Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011		Dec. 31, 2010
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 30,398		$ 22,748
Less than 12 months Gross Unrealized Losses	1,454		845
Twelve months or more Fair Value	15,047		16,878
Twelve months or more Gross Unrealized Losses	3,900		3,491
Total Fair Value	45,445	[1]	39,626	[2]
Total Gross Unrealized Losses	5,354	[1]	4,336	[2]
US Treasury And Government [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	870		3,677
Less than 12 months Gross Unrealized Losses	8		207
Twelve months or more Fair Value	130		422
Twelve months or more Gross Unrealized Losses	10		88
Total Fair Value	1,000		4,099
Total Gross Unrealized Losses	18		295
Obligations of U.S. states and their political subdivisions [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	7		1,273
Less than 12 months Gross Unrealized Losses	0		60
Twelve months or more Fair Value	46		53
Twelve months or more Gross Unrealized Losses	2		6
Total Fair Value	53		1,326
Total Gross Unrealized Losses	2		66
Foreign Government Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	4,017		2,599
Less than 12 months Gross Unrealized Losses	182		76
Twelve months or more Fair Value	306		125
Twelve months or more Gross Unrealized Losses	27		19
Total Fair Value	4,323		2,724
Total Gross Unrealized Losses	209		95
Corporate Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	21,419		12,385
Less than 12 months Gross Unrealized Losses	1,144		460
Twelve months or more Fair Value	9,691		9,982
Twelve months or more Gross Unrealized Losses	1,969		1,596
Total Fair Value	31,110		22,367
Total Gross Unrealized Losses	3,113		2,056
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	917		552
Less than 12 months Gross Unrealized Losses	61		9
Twelve months or more Fair Value	362		350
Twelve months or more Gross Unrealized Losses	47		60
Total Fair Value	1,279		902
Total Gross Unrealized Losses	108		69
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	2,746		1,365
Less than 12 months Gross Unrealized Losses	40		16
Twelve months or more Fair Value	4,134		5,499
Twelve months or more Gross Unrealized Losses	1,785		1,667
Total Fair Value	6,880		6,864
Total Gross Unrealized Losses	1,825		1,683
Residential Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	422		897
Less than 12 months Gross Unrealized Losses	19		17
Twelve months or more Fair Value	378		447
Twelve months or more Gross Unrealized Losses	60		55
Total Fair Value	800		1,344
Total Gross Unrealized Losses	79		72
Held-to-maturity Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Total Fair Value	706		590
Total Gross Unrealized Losses	$ 98		$ 68

[1] Includes $706 million of fair value and $98 million of gross unrealized losses at December 31, 2011 on securities classified as held-to-maturity, a portion of which are not reflected in accumulated other comprehensive income.

[2] Includes $590 million of fair value and $68 million of gross unrealized losses at December 31, 2010 on securities classified as held-to-maturity, a portion of which are not reflected in accumulated other comprehensive income.