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, 2012		Dec. 31, 2011
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 35,220		$ 30,398
Less than 12 months Gross Unrealized Losses	710		1,454
Twelve months or more Fair Value	12,164		15,047
Twelve months or more Gross Unrealized Losses	1,833		3,900
Total Fair Value	47,384	[1]	45,445	[2]
Total Gross Unrealized Losses	2,543	[1]	5,354	[2]
US Treasury And Government [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	2,191		870
Less than 12 months Gross Unrealized Losses	33		8
Twelve months or more Fair Value	42		130
Twelve months or more Gross Unrealized Losses	2		10
Total Fair Value	2,233		1,000
Total Gross Unrealized Losses	35		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	343		7
Less than 12 months Gross Unrealized Losses	5		0
Twelve months or more Fair Value	5		46
Twelve months or more Gross Unrealized Losses	0		2
Total Fair Value	348		53
Total Gross Unrealized Losses	5		2
Foreign Government Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	5,426		4,017
Less than 12 months Gross Unrealized Losses	55		182
Twelve months or more Fair Value	167		306
Twelve months or more Gross Unrealized Losses	11		27
Total Fair Value	5,593		4,323
Total Gross Unrealized Losses	66		209
Corporate Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	25,051		21,419
Less than 12 months Gross Unrealized Losses	599		1,144
Twelve months or more Fair Value	7,961		9,691
Twelve months or more Gross Unrealized Losses	1,057		1,969
Total Fair Value	33,012		31,110
Total Gross Unrealized Losses	1,656		3,113
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	525		917
Less than 12 months Gross Unrealized Losses	3		61
Twelve months or more Fair Value	185		362
Twelve months or more Gross Unrealized Losses	14		47
Total Fair Value	710		1,279
Total Gross Unrealized Losses	17		108
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	911		2,746
Less than 12 months Gross Unrealized Losses	11		40
Twelve months or more Fair Value	3,545		4,134
Twelve months or more Gross Unrealized Losses	720		1,785
Total Fair Value	4,456		6,880
Total Gross Unrealized Losses	731		1,825
Residential Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	773		422
Less than 12 months Gross Unrealized Losses	4		19
Twelve months or more Fair Value	259		378
Twelve months or more Gross Unrealized Losses	29		60
Total Fair Value	1,032		800
Total Gross Unrealized Losses	33		79
Held-to-maturity Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Total Fair Value	526		706
Total Gross Unrealized Losses	$ 67		$ 98

[1] Includes $526 million of fair value and $67 million of gross unrealized losses at December 31, 2012 on securities classified as held-to-maturity, a portion of which are not reflected in accumulated other comprehensive income.

[2] 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.