Investments (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013 item	Mar. 31, 2012	Dec. 31, 2012 item
Number of Securities
Less than 12 months (number of positions)	74		57
12 months or more (number of positions)	62		69
Total (number of positions)	136		126
Fair Value
Less than 12 months	$ 926		$ 594
12 months or more	463		549
Total	1,389		1,143
Unrealized Losses
Less than 12 months	(13)		(4)
12 months or more	(80)		(98)
Total	(93)		(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	87	106
Credit losses for which an other-than-temporary impairment was previously recognized	1	1
Reductions for securities sold during the period (realized)	(13)	(2)
Ending balance	75	105
Corporate debt securities
Number of Securities
Less than 12 months (number of positions)	50		50
12 months or more (number of positions)	5		6
Total (number of positions)	55		56
Fair Value
Less than 12 months	546		477
12 months or more	49		70
Total	595		547
Unrealized Losses
Less than 12 months	(7)		(4)
12 months or more	(3)		(3)
Total	(10)		(7)
Residential mortgage backed securities
Number of Securities
Less than 12 months (number of positions)	16		6
12 months or more (number of positions)	51		56
Total (number of positions)	67		62
Fair Value
Less than 12 months	320		107
12 months or more	250		293
Total	570		400
Unrealized Losses
Less than 12 months	(5)
12 months or more	(47)		(58)
Total	(52)		(58)
State and municipal obligations
Number of Securities
12 months or more (number of positions)	2		2
Total (number of positions)	2		2
Fair Value
12 months or more	105		100
Total	105		100
Unrealized Losses
12 months or more	(28)		(34)
Total	(28)		(34)
Asset backed securities
Number of Securities
Less than 12 months (number of positions)	2		1
12 months or more (number of positions)	4		5
Total (number of positions)	6		6
Fair Value
Less than 12 months	12		10
12 months or more	59		86
Total	71		96
Unrealized Losses
12 months or more	(2)		(3)
Total	(2)		(3)
Commercial mortgage backed securities
Number of Securities
Less than 12 months (number of positions)	6
Total (number of positions)	6
Fair Value
Less than 12 months	48
Total	48
Unrealized Losses
Less than 12 months	(1)
Total	$ (1)