Investments (Details 3) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 item	Dec. 31, 2011 item	Dec. 31, 2010
Number of Securities
Less than 12 months (number of positions)	57	117
12 months or more (number of positions)	69	77
Total (number of positions)	126	194
Fair Value
Less than 12 months	$ 594	$ 1,510
12 months or more	549	723
Total	1,143	2,233
Unrealized Losses
Less than 12 months	(4)	(49)
12 months or more	(98)	(221)
Total	(102)	(270)
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	106	108	82
Credit losses for which an other-than-temporary impairment was not previously recognized	1	13	14
Credit losses for which an other-than-temporary impairment was previously recognized	16	11	12
Reductions for securities sold during the period (realized)	(36)	(26)
Ending balance	87	106	108
Corporate debt securities
Number of Securities
Less than 12 months (number of positions)	50	70
12 months or more (number of positions)	6	9
Total (number of positions)	56	79
Fair Value
Less than 12 months	477	1,004
12 months or more	70	257
Total	547	1,261
Unrealized Losses
Less than 12 months	(4)	(37)
12 months or more	(3)	(41)
Total	(7)	(78)
Residential mortgage backed securities
Number of Securities
Less than 12 months (number of positions)	6	31
12 months or more (number of positions)	56	63
Total (number of positions)	62	94
Fair Value
Less than 12 months	107	344
12 months or more	293	336
Total	400	680
Unrealized Losses
Less than 12 months		(8)
12 months or more	(58)	(130)
Total	(58)	(138)
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	100	87
Total	100	87
Unrealized Losses
12 months or more	(34)	(47)
Total	(34)	(47)
Asset backed securities
Number of Securities
Less than 12 months (number of positions)	1	11
12 months or more (number of positions)	5	3
Total (number of positions)	6	14
Fair Value
Less than 12 months	10	139
12 months or more	86	43
Total	96	182
Unrealized Losses
Less than 12 months		(3)
12 months or more	(3)	(3)
Total	(3)	(6)
Foreign government bonds and obligations
Number of Securities
Less than 12 months (number of positions)		5
Total (number of positions)		5
Fair Value
Less than 12 months		23
Total		23
Unrealized Losses
Less than 12 months		(1)
Total		$ (1)