Guarantees - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended
	May 31, 2009	Mar. 31, 2015		Dec. 31, 2014	Mar. 31, 2014		Dec. 31, 2013
Business Combination, Contingent Consideration, Liability		$ 21		$ 27
Unpaid Principal Balance Of Unresolved Repurchase Requests		48	[1]	47	155	[1]	126
Standby Letters of Credit
Maximum potential amount obligation		3,000		3,000
Mortgage Servicing Rights [Member]
Loss Contingency Accrual, at Carrying Value		25		25
Visa Interest [Member]
Derivative Liability, Current		8		5
Tax Credit Sales [Member]
Maximum potential amount obligation		19
Not Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Liabilities [Member] | Visa Interest [Member]
Number Of Shares Sold To Selected Financial Institutions	3.2
Non-Government Sponsored Agency [Member]
Unpaid Principal Balance Of Unresolved Repurchase Requests		$ 3			$ 3

[1] 1 Comprised of $45 million and $152 million from the GSEs, and $3 million from non-agency investors at both March 31, 2015 and 2014, respectively.