Securities - Details of Securities (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 13,120	$ 11,728	$ 12,768
Gross Unrealized Gains	249	366	438
Gross Unrealized Losses	116		1
Fair Value	13,253	12,094	13,205
Held to maturities, Amortized Cost	4,750	3,931	4,352
Held to maturities, Gross Unrealized Gains	16	61	44
Held to maturities, Gross Unrealized Losses	50
Held to maturities, Fair Value	4,716	3,992	4,396
State and Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	43	47	53
Gross Unrealized Gains	1	2	3
Fair Value	44	49	56
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,503	11,148	12,098
Gross Unrealized Gains	213	316	379
Gross Unrealized Losses	113
Fair Value	12,603	11,464	12,477
Held to maturities, Amortized Cost	4,732	3,913	4,334
Held to maturities, Gross Unrealized Gains	16	61	44
Held to maturities, Gross Unrealized Losses	50
Held to maturities, Fair Value	4,698	3,974	4,378
Other Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	555	491	597
Gross Unrealized Gains	32	47	55
Gross Unrealized Losses	3
Fair Value	584	538	652
Other Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	19	42	20
Gross Unrealized Gains	3	1	1
Gross Unrealized Losses			1
Fair Value	22	43	20
Held to maturities, Amortized Cost	18	18	18
Held to maturities, Fair Value	$ 18	$ 18	$ 18