2,591.5 million and $2,338.4 million as of September 30, 2014, and December 31, 2013, respectively.
-2	Northern Trust did not place any cash collateral with counterparties that was not offset in the consolidated balance sheet that could have been used to offset the net amounts presented in the consolidated balance sheet as of September 30, 2014, and December 31, 2013.
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 set off 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.
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. Northern Trust centrally clears those interest rate derivative instruments addressed under Title VII of the Dodd-Frank Act. These transactions are subject to an agreement similar to a master netting arrangement which has the same rights of offset as described above.

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2014
Assets and Liabilities Measured at Fair Value on Recurring Basis Segregated by Fair Value Hierarchy Level	'
	The following tables present assets and liabilities measured at fair value on a recurring basis as of September 30, 2014, and December 31, 2013, segregated by fair value hierarchy level.
	(In Millions)		Level 1			Level 2			Level 3		Netting			Assets/Liabilities
														at Fair Value
	September 30, 2014
	Securities
	Available for Sale
	U.S. Government		$	3,409.60		$	—		$	—	$	—		$	3,409.60
	Obligations of States and Political Subdivisions			—			4.6			—		—			4.6
	Government Sponsored Agency			—			16,174.40			—		—			16,174.40
	Non-U.S. Government			—			310.5			—		—			310.5
	Corporate Debt			—			3,364.80			—		—			3,364.80
	Covered Bonds			—			1,978.90			—		—			1,978.90
	Supranational and Non-U.S. Agency Bonds			—			360.2			—		—			360.2
	Residential Mortgage-Backed			—			17.6			—		—			17.6
	Other Asset-Backed			—			2,233.10			—		—			2,233.10
	Auction Rate			—			—			85.2		—			85.2
	Other			—			168.8			—		—			168.8
	Total Available for Sale			3,409.60			24,612.90			85.2		—			28,107.70
	Trading Account			—			4.3			—		—			4.3
	Total Available for Sale and Trading Securities			3,409.60			24,617.20			85.2		—			28,112.00
	Other Assets
	Derivative Assets
	Foreign Exchange Contracts			—			4,203.80			—		—			4,203.80
	Interest Rate Contracts			—			213.5			—		—			213.5
	Total Derivative Assets			—			4,417.30			—		(2,358.4	)		2,058.90
	Other Liabilities
	Derivative Liabilities
	Foreign Exchange Contracts			—			4,141.60			—		—			4,141.60
	Interest Rate Swaps			—			123.5			—		—			123.5
	Total Derivative Liabilities		$	—		$	4,265.10		$	—	$	(2,752.3	)	$	1,512.80
	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 September 30, 2014, derivative assets and liabilities shown above also include reductions of $207.4 million and $601.3 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties.
	(In Millions)		Level 1			Level 2			Level 3		Netting			Assets/Liabilities
														at Fair Value
	December 31, 2013
	Securities
	Available for Sale
	U.S. Government		$	1,917.90		$	—		$	—	$	—		$	1,917.90
	Obligations of States and Political Subdivisions			—			4.6			—		—			4.6
	Government Sponsored Agency			—			17,528.00			—		—			17,528.00
	Non-U.S. Government			—			310.6			—		—			310.6
	Corporate Debt			—			3,524.50			—		—			3,524.50
	Covered Bonds			—			1,943.90			—		—			1,943.90
	Supranational and Non-U.S. Agency Bonds			—			410			—		—			410
	Residential Mortgage-Backed			—			48.1			—		—			48.1
	Other Asset-Backed			—			2,391.80			—		—			2,391.80
	Auction Rate			—			—			98.9		—			98.9
	Other			—			214.5			—		—			214.5
	Total Available for Sale			1,917.90			26,376.00			98.9		—			28,392.80
	Trading Account			—			1.7			—		—			1.7
	Total Available for Sale and Trading Securities			1,917.90			26,377.70			98.9		—			28,394.50
	Other Assets
	Derivative Assets
	Foreign Exchange Contracts			—			2,865.70			—		—			2,865.70
	Interest Rate Contracts			—			237.9			—		—			237.9
	Total Derivative Assets			—			3,103.60			—		(1,369.0	)		1,734.60
	Other Liabilities
	Derivative Liabilities
	Foreign Exchange Contracts			—			2,905.70			—		—			2,905.70
	Interest Rate Swaps			—			195.2			—		—			195.2
	Total Derivative Liabilities			—			3,100.90			—		(1,926.0	)		1,174.90
	Contingent Consideration		$	—		$	—		$	55.4	$	—		$	55.4
	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, 2013, derivative assets and liabilities shown above also include reductions of $210.7 million and $767.7 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties.
Changes in Level 3 Assets	'
	The following tables present the changes in Level 3 assets and liabilities for the three and nine months ended September 30, 2014, and 2013.
	Level 3 Assets (In Millions)		Auction Rate Securities
	Three Months Ended September 30,		2014			2013
	Fair Value at July 1		$	98.8		$	99.1
	Total Gains (Losses):
	Included in Earnings			0.7			—
	Included in Other Comprehensive Income (2)			0.1			0.3
	Purchases, Issues, Sales, and Settlements:
	Sales			(14.4	)		—
	Fair Value at September 30		$	85.2		$	98.7
	Nine Months Ended September 30,		2014			2013
	Fair Value at January 1		$	98.9		$	97.8
	Total Gains (Losses):
	Included in Earnings (1)			0.7			0.1
	Included in Other Comprehensive Income (2)			0.4			3
	Purchases, Issues, Sales, and Settlements:
	Sales			(14.4	)		—
	Settlements			(0.4	)		(2.2	)
	Fair Value at September 30		$	85.2		$	98.7
	-1	Realized gains for the three and nine months ended September 30, 2014, of $0.7 million, represent gains from sales of securities. Realized gains for the nine month period ended September 30, 2013, of $0.1 million, represent gains from redemptions by issuers. Gains on sales are recorded in investment security gains (losses) and gains on redemptions are recorded in interest income, within the consolidated statement of income.
	-2	Unrealized gains (losses) are included in net unrealized gains (losses) on securities available for sale within the consolidated statement of comprehensive income.
Changes in Level 3 Liabilities	'
	Level 3 Liabilities (In Millions)		Contingent Consideration
	Three Months Ended September 30,		2014			2013
	Fair Value at July 1		$	—		$	52.7
	Total (Gains) Losses:
	Included in Earnings (1)			—			1.3
	Included in Other Comprehensive Income			—			—
	Purchases, Issues, Sales, and Settlements			—			—
	Fair Value at September 30		$	—		$	54
	Unrealized (Gains) Losses Included in Earnings Related to Financial Instruments Held at September 30 (1)		$	—		$	1.3
	Nine Months Ended September 30,		2014			2013
	Fair Value at January 1		$	55.4		$	50.1
	Total (Gains) Losses:
	Included in Earnings (1)			(0.1	)		3.9
	Included in Other Comprehensive Income			—			—
	Purchases, Issues, Sales, and Settlements:
	Settlements			(55.3	)		—
	Fair Value at September 30		$	—		$	54
	Unrealized (Gains) Losses Included in Earnings Related to Financial Instruments Held at September 30 (1)		$	—		$	3.9
	-1	(Gains) losses are recorded in other operating income (expense) within the consolidated statement of income.
Book and Fair Values of All Financial Instruments	'
	The following tables summarize the fair values of all financial instruments.
	(In Millions)		September 30, 2014
			Book			Total			Fair Value
			Value			Fair Value			Level 1		Level 2			Level 3
	Assets
	Cash and Due from Banks		$	2,918.90		$	2,918.90		$	2,918.90	$	—		$	—
	Federal Funds Sold and Resell Agreements			1,010.00			1,010.00			—		1,010.00			—
	Interest-Bearing Deposits with Banks			15,334.50			15,334.50			—		15,334.50			—
	Federal Reserve Deposits			21,328.00			21,328.00			—		21,328.00			—
	Securities
	Available for Sale (1)			28,107.70			28,107.70			3,409.60		24,612.90			85.2
	Held to Maturity			4,196.70			4,195.10			—		4,195.10			—
	Trading Account			4.3			4.3			—		4.3			—
	Loans (excluding Leases)
	Held for Investment			29,499.60			29,522.70			—		—			29,522.70
	Held for Sale			2.1			2.1			—		—			2.1
	Client Security Settlement Receivables			1,538.60			1,538.60			—		1,538.60			—
	Other Assets
	Federal Reserve and Federal Home Loan Bank Stock			207.5			207.5			—		207.5			—
	Community Development Investments			225.1			223.8			—		223.8			—
	Employee Benefit and Deferred Compensation			145.2			147.4			97.4		50			—
	Liabilities
	Deposits
	Demand, Noninterest-Bearing, Savings and Money Market		$	39,267.40		$	39,267.40		$	39,267.40	$	—		$	—
	Savings Certificates and Other Time			1,869.00			1,869.50			—		1,869.50			—
	Non U.S. Offices Interest-Bearing			50,586.10			50,586.10			—		50,586.10			—
	Federal Funds Purchased			786.4			786.4			—		786.4			—
	Securities Sold under Agreements to Repurchase			866.8			866.8			—		866.8			—
	Other Borrowings			1,758.30			1,758.90			—		1,758.90			—
	Senior Notes			1,496.90			1,526.80			—		1,526.80			—
	Long Term Debt (excluding Leases)
	Subordinated Debt			1,565.50			1,595.50			—		1,595.50			—
	Federal Home Loan Bank Borrowings			—			—			—		—			—
	Floating Rate Capital Debt			277.2			242.8			—		242.8			—
	Other Liabilities
	Standby Letters of Credit			57			57			—		—			57
	Loan Commitments			28.7			28.7			—		—			28.7
	Derivative Instruments
	Asset/Liability Management
	Foreign Exchange Contracts
	Assets		$	71		$	71		$	—	$	71		$	—
	Liabilities			16.1			16.1			—		16.1			—
	Interest Rate Contracts
	Assets			113.3			113.3			—		113.3			—
	Liabilities			27.6			27.6			—		27.6			—
	Client-Related and Trading
	Foreign Exchange Contracts
	Assets			4,132.80			4,132.80			—		4,132.80			—
	Liabilities			4,125.50			4,125.50			—		4,125.50			—
	Interest Rate Contracts
	Assets			100.2			100.2			—		100.2			—
	Liabilities			95.9			95.9			—		95.9			—
	-1	Refer to the table located on page 36 for the disaggregation of available for sale securities.
	(In Millions)		December 31, 2013
			Book			Total			Fair Value
			Value			Fair Value			Level 1		Level 2			Level 3
	Assets
	Cash and Due from Banks		$	3,162.40		$	3,162.40		$	3,162.40	$	—		$	—
	Federal Funds Sold and Resell Agreements			529.6			529.6			—		529.6			—
	Interest-Bearing Deposits with Banks			19,397.40			19,397.40			—		19,397.40			—
	Federal Reserve Deposits and Other Interest-Bearing			12,911.50			12,911.50			—		12,911.50			—
	Securities
	Available for Sale (1)			28,392.80			28,392.80			1,917.90		26,376.00			98.9
Held to Maturity			2,325.80			2,321.40			—		2,321.40			—
Trading Account			1.7			1.7			—		1.7			—
Loans (excluding Leases)
Held for Investment			28,136.50			28,147.20			—		—			28,147.20
Held for Sale			—			—			—		—			—
Client Security Settlement Receivables			1,355.20			1,355.20			—		1,355.20			—
Other Assets
Federal Reserve and Federal Home Loan Bank Stock			194.7			194.7			—		194.7			—
Community Development Investments			228.1			227.8			—		227.8			—
Employee Benefit and Deferred Compensation			132.7			126.9			79.3		47.6			—
Liabilities
Deposits
Demand, Noninterest-Bearing, Savings and Money Market		$	33,762.00		$	33,762.00		$	33,762.00	$	—		$	—
Savings Certificates and Other Time			1,874.40			1,877.10			—		1,877.10			—
Non U.S. Offices Interest-Bearing			48,461.70			48,461.70			—		48,461.70			—
Federal Funds Purchased			965.1			965.1			—		965.1			—
Securities Sold under Agreements to Repurchase			917.3			917.3			—		917.3			—
Other Borrowings			1,558.60			1,558.60			—		1,558.60			—
Senior Notes			1,996.60			1,989.30			—		1,989.30			—
Long Term Debt (excluding Leases)
Subordinated Debt			1,537.30			1,563.50			—		1,563.50			—
Federal Home Loan Bank Borrowings			135			137.2			—		137.2			—
Floating Rate Capital Debt			277.1			230.2			—		230.2			—
Other Liabilities
Standby Letters of Credit			59.6			59.6			—		—			59.6
Contingent Consideration			55.4			55.4			—		—			55.4
Loan Commitments			35.7			35.7			—		—			35.7
Derivative Instruments
Asset/Liability Management
Foreign Exchange Contracts
Assets		$	21		$	21		$	—	$	21		$	—
Liabilities			59.5			59.5			—		59.5			—
Interest Rate Swaps
Assets			115.1			115.1			—		115.1			—
Liabilities			78.2			78.2			—		78.2			—
Client-Related and Trading
Foreign Exchange Contracts
Assets			2,844.70			2,844.70			—		2,844.70			—
Liabilities			2,846.20			2,846.20			—		2,846.20			—
Interest Rate Contracts
Assets			122.8			122.8			—		122.8			—
Liabilities			117			117			—		117			—
-1	Refer to the table located on page 37 for the disaggregation of available for sale securities.
Fair Value, Measurements, Recurring	'
Valuation Techniques, Significant Unobservable Inputs, and Quantitative Information	'
	The following presents the fair values of, and the valuation techniques, significant unobservable inputs, and quantitative information used to develop significant unobservable inputs for, Northern Trust’s Level 3 assets as of September 30, 2014.
	Financial Instrument		Fair Value			Valuation		Unobservable Inputs	Range of Lives
						Technique			and Rates
	Auction Rate Securities		$	85.2 million		Discounted Cash		Remaining lives	1.7 — 8.6 years
						Flow		Discount rates	0.2% — 7.9%
Fair Value, Measurements, Nonrecurring	'
Valuation Techniques, Significant Unobservable Inputs, and Quantitative Information	'
	The following table provides the fair value of, and the valuation technique, significant unobservable inputs, and quantitative information used to develop the significant unobservable inputs for, Northern Trust’s Level 3 assets that were measured at fair value on a nonrecurring basis as of September 30, 2014.
	Financial Instrument		Fair Value		Valuation	Unobservable Input		Range of Discounts
					Technique			Applied
	Loans		$26.6 million		Market Approach	Discount to reflect realizable value		15% — 25%
	OREO		$1.5 million		Market Approach	Discount to reflect realizable value		15% — 20%

Securities_Tables

Securities (Tables)	9 Months Ended
	Sep. 30, 2014
Reconciliation of Amortized Cost to Fair Values of Securities Available for Sale	'
	The following tables provide the amortized cost and fair values of securities at September 30, 2014, and December 31, 2013.
	Securities Available for Sale		September 30, 2014
			Amortized			Gross Unrealized						Fair
	(In Millions)		Cost			Gains			Losses			Value
	U.S. Government		$	3,395.10		$	16		$	1.5		$	3,409.60
	Obligations of States and Political Subdivisions			4.5			0.1			—			4.6
	Government Sponsored Agency			16,114.20			85.4			25.2			16,174.40
	Non-U.S. Government			309.3			1.2			—			310.5
	Corporate Debt			3,393.50			4.7			33.4			3,364.80
	Covered Bonds			1,966.90			12.2			0.2			1,978.90
	Supranational and Non-U.S. Agency Bonds			360			1.4			1.2			360.2
	Residential Mortgage-Backed			18.8			0.1			1.3			17.6
	Other Asset-Backed			2,232.00			1.3			0.2			2,233.10
	Auction Rate			83.4			2.3			0.5			85.2
	Other			168.5			0.3			—			168.8
	Total		$	28,046.20		$	125		$	63.5		$	28,107.70
	Securities Available for Sale		31-Dec-13
			Amortized			Gross Unrealized						Fair
	(In Millions)		Cost			Gains			Losses			Value
	U.S. Government		$	1,896.70		$	22.6		$	1.4		$	1,917.90
	Obligations of States and Political Subdivisions			4.5			0.1			—			4.6
	Government Sponsored Agency			17,495.20			80.7			47.9			17,528.00
	Non-U.S. Government			307			3.6			—			310.6
	Corporate Debt			3,615.20			10.5			101.2			3,524.50
	Covered Bonds			1,898.90			50.9			5.9			1,943.90
	Supranational and Non-U.S. Agency Bonds			410			1.7			1.7			410
	Residential Mortgage-Backed			52.4			0.1			4.4			48.1
	Other Asset-Backed			2,390.80			1.4			0.4			2,391.80
	Auction Rate			97.5			2.2			0.8			98.9
	Other			214.1			0.4			—			214.5
	Total		$	28,382.30		$	174.2		$	163.7		$	28,392.80
Reconciliation of Amortized Cost to Fair Values of Securities Held to Maturity	'
	Securities Held to Maturity		September 30, 2014
			Amortized			Gross Unrealized						Fair
	(In Millions)		Cost			Gains			Losses			Value
	Obligations of States and Political Subdivisions		$	138.8		$	8.5		$	—		$	147.3
	Government Sponsored Agency			22.8			1.1			—			23.9
	Non-U.S. Government			1,094.10			3.7			0.7			1,097.10
	Certificates of Deposit			1,479.50			0.2			0.1			1,479.60
	Supranational and Non-U.S. Agency Bonds			1,393.90			3.9			1.9			1,395.90
	Other			67.6			—			16.3			51.3
	Total		$	4,196.70		$	17.4		$	19		$	4,195.10
	Securities Held to Maturity		December 31, 2013
			Amortized			Gross Unrealized						Fair
	(In Millions)		Cost			Gains			Losses			Value
	Obligations of States and Political Subdivisions		$	225.2		$	10.3		$	—		$	235.5
	Government Sponsored Agency			35.9			1.1			—			37
	Non-U.S. Government			722			0.8			1.1			721.7
	Certificates of Deposit			698.1			—			0.2			697.9
	Supranational and Non-U.S. Agency Bonds			584.7			—			3.2			581.5
	Other			59.9			0.1			12.2			47.8
	Total		$	2,325.80		$	12.3		$	16.7		$	2,321.40
Securities Continuous Unrealized Loss Position	'
	The following tables provide information regarding securities that had been in a continuous unrealized loss position for less than 12 months and for 12 months or longer as of September 30, 2014, and December 31, 2013.
	Securities with Unrealized Losses as of		Less than 12 Months						12 Months or Longer						Total
	September 30, 2014
	(In Millions)		Fair Value			Unrealized			Fair Value			Unrealized			Fair Value			Unrealized
						Losses						Losses						Losses
	U.S. Government		$	1,596.00		$	1.5		$	—		$	—		$	1,596.00		$	1.5
	Government Sponsored Agency			2,099.20			8.3			1,773.50			16.9			3,872.70			25.2
	Non-U.S. Government			235.4			0.1			80.3			0.6			315.7			0.7
	Corporate Debt			862.3			2.8			1,258.00			30.6			2,120.30			33.4
	Covered Bonds			77			0.1			9.9			0.1			86.9			0.2
	Supranational and Non-U.S. Agency Bonds			438.2			0.7			300.8			2.4			739			3.1
	Residential Mortgage-Backed			—			—			15			1.3			15			1.3
	Other Asset-Backed			485.2			0.1			7.1			0.1			492.3			0.2
	Certificates of Deposit			552			0.1			—			—			552			0.1
	Auction Rate			1.1			0.1			5.1			0.4			6.2			0.5
	Other			13			8.5			43.4			7.8			56.4			16.3
	Total		$	6,359.40		$	22.3		$	3,493.10		$	60.2		$	9,852.50		$	82.5
	Securities with Unrealized Losses as of		Less than 12 Months						12 Months or Longer						Total
	December 31, 2013
	(In Millions)		Fair Value			Unrealized			Fair			Unrealized			Fair Value			Unrealized
						Losses			Value			Losses						Losses
	U.S. Government		$	896.4		$	1.4		$	—		$	—		$	896.4		$	1.4
	Government Sponsored Agency			4,340.80			42.6			413.7			5.3			4,754.50			47.9
	Non-U.S. Government			176.7			1.1			—			—			176.7			1.1
	Corporate Debt			1,759.50			85.4			267			15.8			2,026.50			101.2
	Covered Bonds			278.8			5.7			9.9			0.2			288.7			5.9
	Supranational and Non-U.S. Agency Bonds			612.7			4.9			—			—			612.7			4.9
	Residential Mortgage-Backed			—			—			42			4.4			42			4.4
	Other Asset-Backed			677			0.4			—			—			677			0.4
	Certificates of Deposit			684.2			0.2			—			—			684.2			0.2
	Auction Rate			22.1			0.1			14			0.7			36.1			0.8
	Other			25.7			4			29.5			8.2			55.2			12.2
	Total		$	9,473.90		$	145.8		$	776.1		$	34.6		$	10,250.00		$	180.4
Book Values, Ultimate Default Rates, and Loss Severity Rates for Non-Agency Residential Mortgage-Backed Securities Portfolio, by Security Type	'
	Amortized cost, weighted average ultimate default rates, and impairment severity rates for the non-agency residential mortgage-backed securities portfolio, by security type as of September 30, 2014, are provided in the following table.
	($ In Millions)		September 30, 2014
			Amortized			Weighted Average			Loss Severity Rates
	Security Type		Cost			Ultimate Default Rates			Low			High			Weighted
															Average
	Prime		$	2			5.4	%		32.1	%		32.1	%		32.1	%
	Alt-A			11.2			40			62.8			62.8			62.8
	2nd Lien			5.6			32.7			98.7			99			99
	Total Non-Agency Residential Mortgage-Backed Securities		$	18.8			33.1	%		32.1	%		99	%		70.3	%
Credit Related Impairment Losses Recognized in Earnings on Other Than Temporarily Impaired Securities	'
	The table below provides information regarding total other-than-temporarily impaired securities, including noncredit-related amounts recognized in other comprehensive income and net impairment losses recognized in earnings, for the three and nine months ended September 30, 2014, and 2013.
			Three Months Ended						Nine Months Ended
			September 30,						September 30,
	(In Millions)		2014			2013			2014			2013
	Changes in OTTI Losses*		$	—		$	—		$	(4.6	)	$	—
	Noncredit-related Losses Recorded in / (Reclassified from) OCI**			—			—			0.7			—
	Net Impairment Losses Recognized in Earnings		$	—		$	—		$	(3.9	)	$	—
	*	For initial other-than-temporary impairments in the respective period, the balance includes the excess of the amortized cost over the fair value of the impaired securities. For subsequent impairments of the same security, the balance includes any additional changes in fair value of the security subsequent to its most recently recorded OTTI.
	**	For initial other-than-temporary impairments in the respective period, the balance includes the portion of the excess of amortized cost over the fair value of the impaired securities that was recorded in OCI. For subsequent impairments of the same security, the balance includes additional changes in OCI for that security subsequent to its most recently recorded OTTI.
Cumulative Credit-Related Losses Recognized in Earnings on Debt Securities Other-Than-Temporarily Impaired	'
	Provided in the table below are the cumulative credit-related losses recognized in earnings on debt securities other-than-temporarily impaired.
			Three Months Ended						Nine Months Ended
			September 30,						September 30,
	(In Millions)		2014			2013			2014			2013
	Cumulative Credit-Related Losses on Securities Held — Beginning of Period		$	12.7		$	8.8		$	8.8		$	42.3
	Plus: Losses on Newly Identified Impairments			—			—			1.8			—
	Additional Losses on Previously Identified Impairments			—			—			2.1			—
	Less: Current and Prior Period Losses on Securities Sold During the Period			(1.8	)		—			(1.8	)		(33.5	)
	Cumulative Credit-Related Losses on Securities Held — End of Period		$	10.9		$	8.8		$	10.9		$	8.8
Held-to-maturity Securities	'
Remaining Maturity of Securities	'
	Held to Maturity
	Due in One Year or Less			1,914.10			1,915.30
	Due After One Year Through Five Years			2,222.20			2,230.50
	Due After Five Years Through Ten Years			23.3			24.1
	Due After Ten Years			37.1			25.2
	Total		$	4,196.70		$	4,195.10
	Note: Mortgage-backed and asset-backed securities are included in the above table taking into account anticipated future prepayments.
Available for Sale Investment Securities	'
Remaining Maturity of Securities	'
	The following table provides the remaining maturity of securities as of September 30, 2014.
	Remaining Maturity of Securities
	(In Millions)		Amortized			Fair
			Cost			Value
	Available for Sale
	Due in One Year or Less		$	7,195.00		$	7,210.60
	Due After One Year Through Five Years			16,637.90			16,677.90
	Due After Five Years Through Ten Years			3,116.80			3,138.10
	Due After Ten Years			1,096.50			1,081.10
	Total			28,046.20			28,107.70

Loans_and_Leases_Tables

Loans and Leases (Tables)	9 Months Ended
	Sep. 30, 2014
Amounts Outstanding for Loans and Leases by Segment and Class	'
	Amounts outstanding for loans and leases, by segment and class, are shown below.
	(In Millions)	September 30,			December 31,
		2014			2013
	Commercial
	Commercial and Institutional	$	8,212.10		$	7,375.80
	Commercial Real Estate		3,107.70			2,955.80
	Lease Financing, net		952.5			975.1
	Non-U.S.		1,408.40			954.7
	Other		187.9			358.6
	Total Commercial		13,868.60			12,620.00
	Personal
	Residential Real Estate		9,872.70			10,271.30
	Private Client		6,953.10			6,445.60
	Other		25.5			48.6
	Total Personal		16,851.30			16,765.50
	Total Loans and Leases		30,719.90			29,385.50
	Allowance for Credit Losses Assigned to Loans and Leases		(269.4	)		(278.1	)
	Net Loans and Leases	$	30,450.50		$	29,107.40
Loan and Lease Segment and Class Balances Segregated by Borrower Ratings into "1 to 3", "4 to 5" and "6 to 9" (Watch List) Categories	'
	Loan and lease segment and class balances as of September 30, 2014, and December 31, 2013, are provided below, segregated by borrower ratings into “1 to 3”, “4 to 5” and “6 to 9” (watch list), categories.
		September 30, 2014										December 31, 2013
	(In Millions)	1 to 3			4 to 5			6 to 9		Total		1 to 3		4 to 5		6 to 9		Total
		Category			Category			Category				Category		Category		Category
								(Watch List)								(Watch List)
	Commercial
	Commercial and Institutional	$	5,115.40		$	2,983.60		$	113.1	$	8,212.10	$	4,432.50	$	2,801.50	$	141.8	$	7,375.80
	Commercial Real Estate		1,263.60			1,718.20			125.9		3,107.70		1,053.70		1,748.70		153.4		2,955.80
	Lease Financing, net		572.2			376.1			4.2		952.5		685.7		285		4.4		975.1
	Non-U.S.		643.7			763.8			0.9		1,408.40		442.8		511.9		—		954.7
	Other		137.4			50.5			—		187.9		157.7		200.9		—		358.6
	Total Commercial		7,732.30			5,892.20			244.1		13,868.60		6,772.40		5,548.00		299.6		12,620.00
	Personal
	Residential Real Estate		2,995.70			6,439.90			437.1		9,872.70		3,204.60		6,563.60		503.1		10,271.30
	Private Client		4,461.80			2,479.90			11.4		6,953.10		3,957.60		2,481.20		6.8		6,445.60
	Other		18.6			6.9			—		25.5		21.2		27.4		—		48.6
	Total Personal		7,476.10			8,926.70			448.5		16,851.30		7,183.40		9,072.20		509.9		16,765.50
	Total Loans and Leases	$	15,208.40		$	14,818.90		$	692.6	$	30,719.90	$	13,955.80	$	14,620.20	$	809.5	$	29,385.50
Balances and Delinquency Status of Performing and Nonperforming Loans and Leases by Segment and Class as well as Total Other Real Estate Owned and Nonperforming Asset Balances	'
	The following tables provide balances and delinquency status of performing and nonperforming loans and leases by segment and class, as well as the total other real estate owned and nonperforming asset balances, as of September 30, 2014, and December 31, 2013.
	September 30, 2014
	(In Millions)	Current			30-59 Days			60-89 Days		90 Days or		Total		Nonperforming		Total Loans
					Past Due			Past Due		More Past		Performing				and Leases
										Due
	Commercial
	Commercial and Institutional	$	8,153.80		$	10.2		$	13.3	$	3.1	$	8,180.40	$	31.7	$	8,212.10
	Commercial Real Estate		3,044.40			7.8			5.2		10.4		3,067.80		39.9		3,107.70
	Lease Financing, net		952.5			—			—		—		952.5		—		952.5
	Non-U.S.		1,408.40			—			—		—		1,408.40		—		1,408.40
	Other		187.9			—			—		—		187.9		—		187.9
	Total Commercial		13,747.00			18			18.5		13.5		13,797.00		71.6		13,868.60
	Personal
	Residential Real Estate		9,702.10			7.9			9		6.4		9,725.40		147.3		9,872.70
	Private Client		6,917.80			21.1			7.4		5.2		6,951.50		1.6		6,953.10
	Other		25.5			—			—		—		25.5		—		25.5
	Total Personal		16,645.40			29			16.4		11.6		16,702.40		148.9		16,851.30
	Total Loans and Leases	$	30,392.40		$	47		$	34.9	$	25.1	$	30,499.40	$	220.5	$	30,719.90
											Other Real Estate Owned				10.7
											Total Nonperforming Assets			$	231.2
	December 31, 2013
	(In Millions)	Current			30-59 Days			60-89 Days		90 Days or		Total		Nonperforming		Total Loans
					Past Due			Past Due		More Past		Performing				and Leases
										Due
	Commercial
	Commercial and Institutional	$	7,332.30		$	5		$	12.1	$	3.3	$	7,352.70	$	23.1	$	7,375.80
	Commercial Real Estate		2,881.10			4.1			14.6		6.8		2,906.60		49.2		2,955.80
	Lease Financing, net		975.1			—			—		—		975.1		—		975.1
	Non-U.S.		954.7			—			—		—		954.7		—		954.7
	Other		358.6			—			—		—		358.6		—		358.6
	Total Commercial		12,501.80			9.1			26.7		10.1		12,547.70		72.3		12,620.00
	Personal
	Residential Real Estate		9,934.40			129.3			15.6		2.9		10,082.20		189.1		10,271.30
	Private Client		6,404.20			29.1			7.5		3.4		6,444.20		1.4		6,445.60
	Other		48.6			—			—		—		48.6		—		48.6
	Total Personal		16,387.20			158.4			23.1		6.3		16,575.00		190.5		16,765.50
	Total Loans and Leases	$	28,889.00		$	167.5		$	49.8	$	16.4	$	29,122.70	$	262.8	$	29,385.50
											Other Real Estate Owned				11.9
											Total Nonperforming Assets			$	274.7
Impaired Loans By Segment and Class	'
	The following tables provide information related to impaired loans by segment and class.
		As of September 30, 2014								As of December 31, 2013
	(In Millions)	Recorded			Unpaid			Specific		Recorded		Unpaid		Specific
		Investment			Principal			Allowance		Investment		Principal		Allowance
					Balance							Balance
	With No Related Specific Allowance
	Commercial and Institutional	$	11.6		$	14.6		$	—	$	12.2	$	18.1	$	—
	Commercial Real Estate		49.2			54.9			—		46.6		57.1		—
	Lease Financing, net		4.2			4.2			—		4.4		4.4		—
	Residential Real Estate		170.2			214.5			—		185		227.8		—
	Private Client		0.1			0.4			—		0.8		0.8		—
	With a Related Specific Allowance
	Commercial and Institutional		20.5			20.5			5.1		9.6		12.1		3.6
	Commercial Real Estate		12.4			18.4			3.5		26.7		31.5		4.5
	Residential Real Estate		1.3			1.5			0.4		8.1		8.7		2.3
	Private Client		0.9			0.9			0.5		—		—		—
	Total
	Commercial		97.9			112.6			8.6		99.5		123.2		8.1
	Personal		172.5			217.3			0.9		193.9		237.3		2.3
	Total	$	270.4		$	329.9		$	9.5	$	293.4	$	360.5	$	10.4
		Three Months Ended September 30,										Nine Months Ended September 30,
		2014						2013				2014				2013
	(In Millions)	Average			Interest			Average		Interest		Average		Interest		Average		Interest
		Recorded			Income			Recorded		Income		Recorded		Income		Recorded		Income
		Investment			Recognized			Investment		Recognized		Investment		Recognized		Investment		Recognized
	With No Related Specific Allowance
	Commercial and Institutional	$	12.6		$	0.1		$	10.7	$	—	$	11.5	$	0.1	$	11.3	$	0.1
	Commercial Real Estate		48.5			0.2			42		0.2		46		0.7		40.6		0.6
	Lease Financing, net		4.3			0.1			4.5		0.1		4.3		0.2		4.6		0.2
	Residential Real Estate		172			0.8			168.1		0.3		180.8		2.1		155.2		1.4
	Private Client		0.3			—			13.3		0.2		0.6		—		12		0.5
	With a Related Specific Allowance
	Commercial and Institutional		11.9			—			14.1		—		10.6		—		12.5		—
	Commercial Real Estate		13.7			—			31.2		—		20.9		—		31.6		—
	Residential Real Estate		1.3			—			10		—		4.1		—		9.4		—
	Private Client		0.9			—			0.8		—		0.5		—		1.1		—
	Total
	Commercial		91			0.4			102.5		0.3		93.3		1		100.6		0.9
	Personal		174.5			0.8			192.2		0.5		186		2.1		177.7		1.9
	Total	$	265.5		$	1.2		$	294.7	$	0.8	$	279.3	$	3.1	$	278.3	$	2.8
	Note: Average recorded investment in impaired loans is calculated as the average of the month-end impaired loan balances for the period.
Number of Loans and Leases Modified in TDRs and Total Recorded Investments and Unpaid Principal Balances	'
	The following tables provide, by segment and class, the number of loans and leases modified in TDRs during the three and nine month periods ended September 30, 2014, and 2013, and the recorded investments and unpaid principal balances as of September 30, 2014, and 2013.
	($ In Millions)	Three Months Ended								Nine Months Ended
		September 30, 2014								September 30, 2014
		Number of			Recorded			Unpaid Principal		Number of		Recorded		Unpaid Principal
		Loans and Leases			Investment			Balance		Loans and Leases		Investment		Balance
	Commercial
	Commercial and Institutional		1		$	0.4		$	0.4		3	$	0.7	$	0.8
	Commercial Real Estate		5			2.9			3.4		6		3.5		4.1
	Total Commercial		6			3.3			3.8		9		4.2		4.9
	Personal
	Residential Real Estate		28			18			18.7		96		25.3		27.1
	Private Client		—			—			—		3		—		0.3
	Total Personal		28			18			18.7		99		25.3		27.4
	Total Loans and Leases		34		$	21.3		$	22.5		108	$	29.5	$	32.3
	Note: Period end balances reflect all paydowns and charge-offs during the period.
	($ In Millions)	Three Months Ended								Nine Months Ended
		September 30, 2013								September 30, 2013
		Number of			Recorded			Unpaid Principal		Number of		Recorded		Unpaid Principal
		Loans and Leases			Investment			Balance		Loans and Leases		Investment		Balance
	Commercial
	Commercial and Institutional		—		$	—		$	—		7	$	0.5	$	1
	Commercial Real Estate		7			22.8			25		11		27.4		31.9
	Total Commercial		7			22.8			25		18		27.9		32.9
	Personal
	Residential Real Estate		38			6.7			11.4		122		51.2		59.8
	Private Client		—			—			—		6		12.8		12.8
	Total Personal		38			6.7			11.4		128		64		72.6
	Total Loans and Leases		45		$	29.5		$	36.4		146	$	91.9	$	105.5
	Note: Period end balances reflect all paydowns and charge-offs during the period.

Allowance_for_Credit_Losses_Ta

Allowance for Credit Losses (Tables)	9 Months Ended
	Sep. 30, 2014
Changes in Allowance for Credit Losses by Segment	'
	The following tables provide information regarding changes in the total allowance for credit losses by segment during the three and nine months ended September 30, 2014, and 2013.
		Three Months Ended September 30,
		2014									2013
	(In Millions)	Commercial			Personal			Total			Commercial			Personal			Total
	Balance at Beginning of Period	$	168.7		$	134.8		$	303.5		$	184.1		$	136.6		$	320.7
	Charge-Offs		(2.5	)		(6.1	)		(8.6	)		(1.7	)		(9.9	)		(11.6	)
	Recoveries		1.9			1.5			3.4			1.7			1.6			3.3
	Net (Charge-Offs) Recoveries		(0.6	)		(4.6	)		(5.2	)		—			(8.3	)		(8.3	)
	Provision for Credit Losses		1			(1.0	)		—			(4.6	)		9.6			5
	Effect of Foreign Exchange Rates		—			—			—			0.1			—			0.1
	Balance at End of Period	$	169.1		$	129.2		$	298.3		$	179.6		$	137.9		$	317.5
		Nine Months Ended September 30,
		2014									2013
	(In Millions)	Commercial			Personal			Total			Commercial			Personal			Total
	Balance at Beginning of Period	$	168		$	139.9		$	307.9		$	194.2		$	133.4		$	327.6
	Charge-Offs		(8.8	)		(19.1	)		(27.9	)		(6.9	)		(32.9	)		(39.8	)
	Recoveries		10.7			4.6			15.3			8.1			6.6			14.7
	Net (Charge-Offs) Recoveries		1.9			(14.5	)		(12.6	)		1.2			(26.3	)		(25.1	)
	Provision for Credit Losses		(0.8	)		3.8			3			(15.8	)		30.8			15
	Effect of Foreign Exchange Rates		—			—			—			—			—			—
	Balance at End of Period	$	169.1		$	129.2		$	298.3		$	179.6		$	137.9		$	317.5
Allowances for Credit Losses and Recorded Investments in Loans and Leases by Segment	'
	The following table provides information regarding the balances of the recorded investments in loans and leases and the allowance for credit losses by segment as of September 30, 2014, and December 31, 2013.
		September 30, 2014									December 31, 2013
	(In Millions)	Commercial			Personal			Total			Commercial			Personal			Total
	Loans and Leases
	Specifically Evaluated for Impairment	$	97.9		$	172.5		$	270.4		$	99.5		$	193.9		$	293.4
	Evaluated for Inherent Impairment		13,770.70			16,678.80			30,449.50			12,520.50			16,571.60			29,092.10
	Total Loans and Leases		13,868.60			16,851.30			30,719.90			12,620.00			16,765.50			29,385.50
	Allowance for Loans and Leases
	Specifically Evaluated for Impairment		8.6			0.9			9.5			8.1			2.3			10.4
	Evaluated for Inherent Impairment		134.5			125.4			259.9			132.8			134.9			267.7
	Allowance Assigned to Loans and Leases		143.1			126.3			269.4			140.9			137.2			278.1
	Allowance for Unfunded Exposures
	Commitments and Standby Letters of Credit		26			2.9			28.9			27.1			2.7			29.8
	Total Allowance for Credit Losses	$	169.1		$	129.2		$	298.3		$	168		$	139.9		$	307.9

Goodwill_and_Other_Intangibles1

Goodwill and Other Intangibles (Tables)	9 Months Ended
	Sep. 30, 2014
Carrying Amounts of Goodwill	'
	The carrying amounts of goodwill, reflecting the effect of foreign exchange rates on non-U.S. dollar denominated balances, by business unit at September 30, 2014, and December 31, 2013, were as follows:
	(In Millions)	September 30,		December 31,
		2014		2013
	Corporate & Institutional Services	$	466.6	$	469.2
	Wealth Management		71.5		71.5
	Total Goodwill	$	538.1	$	540.7
Other Intangible Assets Subject to Amortization	'
	The gross carrying amount and accumulated amortization of other intangible assets subject to amortization as of September 30, 2014, and December 31, 2013, were as follows:
	(In Millions)	September 30,		December 31,
		2014		2013
	Gross Carrying Amount	$	193.4	$	198.2
	Less: Accumulated Amortization		127.6		115.2
	Net Book Value	$	65.8	$	83

Business_Units_Tables

Business Units (Tables)	9 Months Ended
	Sep. 30, 2014
Earnings Contribution of Northern Trust's Business Units	'
	The following tables show the earnings contributions of Northern Trust’s business units for the three and nine month periods ended September 30, 2014, and 2013.
	Three Months Ended		Corporate &						Wealth						Treasury and						Total
	September 30,		Institutional Services						Management						Other						Consolidated
	($ In Millions)		2014			2013			2014			2013			2014			2013			2014			2013
	Noninterest Income
	Trust, Investment and Other Servicing Fees		$	399.9		$	359.8		$	318.3		$	288.2		$	—		$	—		$	718.2		$	648
	Foreign Exchange Trading Income			44.4			61.8			2			1			—			—			46.4			62.8
	Other Noninterest Income			42.8			44.3			20.9			54.3			1.3			0.8			65			99.4
	Net Interest Income*			78.4			70.1			131.2			136.3			46.6			38.4			256.2			244.8
	Revenue*			565.5			536			472.4			479.8			47.9			39.2			1,085.80			1,055.00
	Provision for Credit Losses			0.9			0.4			(0.9	)		4.6			—			—			—			5
	Noninterest Expense			429.6			412			312.1			297.3			33			31.4			774.7			740.7
	Income before Income Taxes*			135			123.6			161.2			177.9			14.9			7.8			311.1			309.3
	Provision (Benefit) for Income Taxes*			42.4			38.8			60.7			67			3.5			(3.0	)		106.6			102.8
	Net Income		$	92.6		$	84.8		$	100.5		$	110.9		$	11.4		$	10.8		$	204.5		$	206.5
	Percentage of Consolidated Net Income			45	%		41	%		49	%		54	%		6	%		5	%		100	%		100	%
	Average Assets		$	59,907.10		$	53,653.50		$	26,061.80		$	22,923.60		$	19,275.80		$	18,635.40		$	105,244.70		$	95,212.50
	*	Stated on a fully taxable equivalent basis (FTE). Total consolidated includes FTE adjustments of $6.9 million for 2014 and $7.8 million for 2013.
	Nine Months Ended		Corporate &						Wealth						Treasury and						Total
	September 30,		Institutional Services						Management						Other						Consolidated
	($ In Millions)		2014			2013			2014			2013			2014			2013			2014			2013
	Noninterest Income
	Trust, Investment and Other Servicing Fees		$	1,174.50		$	1,072.70		$	930.1		$	863.3		$	—		$	—		$	2,104.60		$	1,936.00
	Foreign Exchange Trading Income			143.2			189.8			6.2			3.8			—			—			149.4			193.6
	Other Noninterest Income			134.3			130.1			66.7			95.8			4.5			5.4			205.5			231.3
	Net Interest Income*			228.8			200.2			398.8			425.3			136.4			81			764			706.5
	Revenue*			1,680.80			1,592.80			1,401.80			1,388.20			140.9			86.4			3,223.50			3,067.40
	Provision for Credit Losses			4.5			(1.1	)		(1.5	)		16.1			—			—			3			15
	Noninterest Expense			1,299.50			1,206.70			960.3			900.9			93.9			91.7			2,353.70			2,199.30
	Income (loss) before Income Taxes*			376.8			387.2			443			471.2			47			(5.3	)		866.8			853.1
	Provision (Benefit) for Income Taxes*			113.3			123			166.9			177.8			18.8			(9.3	)		299			291.5
	Net Income		$	263.5		$	264.2		$	276.1		$	293.4		$	28.2		$	4		$	567.8		$	561.6
	Percentage of Consolidated Net Income			46	%		47	%		49	%		52	%		5	%		1	%		100	%		100	%
	Average Assets		$	59,061.30		$	52,323.80		$	23,613.40		$	22,863.10		$	20,281.10		$	18,036.60		$	102,955.80		$	93,223.50

Accumulated_Other_Comprehensiv1

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2014
Components of Accumulated Other Comprehensive Income (Loss)	'
	The following tables summarize the components of accumulated other comprehensive income (loss) at September 30, 2014, and 2013, and changes during the three and nine month periods then ended.
	(In Millions)	Balance at				Net Change				Balance at
		December 31,								September 30,
		2013								2014
	Net Unrealized Gains (Losses) on Securities Available for Sale	$	6			$	32.3			$	38.3
	Net Unrealized Gains (Losses) on Cash Flow Hedges		2.9				(6.4	)			(3.5	)
	Net Foreign Currency Adjustments		7.1				(10.5	)			(3.4	)
	Net Pension and Other Postretirement Benefit Adjustments		(260.3	)			10.5				(249.8	)
	Total	$	(244.3	)		$	25.9			$	(218.4	)
	(In Millions)	Balance at				Net Change				Balance at
		December 31,								September 30,
		2012								2013
	Net Unrealized Gains (Losses) on Securities Available for Sale	$	101			$	(74.4	)		$	26.6
	Net Unrealized Gains (Losses) on Cash Flow Hedges		(1.4	)			1.2				(0.2	)
	Net Foreign Currency Adjustments		10.5				(2.8	)			7.7
	Net Pension and Other Postretirement Benefit Adjustments		(393.1	)			21.1				(372.0	)
	Total	$	(283.0	)		$	(54.9	)		$	(337.9	)
Components of Changes in Accumulated Other Comprehensive Income (Loss)	'
		Three Months Ended September 30,
		2014											2013
	(In Millions)	Before Tax				Tax Effect				After Tax			Before Tax			Tax Effect			After Tax
	Unrealized Gains (Losses) on Securities Available for Sale
	Noncredit-Related Unrealized Gains (Losses) on Securities OTTI	$	5.5			$	(2.1	)		$	3.4		$	—		$	—		$	—
	Other Unrealized Gains (Losses) on Securities Available for Sale		(14.2	)			5.4				(8.8	)		7.3			(2.8	)		4.5
	Reclassification Adjustment for (Gains) Losses Included in Net Income		(0.3	)			—				(0.3	)		2.1			(0.8	)		1.3
	Net Change		(9.0	)			3.3				(5.7	)		9.4			(3.6	)		5.8
	Unrealized Gains (Losses) on Cash Flow Hedges
	Unrealized Gains (Losses) on Cash Flow Hedges		(7.6	)			2.5				(5.1	)		5.3			(1.7	)		3.6
	Reclassification Adjustment for (Gains) Losses Included in Net Income		(3.7	)			1.4				(2.3	)		1.1			(0.4	)		0.7
	Net Change		(11.3	)			3.9				(7.4	)		6.4			(2.1	)		4.3
	Foreign Currency Adjustments
	Foreign Currency Translation Adjustments		(77.1	)			6.6				(70.5	)		55			(4.0	)		51
	Long-Term Intra-Entity Foreign Currency Transaction Losses		(7.4	)			—				(7.4	)		—			—			—
	Net Investment Hedge Gains (Losses)		119.9				(45.6	)			74.3			(88.8	)		33.4			(55.4	)
	Reclassification Adjustment for (Gains) Losses Included in Net Income		—				—				—			—			—			—
	Net Change		35.4				(39.0	)			(3.6	)		(33.8	)		29.4			(4.4	)
	Pension and Other Postretirement Benefit Adjustments
	Net Actuarial Gain (Loss)		—				—				—			—			—			—
	Reclassification Adjustment for (Gains) Losses Included in Net Income		6.5				(3.0	)			3.5			11.3			(4.2	)		7.1
	Net Change	$	6.5			$	(3.0	)		$	3.5		$	11.3		$	(4.2	)	$	7.1
		Nine Months Ended September 30,
		2014											2013
	(In Millions)	Before Tax				Tax Effect				After Tax			Before Tax			Tax Effect			After Tax
	Unrealized Gains (Losses) on Securities Available for Sale
	Noncredit-Related Unrealized Gains (Losses) on Securities OTTI	$	3.7			$	(1.4	)		$	2.3		$	2.1		$	(0.8	)	$	1.3
	Other Unrealized Gains (Losses) on Securities Available for Sale		48.8				(18.2	)			30.6			(123.2	)		46.3			(76.9	)
	Reclassification Adjustment for (Gains) Losses Included in Net Income		(0.6	)			—				(0.6	)		1.9			(0.7	)		1.2
	Net Change		51.9				(19.6	)			32.3			(119.2	)		44.8			(74.4	)
	Unrealized Gains (Losses) on Cash Flow Hedges
	Unrealized Gains (Losses) on Cash Flow Hedges		(6.5	)			2.2				(4.3	)		(4.0	)		1.6			(2.4	)
	Reclassification Adjustment for (Gains) Losses Included in Net Income		(3.3	)			1.2				(2.1	)		5.7			(2.1	)		3.6
	Net Change		(9.8	)			3.4				(6.4	)		1.7			(0.5	)		1.2
	Foreign Currency Adjustments
	Foreign Currency Translation Adjustments		(57.2	)			6				(51.2	)		5.3			(2.3	)		3
	Long-Term Intra-Entity Foreign Currency Transaction Losses		(9.0	)			—				(9.0	)		—			—			—
	Net Investment Hedge Gains (Losses)		79.7				(30.0	)			49.7			(9.3	)		3.5			(5.8	)
	Reclassification Adjustment for (Gains) Losses Included in Net Income		—				—				—			—			—			—
	Net Change		13.5				(24.0	)			(10.5	)		(4.0	)		1.2			(2.8	)
	Pension and Other Postretirement Benefit Adjustments
	Net Actuarial Gain (Loss)		—				—				—			—			—			—
	Reclassification Adjustment for (Gains) Losses Included in Net Income		19				(8.5	)			10.5			33.7			(12.6	)		21.1
	Net Change	$	19			$	(8.5	)		$	10.5		$	33.7		$	(12.6	)	$	21.1
Reclassification Out of Accumulated Other Comprehensive Income (Loss)	'
	The following table provides the location and before-tax amounts of reclassifications out of accumulated other comprehensive income (loss) during the three and nine months ended September 30, 2014.
	(In Millions)	Location of		Amount of Reclassification
		Reclassification Adjustments		Adjustments Recognized
		Recognized in Income		in Income
				Three Months Ended				Nine Months Ended
				30-Sep-14
	Securities Available for Sale
	Realized (Gains) Losses on Securities Available for Sale	Investment Security Gains (Losses), net		$	(0.3	)		$	(0.6	)
	Realized (Gains) Losses on Cash Flow Hedges
	Foreign Exchange Contracts	Other Operating Income/Expense			(3.7	)			(3.3	)
	Pension and Other Postretirement Benefit Adjustments
	Amortization of Net Actuarial (Gain) Loss	Employee Benefits			(0.3	)			(1.1	)
	Amortization of Prior Service Cost	Employee Benefits			6.8				20.1
	Gross Reclassification Adjustment			$	6.5			$	19

Net_Income_Per_Common_Share_Co1

Net Income Per Common Share Computations (Tables)	9 Months Ended
	Sep. 30, 2014
Computations of Net Income per Common Share	'
	The computations of net income per common share are presented in the following table.
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	($ In Millions Except Per Common Share Information)	2014		2013		2014		2013
	Basic Net Income Per Common Share
	Average Number of Common Shares Outstanding		235,701,076		239,930,074		236,301,789		239,614,868
	Net Income	$	204.5	$	206.5	$	567.8	$	561.6
	Less: Dividends on Preferred Stock		—		—		—		—
	Net Income Applicable to Common Stock		204.5		206.5		567.8		561.6
	Less: Earnings Allocated to Participating Securities		3.5		3.5		9.5		9.1
	Earnings Allocated to Common Shares Outstanding		201		203		558.3		552.5
	Basic Net Income Per Common Share	$	0.85	$	0.85	$	2.36	$	2.31
	Diluted Net Income Per Common Share
	Average Number of Common Shares Outstanding		235,701,076		239,930,074		236,301,789		239,614,868
	Plus: Dilutive Effect of Share-based Compensation		2,036,053		1,400,578		1,873,907		1,242,829
	Average Common and Potential Common Shares		237,737,129		241,330,652		238,175,696		240,857,697
	Earnings Allocated to Common and Potential
	Common Shares	$	201	$	203	$	558.4	$	552.5
	Diluted Net Income Per Common Share		0.84		0.84		2.34		2.29

Net_Interest_Income_Tables

Net Interest Income (Tables)	9 Months Ended
	Sep. 30, 2014
Components of Net Interest Income	'
	The components of net interest income were as follows:
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	(In Millions)	2014		2013		2014		2013
	Interest Income
	Loans and Leases	$	184.8	$	185.4	$	553.5	$	558.5
	Securities — Taxable		65.1		60.9		198		167.6
	— Non-Taxable		1.6		2.7		5.7		9
	Interest-Bearing Deposits with Banks		30.9		36.3		96.6		105.8
	Federal Reserve Deposits and Other		11.4		5.8		29.2		12.2
	Total Interest Income		293.8		291.1		883		853.1
	Interest Expense
	Deposits		21.6		25.8		64.1		79.9
	Federal Funds Purchased		0.5		0.4		1.1		1
	Securities Sold Under Agreements to Repurchase		0.1		0.1		0.3		0.3
	Other Borrowings		0.9		0.8		2.4		2.5
	Senior Notes		11.6		18.4		42.8		56.9
	Long-Term Debt		9.2		8		29		27.5
	Floating Rate Capital Debt		0.6		0.6		1.7		1.8
	Total Interest Expense		44.5		54.1		141.4		169.9
	Net Interest Income	$	249.3	$	237	$	741.6	$	683.2

Pension_and_Other_Postretireme1

Pension and Other Postretirement Plans (Tables)	9 Months Ended
	Sep. 30, 2014
Components of Company's Net Periodic Benefit Cost	'
	The following tables set 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 other postretirement plan for the three and nine months ended September 30, 2014, and 2013.
	Net Periodic Pension Expense	Three Months Ended						Nine Months Ended
	U.S. Plan	September 30,						September 30,
	(In Millions)	2014			2013			2014			2013
	Service Cost	$	8.2		$	7.5		$	24.6		$	22.7
	Interest Cost		11.1			10.5			33.3			31.6
	Expected Return on Plan Assets		(24.4	)		(23.1	)		(73.3	)		(69.2	)
	Amortization
	Net Actuarial Loss		(0.1	)		10.3			(0.3	)		30.9
	Prior Service Cost		5.4			(0.1	)		16.1			(0.3	)
	Net Periodic Pension Expense	$	0.2		$	5.1		$	0.4		$	15.7
	Net Periodic Pension Expense (Benefit)	Three Months Ended						Nine Months Ended
	Non U.S. Plans	September 30,						September 30,
	(In Millions)	2014			2013			2014			2013
	Interest Cost	$	1.8		$	1.6		$	5.3		$	4.9
	Expected Return on Plan Assets		(1.8	)		(1.5	)		(5.3	)		(4.6	)
	Net Actuarial Loss Amortization		(0.4	)		0.2			(1.2	)		0.7
	Net Periodic Pension Expense (Benefit)	$	(0.4	)	$	0.3		$	(1.2	)	$	1
	Net Periodic Pension Expense	Three Months Ended						Nine Months Ended
	Supplemental Plan	September 30,						September 30,
	(In Millions)	2014			2013			2014			2013
	Service Cost	$	0.8		$	0.4		$	2.3		$	1.2
	Interest Cost		1.2			1.1			3.6			3.3
	Amortization
	Net Actuarial Loss		0.2			1.7			0.4			5.1
	Prior Service Cost		1.5			0.2			4.4			0.4
	Net Periodic Pension Expense	$	3.7		$	3.4		$	10.7		$	10
	Net Periodic Postretirement Expense (Benefit)	Three Months Ended						Nine Months Ended
	Other Postretirement Plan	September 30,						September 30,
	(In Millions)	2014			2013			2014			2013
	Service Cost	$	—		$	—		$	0.1		$	0.1
	Interest Cost		0.4			0.3			1.1			0.9
	Amortization
	Net Actuarial Gain		—			(0.3	)		—			(0.9	)
	Prior Service Cost		(0.1	)		(0.7	)		(0.4	)		(2.2	)
	Net Periodic Postretirement Expense (Benefit)	$	0.3		$	(0.7	)	$	0.8		$	(2.1	)

ShareBased_Compensation_Plans_

Share-Based Compensation Plans (Tables)	9 Months Ended
	Sep. 30, 2014
Compensation Expense for Share-Based Payment Arrangements and Associated Tax Impacts	'
	Total compensation expense for share-based payment arrangements and the associated tax impacts were as follows for the three and nine months ended September 30, 2014, and 2013.
		Three Months Ended				Nine Months Ended
		September 30,				September 30,
	(In Millions)	2014		2013		2014		2013
	Restricted Stock Unit Awards	$	12.7	$	12.1	$	41.7	$	36.4
	Stock Options		2.2		3.7		10.7		14.9
	Performance Stock Units		3.1		2.1		8.9		5.4
	Total Share-Based Compensation Expense		18		17.9		61.3		56.7
	Tax Benefits Recognized	$	6.8	$	6.8	$	23	$	21.3

Derivative_Financial_Instrumen1

Derivative Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2014
Notional and Fair Value Amounts of Client-related and Trading Derivative Financial Instruments	'
	The following table shows the notional and fair values of client-related and trading derivative financial instruments. Notional amounts of derivative financial instruments do not represent credit risk, and are not recorded in the consolidated balance sheet. 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, which is significantly less than the notional amount.
		September 30, 2014												December 31, 2013
		Notional				Fair Value								Notional				Fair Value
	(In Millions)	Value				Asset				Liability				Value				Asset			Liability
	Foreign Exchange Contracts	$	270,022.40			$	4,132.80			$	4,125.50			$	243,135.00			$	2,844.70		$	2,846.20
	Interest Rate Contracts		5,048.90				100.2				95.9				5,001.70				122.8			117
	Total	$	275,071.30			$	4,233.00			$	4,221.40			$	248,136.70			$	2,967.50		$	2,963.20
Location and Amount of Gains and Losses Recorded in Consolidated Statement of Income	'
	The following table shows the location and amount of gains and losses recorded in the consolidated statement of income for the three and nine months ended September 30, 2014, and 2013.
		Location of Derivative Gain/(Loss)		Amount of Derivative Gain/(Loss) Recognized in Income
		Recognized in Income		Three Months Ended								Nine Months Ended
				September 30,								September 30,
	(In Millions)			2014				2013				2014				2013
	Foreign Exchange Contracts	Foreign Exchange Trading Income		$	46.4			$	62.8			$	149.4			$	193.6
	Interest Rate Contracts	Security Commissions and Trading Income			0.6				4.4				4.6				11.4
	Total			$	47			$	67.2			$	154			$	205
Types and Classifications of Derivative Instruments	'
	The following table identifies the types and classifications of derivative instruments formally designated as hedges under GAAP and used by Northern Trust to manage risk, their notional and fair values, and the respective risks addressed.
						September 30, 2014												December 31, 2013
	(In Millions)	Derivative		Risk		Notional				Fair Value								Notional			Fair Value
		Instrument		Classification		Value				Asset				Liability				Value			Asset		Liability
	Fair Value Hedges
	Available for Sale Investment Securities	Interest Rate Swap Contracts		Interest		$	2,939.70			$	20.8			$	24.9			$	3,296.90		$	31.5	$	44.8
				Rate
	Senior Notes and Long-Term Subordinated Debt	Interest Rate Swap Contracts		Interest			1,250.00				92.4				2				1,250.00			83.6		33.4
				Rate
	Cash Flow Hedges
	Forecasted Foreign Currency Denominated Transactions	Foreign Exchange Contracts		Foreign			341				5.2				9.5				314			10.2		5.5
				Currency
	Available for Sale Investment Securities	Interest Rate Swap Contracts		Interest			10				—				—				—			—		—
				Rate
	Available for Sale Investment Securities	Interest Rate Option Contracts		Interest			375				0.1				0.7				—			—		—
				Rate
	Net Investment Hedges
	Net Investments in Non-U.S. Affiliates	Foreign Exchange Contracts		Foreign			1,753.60				65.5				3.1				1,684.90			9.8		52.8
				Currency
	Total					$	6,669.30			$	184			$	40.2			$	6,545.80		$	135.1	$	136.5
Gains/Losses of Derivative Financial Instruments	'
	The following table shows the location and amount of derivative gains and losses recorded in the consolidated statement of income related to fair value hedges for the three and nine months ended September 30, 2014, and 2013.
	(In Millions)	Derivative		Location of		Amount of Derivative
		Instrument		Derivative		Gain/(Loss) Recognized in Income
				Gain/(Loss)
				Recognized in		Three Months Ended								Nine Months Ended
				Income		September 30,								September 30,
						2014				2013				2014				2013
	Available for Sale Investment Securities	Interest Rate Swap Contracts		Interest		$	5.1			$	(16.4	)		$	(21.9	)		$	21.6
				Income
	Senior Notes and Long-Term Subordinated Debt	Interest Rate Swap Contracts		Interest			5.8				(3.6	)			66				(16.1	)
				Expense
	Total					$	10.9			$	(20.0	)		$	44.1			$	5.5
Cash Flow Hedge Derivative Gains and Losses Recognized in AOCI and the Amounts Reclassified to Earnings	'
	The following tables provide cash flow hedge derivative gains and losses recognized in AOCI and the amounts reclassified to earnings during the three and nine months ended September 30, 2014, and 2013.
	(In Millions)	Foreign Exchange								Interest Rate Swap								Interest Rate Option
		Contracts (Before Tax)								Contracts (Before Tax)								Contracts (Before Tax)
	Three Months Ended September 30,	2014				2013				2014				2013				2014			2013
	Net Gain/(Loss) Recognized in AOCI	$	(6.9	)		$	5.3			$	—			$	—			$	(0.7	)	$	—
	Net Gain/(Loss) Reclassified from AOCI to Earnings
	Other Operating Income		0.7				—				—				—				—			—
	Interest Income		—				—				—				—				0.1			—
	Other Operating Expense		—				(1.1	)			—				—				—			—
	Total	$	0.7			$	(1.1	)		$	—			$	—			$	0.1		$	—
	(In Millions)	Foreign Exchange								Interest Rate Swap								Interest Rate Option
		Contracts (Before Tax)								Contracts (Before Tax)								Contracts (Before Tax)
	Nine Months Ended September 30,	2014				2013				2014				2013				2014			2013
	Net Gain/(Loss) Recognized in AOCI	$	(5.8	)		$	(4.0	)		$	—			$	—			$	(0.7	)	$	—
	Net Gain/(Loss) Reclassified from AOCI to Earnings
	Other Operating Income		3.4				(1.8	)			—				—				—			—
	Interest Income		—				—				—				—				0.1			—
	Other Operating Expense		(0.2	)			(3.9	)			—				—				—			—
	Total	$	3.2			$	(5.7	)		$	—			$	—			$	0.1		$	—
Net Investment Hedge Gains and Losses Recognized in AOCI	'
	The following table provides net investment hedge gains and losses recognized in AOCI during the three and nine months ended September 30, 2014, and 2013.
		Hedging Gain/(Loss)
		Recognized in OCI (Before Tax)
		Three Months Ended September 30,								Nine Months Ended September 30,
	(In Millions)	2014				2013				2014				2013
	Foreign Exchange Contracts	$	106.2			$	(73.8	)		$	74.3			$	(9.5	)
	Sterling Denominated Subordinated Debt		13.7				(15.0	)			5.4				0.2
	Total	$	119.9			$	(88.8	)		$	79.7			$	(9.3	)
Types of Risk Management Derivative Instruments Not Formally Designated as Hedges, Including Notional Amounts and Fair Values	'
	The following table identifies the types of risk management derivative instruments not formally designated as hedges and their notional amounts and fair values.
	(In Millions)	September 30, 2014												December 31, 2013
		Notional				Fair Value								Notional				Fair Value
		Value				Asset				Liability				Value				Asset			Liability
	Foreign Exchange Contracts	$	192.3			$	0.3			$	3.5			$	168.8			$	1		$	1.2
Gains/Losses of Derivative Financial Instruments	'
	The following table provides the location and amount of gains and losses recorded in the consolidated statement of income for the three and nine months ended September 30, 2014, and 2013.
	(In Millions)	Location of		Amount of Derivative Gain/(Loss)
		Derivative Gain/		Recognized in Income
		(Loss) Recognized		Three Months Ended								Nine Months Ended
		in Income		September 30,								September 30,
				2014				2013				2014				2013
	Credit Default Swap Contracts	Other Operating Income		$	—			$	—			$	—			$	(0.1	)
	Foreign Exchange Contracts	Other Operating Income			(10.1	)			6.7				(9.3	)			(4.3	)
	Total			$	(10.1	)		$	6.7			$	(9.3	)		$	(4.4	)

Offsetting_of_Assets_and_Liabi1

Offsetting of Assets and Liabilities (Tables)	9 Months Ended
	Sep. 30, 2014
Securities Purchased Under Agreements to Resell and Derivative Assets in the Consolidated Balance Sheet	'
	The following tables provide information regarding the offsetting of derivative assets and securities purchased under agreements to resell within the consolidated balance sheet as of September 30, 2014, and December 31, 2013.
	September 30, 2014
	(In Millions)		Gross		Gross		Net		Gross		Net
			Recognized		Amounts		Amounts		Amounts		Amount (3)
			Assets		Offset		Presented		Not Offset
	Derivative Assets (1)
	Foreign Exchange Contracts Over the Counter (OTC)		$	3,265.00	$	2,085.00	$	1,180.00	$	—	$	1,180.00
	Interest Rate Swaps OTC			183.7		31.5		152.2		—		152.2
	Interest Rate Swaps Exchange Cleared			29.8		7.4		22.4		—		22.4
	Cross Product Netting Adjustment			—		27.1		—		—		—
	Cross Product Collateral Adjustment			—		207.4		—		—		—
	Total Derivatives Subject to a Master Netting Arrangement			3,478.50		2,358.40		1,120.10		—		1,120.10
	Total Derivatives Not Subject to a Master Netting Arrangement			938.8		—		938.8		—		938.8
	Total Derivatives			4,417.30		2,358.40		2,058.90		—		2,058.90
	Securities Purchased under Agreements to Resell (2)		$	1,000.00	$	—	$	1,000.00	$	1,000.00	$	—
	December 31, 2013
	(In Millions)		Gross		Gross		Net		Gross		Net
			Recognized		Amounts		Amounts		Amounts		Amount (3)
			Assets		Offset		Presented		Not Offset
	Derivative Assets (1)
	Foreign Exchange Contracts OTC		$	2,612.50	$	1,073.30	$	1,539.20	$	—	$	1,539.20
	Interest Rate Swaps OTC			228.8		47.5		181.3		—		181.3
	Interest Rate Swaps Exchange Cleared			9.1		9.1		—		—		—
	Cross Product Netting Adjustment			—		28.4		—		—		—
	Cross Product Collateral Adjustment			—		210.7		—		—		—
	Total Derivatives Subject to a Master Netting Arrangement			2,850.40		1,369.00		1,481.40		—		1,481.40
	Total Derivatives Not Subject to a Master Netting Arrangement			253.2		—		253.2		—		253.2
	Total Derivatives			3,103.60		1,369.00		1,734.60		—		1,734.60
	Securities Purchased under Agreements to Resell (2)		$	500	$	—	$	500	$	500	$	—
	-1	Derivative assets are reported in other assets in the consolidated balance sheet. Other assets (excluding derivative assets) totaled $3,230.9 million and $3,029.4 million as of September 30, 2014, and December 31, 2013, respectively.
	-2	Securities purchased under agreements to resell are reported in federal funds sold and securities purchased under agreements to resell in the consolidated balance sheet. Federal funds sold totaled $10.0 million and $29.6 million as of September 30, 2014, and December 31, 2013, respectively.
	-3	Northern Trust did not possess any cash collateral that was not offset in the consolidated balance sheet that could have been used to offset the net amounts presented in the consolidated balance sheet as of September 30, 2014, and December 31, 2013.
Securities Sold Under Agreements to Repurchase and Derivative Liabilities in the Consolidated Balance Sheet	'
	The following tables provide information regarding the offsetting of derivative liabilities and securities sold under agreements to repurchase within the consolidated balance sheet as of September 30, 2014, and December 31, 2013.
	September 30, 2014
	(In Millions)		Gross		Gross		Net		Gross		Net
			Recognized		Amounts		Amounts		Amounts		Amount (2)
			Liabilities		Offset		Presented		Not
									Offset
	Derivative Liabilities (1)
	Foreign Exchange Contracts OTC		$	3,404.30	$	2,085.00	$	1,319.30	$	—	$	1,319.30
	Interest Rate Swaps OTC			116.1		31.5		84.6		—		84.6
	Interest Rate Swaps Exchange Cleared			7.4		7.4		—		—		—
	Cross Product Netting Adjustment			—		27.1		—		—		—
	Cross Product Collateral Adjustment			—		601.3		—		—		—
	Total Derivatives Subject to a Master Netting Arrangement			3,527.80		2,752.30		775.5		—		775.5
	Total Derivatives Not Subject to a Master Netting Arrangement			737.3		—		737.3		—		737.3
	Total Derivatives			4,265.10		2,752.30		1,512.80		—		1,512.80
	Securities Sold under Agreements to Repurchase		$	866.8	$	—	$	866.8	$	866.8	$	—
	December 31, 2013
	(In Millions)		Gross		Gross		Net		Gross		Net
			Recognized		Amounts		Amounts		Amounts		Amount (2)
			Liabilities		Offset		Presented		Not
									Offset
	Derivative Liabilities (1)
	Foreign Exchange Contracts OTC		$	2,039.00	$	1,073.30	$	965.7	$	—	$	965.7
	Interest Rate Swaps OTC			163.7		47.5		116.2		—		116.2
	Interest Rate Swaps Exchange Cleared			31.5		9.1		22.4		—		22.4
	Cross Product Netting Adjustment			—		28.4		—		—		—
	Cross Product Collateral Adjustment			—		767.7		—		—		—
	Total Derivatives Subject to a Master Netting Arrangement			2,234.20		1,926.00		308.2		—		308.2
	Total Derivatives Not Subject to a Master Netting Arrangement			866.7		—		866.7				866.7
	Total Derivatives			3,100.90		1,926.00		1,174.90		—		1,174.90
	Securities Sold under Agreements to Repurchase		$	917.3	$	—	$	917.3	$	917.3	$	—
	-1	Derivative liabilities are reported in other liabilities in the consolidated balance sheet. Other liabilities (excluding derivative liabilities) totaled $2,591.5 million and $2,338.4 million as of September 30, 2014, and December 31, 2013, respectively.
	-2	Northern Trust did not place any cash collateral with counterparties that was not offset in the consolidated balance sheet that could have been used to offset the net amounts presented in the consolidated balance sheet as of September 30, 2014, and December 31, 2013.

Fair_Value_Measurements_Additi

Fair Value Measurements - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	Apr. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'	'	'
Available for sale securities portfolio, value	'	$28,107,700,000	'	$28,392,800,000
Trading account securities	'	4,300,000	'	1,700,000
Settlement of contingent consideration	55,300,000	'	'	'
Transfers into Level 3 assets	'	0	0	'
Transfers out of Level 3 assets	'	0	0	'
Transfers into Level 3 liabilities	'	0	0	'
Transfers out of Level 3 liabilities	'	0	0	'
Level 2	'	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'	'	'
Number of available for sale securities portfolio	'	843	'	831
Available for sale securities portfolio, value	'	24,600,000,000	'	26,400,000,000
Loans | Level 3	'	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'	'	'
Financial Instrument, fair value	'	26,600,000	38,100,000	'
Other Real Estate Owned | Level 3	'	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'	'	'
Financial Instrument, fair value	'	1,500,000	1,600,000	'
External Pricing | Level 2	'	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'	'	'
Number of available for sale securities portfolio	'	842	'	829
Available for sale securities portfolio, value	'	24,500,000,000	'	26,300,000,000
Trading account securities	'	4,300,000	'	1,700,000
Internal Pricing | Level 2	'	'	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'	'	'
Number of available for sale securities portfolio	'	'	'	2
Available for sale securities portfolio, value	'	$88,000,000	'	$57,400,000

Valuation_Techniques_Significa

Valuation Techniques, Significant Unobservable Inputs, and Quantitative Information (Detail) (Fair Value, Inputs, Level 3, Auction Rate Securities, USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'
Financial instrument, fair value	85.2
Group One	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'
Valuation Technique	'Discounted Cash Flow
Unobservable Inputs	'Remaining lives
Group Two	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'
Valuation Technique	'Discounted Cash Flow
Unobservable Inputs	'Discount rates
Lower Limit	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'
Financial instrument remaining lives	'1 year 8 months 12 days
Financial instrument discount rate	0.20%
Upper Limit	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'
Financial instrument remaining lives	'8 years 7 months 6 days
Financial instrument discount rate	7.90%

Assets_and_Liabilities_Measure

Assets and Liabilities Measured at Fair Value on Recurring Basis Segregated by Fair Value Hierarchy Level (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	$28,107.70		$28,392.80
Trading Account	4.3		1.7
Contingent Consideration	'		55.4
Fair Value, Measurements, Recurring	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Total Available for Sale and Trading Securities	28,112		28,394.50
Contingent Consideration	'		55.4
Fair Value, Measurements, Recurring | Securities Investment	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	28,107.70		28,392.80
Trading Account	4.3		1.7
Fair Value, Measurements, Recurring | Securities Investment | U.S. Government	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	3,409.60		1,917.90
Fair Value, Measurements, Recurring | Securities Investment | Obligations of States and Political Subdivisions	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	4.6		4.6
Fair Value, Measurements, Recurring | Securities Investment | U.S. Government Sponsored Agency	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	16,174.40		17,528
Fair Value, Measurements, Recurring | Securities Investment | Non-U.S. Government	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	310.5		310.6
Fair Value, Measurements, Recurring | Securities Investment | Corporate Debt	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	3,364.80		3,524.50
Fair Value, Measurements, Recurring | Securities Investment | Covered Bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	1,978.90		1,943.90
Fair Value, Measurements, Recurring | Securities Investment | Supranational and Non-U.S. Agency Bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	360.2		410
Fair Value, Measurements, Recurring | Securities Investment | Residential Mortgage-Backed	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	17.6		48.1
Fair Value, Measurements, Recurring | Securities Investment | Other Asset-Backed	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	2,233.10		2,391.80
Fair Value, Measurements, Recurring | Securities Investment | Auction Rate Securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	85.2		98.9
Fair Value, Measurements, Recurring | Securities Investment | Others	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	168.8		214.5
Fair Value, Measurements, Recurring | Other Assets	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Assets	2,058.90		1,734.60
Fair Value, Measurements, Recurring | Other Assets | Foreign Exchange Contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Assets	4,203.80		2,865.70
Fair Value, Measurements, Recurring | Other Assets | Interest Rate Contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Assets	213.5		237.9
Fair Value, Measurements, Recurring | Other Liabilities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Liabilities	1,512.80		1,174.90
Fair Value, Measurements, Recurring | Other Liabilities | Foreign Exchange Contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Liabilities	4,141.60		2,905.70
Fair Value, Measurements, Recurring | Other Liabilities | Interest Rate Contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Liabilities	123.5		195.2
Fair Value, Measurements, Recurring | Subject to master netting arrangement or similar arrangement | Other Assets	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Assets	-2,358.40	[1]	-1,369	[2]
Fair Value, Measurements, Recurring | Subject to master netting arrangement or similar arrangement | Other Liabilities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Liabilities	-2,752.30	[1]	-1,926	[2]
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Total Available for Sale and Trading Securities	3,409.60		1,917.90
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Securities Investment	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	3,409.60		1,917.90
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 1 | Securities Investment | U.S. Government	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	3,409.60		1,917.90
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Total Available for Sale and Trading Securities	24,617.20		26,377.70
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	24,612.90		26,376
Trading Account	4.3		1.7
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Obligations of States and Political Subdivisions	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	4.6		4.6
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | U.S. Government Sponsored Agency	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	16,174.40		17,528
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Non-U.S. Government	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	310.5		310.6
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Corporate Debt	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	3,364.80		3,524.50
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Covered Bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	1,978.90		1,943.90
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Supranational and Non-U.S. Agency Bonds	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	360.2		410
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Residential Mortgage-Backed	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	17.6		48.1
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Other Asset-Backed	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	2,233.10		2,391.80
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Securities Investment | Others	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	168.8		214.5
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Assets	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Assets	4,417.30		3,103.60
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Assets | Foreign Exchange Contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Assets	4,203.80		2,865.70
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Assets | Interest Rate Contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Assets	213.5		237.9
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Liabilities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Liabilities	4,265.10		3,100.90
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Liabilities | Foreign Exchange Contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Liabilities	4,141.60		2,905.70
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 2 | Other Liabilities | Interest Rate Contracts	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Derivative Liabilities	123.5		195.2
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Total Available for Sale and Trading Securities	85.2		98.9
Contingent Consideration	'		55.4
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Securities Investment	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	85.2		98.9
Fair Value, Measurements, Recurring | Fair Value, Inputs, Level 3 | Securities Investment | Auction Rate Securities	'		'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'		'
Available for Sale	$85.20		$98.90
[1]	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 September 30, 2014, derivative assets and liabilities shown above also include reductions of $207.4 million and $601.3 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties.
[2]	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, 2013, derivative assets and liabilities shown above also include reductions of $210.7 million and $767.7 million, respectively, as a result of cash collateral received from and deposited with derivative counterparties.

Assets_and_Liabilities_Measure1

Assets and Liabilities Measured at Fair Value on Recurring Basis Segregated by Fair Value Hierarchy Level (Parenthetical) (Detail) (Subject to master netting arrangement or similar arrangement, Fair Value, Measurements, Recurring, USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Derivative Financial Instruments, Liabilities	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	$601.30	$767.70
Derivative Financial Instruments, Assets	'	'
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]	'	'
Reduction in derivatives due to cash collateral received from and deposited with derivative counterparties	$207.40	$210.70

Changes_in_Level_3_Assets_Deta

Changes in Level 3 Assets (Detail) (Auction Rate Securities, USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Auction Rate Securities	'		'		'		'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'		'
Fair Value Assets Beginning Balance	$98.80		$99.10		$98.90		$97.80
Total Gains (Losses):	'		'		'		'
Included in Earnings	0.7		'		0.7	[1]	0.1	[1]
Included in Other Comprehensive Income	0.1	[2]	0.3	[2]	0.4	[2]	3	[2]
Purchases, Issuances, Sales, and Settlements:	'		'		'		'
Sales	-14.4		'		-14.4		'
Settlements	'		'		-0.4		-2.2
Fair Value Assets Ending Balance	$85.20		$98.70		$85.20		$98.70
[1]	Realized gains for the three and nine months ended September 30, 2014, of $0.7 million, represent gains from sales of securities. Realized gains for the nine month period ended September 30, 2013, of $0.1 million, represent gains from redemptions by issuers. Gains on sales are recorded in investment security gains (losses) and gains on redemptions are recorded in interest income, within the consolidated statement of income.
[2]	Unrealized gains (losses) are included in net unrealized gains (losses) on securities available for sale within the consolidated statement of comprehensive income.

Changes_in_Level_3_Assets_Pare

Changes in Level 3 Assets (Parenthetical) (Detail) (Auction Rate Securities, Redemptions by Issuers, USD $)	3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013
Auction Rate Securities | Redemptions by Issuers	'	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'	'	'
Realized gains (losses) on securities	$0.70	$0.70	$0.10

Changes_in_Level_3_Liabilities

Changes in Level 3 Liabilities (Detail) (Contingent Consideration, USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Contingent Consideration	'		'		'
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]	'		'		'
Fair Value Liabilities Beginning Balance	$52.70		$55.40		$50.10
Total (Gains) and Losses:	'		'		'
Included in Earnings	1.3	[1]	-0.1	[1]	3.9	[1]
Purchases, Issues, Sales, and Settlements	'		'		'
Settlements	'		-55.3		'
Fair Value Liabilities Ending Balance	54		'		54
Unrealized (Gains) Losses Included in Earnings Related to Financial Instruments Held at June 30	$1.30	[1]	'		$3.90	[1]
[1]	(Gains) losses are recorded in other operating income (expense) within the consolidated statement of income.

Valuation_Techniques_Significa1

Valuation Techniques, Significant Unobservable Inputs, Quantitative Information Non-recurring Basis (Detail) (Fair Value, Inputs, Level 3, USD $)	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014
Loans	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Financial Instrument, fair value	$26.60
Valuation Technique	'Market Approach
Unobservable Input	'Discount to reflect realizable value
Other Real Estate Owned	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Financial Instrument, fair value	$1.50
Valuation Technique	'Market Approach
Unobservable Input	'Discount to reflect realizable value
Lower Limit | Loans	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Range of Discounts Applied	15.00%
Lower Limit | Other Real Estate Owned	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Range of Discounts Applied	15.00%
Upper Limit | Loans	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Range of Discounts Applied	25.00%
Upper Limit | Other Real Estate Owned	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'
Range of Discounts Applied	20.00%

Book_and_Fair_Values_of_All_Fi

Book and Fair Values of All Financial Instruments (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013		Sep. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Assets	'		'		'	'
Cash and Due from Banks	$2,918.90		$3,162.40		$2,690.70	$3,752.70
Federal Funds Sold and Resell Agreements	1,010		529.6		'	'
Interest-Bearing Deposits with Banks	15,334.50		19,397.40		'	'
Federal Reserve Deposits	21,328		12,911.50		'	'
Securities	'		'		'	'
Available for Sale	28,107.70		28,392.80		'	'
Held to Maturity	4,196.70		2,325.80		'	'
Trading Account	4.3		1.7		'	'
Loans (excluding Leases)	'		'		'	'
Client Security Settlement Receivables	1,538.60		1,355.20		'	'
Deposits	'		'		'	'
Savings Certificates and Other Time	1,869		1,874.40		'	'
Non U.S. Offices Interest-Bearing	50,586.10		48,461.70		'	'
Federal Funds Purchased	786.4		965.1		'	'
Securities Sold under Agreements to Repurchase	866.8		917.3		'	'
Other Borrowings	1,758.30		1,558.60		'	'
Senior Notes	1,496.90		1,996.60		'	'
Long Term Debt (excluding Leases)	'		'		'	'
Floating Rate Capital Debt	277.2		277.1		'	'
Other Liabilities	'		'		'	'
Contingent Consideration	'		55.4		'	'
Asset And Liability Management	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	184		135.1		'	'
Liabilities	40.2		136.5		'	'
Client Related and Trading	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	4,233		2,967.50		'	'
Liabilities	4,221.40		2,963.20		'	'
Carrying (Reported) Amount, Fair Value Disclosure	'		'		'	'
Assets	'		'		'	'
Cash and Due from Banks	2,918.90		3,162.40		'	'
Federal Funds Sold and Resell Agreements	1,010		529.6		'	'
Interest-Bearing Deposits with Banks	15,334.50		19,397.40		'	'
Federal Reserve Deposits and Other Interest-Bearing	'		12,911.50		'	'
Federal Reserve Deposits	21,328		'		'	'
Securities	'		'		'	'
Available for Sale	28,107.70	[1]	28,392.80	[2]	'	'
Held to Maturity	4,196.70		2,325.80		'	'
Trading Account	4.3		1.7		'	'
Loans (excluding Leases)	'		'		'	'
Held for Investment	29,499.60		28,136.50		'	'
Held for Sale	2.1		'		'	'
Client Security Settlement Receivables	1,538.60		1,355.20		'	'
Other Assets	'		'		'	'
Federal Reserve and Federal Home Loan Bank Stock	207.5		194.7		'	'
Community Development Investments	225.1		228.1		'	'
Employee Benefit and Deferred Compensation	145.2		132.7		'	'
Deposits	'		'		'	'
Demand, Noninterest-Bearing, Savings and Money Market	39,267.40		33,762		'	'
Savings Certificates and Other Time	1,869		1,874.40		'	'
Non U.S. Offices Interest-Bearing	50,586.10		48,461.70		'	'
Federal Funds Purchased	786.4		965.1		'	'
Securities Sold under Agreements to Repurchase	866.8		917.3		'	'
Other Borrowings	1,758.30		1,558.60		'	'
Senior Notes	1,496.90		1,996.60		'	'
Long Term Debt (excluding Leases)	'		'		'	'
Subordinated Debt	1,565.50		1,537.30		'	'
Federal Home Loan Bank Borrowings	'		135		'	'
Floating Rate Capital Debt	277.2		277.1		'	'
Other Liabilities	'		'		'	'
Standby Letters of Credit	57		59.6		'	'
Contingent Consideration	'		55.4		'	'
Loan Commitments	28.7		35.7		'	'
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Foreign Exchange Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	71		21		'	'
Liabilities	16.1		59.5		'	'
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Interest Rate Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	113.3		'		'	'
Liabilities	27.6		'		'	'
Carrying (Reported) Amount, Fair Value Disclosure | Asset And Liability Management | Interest Rate Swap Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	'		115.1		'	'
Liabilities	'		78.2		'	'
Carrying (Reported) Amount, Fair Value Disclosure | Client Related and Trading | Foreign Exchange Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	4,132.80		2,844.70		'	'
Liabilities	4,125.50		2,846.20		'	'
Carrying (Reported) Amount, Fair Value Disclosure | Client Related and Trading | Interest Rate Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	100.2		122.8		'	'
Liabilities	95.9		117		'	'
Estimate of Fair Value, Fair Value Disclosure	'		'		'	'
Assets	'		'		'	'
Cash and Due from Banks	2,918.90		3,162.40		'	'
Federal Funds Sold and Resell Agreements	1,010		529.6		'	'
Interest-Bearing Deposits with Banks	15,334.50		19,397.40		'	'
Federal Reserve Deposits and Other Interest-Bearing	'		12,911.50		'	'
Federal Reserve Deposits	21,328		'		'	'
Securities	'		'		'	'
Available for Sale	28,107.70	[1]	28,392.80	[2]	'	'
Held to Maturity	4,195.10		2,321.40		'	'
Trading Account	4.3		1.7		'	'
Loans (excluding Leases)	'		'		'	'
Held for Investment	29,522.70		28,147.20		'	'
Held for Sale	2.1		'		'	'
Client Security Settlement Receivables	1,538.60		1,355.20		'	'
Other Assets	'		'		'	'
Federal Reserve and Federal Home Loan Bank Stock	207.5		194.7		'	'
Community Development Investments	223.8		227.8		'	'
Employee Benefit and Deferred Compensation	147.4		126.9		'	'
Deposits	'		'		'	'
Demand, Noninterest-Bearing, Savings and Money Market	39,267.40		33,762		'	'
Savings Certificates and Other Time	1,869.50		1,877.10		'	'
Non U.S. Offices Interest-Bearing	50,586.10		48,461.70		'	'
Federal Funds Purchased	786.4		965.1		'	'
Securities Sold under Agreements to Repurchase	866.8		917.3		'	'
Other Borrowings	1,758.90		1,558.60		'	'
Senior Notes	1,526.80		1,989.30		'	'
Long Term Debt (excluding Leases)	'		'		'	'
Subordinated Debt	1,595.50		1,563.50		'	'
Federal Home Loan Bank Borrowings	'		137.2		'	'
Floating Rate Capital Debt	242.8		230.2		'	'
Other Liabilities	'		'		'	'
Standby Letters of Credit	57		59.6		'	'
Contingent Consideration	'		55.4		'	'
Loan Commitments	28.7		35.7		'	'
Estimate of Fair Value, Fair Value Disclosure | Asset And Liability Management | Foreign Exchange Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	71		21		'	'
Liabilities	16.1		59.5		'	'
Estimate of Fair Value, Fair Value Disclosure | Asset And Liability Management | Interest Rate Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	113.3		'		'	'
Liabilities	27.6		'		'	'
Estimate of Fair Value, Fair Value Disclosure | Asset And Liability Management | Interest Rate Swap Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	'		115.1		'	'
Liabilities	'		78.2		'	'
Estimate of Fair Value, Fair Value Disclosure | Client Related and Trading | Foreign Exchange Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	4,132.80		2,844.70		'	'
Liabilities	4,125.50		2,846.20		'	'
Estimate of Fair Value, Fair Value Disclosure | Client Related and Trading | Interest Rate Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	100.2		122.8		'	'
Liabilities	95.9		117		'	'
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 1	'		'		'	'
Assets	'		'		'	'
Cash and Due from Banks	2,918.90		3,162.40		'	'
Securities	'		'		'	'
Available for Sale	3,409.60	[1]	1,917.90	[2]	'	'
Other Assets	'		'		'	'
Employee Benefit and Deferred Compensation	97.4		79.3		'	'
Deposits	'		'		'	'
Demand, Noninterest-Bearing, Savings and Money Market	39,267.40		33,762		'	'
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2	'		'		'	'
Assets	'		'		'	'
Federal Funds Sold and Resell Agreements	1,010		529.6		'	'
Interest-Bearing Deposits with Banks	15,334.50		19,397.40		'	'
Federal Reserve Deposits and Other Interest-Bearing	'		12,911.50		'	'
Federal Reserve Deposits	21,328		'		'	'
Securities	'		'		'	'
Available for Sale	24,612.90	[1]	26,376	[2]	'	'
Held to Maturity	4,195.10		2,321.40		'	'
Trading Account	4.3		1.7		'	'
Loans (excluding Leases)	'		'		'	'
Client Security Settlement Receivables	1,538.60		1,355.20		'	'
Other Assets	'		'		'	'
Federal Reserve and Federal Home Loan Bank Stock	207.5		194.7		'	'
Community Development Investments	223.8		227.8		'	'
Employee Benefit and Deferred Compensation	50		47.6		'	'
Deposits	'		'		'	'
Savings Certificates and Other Time	1,869.50		1,877.10		'	'
Non U.S. Offices Interest-Bearing	50,586.10		48,461.70		'	'
Federal Funds Purchased	786.4		965.1		'	'
Securities Sold under Agreements to Repurchase	866.8		917.3		'	'
Other Borrowings	1,758.90		1,558.60		'	'
Senior Notes	1,526.80		1,989.30		'	'
Long Term Debt (excluding Leases)	'		'		'	'
Subordinated Debt	1,595.50		1,563.50		'	'
Federal Home Loan Bank Borrowings	'		137.2		'	'
Floating Rate Capital Debt	242.8		230.2		'	'
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Foreign Exchange Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	71		21		'	'
Liabilities	16.1		59.5		'	'
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Interest Rate Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	113.3		'		'	'
Liabilities	27.6		'		'	'
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Asset And Liability Management | Interest Rate Swap Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	'		115.1		'	'
Liabilities	'		78.2		'	'
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Foreign Exchange Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	4,132.80		2,844.70		'	'
Liabilities	4,125.50		2,846.20		'	'
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 2 | Client Related and Trading | Interest Rate Contracts	'		'		'	'
Derivative Instruments	'		'		'	'
Assets	100.2		122.8		'	'
Liabilities	95.9		117		'	'
Estimate of Fair Value, Fair Value Disclosure | Fair Value, Inputs, Level 3	'		'		'	'
Securities	'		'		'	'
Available for Sale	85.2	[1]	98.9	[2]	'	'
Loans (excluding Leases)	'		'		'	'
Held for Investment	29,522.70		28,147.20		'	'
Held for Sale	2.1		'		'	'
Other Liabilities	'		'		'	'
Standby Letters of Credit	57		59.6		'	'
Contingent Consideration	'		55.4		'	'
Loan Commitments	$28.70		$35.70		'	'
[1]	Refer to the table located on page 36 for the disaggregation of available for sale securities.
[2]	Refer to the table located on page 37 for the disaggregation of available for sale securities.

Reconciliation_of_Amortized_Co

Reconciliation of Amortized Cost to Fair Values of Securities Available for Sale (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Investment Holdings [Line Items]	'	'
Amortized Cost	$28,046.20	$28,382.30
Gross Unrealized Gains	125	174.2
Gross Unrealized Losses	63.5	163.7
Fair Value	28,107.70	28,392.80
U.S. Government	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	3,395.10	1,896.70
Gross Unrealized Gains	16	22.6
Gross Unrealized Losses	1.5	1.4
Fair Value	3,409.60	1,917.90
Obligations of States and Political Subdivisions	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	4.5	4.5
Gross Unrealized Gains	0.1	0.1
Fair Value	4.6	4.6
U.S. Government Sponsored Agency	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	16,114.20	17,495.20
Gross Unrealized Gains	85.4	80.7
Gross Unrealized Losses	25.2	47.9
Fair Value	16,174.40	17,528
Non-U.S. Government	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	309.3	307
Gross Unrealized Gains	1.2	3.6
Fair Value	310.5	310.6
Corporate Debt	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	3,393.50	3,615.20
Gross Unrealized Gains	4.7	10.5
Gross Unrealized Losses	33.4	101.2
Fair Value	3,364.80	3,524.50
Covered Bonds	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	1,966.90	1,898.90
Gross Unrealized Gains	12.2	50.9
Gross Unrealized Losses	0.2	5.9
Fair Value	1,978.90	1,943.90
Supranational and Non-U.S. Agency Bonds	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	360	410
Gross Unrealized Gains	1.4	1.7
Gross Unrealized Losses	1.2	1.7
Fair Value	360.2	410
Residential Mortgage-Backed	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	18.8	52.4
Gross Unrealized Gains	0.1	0.1
Gross Unrealized Losses	1.3	4.4
Fair Value	17.6	48.1
Other Asset-Backed	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	2,232	2,390.80
Gross Unrealized Gains	1.3	1.4
Gross Unrealized Losses	0.2	0.4
Fair Value	2,233.10	2,391.80
Auction Rate Securities	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	83.4	97.5
Gross Unrealized Gains	2.3	2.2
Gross Unrealized Losses	0.5	0.8
Fair Value	85.2	98.9
Others	'	'
Investment Holdings [Line Items]	'	'
Amortized Cost	168.5	214.1
Gross Unrealized Gains	0.3	0.4
Fair Value	$168.80	$214.50

Reconciliation_of_Amortized_Co1

Reconciliation of Amortized Cost to Fair Values of Securities Held to Maturity (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Schedule of Held-to-maturity Securities [Line Items]	'	'
Amortized Cost	$4,196.70	$2,325.80
Gross Unrealized Gains	17.4	12.3
Gross Unrealized Losses	19	16.7
Fair Value	4,195.10	2,321.40
Obligations of States and Political Subdivisions	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Amortized Cost	138.8	225.2
Gross Unrealized Gains	8.5	10.3
Fair Value	147.3	235.5
U.S. Government Sponsored Agency	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Amortized Cost	22.8	35.9
Gross Unrealized Gains	1.1	1.1
Fair Value	23.9	37
Non-U.S. Government	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Amortized Cost	1,094.10	722
Gross Unrealized Gains	3.7	0.8
Gross Unrealized Losses	0.7	1.1
Fair Value	1,097.10	721.7
Certificates of Deposit	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Amortized Cost	1,479.50	698.1
Gross Unrealized Gains	0.2	'
Gross Unrealized Losses	0.1	0.2
Fair Value	1,479.60	697.9
Supranational and Non-U.S. Agency Bonds	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Amortized Cost	1,393.90	584.7
Gross Unrealized Gains	3.9	'
Gross Unrealized Losses	1.9	3.2
Fair Value	1,395.90	581.5
Others	'	'
Schedule of Held-to-maturity Securities [Line Items]	'	'
Amortized Cost	67.6	59.9
Gross Unrealized Gains	'	0.1
Gross Unrealized Losses	16.3	12.2
Fair Value	$51.30	$47.80

Remaining_Maturity_of_Securiti

Remaining Maturity of Securities Available for Sale (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Available for Sale - Cost	'	'
Due in One Year or Less	$7,195	'
Due After One Year Through Five Years	16,637.90	'
Due After Five Years Through Ten Years	3,116.80	'
Due After Ten Years	1,096.50	'
Total	28,046.20	'
Held to Maturity - Amortized Cost	'	'
Due in One Year or Less	1,914.10	'
Due After One Year Through Five Years	2,222.20	'
Due After Five Years Through Ten Years	23.3	'
Due After Ten Years	37.1	'
Amortized Cost	4,196.70	2,325.80
Available for Sale - Value	'	'
Due in One Year or Less	7,210.60	'
Due After One Year Through Five Years	16,677.90	'
Due After Five Years Through Ten Years	3,138.10	'
Due After Ten Years	1,081.10	'
Total	28,107.70	'
Held to Maturity - Fair Value	'	'
Due in One Year or Less	1,915.30	'
Due After One Year Through Five Years	2,230.50	'
Due After Five Years Through Ten Years	24.1	'
Due After Ten Years	25.2	'
Total	$4,195.10	$2,321.40

Securities_Additional_Informat

Securities - Additional Information (Detail) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
	Investment				Investment
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Investment Security Gains (Losses), net	$300,000	[1]	($2,200,000)	[1]	($3,300,000)	[1]	($1,900,000)	[1]	'
Gross proceeds from sale of securities	337,300,000		316,400,000		801,200,000		398,100,000		'
Gross realized securities gains	1,000,000		100,000		1,700,000		400,000		'
Gross realized securities losses	700,000		2,300,000		1,100,000		2,300,000		'
Number of securities in an unrealized loss position	471		'		471		'		'
Total Fair Value	9,852,500,000		'		9,852,500,000		'		10,250,000,000
Total Unrealized Losses	82,500,000		'		82,500,000		'		180,400,000
Net impairment losses recognized in earnings	0		0		3,900,000		0		'
U.S. Government Sponsored Agency	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Total Unrealized Losses	25,200,000		'		25,200,000		'		'
Others | Community Reinvestment Act CRA	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Total Unrealized Losses	16,300,000		'		16,300,000		'		'
Auction Rate Securities	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Total Unrealized Losses	500,000		'		500,000		'		'
Corporate Debt	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Total Unrealized Losses	33,400,000		'		33,400,000		'		'
Percent of corporate debt portfolio	40.00%		'		40.00%		'		'
Non-Agency RMBS | Financing Receivable, Current | Lower Limit	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Expected loss on subprime, Alt-A, prime and 2nd lien portfolios developed using default roll rate	5.00%		'		5.00%		'		'
Non-Agency RMBS | Financing Receivable, Current | Upper Limit	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Expected loss on subprime, Alt-A, prime and 2nd lien portfolios developed using default roll rate	30.00%		'		30.00%		'		'
Non-Agency RMBS | Financing Receivable, 30 to 59 Days Past Due	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Expected loss on subprime, Alt-A, prime and 2nd lien portfolios developed using default roll rate	30.00%		'		30.00%		'		'
Non-Agency RMBS | Financing Receivable, 60 to 89 Days Past Due	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Expected loss on subprime, Alt-A, prime and 2nd lien portfolios developed using default roll rate	80.00%		'		80.00%		'		'
Non-Agency RMBS | Financing Receivable, 90 Days and Greater Past Due	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Expected loss on subprime, Alt-A, prime and 2nd lien portfolios developed using default roll rate	90.00%		'		90.00%		'		'
Non-Agency RMBS | Other Real Estate Owned and Loans in Foreclosure	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Expected loss on subprime, Alt-A, prime and 2nd lien portfolios developed using default roll rate	100.00%		'		100.00%		'		'
Residential Mortgage-Backed	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Total Unrealized Losses	$1,300,000		'		$1,300,000		'		'
Number of securities in an unrealized loss position for more than 12 months	2		'		2		'		'
Other Asset-Backed | Floating Rate Securities	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Percentage of "other asset-backed" securities rated triple-A	100.00%		'		100.00%		'		'
Credit Rating	'		'		'AAA		'		'
Other Asset-Backed | Floating Rate Securities | Upper Limit	'		'		'		'		'
Schedule of Trading Securities and Other Trading Assets [Line Items]	'		'		'		'		'
Average life	'		'		'5 years		'		'
[1]	Changes in Other-Than-Temporary-Impairment (OTTI) Losses $ - $ - $ (4.6 ) $ - Noncredit-related OTTI Losses Recorded in/(Reclassified from) OCI - - 0.7 - Other Security Gains (Losses), net 0.3 (2.2 ) 0.6 (1.9 ) Investment Security Gains (Losses), net $ 0.3 $ (2.2 ) $ (3.3 ) $ (1.9 )

Securities_Continuous_Unrealiz

Securities Continuous Unrealized Loss Position (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	$6,359.40	$9,473.90
Less than 12 Months Unrealized Losses	22.3	145.8
12 Months or Longer Fair Value	3,493.10	776.1
12 Months or Longer Unrealized Losses	60.2	34.6
Total Fair Value	9,852.50	10,250
Total Unrealized Losses	82.5	180.4
U.S. Government	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	1,596	896.4
Less than 12 Months Unrealized Losses	1.5	1.4
Total Fair Value	1,596	896.4
Total Unrealized Losses	1.5	1.4
U.S. Government Sponsored Agency	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	2,099.20	4,340.80
Less than 12 Months Unrealized Losses	8.3	42.6
12 Months or Longer Fair Value	1,773.50	413.7
12 Months or Longer Unrealized Losses	16.9	5.3
Total Fair Value	3,872.70	4,754.50
Total Unrealized Losses	25.2	47.9
Non-U.S. Government	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	235.4	176.7
Less than 12 Months Unrealized Losses	0.1	1.1
12 Months or Longer Fair Value	80.3	'
12 Months or Longer Unrealized Losses	0.6	'
Total Fair Value	315.7	176.7
Total Unrealized Losses	0.7	1.1
Corporate Debt	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	862.3	1,759.50
Less than 12 Months Unrealized Losses	2.8	85.4
12 Months or Longer Fair Value	1,258	267
12 Months or Longer Unrealized Losses	30.6	15.8
Total Fair Value	2,120.30	2,026.50
Total Unrealized Losses	33.4	101.2
Covered Bonds	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	77	278.8
Less than 12 Months Unrealized Losses	0.1	5.7
12 Months or Longer Fair Value	9.9	9.9
12 Months or Longer Unrealized Losses	0.1	0.2
Total Fair Value	86.9	288.7
Total Unrealized Losses	0.2	5.9
Supranational and Non-U.S. Agency Bonds	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	438.2	612.7
Less than 12 Months Unrealized Losses	0.7	4.9
12 Months or Longer Fair Value	300.8	'
12 Months or Longer Unrealized Losses	2.4	'
Total Fair Value	739	612.7
Total Unrealized Losses	3.1	4.9
Residential Mortgage-Backed	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
12 Months or Longer Fair Value	15	42
12 Months or Longer Unrealized Losses	1.3	4.4
Total Fair Value	15	42
Total Unrealized Losses	1.3	4.4
Other Asset-Backed	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	485.2	677
Less than 12 Months Unrealized Losses	0.1	0.4
12 Months or Longer Fair Value	7.1	'
12 Months or Longer Unrealized Losses	0.1	'
Total Fair Value	492.3	677
Total Unrealized Losses	0.2	0.4
Certificates of Deposit	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	552	684.2
Less than 12 Months Unrealized Losses	0.1	0.2
Total Fair Value	552	684.2
Total Unrealized Losses	0.1	0.2
Auction Rate Securities	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	1.1	22.1
Less than 12 Months Unrealized Losses	0.1	0.1
12 Months or Longer Fair Value	5.1	14
12 Months or Longer Unrealized Losses	0.4	0.7
Total Fair Value	6.2	36.1
Total Unrealized Losses	0.5	0.8
Others	'	'
Investments, Unrealized Loss Position [Line Items]	'	'
Less than 12 Months Fair Value	13	25.7
Less than 12 Months Unrealized Losses	8.5	4
12 Months or Longer Fair Value	43.4	29.5
12 Months or Longer Unrealized Losses	7.8	8.2
Total Fair Value	56.4	55.2
Total Unrealized Losses	$16.30	$12.20

Book_Values_Ultimate_Default_R

Book Values, Ultimate Default Rates, and Loss Severity Rates for Non-Agency Residential Mortgage-Backed Securities Portfolio, by Security Type (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	$28,046.20	$28,382.30
Non-Agency RMBS	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	18.8	'
Weighted Average Ultimate Default Rates	33.10%	'
Loss Severity Rates - Weighted Average	70.30%	'
Non-Agency RMBS | Lower Limit	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Loss Severity Rates	32.10%	'
Non-Agency RMBS | Upper Limit	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Loss Severity Rates	99.00%	'
Non-Agency RMBS | Prime	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	2	'
Weighted Average Ultimate Default Rates	5.40%	'
Loss Severity Rates - Weighted Average	32.10%	'
Non-Agency RMBS | Prime | Lower Limit	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Loss Severity Rates	32.10%	'
Non-Agency RMBS | Prime | Upper Limit	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Loss Severity Rates	32.10%	'
Non-Agency RMBS | Alt-A	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	11.2	'
Weighted Average Ultimate Default Rates	40.00%	'
Loss Severity Rates - Weighted Average	62.80%	'
Non-Agency RMBS | Alt-A | Lower Limit	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Loss Severity Rates	62.80%	'
Non-Agency RMBS | Alt-A | Upper Limit	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Loss Severity Rates	62.80%	'
Non-Agency RMBS | 2nd Lien	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Amortized Cost	$5.60	'
Weighted Average Ultimate Default Rates	32.70%	'
Loss Severity Rates - Weighted Average	99.00%	'
Non-Agency RMBS | 2nd Lien | Lower Limit	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Loss Severity Rates	98.70%	'
Non-Agency RMBS | 2nd Lien | Upper Limit	'	'
Schedule of Available-for-sale Securities [Line Items]	'	'
Loss Severity Rates	99.00%	'

Credit_Related_Impairment_Loss

Credit Related Impairment Losses Recognized in Earnings on Other Than Temporarily Impaired Securities (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014		Sep. 30, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'		'
Changes in OTTI Losses	'	'	($4,600,000)	[1]	'
Noncredit-related Losses Recorded in / (Reclassified from) OCI	'	'	700,000	[2]	'
Net Impairment Losses Recognized in Earnings	$0	$0	($3,900,000)		$0
[1]	For initial other-than-temporary impairments in the respective period, the balance includes the excess of the amortized cost over the fair value of the impaired securities. For subsequent impairments of the same security, the balance includes any additional changes in fair value of the security subsequent to its most recently recorded OTTI.
[2]	For initial other-than-temporary impairments in the respective period, the balance includes the portion of the excess of amortized cost over the fair value of the impaired securities that was recorded in OCI. For subsequent impairments of the same security, the balance includes additional changes in OCI for that security subsequent to its most recently recorded OTTI.

CreditRelated_Losses_Recognize

Credit-Related Losses Recognized in Earnings on Debt Securities Other-Than-Temporarily Impaired (Detail) (USD $)	3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2013	Jun. 30, 2013
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Line Items]	'	'	'	'
Cumulative Credit-Related Losses on Securities Held - Beginning of Period	$12.70	$8.80	$42.30	$8.80
Plus: Losses on Newly Identified Impairments	'	1.8	'	'
Additional Losses on Previously Identified Impairments	'	2.1	'	'
Less: Current and Prior Period Losses on Securities Sold During the Period	-1.8	-1.8	-33.5	'
Cumulative Credit-Related Losses on Securities Held - End of Period	$10.90	$10.90	$8.80	$8.80

Amounts_Outstanding_for_Loans_

Amounts Outstanding for Loans and Leases by Segment and Class (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Total Loans and Leases	$30,719.90	$29,385.50
Allowance for Credit Losses Assigned to Loans and Leases	-269.4	-278.1
Net Loans and Leases	30,450.50	29,107.40
Commercial	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Commercial and Institutional	8,212.10	7,375.80
Commercial Real Estate	3,107.70	2,955.80
Lease Financing, net	952.5	975.1
Non-U.S.	1,408.40	954.7
Other	187.9	358.6
Total Loans and Leases	13,868.60	12,620
Allowance for Credit Losses Assigned to Loans and Leases	-143.1	-140.9
Personal	'	'
Accounts, Notes, Loans and Financing Receivable [Line Items]	'	'
Residential Real Estate	9,872.70	10,271.30
Private Client	6,953.10	6,445.60
Other	25.5	48.6
Total Loans and Leases	16,851.30	16,765.50
Allowance for Credit Losses Assigned to Loans and Leases	($126.30)	($137.20)

Loans_and_Leases_Additional_In

Loans and Leases - Additional Information (Detail) (USD $)

3 Months Ended

9 Months Ended

9 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2014

Sep. 30, 2013

Sep. 30, 2014

Sep. 30, 2013

Dec. 31, 2013

Sep. 30, 2014

Sep. 30, 2014

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Dec. 31, 2013

Sep. 30, 2014

Jun. 30, 2014

Jun. 30, 2013

Lower Limit

Upper Limit

First Lien

First Lien

Equity

Equity

Nonperforming Financing Receivable

Nonperforming Financing Receivable

Performing Financing Receivable

Performing Financing Receivable

Performing Financing Receivable

Residential Real Estate

Residential Real Estate

Lower Limit

Re-Defaulted

Re-Defaulted

Loan

Loan

Accounts, Notes, Loans and Financing Receivable [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Collateral required on Residential real estate loan, lower limit

65.00%

'

65.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Collateral required on Residential real estate loan, upper limit

80.00%

'

80.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Draw period for credit line products

'

'

'10 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Equity credit lines

'

'

'

'

'

'

'

'

'

$1,800,000,000

$2,000,000,000

'

'

'

'

'

'

'

Loans held by Northern trust

'

'

'

'

'

'

'

88.00%

87.00%

'

'

'

'

'

'

'

'

'

Other U.S. loans and non-U.S. loans, short duration advances

1,400,000,000

'

1,400,000,000

'

1,300,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Demand deposits

109,000,000

'

109,000,000

'

104,100,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Loans held for sale

2,100,000

'

2,100,000

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

Days contractually past due for interest and principal and the loan is not well-secured and in the process of collection

'

'

'

'

'

'90 days

'

'

'

'

'

'

'

'

'

'

'

'

Number of days past due for disclosure purposes to be categorized as a current

'

'

'

'

'

'

'29 days

'

'

'

'

'

'

'

'

'

'

'

Maximum limit of individual homogeneous loans collective evaluation for impairment and excluded from impaired loan disclosures

250,000

'

250,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest income that would have been recorded for nonperforming loans

2,200,000

2,800,000

7,100,000

8,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Undrawn loan commitments and standby letters of credit

3,500,000

'

3,500,000

'

3,400,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Total Loans and Leases

$30,719,900,000

'

$30,719,900,000

'

$29,385,500,000

'

'

'

'

'

'

$58,600,000

$72,700,000

$96,900,000

$89,800,000

'

'

'

Period for which troubled debt restructurings with modified terms is performing before ceasing to be classified as impaired loan

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'6 months

'

'

Troubled debt restructuring loans and leases receivable to Performing status

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'6 months

'

'

Number of Loans and Leases

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

0

Loan_and_Lease_Segment_and_Cla

Loan and Lease Segment and Class Balances Segregated by Borrower Ratings into "One to Three", "Four to Five" and "Six to Nine" (Watch List) Categories (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	$30,719.90	$29,385.50
1 to 3 Category	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	15,208.40	13,955.80
4 to 5 Category	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	14,818.90	14,620.20
6 to 9 Category (Watch List)	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	692.6	809.5
Commercial	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Commercial and Institutional	8,212.10	7,375.80
Commercial Real Estate	3,107.70	2,955.80
Lease Financing, net	952.5	975.1
Non-U.S.	1,408.40	954.7
Other	187.9	358.6
Total Loans and Leases	13,868.60	12,620
Commercial | 1 to 3 Category	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Commercial and Institutional	5,115.40	4,432.50
Commercial Real Estate	1,263.60	1,053.70
Lease Financing, net	572.2	685.7
Non-U.S.	643.7	442.8
Other	137.4	157.7
Total Loans and Leases	7,732.30	6,772.40
Commercial | 4 to 5 Category	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Commercial and Institutional	2,983.60	2,801.50
Commercial Real Estate	1,718.20	1,748.70
Lease Financing, net	376.1	285
Non-U.S.	763.8	511.9
Other	50.5	200.9
Total Loans and Leases	5,892.20	5,548
Commercial | 6 to 9 Category (Watch List)	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Commercial and Institutional	113.1	141.8
Commercial Real Estate	125.9	153.4
Lease Financing, net	4.2	4.4
Non-U.S.	0.9	'
Total Loans and Leases	244.1	299.6
Personal	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Residential Real Estate	9,872.70	10,271.30
Private Client	6,953.10	6,445.60
Other	25.5	48.6
Total Loans and Leases	16,851.30	16,765.50
Personal | 1 to 3 Category	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Residential Real Estate	2,995.70	3,204.60
Private Client	4,461.80	3,957.60
Other	18.6	21.2
Total Loans and Leases	7,476.10	7,183.40
Personal | 4 to 5 Category	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Residential Real Estate	6,439.90	6,563.60
Private Client	2,479.90	2,481.20
Other	6.9	27.4
Total Loans and Leases	8,926.70	9,072.20
Personal | 6 to 9 Category (Watch List)	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Residential Real Estate	437.1	503.1
Private Client	11.4	6.8
Total Loans and Leases	$448.50	$509.90

Balances_and_Delinquency_Statu

Balances and Delinquency Status of Performing and Nonperforming Loans and Leases by Segment and Class as well as Total Other Real Estate Owned and Nonperforming Asset Balances (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Financing Receivable, Recorded Investment [Line Items]	'	'
Other Real Estate Owned	$10.70	$11.90
Total Nonperforming Assets	231.2	274.7
Total Loans and Leases	30,719.90	29,385.50
Commercial	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	13,868.60	12,620
Commercial | Commercial and Institutional	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	8,212.10	7,375.80
Commercial | Commercial Real Estate	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	3,107.70	2,955.80
Commercial | Lease Financing, net	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	952.5	975.1
Commercial | Non-U.S.	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	1,408.40	954.7
Commercial | Other	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	187.9	358.6
Personal	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	16,851.30	16,765.50
Personal | Residential Real Estate	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	9,872.70	10,271.30
Personal | Private Client	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	6,953.10	6,445.60
Personal | Other	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	25.5	48.6
Performing Financing Receivable	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	30,392.40	28,889
30-59 Days Past Due	47	167.5
60-89 Days Past Due	34.9	49.8
90 Days or More Past Due	25.1	16.4
Total Loans and Leases	30,499.40	29,122.70
Performing Financing Receivable | Commercial	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	13,747	12,501.80
30-59 Days Past Due	18	9.1
60-89 Days Past Due	18.5	26.7
90 Days or More Past Due	13.5	10.1
Total Loans and Leases	13,797	12,547.70
Performing Financing Receivable | Commercial | Commercial and Institutional	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	8,153.80	7,332.30
30-59 Days Past Due	10.2	5
60-89 Days Past Due	13.3	12.1
90 Days or More Past Due	3.1	3.3
Total Loans and Leases	8,180.40	7,352.70
Performing Financing Receivable | Commercial | Commercial Real Estate	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	3,044.40	2,881.10
30-59 Days Past Due	7.8	4.1
60-89 Days Past Due	5.2	14.6
90 Days or More Past Due	10.4	6.8
Total Loans and Leases	3,067.80	2,906.60
Performing Financing Receivable | Commercial | Lease Financing, net	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	952.5	975.1
Total Loans and Leases	952.5	975.1
Performing Financing Receivable | Commercial | Non-U.S.	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	1,408.40	954.7
Total Loans and Leases	1,408.40	954.7
Performing Financing Receivable | Commercial | Other	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	187.9	358.6
Total Loans and Leases	187.9	358.6
Performing Financing Receivable | Personal	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	16,645.40	16,387.20
30-59 Days Past Due	29	158.4
60-89 Days Past Due	16.4	23.1
90 Days or More Past Due	11.6	6.3
Total Loans and Leases	16,702.40	16,575
Performing Financing Receivable | Personal | Residential Real Estate	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	9,702.10	9,934.40
30-59 Days Past Due	7.9	129.3
60-89 Days Past Due	9	15.6
90 Days or More Past Due	6.4	2.9
Total Loans and Leases	9,725.40	10,082.20
Performing Financing Receivable | Personal | Private Client	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	6,917.80	6,404.20
30-59 Days Past Due	21.1	29.1
60-89 Days Past Due	7.4	7.5
90 Days or More Past Due	5.2	3.4
Total Loans and Leases	6,951.50	6,444.20
Performing Financing Receivable | Personal | Other	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Current	25.5	48.6
Total Loans and Leases	25.5	48.6
Nonperforming Financing Receivable	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	220.5	262.8
Nonperforming Financing Receivable | Commercial	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	71.6	72.3
Nonperforming Financing Receivable | Commercial | Commercial and Institutional	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	31.7	23.1
Nonperforming Financing Receivable | Commercial | Commercial Real Estate	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	39.9	49.2
Nonperforming Financing Receivable | Personal	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	148.9	190.5
Nonperforming Financing Receivable | Personal | Residential Real Estate	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	147.3	189.1
Nonperforming Financing Receivable | Personal | Private Client	'	'
Financing Receivable, Recorded Investment [Line Items]	'	'
Total Loans and Leases	$1.60	$1.40

Impaired_Loans_by_Segment_and_

Impaired Loans by Segment and Class (Detail) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013
Financing Receivable, Impaired [Line Items]	'		'		'		'		'
Recorded Investment	$270.40		'		$270.40		'		$293.40
Unpaid principal balance	329.9		'		329.9		'		360.5
Specific allowance	9.5		'		9.5		'		10.4
Average recorded investment	265.5	[1]	294.7	[1]	279.3	[1]	278.3	[1]	'
Interest income recognized	1.2		0.8		3.1		2.8		'
Commercial	'		'		'		'		'
Financing Receivable, Impaired [Line Items]	'		'		'		'		'
Recorded Investment	97.9		'		97.9		'		99.5
Unpaid principal balance	112.6		'		112.6		'		123.2
Specific allowance	8.6		'		8.6		'		8.1
Average recorded investment	91	[1]	102.5	[1]	93.3	[1]	100.6	[1]	'
Interest income recognized	0.4		0.3		1		0.9		'
Commercial | Commercial and Institutional	'		'		'		'		'
Financing Receivable, Impaired [Line Items]	'		'		'		'		'
With no related specific reserve, recorded investment	11.6		'		11.6		'		12.2
With a related specific reserve, recorded investment	20.5		'		20.5		'		9.6
With no related specific reserve, unpaid principal balance	14.6		'		14.6		'		18.1
With a related specific reserve, unpaid principal balance	20.5		'		20.5		'		12.1
Specific allowance	5.1		'		5.1		'		3.6
With no related specific reserve, average recorded investment	12.6	[1]	10.7	[1]	11.5	[1]	11.3	[1]	'
With a related specific reserve, average recorded investment	11.9	[1]	14.1	[1]	10.6	[1]	12.5	[1]	'
With no related specific reserve, interest income recognized	0.1		'		0.1		0.1		'
With a related specific reserve, interest income recognized	'		'		'		'		'
Commercial | Commercial Real Estate	'		'		'		'		'
Financing Receivable, Impaired [Line Items]	'		'		'		'		'
With no related specific reserve, recorded investment	49.2		'		49.2		'		46.6
With a related specific reserve, recorded investment	12.4		'		12.4		'		26.7
With no related specific reserve, unpaid principal balance	54.9		'		54.9		'		57.1
With a related specific reserve, unpaid principal balance	18.4		'		18.4		'		31.5
Specific allowance	3.5		'		3.5		'		4.5
With no related specific reserve, average recorded investment	48.5	[1]	42	[1]	46	[1]	40.6	[1]	'
With a related specific reserve, average recorded investment	13.7	[1]	31.2	[1]	20.9	[1]	31.6	[1]	'
With no related specific reserve, interest income recognized	0.2		0.2		0.7		0.6		'
With a related specific reserve, interest income recognized	'		'		'		'		'
Commercial | Lease Financing, net	'		'		'		'		'
Financing Receivable, Impaired [Line Items]	'		'		'		'		'
With no related specific reserve, recorded investment	4.2		'		4.2		'		4.4
With no related specific reserve, unpaid principal balance	4.2		'		4.2		'		4.4
With no related specific reserve, average recorded investment	4.3	[1]	4.5	[1]	4.3	[1]	4.6	[1]	'
With no related specific reserve, interest income recognized	0.1		0.1		0.2		0.2		'
Personal	'		'		'		'		'
Financing Receivable, Impaired [Line Items]	'		'		'		'		'
Recorded Investment	172.5		'		172.5		'		193.9
Unpaid principal balance	217.3		'		217.3		'		237.3
Specific allowance	0.9		'		0.9		'		2.3
Average recorded investment	174.5	[1]	192.2	[1]	186	[1]	177.7	[1]	'
Interest income recognized	0.8		0.5		2.1		1.9		'
Personal | Residential Real Estate	'		'		'		'		'
Financing Receivable, Impaired [Line Items]	'		'		'		'		'
With no related specific reserve, recorded investment	170.2		'		170.2		'		185
With a related specific reserve, recorded investment	1.3		'		1.3		'		8.1
With no related specific reserve, unpaid principal balance	214.5		'		214.5		'		227.8
With a related specific reserve, unpaid principal balance	1.5		'		1.5		'		8.7
Specific allowance	0.4		'		0.4		'		2.3
With no related specific reserve, average recorded investment	172	[1]	168.1	[1]	180.8	[1]	155.2	[1]	'
With a related specific reserve, average recorded investment	1.3	[1]	10	[1]	4.1	[1]	9.4	[1]	'
With no related specific reserve, interest income recognized	0.8		0.3		2.1		1.4		'
With a related specific reserve, interest income recognized	'		'		'		'		'
Personal | Private Client	'		'		'		'		'
Financing Receivable, Impaired [Line Items]	'		'		'		'		'
With no related specific reserve, recorded investment	0.1		'		0.1		'		0.8
With a related specific reserve, recorded investment	0.9		'		0.9		'		'
With no related specific reserve, unpaid principal balance	0.4		'		0.4		'		0.8
With a related specific reserve, unpaid principal balance	0.9		'		0.9		'		'
Specific allowance	0.5		'		0.5		'		'
With no related specific reserve, average recorded investment	0.3	[1]	13.3	[1]	0.6	[1]	12	[1]	'
With a related specific reserve, average recorded investment	0.9	[1]	0.8	[1]	0.5	[1]	1.1	[1]	'
With no related specific reserve, interest income recognized	'		0.2		'		0.5		'
With a related specific reserve, interest income recognized	'		'		'		'		'
[1]	Average recorded investment in impaired loans is calculated as the average of the month-end impaired loan balances for the period.

Number_of_Loans_and_Leases_Mod

Number of Loans and Leases Modified in TDRs and Total Recorded Investments and Unpaid Principal Balances (Detail) (Class of Financing Receivable, USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
	Contract	Contract	Contract	Contract
Financing Receivable, Modifications [Line Items]	'	'	'	'
Number of Loans and Leases	34	45	108	146
Recorded Investment	$21.30	$29.50	$29.50	$91.90
Unpaid Principal Balance	22.5	36.4	32.3	105.5
Commercial	'	'	'	'
Financing Receivable, Modifications [Line Items]	'	'	'	'
Number of Loans and Leases	6	7	9	18
Recorded Investment	3.3	22.8	4.2	27.9
Unpaid Principal Balance	3.8	25	4.9	32.9
Commercial | Commercial and Institutional	'	'	'	'
Financing Receivable, Modifications [Line Items]	'	'	'	'
Number of Loans and Leases	1	'	3	7
Recorded Investment	0.4	'	0.7	0.5
Unpaid Principal Balance	0.4	'	0.8	1
Commercial | Commercial Real Estate Portfolio Segment	'	'	'	'
Financing Receivable, Modifications [Line Items]	'	'	'	'
Number of Loans and Leases	5	7	6	11
Recorded Investment	2.9	22.8	3.5	27.4
Unpaid Principal Balance	3.4	25	4.1	31.9
Personal	'	'	'	'
Financing Receivable, Modifications [Line Items]	'	'	'	'
Number of Loans and Leases	28	38	99	128
Recorded Investment	18	6.7	25.3	64
Unpaid Principal Balance	18.7	11.4	27.4	72.6
Personal | Residential Real Estate	'	'	'	'
Financing Receivable, Modifications [Line Items]	'	'	'	'
Number of Loans and Leases	28	38	96	122
Recorded Investment	18	6.7	25.3	51.2
Unpaid Principal Balance	18.7	11.4	27.1	59.8
Personal | Private Client	'	'	'	'
Financing Receivable, Modifications [Line Items]	'	'	'	'
Number of Loans and Leases	'	'	3	6
Recorded Investment	'	'	'	12.8
Unpaid Principal Balance	'	'	$0.30	$12.80

Changes_in_Allowance_for_Credi

Changes in Allowance for Credit Losses by Segment (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Balance at Beginning of Period	$303.50	$320.70	$307.90	$327.60
Charge-Offs	-8.6	-11.6	-27.9	-39.8
Recoveries	3.4	3.3	15.3	14.7
Net (Charge-Offs) Recoveries	-5.2	-8.3	-12.6	-25.1
Provision for Credit Losses	'	5	3	15
Effect of Foreign Exchange Rates	'	0.1	'	'
Balance at End of Period	298.3	317.5	298.3	317.5
Commercial	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Balance at Beginning of Period	168.7	184.1	168	194.2
Charge-Offs	-2.5	-1.7	-8.8	-6.9
Recoveries	1.9	1.7	10.7	8.1
Net (Charge-Offs) Recoveries	-0.6	'	1.9	1.2
Provision for Credit Losses	1	-4.6	-0.8	-15.8
Effect of Foreign Exchange Rates	'	0.1	'	'
Balance at End of Period	169.1	179.6	169.1	179.6
Personal	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'
Balance at Beginning of Period	134.8	136.6	139.9	133.4
Charge-Offs	-6.1	-9.9	-19.1	-32.9
Recoveries	1.5	1.6	4.6	6.6
Net (Charge-Offs) Recoveries	-4.6	-8.3	-14.5	-26.3
Provision for Credit Losses	-1	9.6	3.8	30.8
Balance at End of Period	$129.20	$137.90	$129.20	$137.90

Allowances_for_Credit_Losses_a

Allowances for Credit Losses and Recorded Investments in Loans and Leases by Segment (Detail) (USD $)	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'	'
Specifically Evaluated for Impairment	$270.40	'	$293.40	'	'	'
Evaluated for Inherent Impairment	30,449.50	'	29,092.10	'	'	'
Total Loans and Leases	30,719.90	'	29,385.50	'	'	'
Specifically Evaluated for Impairment	9.5	'	10.4	'	'	'
Evaluated for Inherent Impairment	259.9	'	267.7	'	'	'
Allowance Assigned to Loans and Leases	269.4	'	278.1	'	'	'
Allowance for Undrawn Exposures Commitments and Standby Letters of Credit	28.9	'	29.8	'	'	'
Total Allowance for Credit Losses	298.3	303.5	307.9	317.5	320.7	327.6
Commercial	'	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'	'
Specifically Evaluated for Impairment	97.9	'	99.5	'	'	'
Evaluated for Inherent Impairment	13,770.70	'	12,520.50	'	'	'
Total Loans and Leases	13,868.60	'	12,620	'	'	'
Specifically Evaluated for Impairment	8.6	'	8.1	'	'	'
Evaluated for Inherent Impairment	134.5	'	132.8	'	'	'
Allowance Assigned to Loans and Leases	143.1	'	140.9	'	'	'
Allowance for Undrawn Exposures Commitments and Standby Letters of Credit	26	'	27.1	'	'	'
Total Allowance for Credit Losses	169.1	168.7	168	179.6	184.1	194.2
Personal	'	'	'	'	'	'
Financing Receivable, Allowance for Credit Losses [Line Items]	'	'	'	'	'	'
Specifically Evaluated for Impairment	172.5	'	193.9	'	'	'
Evaluated for Inherent Impairment	16,678.80	'	16,571.60	'	'	'
Total Loans and Leases	16,851.30	'	16,765.50	'	'	'
Specifically Evaluated for Impairment	0.9	'	2.3	'	'	'
Evaluated for Inherent Impairment	125.4	'	134.9	'	'	'
Allowance Assigned to Loans and Leases	126.3	'	137.2	'	'	'
Allowance for Undrawn Exposures Commitments and Standby Letters of Credit	2.9	'	2.7	'	'	'
Total Allowance for Credit Losses	$129.20	$134.80	$139.90	$137.90	$136.60	$133.40

Pledged_Assets_Additional_Info

Pledged Assets - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013
Financial Instruments Owned and Pledged as Collateral [Line Items]	'	'	'	'	'
Amount of securities and loans pledged	$32,400,000,000	'	$32,400,000,000	'	$32,400,000,000
Fair value of accepted collateral	1,000,000,000	'	1,000,000,000	'	500,000,000
Amount of securities repledged or sold collateral	0	'	0	'	0
Average deposits maintained to meet Federal Reserve Bank reserve requirements	1,300,000,000	900,000,000	1,300,000,000	900,000,000	'
US Government Corporations and Agencies Securities	'	'	'	'	'
Financial Instruments Owned and Pledged as Collateral [Line Items]	'	'	'	'	'
Amount of securities and loans pledged	23,500,000,000	'	23,500,000,000	'	22,600,000,000
Obligations of States and Political Subdivisions	'	'	'	'	'
Financial Instruments Owned and Pledged as Collateral [Line Items]	'	'	'	'	'
Amount of securities and loans pledged	137,000,000	'	137,000,000	'	222,700,000
Loans	'	'	'	'	'
Financial Instruments Owned and Pledged as Collateral [Line Items]	'	'	'	'	'
Amount of securities and loans pledged	8,800,000,000	'	8,800,000,000	'	9,600,000,000
Collateral Requirements	'	'	'	'	'
Financial Instruments Owned and Pledged as Collateral [Line Items]	'	'	'	'	'
Amount of securities and loans pledged	3,500,000,000	'	3,500,000,000	'	5,000,000,000
Available for Sale Investment Securities	'	'	'	'	'
Financial Instruments Owned and Pledged as Collateral [Line Items]	'	'	'	'	'
Amount of securities and loans pledged	$865,500,000	'	$865,500,000	'	$915,300,000

Carrying_Amounts_of_Goodwill_D

Carrying Amounts of Goodwill (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Goodwill [Line Items]	'	'
Total Goodwill	$538.10	$540.70
Corporate & Institutional Services	'	'
Goodwill [Line Items]	'	'
Total Goodwill	466.6	469.2
Wealth Management	'	'
Goodwill [Line Items]	'	'
Total Goodwill	$71.50	$71.50

Other_Intangible_Assets_Subjec

Other Intangible Assets Subject to Amortization (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Finite-Lived Intangible Assets [Line Items]	'	'
Gross Carrying Amount	$193.40	$198.20
Less: Accumulated Amortization	127.6	115.2
Net Book Value	$65.80	$83

Goodwill_and_Other_Intangibles2

Goodwill and Other Intangibles - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Goodwill and Intangible Assets Disclosure [Line Items]	'	'	'	'
Estimated future amortization expense for 2014	$4.80	'	$4.80	'
Estimated future amortization expense for 2015	11.5	'	11.5	'
Estimated future amortization expense for 2016	9	'	9	'
Estimated future amortization expense for 2017	8.9	'	8.9	'
Estimated future amortization expense for 2018	8.2	'	8.2	'
Other Intangible Assets	'	'	'	'
Goodwill and Intangible Assets Disclosure [Line Items]	'	'	'	'
Amortization expense related to other intangible assets	$4.80	$5.20	$14.70	$15.50

Issuance_of_Preferred_Stock_Ad

Issuance of Preferred Stock - Additional Information (Detail) (USD $)	9 Months Ended	0 Months Ended	9 Months Ended		0 Months Ended
	Sep. 30, 2014	Aug. 05, 2014	Sep. 30, 2014	Aug. 05, 2014	Oct. 21, 2014
		Series C Preferred Stock	Series C Preferred Stock	Series C Preferred Stock	Series C Preferred Stock
					Subsequent Event
Class of Stock [Line Items]	'	'	'	'	'
Preferred stock, shares authorized	10,000,000	'	'	'	'
Stock issued during period	'	16,000,000	'	'	'
Per share ownership interest, percentage	'	'	'	0.10%	'
Preferred stock, without par value	'	'	'	'	'
Preferred stock, liquidation preference	'	'	'	$25,000	'
Depository shares, liquidation preference per share	'	'	'	$25	'
Proceeds from preferred stock issued during period	$388,500,000	$388,500,000	'	'	'
Preferred stock, annual dividend rate	'	'	5.85%	'	'
Preferred Stock, Dividends Per Share, Declared	'	'	'	'	$593.13
Dividends Payable, Date to be Paid	'	'	'	'	1-Jan-15
Dividends Payable, Date of Record	'	'	'	'	15-Dec-14
Preferred Stock, redemption start date	'	'	1-Oct-19	'	'
Preferred Stock, redemption terms	'	'	'The Series C Preferred Stock is redeemable at Northern Trust's option, in whole or in part, on any dividend payment date on or after October 1, 2019. The Series C Preferred stock is redeemable at the Company's option, in whole, but not in part, prior to October 1, 2019 within 90 days of a regulatory capital treatment event	'	'
Preferred stock redemption period following regulatory capital treatment event	'	'	'90 days	'	'

Earnings_Contribution_of_North

Earnings Contribution of Northern Trust's Business Units (Detail) (USD $)	3 Months Ended				9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014		Sep. 30, 2013		Sep. 30, 2014		Sep. 30, 2013
Segment Reporting Information [Line Items]	'		'		'		'
Trust, Investment and Other Servicing Fees	$718.20		$648		$2,104.60		$1,936
Foreign Exchange Trading Income	46.4		62.8		149.4		193.6
Other Noninterest Income	65		99.4		205.5		231.3
Net Interest Income	256.2	[1]	244.8	[1]	764	[2]	706.5	[2]
Revenue	1,085.80	[1]	1,055	[1]	3,223.50	[2]	3,067.40	[2]
Provision for Credit Losses	'		5		3		15
Noninterest Expense	774.7		740.7		2,353.70		2,199.30
Income (loss) before Income Taxes	311.1	[1]	309.3	[1]	866.8	[2]	853.1	[2]
Provision (Benefit) for Income Taxes	106.6	[1]	102.8	[1]	299	[2]	291.5	[2]
Net Income	204.5		206.5		567.8		561.6
Percentage of Consolidated Net Income	100.00%		100.00%		100.00%		100.00%
Average Assets	105,244.70		95,212.50		102,955.80		93,223.50
Corporate & Institutional Services	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Trust, Investment and Other Servicing Fees	399.9		359.8		1,174.50		1,072.70
Foreign Exchange Trading Income	44.4		61.8		143.2		189.8
Other Noninterest Income	42.8		44.3		134.3		130.1
Net Interest Income	78.4	[1]	70.1	[1]	228.8	[2]	200.2	[2]
Revenue	565.5	[1]	536	[1]	1,680.80	[2]	1,592.80	[2]
Provision for Credit Losses	0.9		0.4		4.5		-1.1
Noninterest Expense	429.6		412		1,299.50		1,206.70
Income (loss) before Income Taxes	135	[1]	123.6	[1]	376.8	[2]	387.2	[2]
Provision (Benefit) for Income Taxes	42.4	[1]	38.8	[1]	113.3	[2]	123	[2]
Net Income	92.6		84.8		263.5		264.2
Percentage of Consolidated Net Income	45.00%		41.00%		46.00%		47.00%
Average Assets	59,907.10		53,653.50		59,061.30		52,323.80
Wealth Management	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Trust, Investment and Other Servicing Fees	318.3		288.2		930.1		863.3
Foreign Exchange Trading Income	2		1		6.2		3.8
Other Noninterest Income	20.9		54.3		66.7		95.8
Net Interest Income	131.2	[1]	136.3	[1]	398.8	[2]	425.3	[2]
Revenue	472.4	[1]	479.8	[1]	1,401.80	[2]	1,388.20	[2]
Provision for Credit Losses	-0.9		4.6		-1.5		16.1
Noninterest Expense	312.1		297.3		960.3		900.9
Income (loss) before Income Taxes	161.2	[1]	177.9	[1]	443	[2]	471.2	[2]
Provision (Benefit) for Income Taxes	60.7	[1]	67	[1]	166.9	[2]	177.8	[2]
Net Income	100.5		110.9		276.1		293.4
Percentage of Consolidated Net Income	49.00%		54.00%		49.00%		52.00%
Average Assets	26,061.80		22,923.60		23,613.40		22,863.10
Treasury and Other	'		'		'		'
Segment Reporting Information [Line Items]	'		'		'		'
Other Noninterest Income	1.3		0.8		4.5		5.4
Net Interest Income	46.6	[1]	38.4	[1]	136.4	[2]	81	[2]
Revenue	47.9	[1]	39.2	[1]	140.9	[2]	86.4	[2]
Noninterest Expense	33		31.4		93.9		91.7
Income (loss) before Income Taxes	14.9	[1]	7.8	[1]	47	[2]	-5.3	[2]
Provision (Benefit) for Income Taxes	3.5	[1]	-3	[1]	18.8	[2]	-9.3	[2]
Net Income	11.4		10.8		28.2		4
Percentage of Consolidated Net Income	6.00%		5.00%		5.00%		1.00%
Average Assets	$19,275.80		$18,635.40		$20,281.10		$18,036.60
[1]	Stated on a fully taxable equivalent basis (FTE). Total consolidated includes FTE adjustments of $6.9 million for 2014 and $7.8 million for 2013.
[2]	Stated on a fully taxable equivalent basis (FTE). Total consolidated includes FTE adjustments of $22.4 million for 2014 and $23.3 million for 2013.

Earnings_Contribution_of_North1

Earnings Contribution of Northern Trust's Business Units (Parenthetical) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Segment Reporting Information [Line Items]	'	'	'	'
Fully taxable equivalent basis adjustments	$6.90	$7.80	$22.40	$23.30

Components_of_Accumulated_Othe

Components of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning Balance	'	'	($244.30)	($283)
Net Change	-13.2	12.8	25.9	-54.9
Ending Balance	-218.4	-337.9	-218.4	-337.9
Net Unrealized Gains (Losses) on Securities Available for Sale	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning Balance	'	'	6	101
Net Change	'	'	32.3	-74.4
Ending Balance	38.3	26.6	38.3	26.6
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning Balance	'	'	2.9	-1.4
Net Change	'	'	-6.4	1.2
Ending Balance	-3.5	-0.2	-3.5	-0.2
Net Foreign Currency Adjustments	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning Balance	'	'	7.1	10.5
Net Change	'	'	-10.5	-2.8
Ending Balance	-3.4	7.7	-3.4	7.7
Net Pension and Other Postretirement Benefit Adjustments	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Beginning Balance	'	'	-260.3	-393.1
Net Change	'	'	10.5	21.1
Ending Balance	($249.80)	($372)	($249.80)	($372)

Accumulated_Other_Comprehensiv2

Accumulated Other Comprehensive Income (Loss) Changes During Period (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Other Comprehensive Income (Loss)	($13.20)	$12.80	$25.90	($54.90)
Net Unrealized Gains (Losses) on Securities Available for Sale	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	-9	9.4	51.9	-119.2
Tax Effect	3.3	-3.6	-19.6	44.8
Other Comprehensive Income (Loss)	-5.7	5.8	32.3	-74.4
Net Unrealized Gains (Losses) on Securities Available for Sale | Noncredit-Related Unrealized Losses on Securities OTTI	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	5.5	'	3.7	2.1
Tax Effect	-2.1	'	-1.4	-0.8
Other Comprehensive Income (Loss)	3.4	'	2.3	1.3
Net Unrealized Gains (Losses) on Securities Available for Sale | Other Unrealized Gains (Losses) on Securities Available-for-Sale	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	-14.2	7.3	48.8	-123.2
Tax Effect	5.4	-2.8	-18.2	46.3
Other Comprehensive Income (Loss)	-8.8	4.5	30.6	-76.9
Net Unrealized Gains (Losses) on Securities Available for Sale | Reclassification Adjustment for (Gains) Losses Included in Net Income	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	-0.3	2.1	-0.6	1.9
Tax Effect	'	-0.8	'	-0.7
Other Comprehensive Income (Loss)	-0.3	1.3	-0.6	1.2
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	-11.3	6.4	-9.8	1.7
Tax Effect	3.9	-2.1	3.4	-0.5
Other Comprehensive Income (Loss)	-7.4	4.3	-6.4	1.2
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations | Reclassification Adjustment for (Gains) Losses Included in Net Income	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	-3.7	1.1	-3.3	5.7
Tax Effect	1.4	-0.4	1.2	-2.1
Other Comprehensive Income (Loss)	-2.3	0.7	-2.1	3.6
Net Unrealized Gains (Losses) on Cash Flow Hedge Designations | Unrealized Gains (Losses) on Cash Flow Hedges	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	-7.6	5.3	-6.5	-4
Tax Effect	2.5	-1.7	2.2	1.6
Other Comprehensive Income (Loss)	-5.1	3.6	-4.3	-2.4
Net Foreign Currency Adjustments	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	35.4	-33.8	13.5	-4
Tax Effect	-39	29.4	-24	1.2
Other Comprehensive Income (Loss)	-3.6	-4.4	-10.5	-2.8
Net Foreign Currency Adjustments | Foreign Currency Translation Adjustments	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	-77.1	55	-57.2	5.3
Tax Effect	6.6	-4	6	-2.3
Other Comprehensive Income (Loss)	-70.5	51	-51.2	3
Net Foreign Currency Adjustments | Net Investment Hedge Gains (Losses)	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	119.9	-88.8	79.7	-9.3
Tax Effect	-45.6	33.4	-30	3.5
Other Comprehensive Income (Loss)	74.3	-55.4	49.7	-5.8
Net Foreign Currency Adjustments | Long Term Intra Entity Foreign Currency Transaction Losses	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	-7.4	'	-9	'
Other Comprehensive Income (Loss)	-7.4	'	-9	'
Net Pension and Other Postretirement Benefit Adjustments	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	6.5	11.3	19	33.7
Tax Effect	-3	-4.2	-8.5	-12.6
Other Comprehensive Income (Loss)	3.5	7.1	10.5	21.1
Net Pension and Other Postretirement Benefit Adjustments | Reclassification Adjustment for (Gains) Losses Included in Net Income	'	'	'	'
Accumulated Other Comprehensive Income (Loss) [Line Items]	'	'	'	'
Before Tax	6.5	11.3	19	33.7
Tax Effect	-3	-4.2	-8.5	-12.6
Other Comprehensive Income (Loss)	$3.50	$7.10	$10.50	$21.10

Reclassification_Adjustments_o

Reclassification Adjustments out of Accumulated Other Comprehensive Income (Loss) (Detail) (USD $)	3 Months Ended	9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2014
Available for Sale Investment Securities | Realized (Gains) Losses on Securities Available for Sale | Investment Security Gains (Losses), net	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'
Gross Reclassification Adjustment	($0.30)	($0.60)
CASH FLOW HEDGES | Foreign Exchange Contracts | Other Operating Income/Expense	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'
Gross Reclassification Adjustment	-3.7	-3.3
Pension and Other Postretirement Benefit Adjustments	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'
Gross Reclassification Adjustment	6.5	19
Pension and Other Postretirement Benefit Adjustments | Employee Benefits	'	'
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]	'	'
Amortization of Net Actuarial (Gain) Loss	-0.3	-1.1
Amortization of Prior Service Cost	$6.80	$20.10

Computations_of_Net_Income_Per

Computations of Net Income Per Common Share (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, except Share data, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Basic Net Income Per Common Share	'	'	'	'
Average Number of Common Shares Outstanding	235,701,076	239,930,074	236,301,789	239,614,868
Net Income	$204.50	$206.50	$567.80	$561.60
Less: Dividends on Preferred Stock	'	'	'	'
Net Income Applicable to Common Stock	204.5	206.5	567.8	561.6
Less: Earnings Allocated to Participating Securities	3.5	3.5	9.5	9.1
Earnings Allocated to Common Shares Outstanding	201	203	558.3	552.5
Basic Net Income Per Common Share	$0.85	$0.85	$2.36	$2.31
Diluted Net Income Per Common Share	'	'	'	'
Average Number of Common Shares Outstanding	235,701,076	239,930,074	236,301,789	239,614,868
Plus: Dilutive Effect of Share-based Compensation	2,036,053	1,400,578	1,873,907	1,242,829
Average Common and Potential Common Shares	237,737,129	241,330,652	238,175,696	240,857,697
Earnings Allocated to Common and Potential Common Shares	$201	$203	$558.40	$552.50
Diluted Net Income Per Common Share	$0.84	$0.84	$2.34	$2.29

Net_Income_Per_Common_Share_Co2

Net Income Per Common Share Computations - Additional Information (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]	'	'	'	'
Common stock equivalents not included in the computation of diluted earnings per share because their inclusion would have been antidilutive	1,071,654	3,371,680	1,671,849	3,783,018

Components_of_Net_Interest_Inc

Components of Net Interest Income (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Interest Income	'	'	'	'
Loans and Leases	$184.80	$185.40	$553.50	$558.50
Securities - Taxable	65.1	60.9	198	167.6
- Non-Taxable	1.6	2.7	5.7	9
Interest-Bearing Deposits with Banks	30.9	36.3	96.6	105.8
Federal Reserve Deposits and Other	11.4	5.8	29.2	12.2
Total Interest Income	293.8	291.1	883	853.1
Interest Expense	'	'	'	'
Deposits	21.6	25.8	64.1	79.9
Federal Funds Purchased	0.5	0.4	1.1	1
Securities Sold Under Agreements to Repurchase	0.1	0.1	0.3	0.3
Other Borrowings	0.9	0.8	2.4	2.5
Senior Notes	11.6	18.4	42.8	56.9
Long-Term Debt	9.2	8	29	27.5
Floating Rate Capital Debt	0.6	0.6	1.7	1.8
Total Interest Expense	44.5	54.1	141.4	169.9
Net Interest Income	$249.30	$237	$741.60	$683.20

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Taxes [Line Items]	'	'	'	'
Income tax expense	$99.70	$95	$276.60	$268.20
Effective tax rate	32.80%	31.50%	32.80%	32.30%

Components_of_Companys_Net_Per

Components of Company's Net Periodic Benefit Cost (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
U.S. Plan	'	'	'	'
Defined Benefit plan Net periodic benefit cost	'	'	'	'
Service Cost	$8.20	$7.50	$24.60	$22.70
Interest Cost	11.1	10.5	33.3	31.6
Expected Return on Plan Assets	-24.4	-23.1	-73.3	-69.2
Amortization	'	'	'	'
Net Actuarial (Gain) Loss	-0.1	10.3	-0.3	30.9
Prior Service Cost	5.4	-0.1	16.1	-0.3
Net Periodic Pension Expense (Benefit)	0.2	5.1	0.4	15.7
Non U.S. Plans	'	'	'	'
Defined Benefit plan Net periodic benefit cost	'	'	'	'
Interest Cost	1.8	1.6	5.3	4.9
Expected Return on Plan Assets	-1.8	-1.5	-5.3	-4.6
Amortization	'	'	'	'
Net Actuarial (Gain) Loss	-0.4	0.2	-1.2	0.7
Net Periodic Pension Expense (Benefit)	-0.4	0.3	-1.2	1
Supplemental Plan	'	'	'	'
Defined Benefit plan Net periodic benefit cost	'	'	'	'
Service Cost	0.8	0.4	2.3	1.2
Interest Cost	1.2	1.1	3.6	3.3
Amortization	'	'	'	'
Net Actuarial (Gain) Loss	0.2	1.7	0.4	5.1
Prior Service Cost	1.5	0.2	4.4	0.4
Net Periodic Pension Expense (Benefit)	3.7	3.4	10.7	10
Other Postretirement Plan	'	'	'	'
Defined Benefit plan Net periodic benefit cost	'	'	'	'
Service Cost	'	'	0.1	0.1
Interest Cost	0.4	0.3	1.1	0.9
Amortization	'	'	'	'
Net Actuarial (Gain) Loss	'	-0.3	'	-0.9
Prior Service Cost	-0.1	-0.7	-0.4	-2.2
Net Periodic Pension Expense (Benefit)	$0.30	($0.70)	$0.80	($2.10)

Compensation_Expense_for_Share

Compensation Expense for Share-Based Payment Arrangements and Associated Tax Impacts (Detail) (USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Share-Based Compensation Expense	$18	$17.90	$61.30	$56.70
Tax Benefits Recognized	6.8	6.8	23	21.3
Restricted Stock Unit Awards	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Share-Based Compensation Expense	12.7	12.1	41.7	36.4
Stock Options	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Share-Based Compensation Expense	2.2	3.7	10.7	14.9
Performance Stock Units	'	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'	'
Share-Based Compensation Expense	$3.10	$2.10	$8.90	$5.40

Variable_Interest_Entities_Add

Variable Interest Entities - Additional Information (Detail) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
	Tax Credit Structures	Tax Credit Structures	Tax Credit Structures	Leveraged Leasing Transactions	Leveraged Leasing Transactions	Leveraged Leasing Transactions	Leveraged Leasing Transactions	Leveraged Leasing Transactions	Leveraged Leasing Transactions
						Lower Limit	Lower Limit	Upper Limit	Upper Limit
Variable Interest Entity [Line Items]	'	'	'	'	'	'	'	'	'
Funding of asset's cost via an equity interest	'	'	'	'	'	20.00%	20.00%	30.00%	30.00%
Funding of asset's cost via third party non recourse debt holders	'	'	'	'	'	70.00%	70.00%	80.00%	80.00%
Carrying amounts	$224,100,000	$224,100,000	$222,300,000	$579,100,000	$671,200,000	'	'	'	'
Exposure to loss from liquidity arrangements and obligations to purchase assets	0	0	'	0	'	'	'	'	'
Liabilities related to unfunded commitments	27,400,000	27,400,000	19,800,000	'	'	'	'	'	'
Affordable housing tax credits and other tax benefits	$14,500,000	$43,200,000	'	'	'	'	'	'	'

Contingent_Liabilities_Additio

Contingent Liabilities - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended
	Apr. 30, 2014	Dec. 31, 2013	Sep. 30, 2014
Commitments and Contingencies Disclosure [Line Items]	'	'	'
Standby letters of credit outstanding	'	$4,500,000,000	$4,300,000,000
Minimum securities lending related collateral percentage	'	'	100.00%
Possible loss in future periods in excess of accrual	'	'	130,000,000
Legal Settlement Charge	'	19,200,000	'
Remaining Visa shares held by Northern Trust, original cost basis	'	'	0
Fair value of contingent consideration	'	55,400,000	'
Settlement of contingent consideration	55,300,000	'	'
Indemnification Agreement	'	'	'
Commitments and Contingencies Disclosure [Line Items]	'	'	'
Collateralized securities loaned, subject to indemnification	'	82,700,000,000	99,900,000,000
Credit loss liability	'	$0	$0

Derivative_Financial_Instrumen2

Derivative Financial Instruments - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Dec. 31, 2013	Sep. 30, 2014	Sep. 30, 2014	Sep. 30, 2014	Dec. 31, 2013	Sep. 30, 2014	Dec. 31, 2013
						Available for Sale Investment Securities	Foreign Exchange Contracts	Net Investment Hedges	Net Investment Hedges	Client Related and Trading	Client Related and Trading
Derivative [Line Items]	'	'	'	'	'	'	'	'	'	'	'
Derivative assets recorded on the consolidated balance sheet, reduced as a result of master netting agreements	$2,200,000,000	'	$2,200,000,000	'	$1,200,000,000	'	'	'	'	'	'
Derivative liabilities recorded on the consolidated balance sheet, reduced as a result of master netting agreements	2,200,000,000	'	2,200,000,000	'	1,200,000,000	'	'	'	'	'	'
Reduction in derivative assets due to cash collateral received from derivative counterparties	207,400,000	'	207,400,000	'	210,700,000	'	'	'	'	'	'
Reduction in derivative liabilities due to cash collateral deposited with derivative counterparties	601,300,000	'	601,300,000	'	767,700,000	'	'	'	'	'	'
This amount represents additional cash collateral received from derivative counterparties not offset against derivative assets	42,000,000	'	42,000,000	'	36,400,000	'	'	'	'	'	'
This amount represents additional cash collateral deposited with derivative counterparties not offset against derivative liabilities	51,300,000	'	51,300,000	'	39,300,000	'	'	'	'	'	'
Securities posted as collateral	27,500,000	'	27,500,000	'	27,600,000	'	'	'	'	'	'
Aggregate fair value of all derivative instruments with credit-risk-related contingent features that are in a liability position	113,400,000	'	113,400,000	'	257,300,000	'	'	'	'	'	'
Collateral deposited with derivative counterparties for derivatives instruments with credit-risk-related contingent features that are in a liability position	41,500,000	'	41,500,000	'	197,000,000	'	'	'	'	'	'
Termination payments that could have been required for derivative instruments with credit-risk-related contingent features	71,900,000	'	71,900,000	'	60,300,000	'	'	'	'	'	'
Percentage of derivatives outstanding related to client-related and trading activities	'	'	'	'	'	'	'	'	'	0.97%	0.97%
Sterling denominated debt designated as hedges of foreign exchange risk	'	'	'	'	'	'	'	250,400,000	259,100,000	'	'
Changes recorded in the fair value of the hedged items in a fair value hedge	0	300,000	0	900,000	'	'	'	'	'	'	'
The net gain/loss recognized in earnings during the period representing the amount of hedge ineffectiveness for fair value hedges of available for sale investment securities, senior notes, or subordinated debt	0	300,000	0	800,000	'	'	'	'	'	'	'
Maximum length of time being hedged for exposure to variability in future cash flows of forecasted foreign currency denominated transactions	'	'	'23 months	'	'	'	'	'	'	'	'
The net gain/loss recognized in earnings during the period representing the amount of hedge ineffectiveness cash flow hedges	0	0	0	0	'	'	'	'	'	'	'
Net foreign exchange contract gains (losses) reclassified from AOCI	0	0	0	0	'	'	'	'	'	'	'
Estimated net gain (loss) to be reclassified into earnings within the next twelve months relating to cash flow hedges	'	'	'	'	'	2,200,000	-1,800,000	'	'	'	'
Ineffectiveness from net investment hedges	$0	$0	$0	$0	'	'	'	'	'	'	'

Notional_and_Fair_Value_Amount

Notional and Fair Value Amounts of Client-related and Trading Derivative Financial Instruments (Detail) (Client Related and Trading, USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Derivative [Line Items]	'	'
Notional Value	$275,071.30	$248,136.70
Fair Value Asset	4,233	2,967.50
Fair Value Liability	4,221.40	2,963.20
Foreign Exchange Contracts	'	'
Derivative [Line Items]	'	'
Notional Value	270,022.40	243,135
Fair Value Asset	4,132.80	2,844.70
Fair Value Liability	4,125.50	2,846.20
Interest Rate Contracts	'	'
Derivative [Line Items]	'	'
Notional Value	5,048.90	5,001.70
Fair Value Asset	100.2	122.8
Fair Value Liability	$95.90	$117

Gains_and_Losses_Recorded_in_C

Gains and Losses Recorded in Consolidated Statement of Income Related to Client Related and Trading Derivative Financial Instruments (Detail) (Client Related and Trading, USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Derivative Gain/(Loss) Recognized in Income	$47	$67.20	$154	$205
Foreign Exchange Contracts | Foreign Exchange Trading Income	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Derivative Gain/(Loss) Recognized in Income	46.4	62.8	149.4	193.6
Interest Rate Contracts | Security Commissions and Trading Income	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Derivative Gain/(Loss) Recognized in Income	$0.60	$4.40	$4.60	$11.40

Types_and_Classifications_of_D

Types and Classifications of Derivative Instruments Designated as Hedges (Detail) (Asset And Liability Management, USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Derivative [Line Items]	'	'
Notional Value	$6,669.30	$6,545.80
Fair Value Asset	184	135.1
Fair Value Liability	40.2	136.5
FAIR VALUE HEDGES | Senior Notes and Long- Term Subordinated Debt | Interest Rate Swap Contracts	'	'
Derivative [Line Items]	'	'
Notional Value	1,250	1,250
Fair Value Asset	92.4	83.6
Fair Value Liability	2	33.4
FAIR VALUE HEDGES | Available for Sale Investment Securities | Interest Rate Swap Contracts	'	'
Derivative [Line Items]	'	'
Notional Value	2,939.70	3,296.90
Fair Value Asset	20.8	31.5
Fair Value Liability	24.9	44.8
CASH FLOW HEDGES | Forecasted Foreign Currency Denominated Transactions | Foreign Exchange Contracts	'	'
Derivative [Line Items]	'	'
Notional Value	341	314
Fair Value Asset	5.2	10.2
Fair Value Liability	9.5	5.5
CASH FLOW HEDGES | Available for Sale Investment Securities | Interest Rate Swap Contracts	'	'
Derivative [Line Items]	'	'
Notional Value	10	'
CASH FLOW HEDGES | Available for Sale Investment Securities | Interest Rate Option Contracts	'	'
Derivative [Line Items]	'	'
Notional Value	375	'
Fair Value Asset	0.1	'
Fair Value Liability	0.7	'
Net Investment Hedges | Net Investments in Non-U.S. Affiliates | Foreign Exchange Contracts	'	'
Derivative [Line Items]	'	'
Notional Value	1,753.60	1,684.90
Fair Value Asset	65.5	9.8
Fair Value Liability	$3.10	$52.80

Gains_and_Losses_Recorded_in_C1

Gains and Losses Recorded in Consolidated Statement of Income Related to Fair Value Hedges (Detail) (Asset And Liability Management, FAIR VALUE HEDGES, USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Derivative Gain/(Loss) Recognized in Income	$10.90	($20)	$44.10	$5.50
Available for Sale Investment Securities | Interest Rate Swap Contracts | Interest Income	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Derivative Gain/(Loss) Recognized in Income	5.1	-16.4	-21.9	21.6
Senior Notes and Long- Term Subordinated Debt | Interest Rate Swap Contracts | Interest Expense	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Derivative Gain/(Loss) Recognized in Income	$5.80	($3.60)	$66	($16.10)

Cash_Flow_Hedge_Derivative_Gai

Cash Flow Hedge Derivative Gains and Losses Recognized in AOCI and the Amounts Reclassified to Earnings (Detail) (Asset And Liability Management, USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Foreign Exchange Contracts	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Net Gain/(Loss) Recognized in AOCI	($6.90)	$5.30	($5.80)	($4)
Net Gain/(Loss) Reclassified from AOCI to Earnings	0.7	-1.1	3.2	-5.7
Interest Rate Option Contracts	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Net Gain/(Loss) Recognized in AOCI	-0.7	'	-0.7	'
Net Gain/(Loss) Reclassified from AOCI to Earnings	0.1	'	0.1	'
Net Gain/(Loss) Reclassified from AOCI to Earnings | Foreign Exchange Contracts	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Other Operating Income	0.7	'	3.4	-1.8
Other Operating Expense	'	($1.10)	($0.20)	($3.90)

Net_Investment_Hedge_Gains_and

Net Investment Hedge Gains and Losses Recognized in AOCI (Detail) (Net Investment Hedges, USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative [Line Items]	'	'	'	'
Hedging Instrument Gain/(Loss) Recognized in AOCI (Before Tax)	$119.90	($88.80)	$79.70	($9.30)
Foreign Exchange Contracts	'	'	'	'
Derivative [Line Items]	'	'	'	'
Hedging Instrument Gain/(Loss) Recognized in AOCI (Before Tax)	106.2	-73.8	74.3	-9.5
Sterling Denominated Subordinated Debt	'	'	'	'
Derivative [Line Items]	'	'	'	'
Hedging Instrument Gain/(Loss) Recognized in AOCI (Before Tax)	$13.70	($15)	$5.40	$0.20

Types_of_Risk_Management_Deriv

Types of Risk Management Derivative Instruments Not Formally Designated as Hedges and Their Notional Amounts and Fair Values (Detail) (Nondesignated, Foreign Exchange Contracts, USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Nondesignated | Foreign Exchange Contracts	'	'
Derivative [Line Items]	'	'
Notional Value	$192.30	$168.80
Fair Value Asset	0.3	1
Fair Value Liability	$3.50	$1.20

Gains_and_Losses_Recorded_in_C2

Gains and Losses Recorded in Consolidated Statement of Income related to Derivative Instruments Not Formally Designated as Hedges (Detail) (Nondesignated, USD $)	3 Months Ended		9 Months Ended
In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Derivative Gain/(Loss) Recognized in Income	($10.10)	$6.70	($9.30)	($4.40)
Credit Default Swap Contracts | Others Operating Income	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Derivative Gain/(Loss) Recognized in Income	'	'	'	-0.1
Foreign Exchange Contracts | Others Operating Income	'	'	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'	'	'
Amount of Derivative Gain/(Loss) Recognized in Income	($10.10)	$6.70	($9.30)	($4.30)

Offsetting_of_Derivative_Asset

Offsetting of Derivative Assets and of Securities Purchased Under Agreements to Resell Within Consolidated Balance Sheet (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Securities Purchased under Agreements to Resell	'		'
Derivative [Line Items]	'		'
Gross Recognized Assets	$1,000	[1]	$500	[1]
Net Amount Presented	1,000	[1]	500	[1]
Gross Amounts Not Offset	1,000	[1]	500	[1]
Derivatives	'		'
Derivative [Line Items]	'		'
Gross Recognized Assets	4,417.30	[2]	3,103.60	[2]
Gross Amounts Offset	2,358.40	[2]	1,369	[2]
Net Amount Presented	2,058.90	[2]	1,734.60	[2]
Net Amount	2,058.90	[2],[3]	1,734.60	[2],[3]
Derivatives | Subject to Master Netting Arrangement	'		'
Derivative [Line Items]	'		'
Gross Recognized Assets	3,478.50	[2]	2,850.40	[2]
Gross Amounts Offset	2,358.40	[2]	1,369	[2]
Net Amount Presented	1,120.10	[2]	1,481.40	[2]
Net Amount	1,120.10	[2],[3]	1,481.40	[2],[3]
Derivatives | Not Subject to Master Netting Arrangement	'		'
Derivative [Line Items]	'		'
Gross Recognized Assets	938.8	[2]	253.2	[2]
Net Amount Presented	938.8	[2]	253.2	[2]
Net Amount	938.8	[2],[3]	253.2	[2],[3]
Derivatives | Foreign Exchange Contracts | Over the Counter Derivative	'		'
Derivative [Line Items]	'		'
Gross Recognized Assets	3,265	[2]	2,612.50	[2]
Gross Amounts Offset	2,085	[2]	1,073.30	[2]
Net Amount Presented	1,180	[2]	1,539.20	[2]
Net Amount	1,180	[2],[3]	1,539.20	[2],[3]
Derivatives | Interest Rate Swap Contracts | Over the Counter Derivative	'		'
Derivative [Line Items]	'		'
Gross Recognized Assets	183.7	[2]	228.8	[2]
Gross Amounts Offset	31.5	[2]	47.5	[2]
Net Amount Presented	152.2	[2]	181.3	[2]
Net Amount	152.2	[2],[3]	181.3	[2],[3]
Derivatives | Interest Rate Swap Contracts | Exchange Cleared	'		'
Derivative [Line Items]	'		'
Gross Recognized Assets	29.8	[2]	9.1	[2]
Gross Amounts Offset	7.4	[2]	9.1	[2]
Net Amount Presented	22.4	[2]	'
Net Amount	22.4	[2],[3]	'
Derivatives | Cross Product Netting Adjustment	'		'
Derivative [Line Items]	'		'
Gross Amounts Offset	27.1	[2]	28.4	[2]
Derivatives | Cross Product Collateral Adjustment	'		'
Derivative [Line Items]	'		'
Gross Amounts Offset	$207.40	[2]	$210.70	[2]
[1]	Securities purchased under agreements to resell are reported in federal funds sold and securities purchased under agreements to resell in the consolidated balance sheet. Federal funds sold totaled $10.0 million and $29.6 million as of September 30, 2014, and December 31, 2013, respectively.
[2]	Derivative assets are reported in other assets in the consolidated balance sheet. Other assets (excluding derivative assets) totaled $3,230.9 million and $3,029.4 million as of September 30, 2014, and December 31, 2013, respectively.
[3]	Northern Trust did not possess any cash collateral that was not offset in the consolidated balance sheet that could have been used to offset the net amounts presented in the consolidated balance sheet as of September 30, 2014, and December 31, 2013.

Offsetting_of_Derivative_Asset1

Offsetting of Derivative Assets and of Securities Purchased Under Agreements to Resell Within Consolidated Balance Sheet (Parenthetical) (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Derivative [Line Items]	'	'
Other Assets (excluding Derivative Assets)	$3,230.90	$3,029.40
Federal Funds Sold	$10	$29.60

Offsetting_of_Derivative_Liabi

Offsetting of Derivative Liabilities and of Securities Sold Under Agreements to Repurchase Within Consolidated Balance Sheet (Detail) (USD $)	Sep. 30, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Derivative [Line Items]	'		'
Net Amounts Presented	$866.80		$917.30
Securities Sold under Agreements to Repurchase	'		'
Derivative [Line Items]	'		'
Gross Recognized Liabilities	866.8		917.3
Net Amounts Presented	866.8		917.3
Gross Amounts Not Offset	866.8		917.3
Derivatives	'		'
Derivative [Line Items]	'		'
Gross Recognized Liabilities	4,265.10	[1]	3,100.90	[1]
Gross Amounts Offset	2,752.30	[1]	1,926	[1]
Net Amounts Presented	1,512.80	[1]	1,174.90	[1]
Net Amount	1,512.80	[1],[2]	1,174.90	[1],[2]
Derivatives | Subject to Master Netting Arrangement	'		'
Derivative [Line Items]	'		'
Gross Recognized Liabilities	3,527.80	[1]	2,234.20	[1]
Gross Amounts Offset	2,752.30	[1]	1,926	[1]
Net Amounts Presented	775.5	[1]	308.2	[1]
Net Amount	775.5	[1],[2]	308.2	[1],[2]
Derivatives | Not Subject to Master Netting Arrangement	'		'
Derivative [Line Items]	'		'
Gross Recognized Liabilities	737.3	[1]	866.7	[1]
Net Amounts Presented	737.3	[1]	866.7	[1]
Net Amount	737.3	[1],[2]	866.7	[1],[2]
Derivatives | Foreign Exchange Contracts | Over the Counter Derivative	'		'
Derivative [Line Items]	'		'
Gross Recognized Liabilities	3,404.30	[1]	2,039	[1]
Gross Amounts Offset	2,085	[1]	1,073.30	[1]
Net Amounts Presented	1,319.30	[1]	965.7	[1]
Net Amount	1,319.30	[1],[2]	965.7	[1],[2]
Derivatives | Interest Rate Swap Contracts | Over the Counter Derivative	'		'
Derivative [Line Items]	'		'
Gross Recognized Liabilities	116.1	[1]	163.7	[1]
Gross Amounts Offset	31.5	[1]	47.5	[1]
Net Amounts Presented	84.6	[1]	116.2	[1]
Net Amount	84.6	[1],[2]	116.2	[1],[2]
Derivatives | Interest Rate Swap Contracts | Exchange Cleared	'		'
Derivative [Line Items]	'		'
Gross Recognized Liabilities	7.4	[1]	31.5	[1]
Gross Amounts Offset	7.4	[1]	9.1	[1]
Net Amounts Presented	'		22.4	[1]
Net Amount	'		22.4	[1],[2]
Derivatives | Cross Product Netting Adjustment	'		'
Derivative [Line Items]	'		'
Gross Amounts Offset	27.1	[1]	28.4	[1]
Derivatives | Cross Product Collateral Adjustment	'		'
Derivative [Line Items]	'		'
Gross Amounts Offset	$601.30	[1]	$767.70	[1]
[1]	Derivative liabilities are reported in other liabilities in the consolidated balance sheet. Other liabilities (excluding derivative liabilities) totaled $2,591.5 million and $2,338.4 million as of September 30, 2014, and December 31, 2013, respectively.
[2]	Northern Trust did not place any cash collateral with counterparties that was not offset in the consolidated balance sheet that could have been used to offset the net amounts presented in the consolidated balance sheet as of September 30, 2014, and December 31, 2013.

Offsetting_of_Derivative_Liabi1

Offsetting of Derivative Liabilities and of Securities Sold Under Agreements to Repurchase Within Consolidated Balance Sheet (Parenthetical) (Detail) (USD $)	Sep. 30, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Derivative [Line Items]	'	'
Other liabilities	$2,591.50	$2,338.40