Aggregate Fair Value of Investments with a Continuous Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	$ 20,170		$ 10,942
Less than 12 months Unrealized losses	212		183
12 months or more Fair value	4,064		4,043
12 months or more Unrealized losses	714		818
Total Fair value	24,234		14,985
Total Unrealized losses	926		1,001
Available-for-sale
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	19,425		10,766
Less than 12 months Unrealized losses	209		178
12 months or more Fair value	3,205		3,321
12 months or more Unrealized losses	601		696
Total Fair value	22,630		14,087
Total Unrealized losses	810		874
Available-for-sale | U.S. Treasury
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	4,727		118
Less than 12 months Unrealized losses	101		2
Total Fair value	4,727		118
Total Unrealized losses	101		2
Available-for-sale | State And Political Subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	1,450		483
Less than 12 months Unrealized losses	12		2
12 months or more Fair value	176		157
12 months or more Unrealized losses	37		45
Total Fair value	1,626		640
Total Unrealized losses	49		47
Available-for-sale | Agency RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	8,547		3,844
Less than 12 months Unrealized losses	27		10
12 months or more Fair value	133		140
12 months or more Unrealized losses	1		1
Total Fair value	8,680		3,984
Total Unrealized losses	28		11
Available-for-sale | Alt-A RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	53		132
Less than 12 months Unrealized losses	5		16
12 months or more Fair value	50		69
12 months or more Unrealized losses	19		26
Total Fair value	103		201
Total Unrealized losses	24		42
Available-for-sale | Prime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	113		324
Less than 12 months Unrealized losses	8		25
12 months or more Fair value	518		447
12 months or more Unrealized losses	49		77
Total Fair value	631		771
Total Unrealized losses	57		102
Available-for-sale | Subprime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	22
Less than 12 months Unrealized losses	13
12 months or more Fair value	382		400
12 months or more Unrealized losses	162		190
Total Fair value	404		400
Total Unrealized losses	175		190
Available-for-sale | Other RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	168		5
Less than 12 months Unrealized losses	4		4
12 months or more Fair value	822		895
12 months or more Unrealized losses	210		226
Total Fair value	990		900
Total Unrealized losses	214		230
Available-for-sale | Commercial MBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	230		340
Less than 12 months Unrealized losses	1		2
12 months or more Fair value	471		495
12 months or more Unrealized losses	75		75
Total Fair value	701		835
Total Unrealized losses	76		77
Available-for-sale | Asset-Backed CLOs
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	845		1,143
Less than 12 months Unrealized losses	12		26
12 months or more Fair value	280		211
12 months or more Unrealized losses	9		11
Total Fair value	1,125		1,354
Total Unrealized losses	21		37
Available-for-sale | Other Asset-Backed Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	141		60
Less than 12 months Unrealized losses	1		1
12 months or more Fair value	18		18
12 months or more Unrealized losses	2		2
Total Fair value	159		78
Total Unrealized losses	3		3
Available-for-sale | Foreign Covered Bonds
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	321		368
Less than 12 months Unrealized losses	2		1
12 months or more Fair value	161		406
12 months or more Unrealized losses			2
Total Fair value	482		774
Total Unrealized losses	2		3
Available-for-sale | Corporate Bonds
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	120		254
Less than 12 months Unrealized losses	3		5
Total Fair value	120		254
Total Unrealized losses	3		5
Available-for-sale | Other Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	2,311		2,613
Less than 12 months Unrealized losses	2		7
12 months or more Fair value	58		54
12 months or more Unrealized losses	22		26
Total Fair value	2,369		2,667
Total Unrealized losses	24		33
Available-for-sale | Grantor Trust Alt-A RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	266	[1]	595	[1]
Less than 12 months Unrealized losses	11	[1]	53	[1]
12 months or more Fair value	99	[1]	29	[1]
12 months or more Unrealized losses	13	[1]	15	[1]
Total Fair value	365	[1]	624	[1]
Total Unrealized losses	24	[1]	68	[1]
Available-for-sale | Grantor Trust Prime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	84	[1]	437	[1]
Less than 12 months Unrealized losses	5	[1]	21	[1]
12 months or more Fair value	37	[1]
12 months or more Unrealized losses	2	[1]
Total Fair value	121	[1]	437	[1]
Total Unrealized losses	7	[1]	21	[1]
Available-for-sale | Grantor Trust Sub Prime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	27	[1]	50	[1]
Less than 12 months Unrealized losses	2	[1]	3	[1]
Total Fair value	27	[1]	50	[1]
Total Unrealized losses	2	[1]	3	[1]
Held-to-maturity
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	745		176
Less than 12 months Unrealized losses	3		5
12 months or more Fair value	859		722
12 months or more Unrealized losses	113		122
Total Fair value	1,604		898
Total Unrealized losses	116		127
Held-to-maturity | Alt-A RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	47		69
Less than 12 months Unrealized losses	1		3
12 months or more Fair value	79		42
12 months or more Unrealized losses	13		16
Total Fair value	126		111
Total Unrealized losses	14		19
Held-to-maturity | Prime RMBS
Investments, Unrealized Loss Position [Line Items]
12 months or more Fair value	57		56
12 months or more Unrealized losses	7		10
Total Fair value	57		56
Total Unrealized losses	7		10
Held-to-maturity | Subprime RMBS
Investments, Unrealized Loss Position [Line Items]
12 months or more Fair value	25		25
12 months or more Unrealized losses	3		3
Total Fair value	25		25
Total Unrealized losses	3		3
Held-to-maturity | Other RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	698		107
Less than 12 months Unrealized losses	2		2
12 months or more Fair value	672		573
12 months or more Unrealized losses	87		91
Total Fair value	1,370		680
Total Unrealized losses	89		93
Held-to-maturity | Commercial MBS
Investments, Unrealized Loss Position [Line Items]
12 months or more Fair value	26		26
12 months or more Unrealized losses	3		2
Total Fair value	26		26
Total Unrealized losses	$ 3		$ 2

[1] Previously included in the Grantor Trust. The Grantor Trust was dissolved in the first quarter of 2011.