Securities - Amortized Cost and Fair Value of Securities Available-for-Sale and Held-to-Maturity (Detail) (USD $)	Dec. 31, 2012		Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	$ 66,041,000,000		$ 51,791,000,000
Unrealized Gain, Available-for-sale securities	1,828,000,000		1,840,000,000
Unrealized Losses, Available-for-sale securities	(153,000,000)		(350,000,000)
Fair Value, Available-for-sale securities	67,716,000,000		53,281,000,000
Amortized Cost, Held-to-maturity securities	1,620,000,000		2,035,000,000
Unrealized Gain, Held-to-maturity securities	211,000,000		264,000,000
Unrealized Losses, Held-to-maturity securities	0		(1,000,000)
Fair Value, Held-to-maturity securities	1,831,000,000		2,298,000,000
U.S. Treasury [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	34,800,000,000		18,199,000,000
Unrealized Gain, Available-for-sale securities	566,000,000		498,000,000
Unrealized Losses, Available-for-sale securities	(24,000,000)		(121,000,000)
Fair Value, Available-for-sale securities	35,342,000,000		18,576,000,000
Mortgage-backed securities, U.S. Government sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	166,000,000	[1]	40,000,000	[1]
Unrealized Gain, Available-for-sale securities	1,000,000	[1]	1,000,000	[1]
Unrealized Losses, Available-for-sale securities	(1,000,000)	[1]	0	[1]
Fair Value, Available-for-sale securities	166,000,000	[1]	41,000,000	[1]
Amortized Cost, Held-to-maturity securities	1,121,000,000	[2]	1,421,000,000	[2]
Unrealized Gain, Held-to-maturity securities	148,000,000	[2]	195,000,000	[2]
Unrealized Losses, Held-to-maturity securities	0	[2]	0	[2]
Fair Value, Held-to-maturity securities	1,269,000,000	[2]	1,616,000,000	[2]
Direct agency obligations, U.S. Government sponsored enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	4,039,000,000	[1]	2,501,000,000	[1]
Unrealized Gain, Available-for-sale securities	364,000,000	[1]	352,000,000	[1]
Unrealized Losses, Available-for-sale securities	(2,000,000)	[1]	0	[1]
Fair Value, Available-for-sale securities	4,401,000,000	[1]	2,853,000,000	[1]
Mortgage-backed securities, U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	15,646,000,000		15,357,000,000
Unrealized Gain, Available-for-sale securities	674,000,000		728,000,000
Unrealized Losses, Available-for-sale securities	(6,000,000)		(3,000,000)
Fair Value, Available-for-sale securities	16,314,000,000		16,082,000,000
Amortized Cost, Held-to-maturity securities	66,000,000		79,000,000
Unrealized Gain, Held-to-maturity securities	12,000,000		13,000,000
Unrealized Losses, Held-to-maturity securities	0		0
Fair Value, Held-to-maturity securities	78,000,000		92,000,000
Collateralized mortgage obligations, U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	4,315,000,000		6,881,000,000
Unrealized Gain, Available-for-sale securities	156,000,000		177,000,000
Unrealized Losses, Available-for-sale securities	0		(3,000,000)
Fair Value, Available-for-sale securities	4,471,000,000		7,055,000,000
Amortized Cost, Held-to-maturity securities	277,000,000		308,000,000
Unrealized Gain, Held-to-maturity securities	42,000,000		44,000,000
Unrealized Losses, Held-to-maturity securities	0		0
Fair Value, Held-to-maturity securities	319,000,000		352,000,000
Direct agency obligations, U.S. Government agency issued or guaranteed [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	1,000,000		2,000,000
Unrealized Gain, Available-for-sale securities	0		0
Unrealized Losses, Available-for-sale securities	0		0
Fair Value, Available-for-sale securities	1,000,000		2,000,000
Obligations of U.S. states and political subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	877,000,000		566,000,000
Unrealized Gain, Available-for-sale securities	37,000,000		35,000,000
Unrealized Losses, Available-for-sale securities	(2,000,000)		(1,000,000)
Fair Value, Available-for-sale securities	912,000,000		600,000,000
Amortized Cost, Held-to-maturity securities	38,000,000		61,000,000
Unrealized Gain, Held-to-maturity securities	3,000,000		3,000,000
Unrealized Losses, Held-to-maturity securities	0		0
Fair Value, Held-to-maturity securities	41,000,000		64,000,000
Residential mortgage backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	1,000,000		6,000,000
Unrealized Gain, Available-for-sale securities	0		0
Unrealized Losses, Available-for-sale securities	0		(1,000,000)
Fair Value, Available-for-sale securities	1,000,000		5,000,000
Amortized Cost, Held-to-maturity securities	118,000,000		166,000,000
Unrealized Gain, Held-to-maturity securities	6,000,000		9,000,000
Unrealized Losses, Held-to-maturity securities	0		(1,000,000)
Fair Value, Held-to-maturity securities	124,000,000		174,000,000
Commercial mortgages [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	208,000,000		444,000,000
Unrealized Gain, Available-for-sale securities	6,000,000		9,000,000
Unrealized Losses, Available-for-sale securities	0		(2,000,000)
Fair Value, Available-for-sale securities	214,000,000		451,000,000
Home equity backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	310,000,000		369,000,000
Unrealized Gain, Available-for-sale securities	0		0
Unrealized Losses, Available-for-sale securities	(52,000,000)		(99,000,000)
Fair Value, Available-for-sale securities	258,000,000		270,000,000
Student loans backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	0		13,000,000
Unrealized Gain, Available-for-sale securities	0		0
Unrealized Losses, Available-for-sale securities	0		(1,000,000)
Fair Value, Available-for-sale securities	0		12,000,000
Other securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	102,000,000		102,000,000
Unrealized Gain, Available-for-sale securities	0		0
Unrealized Losses, Available-for-sale securities	(18,000,000)		(22,000,000)
Fair Value, Available-for-sale securities	84,000,000		80,000,000
Corporate and other domestic debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	24,000,000	[3]	541,000,000	[3]
Unrealized Gain, Available-for-sale securities	2,000,000	[3]	3,000,000	[3]
Unrealized Losses, Available-for-sale securities	0	[3]	0	[3]
Fair Value, Available-for-sale securities	26,000,000	[3]	544,000,000	[3]
Foreign debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	5,385,000,000	[4],[5]	6,640,000,000	[4],[5]
Unrealized Gain, Available-for-sale securities	16,000,000	[4],[5]	27,000,000	[4],[5]
Unrealized Losses, Available-for-sale securities	(48,000,000)	[4],[5]	(97,000,000)	[4],[5]
Fair Value, Available-for-sale securities	5,353,000,000	[4],[5]	6,570,000,000	[4],[5]
Equity securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost, Available-for-sale securities	167,000,000	[6]	130,000,000	[6]
Unrealized Gain, Available-for-sale securities	6,000,000	[6]	10,000,000	[6]
Unrealized Losses, Available-for-sale securities	0	[6]	0	[6]
Fair Value, Available-for-sale securities	$ 173,000,000	[6]	$ 140,000,000	[6]

[1] Includes securities at amortized cost of $153 million and $27 million issued or guaranteed by FNMA at December 31, 2012 and 2011, respectively, and $13 million and $13 million issued or guaranteed by FHLMC at December 31, 2012 and 2011, respectively.

[2] Includes securities at amortized cost of $507 million and $591 million issued or guaranteed by FNMA at December 31, 2012 and 2011, respectively, and $614 million and $830 million issued and guaranteed by FHLMC at December 31, 2012 and 2011, respectively.

[3] At December 31, 2011 other domestic debt securities included $516 million of securities at amortized cost fully backed by the Federal Deposit Insurance Corporation (“FDIC”).

[4] We did not hold any foreign debt securities issued by the governments of Greece, Ireland, Italy, Portugal or Spain at December 31, 2012 and 2011.

[5] At December 31, 2012 and 2011, foreign debt securities consisted of $1.5 billion and $2.7 billion, respectively, of securities fully backed by foreign governments. The remainder of foreign debt securities represents foreign bank or corporate debt.

[6] Includes preferred equity securities at amortized cost issued by FNMA of $2 million at December 31, 2011 which reflects cumulative other-than-temporary impairment charges of $173 million.