Investments (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013 item	Jun. 30, 2012	Jun. 30, 2013 item	Jun. 30, 2012	Dec. 31, 2012 item
Number of Securities
Less than 12 months (number of positions)	239		239		57
12 months or more (number of positions)	56		56		69
Total (number of positions)	295		295		126
Fair Value
Less than 12 months	$ 3,341		$ 3,341		$ 594
12 months or more	396		396		549
Total	3,737		3,737		1,143
Unrealized Losses
Less than 12 months	(128)		(128)		(4)
12 months or more	(81)		(81)		(98)
Total	(209)		(209)		(102)
Rollforward of the cumulative amounts recognized in the Consolidated Statements of Income for other-than-temporary impairments related to credit losses on securities
Beginning balance	75	105	87	106
Credit losses for which an other-than-temporary impairment was not previously recognized		1		1
Credit losses for which an other-than-temporary impairment was previously recognized	1	5	2	6
Reductions for securities sold during the period (realized)	(10)	(21)	(23)	(23)
Ending balance	66	90	66	90
Corporate debt securities
Number of Securities
Less than 12 months (number of positions)	149		149		50
12 months or more (number of positions)	3		3		6
Total (number of positions)	152		152		56
Fair Value
Less than 12 months	2,033		2,033		477
12 months or more	41		41		70
Total	2,074		2,074		547
Unrealized Losses
Less than 12 months	(74)		(74)		(4)
12 months or more	(6)		(6)		(3)
Total	(80)		(80)		(7)
Residential mortgage backed securities
Number of Securities
Less than 12 months (number of positions)	36		36		6
12 months or more (number of positions)	48		48		56
Total (number of positions)	84		84		62
Fair Value
Less than 12 months	917		917		107
12 months or more	234		234		293
Total	1,151		1,151		400
Unrealized Losses
Less than 12 months	(37)		(37)
12 months or more	(45)		(45)		(58)
Total	(82)		(82)		(58)
Commercial mortgage backed securities
Number of Securities
Less than 12 months (number of positions)	20		20
Total (number of positions)	20		20
Fair Value
Less than 12 months	198		198
Total	198		198
Unrealized Losses
Less than 12 months	(9)		(9)
Total	(9)		(9)
State and municipal obligations
Number of Securities
12 months or more (number of positions)	2		2		2
Total (number of positions)	2		2		2
Fair Value
12 months or more	100		100		100
Total	100		100		100
Unrealized Losses
12 months or more	(29)		(29)		(34)
Total	(29)		(29)		(34)
Asset backed securities
Number of Securities
Less than 12 months (number of positions)	9		9		1
12 months or more (number of positions)	3		3		5
Total (number of positions)	12		12		6
Fair Value
Less than 12 months	100		100		10
12 months or more	21		21		86
Total	121		121		96
Unrealized Losses
Less than 12 months	(3)		(3)
12 months or more	(1)		(1)		(3)
Total	(4)		(4)		(3)
Foreign government bonds and obligations
Number of Securities
Less than 12 months (number of positions)	25		25
Total (number of positions)	25		25
Fair Value
Less than 12 months	93		93
Total	93		93
Unrealized Losses
Less than 12 months	(5)		(5)
Total	$ (5)		$ (5)