Aggregate Fair Value of Investments with Continuous Unrealized Loss Position (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	$ 10,312		$ 10,942
Less than 12 months Unrealized losses	95		183
12 months or more Fair value	3,202		4,043
12 months or more Unrealized losses	593		818
Total Fair value	13,514		14,985
Total Unrealized losses	688		1,001
Available-for-sale
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	8,575		10,766
Less than 12 months Unrealized losses	85		178
12 months or more Fair value	2,592		3,321
12 months or more Unrealized losses	490		696
Total Fair value	11,167		14,087
Total Unrealized losses	575		874
Available-for-sale | U.S. Treasury
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value			118
Less than 12 months Unrealized losses			2
Total Fair value			118
Total Unrealized losses			2
Available-for-sale | State And Political Subdivisions
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	1,659		483
Less than 12 months Unrealized losses	7		2
12 months or more Fair value	165		157
12 months or more Unrealized losses	30		45
Total Fair value	1,824		640
Total Unrealized losses	37		47
Available-for-sale | Agency RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	2,657		3,844
Less than 12 months Unrealized losses	3		10
12 months or more Fair value	118		140
12 months or more Unrealized losses	1		1
Total Fair value	2,775		3,984
Total Unrealized losses	4		11
Available-for-sale | Alt-A RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	92		132
Less than 12 months Unrealized losses	7		16
12 months or more Fair value	48		69
12 months or more Unrealized losses	18		26
Total Fair value	140		201
Total Unrealized losses	25		42
Available-for-sale | Prime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	99		324
Less than 12 months Unrealized losses	7		25
12 months or more Fair value	489		447
12 months or more Unrealized losses	47		77
Total Fair value	588		771
Total Unrealized losses	54		102
Available-for-sale | Subprime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	26
Less than 12 months Unrealized losses	11
12 months or more Fair value	375		400
12 months or more Unrealized losses	125		190
Total Fair value	401		400
Total Unrealized losses	136		190
Available-for-sale | Other RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	663		5
Less than 12 months Unrealized losses	5		4
12 months or more Fair value	697		895
12 months or more Unrealized losses	171		226
Total Fair value	1,360		900
Total Unrealized losses	176		230
Available-for-sale | Commercial MBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	180		340
Less than 12 months Unrealized losses	1		2
12 months or more Fair value	433		495
12 months or more Unrealized losses	71		75
Total Fair value	613		835
Total Unrealized losses	72		77
Available-for-sale | Asset-Backed CLOs
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	783		1,143
Less than 12 months Unrealized losses	13		26
12 months or more Fair value	111		211
12 months or more Unrealized losses	12		11
Total Fair value	894		1,354
Total Unrealized losses	25		37
Available-for-sale | Other Asset-Backed Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	435		60
Less than 12 months Unrealized losses	1		1
12 months or more Fair value	8		18
12 months or more Unrealized losses	2		2
Total Fair value	443		78
Total Unrealized losses	3		3
Available-for-sale | Foreign Covered Bonds
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	429		368
Less than 12 months Unrealized losses	2		1
12 months or more Fair value	13		406
12 months or more Unrealized losses			2
Total Fair value	442		774
Total Unrealized losses	2		3
Available-for-sale | Corporate Bonds
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	36		254
Less than 12 months Unrealized losses	2		5
Total Fair value	36		254
Total Unrealized losses	2		5
Available-for-sale | Other Debt Securities
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	1,044		2,613
Less than 12 months Unrealized losses	1		7
12 months or more Fair value	17		54
12 months or more Unrealized losses			26
Total Fair value	1,061		2,667
Total Unrealized losses	1		33
Available-for-sale | Grantor Trust Alt-A RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	282	[1]	595	[1]
Less than 12 months Unrealized losses	15	[1]	53	[1]
12 months or more Fair value	95	[1]	29	[1]
12 months or more Unrealized losses	12	[1]	15	[1]
Total Fair value	377	[1]	624	[1]
Total Unrealized losses	27	[1]	68	[1]
Available-for-sale | Grantor Trust Prime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	159	[1]	437	[1]
Less than 12 months Unrealized losses	7	[1]	21	[1]
12 months or more Fair value	23	[1]
12 months or more Unrealized losses	1	[1]
Total Fair value	182	[1]	437	[1]
Total Unrealized losses	8	[1]	21	[1]
Available-for-sale | Grantor Trust Sub Prime RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	31	[1]	50	[1]
Less than 12 months Unrealized losses	3	[1]	3	[1]
Total Fair value	31	[1]	50	[1]
Total Unrealized losses	3	[1]	3	[1]
Held-to-maturity
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	1,737		176
Less than 12 months Unrealized losses	10		5
12 months or more Fair value	610		722
12 months or more Unrealized losses	103		122
Total Fair value	2,347		898
Total Unrealized losses	113		127
Held-to-maturity | Agency RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	1,652
Less than 12 months Unrealized losses	6
Total Fair value	1,652
Total Unrealized losses	6
Held-to-maturity | Alt-A RMBS
Investments, Unrealized Loss Position [Line Items]
Less than 12 months Fair value	25		69
Less than 12 months Unrealized losses	2		3
12 months or more Fair value	39		42
12 months or more Unrealized losses	10		16
Total Fair value	64		111
Total Unrealized losses	12		19
Held-to-maturity | Prime RMBS
Investments, Unrealized Loss Position [Line Items]
12 months or more Fair value	55		56
12 months or more Unrealized losses	6		10
Total Fair value	55		56
Total Unrealized losses	6		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	60		107
Less than 12 months Unrealized losses	2		2
12 months or more Fair value	468		573
12 months or more Unrealized losses	81		91
Total Fair value	528		680
Total Unrealized losses	83		93
Held-to-maturity | Commercial MBS
Investments, Unrealized Loss Position [Line Items]
12 months or more Fair value	23		26
12 months or more Unrealized losses	3		2
Total Fair value	23		26
Total Unrealized losses	$ 3		$ 2

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