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, 2013		Dec. 31, 2012		Jun. 30, 2012
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	$ 61,406		$ 35,220
Less than 12 months Gross Unrealized Losses	4,265		710
Twelve months or more Fair Value	7,096		12,164
Twelve months or more Gross Unrealized Losses	755		1,833		1,833
Total Fair Value	68,502	[1]	47,384	[2]
Total Gross Unrealized Losses	5,020	[1]	2,543	[2]
US Treasury And Government [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	1,303		2,191
Less than 12 months Gross Unrealized Losses	105		33
Twelve months or more Fair Value	7		42
Twelve months or more Gross Unrealized Losses	1		2
Total Fair Value	1,310		2,233
Total Gross Unrealized Losses	106		35
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	1,183		343
Less than 12 months Gross Unrealized Losses	113		5
Twelve months or more Fair Value	0		5
Twelve months or more Gross Unrealized Losses	0		0
Total Fair Value	1,183		348
Total Gross Unrealized Losses	113		5
Foreign Government Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	4,588		5,426
Less than 12 months Gross Unrealized Losses	180		55
Twelve months or more Fair Value	28		167
Twelve months or more Gross Unrealized Losses	3		11
Total Fair Value	4,616		5,593
Total Gross Unrealized Losses	183		66
Corporate Debt Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	46,781		25,051
Less than 12 months Gross Unrealized Losses	3,613		599
Twelve months or more Fair Value	3,974		7,961
Twelve months or more Gross Unrealized Losses	345		1,057
Total Fair Value	50,755		33,012
Total Gross Unrealized Losses	3,958		1,656
Commercial Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	3,697		525
Less than 12 months Gross Unrealized Losses	177		3
Twelve months or more Fair Value	104		185
Twelve months or more Gross Unrealized Losses	2		14
Total Fair Value	3,801		710
Total Gross Unrealized Losses	179		17
Asset-backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	1,629		911
Less than 12 months Gross Unrealized Losses	12		11
Twelve months or more Fair Value	2,798		3,545
Twelve months or more Gross Unrealized Losses	398		720
Total Fair Value	4,427		4,456
Total Gross Unrealized Losses	410		731
Residential Mortgage Backed Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Less than twelve months Fair Value	2,225		773
Less than 12 months Gross Unrealized Losses	65		4
Twelve months or more Fair Value	185		259
Twelve months or more Gross Unrealized Losses	6		29
Total Fair Value	2,410		1,032
Total Gross Unrealized Losses	71		33
Held-to-maturity Securities [Member]
Duration Of Unrealized Losses On Fixed Maturities Investments [Line Items]
Total Fair Value	421		526
Total Gross Unrealized Losses	$ 37		$ 67

[1]          Includes $421 million of fair value and $37 million of gross unrealized losses at June 30, 2013, on securities classified as held-to-maturity, a portion of which are not reflected in

[2]          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 AOCI.