Contingent Liabilities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	12 Months Ended
Apr. 30, 2014	Dec. 31, 2013	Dec. 31, 2014
Commitments and Contingencies Disclosure [Line Items]
Possible loss in future periods in excess of accrual			$ 130
Legal Settlement Charge		19.2
Remaining Visa shares held by Northern Trust, original cost basis			0us-gaap_CostMethodInvestments
Fair value of contingent consideration		55.4
Settlement of contingent consideration	$ 55.3

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Pre-tax charge in connection with the agreement to resolve certain long-standing class action litigation related to Northern Trust Corporation's securities lending program.

+ References

No definition available.

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- Definition

Amount of increase (decrease) in the value of a contingent consideration liability, including, but not limited to, differences arising upon settlement.

+ References

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-Publisher FASB

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- Definition

Amount of liability recognized arising from contingent consideration in a business combination.

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- Definition

Amount, after adjustment, of cost-method investment. Adjustments include, but are not limited to, dividends received in excess of earnings after date of investment that are considered a return of investment and other than temporary impairments.

+ References

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- Definition

The estimated maximum amount of possible loss from the contingency.

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