Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 19,367		$ 30,398
Less than 12 months Gross Unrealized Losses	647		1,454
Twelve months or more Fair Value	15,271		15,047
Twelve months or more Gross Unrealized Losses	3,246		3,900
Total Fair Value	34,638	[1]	45,445
Total Gross Unrealized Losses	3,893	[1]	5,354
US Treasury And Government [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	432		870
Less than 12 months Gross Unrealized Losses	6		8
Twelve months or more Fair Value	57		130
Twelve months or more Gross Unrealized Losses	5		10
Total Fair Value	489		1,000
Total Gross Unrealized Losses	11		18
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	59		7
Less than 12 months Gross Unrealized Losses	0		0
Twelve months or more Fair Value	5		46
Twelve months or more Gross Unrealized Losses	1		2
Total Fair Value	64		53
Total Gross Unrealized Losses	1		2
Foreign Government Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	1,686		4,017
Less than 12 months Gross Unrealized Losses	117		182
Twelve months or more Fair Value	155		306
Twelve months or more Gross Unrealized Losses	21		27
Total Fair Value	1,841		4,323
Total Gross Unrealized Losses	138		209
Corporate Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	14,494		21,419
Less than 12 months Gross Unrealized Losses	472		1,144
Twelve months or more Fair Value	10,158		9,691
Twelve months or more Gross Unrealized Losses	1,704		1,969
Total Fair Value	24,652		31,110
Total Gross Unrealized Losses	2,176		3,113
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	1,356		917
Less than 12 months Gross Unrealized Losses	25		61
Twelve months or more Fair Value	246		362
Twelve months or more Gross Unrealized Losses	35		47
Total Fair Value	1,602		1,279
Total Gross Unrealized Losses	60		108
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	1,130		2,746
Less than 12 months Gross Unrealized Losses	23		40
Twelve months or more Fair Value	4,200		4,134
Twelve months or more Gross Unrealized Losses	1,432		1,785
Total Fair Value	5,330		6,880
Total Gross Unrealized Losses	1,455		1,825
Residential Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	210		422
Less than 12 months Gross Unrealized Losses	4		19
Twelve months or more Fair Value	450		378
Twelve months or more Gross Unrealized Losses	48		60
Total Fair Value	660		800
Total Gross Unrealized Losses	52		79
Held-to-maturity Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Total Fair Value	600		706
Total Gross Unrealized Losses	$ 76		$ 98

[1] Includes $600 million of fair value and $76 million of gross unrealized losses at June 30, 2012, on securities classified as held-to-maturity, a portion of which are not reflected in “Accumulated other comprehensive income (loss).”