Investment Securities - Investment Securities Held to Maturity (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	$ 34,716	$ 34,389
Held-to-maturity securities, Unrealized Gains	507	590
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	(2)	(3)
Held-to-maturity securities, Unrealized Losses Other	(38)	(24)
Held-to-maturity securities, Fair Value	35,183	34,952
U.S. Treasury and Agencies [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	3,473	3,154
Held-to-maturity securities, Unrealized Gains	23	27
Held-to-maturity securities, Unrealized Losses Other	(2)
Held-to-maturity securities, Fair Value	3,494	3,181
Collateralized debt/loan obligation asset-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	4	7
Held-to-maturity securities, Unrealized Gains	11	15
Held-to-maturity securities, Fair Value	15	22
Asset Backed Securities Other [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	18	19
Held-to-maturity securities, Unrealized Gains	3	2
Held-to-maturity securities, Unrealized Losses Other-than-Temporary	(2)	(3)
Held-to-maturity securities, Unrealized Losses Other	(1)	(1)
Held-to-maturity securities, Fair Value	18	17
Obligations of State and Political Subdivisions [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	19	20
Held-to-maturity securities, Unrealized Gains	1	1
Held-to-maturity securities, Fair Value	20	21
Obligations of foreign governments [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	7	7
Held-to-maturity securities, Fair Value	7	7
Other debt securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	114	115
Held-to-maturity securities, Unrealized Losses Other	(15)	(17)
Held-to-maturity securities, Fair Value	99	98
Residential Agency [Member] | Residential [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	31,078	31,064
Held-to-maturity securities, Unrealized Gains	469	545
Held-to-maturity securities, Unrealized Losses Other	(20)	(6)
Held-to-maturity securities, Fair Value	31,527	31,603
Residential Non-agency Non-prime [Member] | Residential [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	1	1
Held-to-maturity securities, Fair Value	1	1
Non-agency [Member] | Commercial Mortgage-backed securities [Member]
Schedule of Held-to-maturity Securities [Line Items]
Held-to-maturity securities, Amortized Cost	2	2
Held-to-maturity securities, Fair Value	$ 2	$ 2