Securities - Details of Securities (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 11,728	$ 15,490
Gross Unrealized Gains	366	522
Gross Unrealized Losses
Fair Value	12,094	16,012
Held to maturities, Amortized Cost	3,931	2,109
Held to maturities, Gross Unrealized Gains	61	24
Held to maturities, Gross Unrealized Losses
Held to maturities, Fair Value	3,992	2,133
Collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,148	14,707
Gross Unrealized Gains	316	455
Gross Unrealized Losses
Fair Value	11,464	15,162
Held to maturities, Amortized Cost	3,913	2,091
Held to maturities, Gross Unrealized Gains	61	24
Held to maturities, Gross Unrealized Losses
Held to maturities, Fair Value	3,974	2,115
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42	8
Gross Unrealized Gains	1	1
Gross Unrealized Losses
Fair Value	43	9
Held to maturities, Amortized Cost	18	18
Held to maturities, Gross Unrealized Losses
Held to maturities, Fair Value	18	18
States and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	47	60
Gross Unrealized Gains	2	3
Gross Unrealized Losses
Fair Value	49	63
Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	491	715
Gross Unrealized Gains	47	63
Gross Unrealized Losses
Fair Value	$ 538	$ 778