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