Securities Securities - Amortized Cost and Fair Value of Asset Backed Securities (Detail) (USD $)	Sep. 30, 2013		Dec. 31, 2012
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	$ 47,706,000,000		$ 66,041,000,000
Unrealized Gains, Available-for-sale securities	940,000,000		1,828,000,000
Unrealized Losses, Available-for-sale securities	(593,000,000)		(153,000,000)
Fair Value, Available-for-sale securities	48,053,000,000		67,716,000,000
Amortized Cost, Held-to-Maturity Securities	1,545,000,000		1,620,000,000
Non-Credit Loss Component of OTTI Securities, Held-to-Maturity Securities	(112,000,000)
Unrealized Gains, Held-to-Maturity Securities	165,000,000		211,000,000
Unrealized Losses, Held-to-Maturity Securities	0		0
Held-to-maturity Securities, Fair Value	1,598,000,000		1,831,000,000
US Government Agencies Debt Securities [Member] | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	170,000,000		153,000,000
US Government Agencies Debt Securities [Member] | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	34,000,000		13,000,000
U.S. Treasury [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	18,228,000,000		34,800,000,000
Unrealized Gains, Available-for-sale securities	423,000,000		566,000,000
Unrealized Losses, Available-for-sale securities	(60,000,000)		(24,000,000)
Fair Value, Available-for-sale securities	18,591,000,000		35,342,000,000
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	161,000,000	[1]	144,000,000	[1]
Unrealized Gains, Available-for-sale securities	0	[1]	1,000,000	[1]
Unrealized Losses, Available-for-sale securities	(11,000,000)	[1]	(1,000,000)	[1]
Fair Value, Available-for-sale securities	150,000,000	[1]	144,000,000	[1]
Amortized Cost, Held-to-Maturity Securities	893,000,000	[2]	1,121,000,000	[2]
Non-Credit Loss Component of OTTI Securities, Held-to-Maturity Securities	0	[2]
Unrealized Gains, Held-to-Maturity Securities	105,000,000	[2]	148,000,000	[2]
Unrealized Losses, Held-to-Maturity Securities	0	[2]	0	[2]
Held-to-maturity Securities, Fair Value	998,000,000	[2]	1,269,000,000	[2]
Collateralized Mortgage Obligations [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	43,000,000	[1]	22,000,000	[1]
Unrealized Gains, Available-for-sale securities	0	[1]	0	[1]
Unrealized Losses, Available-for-sale securities	(1,000,000)	[1]	0	[1]
Fair Value, Available-for-sale securities	42,000,000	[1]	22,000,000	[1]
Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	10,800,000,000		15,646,000,000
Unrealized Gains, Available-for-sale securities	179,000,000		674,000,000
Unrealized Losses, Available-for-sale securities	(270,000,000)		(6,000,000)
Fair Value, Available-for-sale securities	10,709,000,000		16,314,000,000
Amortized Cost, Held-to-Maturity Securities	55,000,000		66,000,000
Non-Credit Loss Component of OTTI Securities, Held-to-Maturity Securities	0
Unrealized Gains, Held-to-Maturity Securities	9,000,000		12,000,000
Unrealized Losses, Held-to-Maturity Securities	0		0
Held-to-maturity Securities, Fair Value	64,000,000		78,000,000
Mortgage-backed securities [Member] | Federal National Mortgage Association Certificates and Obligations (FNMA) [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Held-to-maturity Securities, Fair Value	422,000,000		507,000,000
Mortgage-backed securities [Member] | Federal Home Loan Mortgage Corporation Certificates and Obligations (FHLMC) [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Held-to-maturity Securities, Fair Value	471,000,000		614,000,000
Direct agency obligations [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	4,082,000,000	[1]	4,039,000,000	[1]
Unrealized Gains, Available-for-sale securities	276,000,000	[1]	364,000,000	[1]
Unrealized Losses, Available-for-sale securities	(14,000,000)	[1]	(2,000,000)	[1]
Fair Value, Available-for-sale securities	4,344,000,000	[1]	4,401,000,000	[1]
Collateralized mortgage obligations [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	8,045,000,000		4,315,000,000
Unrealized Gains, Available-for-sale securities	30,000,000		156,000,000
Unrealized Losses, Available-for-sale securities	(139,000,000)		0
Fair Value, Available-for-sale securities	7,936,000,000		4,471,000,000
Amortized Cost, Held-to-Maturity Securities	225,000,000		277,000,000
Non-Credit Loss Component of OTTI Securities, Held-to-Maturity Securities	0
Unrealized Gains, Held-to-Maturity Securities	28,000,000		42,000,000
Unrealized Losses, Held-to-Maturity Securities	0		0
Held-to-maturity Securities, Fair Value	253,000,000		319,000,000
Direct agency obligations [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	1,000,000		1,000,000
Unrealized Gains, Available-for-sale securities	0		0
Unrealized Losses, Available-for-sale securities	0		0
Fair Value, Available-for-sale securities	1,000,000		1,000,000
Obligations of U.S. states and political subdivision [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	867,000,000		877,000,000
Unrealized Gains, Available-for-sale securities	17,000,000		37,000,000
Unrealized Losses, Available-for-sale securities	(26,000,000)		(2,000,000)
Fair Value, Available-for-sale securities	858,000,000		912,000,000
Amortized Cost, Held-to-Maturity Securities	31,000,000		38,000,000
Non-Credit Loss Component of OTTI Securities, Held-to-Maturity Securities	0
Unrealized Gains, Held-to-Maturity Securities	1,000,000		3,000,000
Unrealized Losses, Held-to-Maturity Securities	0		0
Held-to-maturity Securities, Fair Value	32,000,000		41,000,000
Residential mortgages [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	1,000,000		1,000,000
Unrealized Gains, Available-for-sale securities	1,000,000		0
Unrealized Losses, Available-for-sale securities	0		0
Fair Value, Available-for-sale securities	2,000,000		1,000,000
Amortized Cost, Held-to-Maturity Securities	21,000,000		118,000,000
Non-Credit Loss Component of OTTI Securities, Held-to-Maturity Securities	0
Unrealized Gains, Held-to-Maturity Securities	1,000,000		6,000,000
Unrealized Losses, Held-to-Maturity Securities	0		0
Held-to-maturity Securities, Fair Value	22,000,000		124,000,000
Commercial mortgages [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	133,000,000		208,000,000
Unrealized Gains, Available-for-sale securities	2,000,000		6,000,000
Unrealized Losses, Available-for-sale securities	0		0
Fair Value, Available-for-sale securities	135,000,000		214,000,000
Home equity [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	272,000,000		310,000,000
Unrealized Gains, Available-for-sale securities	0		0
Unrealized Losses, Available-for-sale securities	(42,000,000)		(52,000,000)
Fair Value, Available-for-sale securities	230,000,000		258,000,000
Other Debt Obligations [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	103,000,000		102,000,000
Unrealized Gains, Available-for-sale securities	0		0
Unrealized Losses, Available-for-sale securities	0		(18,000,000)
Fair Value, Available-for-sale securities	103,000,000		84,000,000
Corporate and other domestic debt securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities			24,000,000
Unrealized Gains, Available-for-sale securities			2,000,000
Unrealized Losses, Available-for-sale securities			0
Fair Value, Available-for-sale securities			26,000,000
Foreign debt securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	4,805,000,000	[3],[4]	5,385,000,000	[3],[4]
Unrealized Gains, Available-for-sale securities	10,000,000	[3],[4]	16,000,000	[3],[4]
Unrealized Losses, Available-for-sale securities	(27,000,000)	[3],[4]	(48,000,000)	[3],[4]
Fair Value, Available-for-sale securities	4,788,000,000	[3],[4]	5,353,000,000	[3],[4]
Foreign debt securities [Member] | Foreign Government [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Foreign debt securities fully backed by foreign governments	1,200,000,000		1,500,000,000
Equity securities [Member]
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Available-for-sale securities	165,000,000		167,000,000
Unrealized Gains, Available-for-sale securities	2,000,000		6,000,000
Unrealized Losses, Available-for-sale securities	(3,000,000)		0
Fair Value, Available-for-sale securities	164,000,000		173,000,000
Asset-backed securities collateralized by residential mortgages
Schedule of Available-for-sale Securities and Held-to-Maturity Securities [Line Items]
Amortized Cost, Held-to-Maturity Securities	320,000,000
Non-Credit Loss Component of OTTI Securities, Held-to-Maturity Securities	(112,000,000)
Unrealized Gains, Held-to-Maturity Securities	21,000,000
Unrealized Losses, Held-to-Maturity Securities	0
Held-to-maturity Securities, Fair Value	$ 229,000,000

[1] Includes securities at amortized cost of $170 million and $153 million issued or guaranteed by FNMA at September 30, 2013 and December 31, 2012, respectively, and $34 million and $13 million issued or guaranteed by FHLMC at September 30, 2013 and December 31, 2012, respectively.

[2] Includes securities at amortized cost of $422 million and $507 million issued or guaranteed by FNMA at September 30, 2013 and December 31, 2012, respectively, and $471 million and $614 million issued and guaranteed by FHLMC at September 30, 2013 and December 31, 2012, respectively.

[3] At September 30, 2013 and December 31, 2012, foreign debt securities consisted of $1.2 billion and $1.5 billion, respectively, of securities fully backed by foreign governments. The remainder of foreign debt securities represents foreign bank or corporate debt.

[4] We did not hold any foreign debt securities issued by the governments of Greece, Ireland, Italy, Portugal or Spain at September 30, 2013 and December 31, 2012.