Contingent Liabilities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Mar. 31, 2015	Dec. 31, 2014
Commitments and Contingencies Disclosure [Line Items]
Commitments and Letters of Credit		$ 35,600,000,000	$ 35,100,000,000
Legally binding commitments		477,200,000	481,400,000
Standby letters of credit outstanding		4,400,000,000	4,500,000,000
Minimum securities lending related collateral percentage		100.00%
Possible loss in future periods in excess of accrual		125,000,000
Legal Settlement Charge	19,200,000
Remaining Visa shares held by Northern Trust, original cost basis		0
Indemnification Agreement
Commitments and Contingencies Disclosure [Line Items]
Collateralized securities loaned, subject to indemnification		105,500,000,000	98,100,000,000
Credit loss liability		$ 0	$ 0