Guarantees - Additional Information (Detail) - USD ($) shares in Millions, $ in Millions	1 Months Ended	9 Months Ended
	May. 31, 2009	Sep. 30, 2015		Dec. 31, 2014	Sep. 30, 2014		Dec. 31, 2013
Document Period End Date		Sep. 30, 2015
Guarantee, Expiry Range of Tax Credits Sold, Minimum		3 years
Guarantee Period of Tax Credits Sold, Maximum		15 years
Business Combination, Contingent Consideration, Liability		$ 23		$ 27
Unpaid Principal Balance Of Unresolved Repurchase Requests		$ 16	[1]	47	$ 45	[1]	$ 126
Guarantee, Expiry Range of Tax Credits Sold, Maximum		7 years
Standby Letters of Credit
Maximum potential amount obligation		$ 2,900		3,000
Mortgage Servicing Rights [Member]
Loss Contingency Accrual, at Carrying Value		18		25
Visa Interest [Member]
Derivative Liability, Current		6		$ 5
Tax Credit Sales [Member]
Maximum potential amount obligation		19
Derivative Financial Instruments, Liabilities [Member] | Visa Interest [Member]
Number Of Shares Sold To Selected Financial Institutions	3.0
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		$ 1			$ 3

[1] 1 Comprised of $15 million and $42 million from the GSEs, and $1 million and $3 million from non-agency investors at September 30, 2015 and 2014, respectively.