Investments (Details 10) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014 security	Dec. 31, 2013 security
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	639	686
Fair value, continuous unrealized loss position for less than 12 months	$ 2,402	$ 5,988
Unrealized losses, continuous unrealized loss position for less than 12 months	(85)	(262)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	174	165
Fair value, continuous unrealized loss position for 12 months or more	1,265	1,160
Unrealized losses, continuous unrealized loss position for 12 months or more	(120)	(161)
Total unrealized losses
Total unrealized losses	(205)	(423)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	345	661
Fair value, continuous unrealized loss position for less than 12 months	2,075	5,908
Unrealized losses, continuous unrealized loss position for less than 12 months	(72)	(257)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	173	165
Fair value, continuous unrealized loss position for 12 months or more	1,259	1,160
Unrealized losses, continuous unrealized loss position for 12 months or more	(119)	(161)
Total unrealized losses
Gross unrealized losses	(191)	(418)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1	4
Fair value, continuous unrealized loss position for less than 12 months	1	76
Unrealized losses, continuous unrealized loss position for less than 12 months	0	(2)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	0	0
Fair value, continuous unrealized loss position for 12 months or more	0	0
Unrealized losses, continuous unrealized loss position for 12 months or more	0	0
Total unrealized losses
Total unrealized losses	0	(2)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	17	63
Fair value, continuous unrealized loss position for less than 12 months	90	347
Unrealized losses, continuous unrealized loss position for less than 12 months	(1)	(24)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	10	21
Fair value, continuous unrealized loss position for 12 months or more	47	99
Unrealized losses, continuous unrealized loss position for 12 months or more	(13)	(38)
Total unrealized losses
Total unrealized losses	(14)	(62)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	281	530
Fair value, continuous unrealized loss position for less than 12 months	1,780	5,191
Unrealized losses, continuous unrealized loss position for less than 12 months	(69)	(224)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	91	48
Fair value, continuous unrealized loss position for 12 months or more	875	467
Unrealized losses, continuous unrealized loss position for 12 months or more	(81)	(71)
Total unrealized losses
Total unrealized losses	(150)	(295)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	0	7
Fair value, continuous unrealized loss position for less than 12 months	0	76
Unrealized losses, continuous unrealized loss position for less than 12 months	0	(4)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	1	1
Fair value, continuous unrealized loss position for 12 months or more	15	13
Unrealized losses, continuous unrealized loss position for 12 months or more	0	(2)
Total unrealized losses
Total unrealized losses	0	(6)
ABS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	19	17
Fair value, continuous unrealized loss position for less than 12 months	168	162
Unrealized losses, continuous unrealized loss position for less than 12 months	(2)	(1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	23	42
Fair value, continuous unrealized loss position for 12 months or more	217	400
Unrealized losses, continuous unrealized loss position for 12 months or more	(19)	(33)
Total unrealized losses
Total unrealized losses	(21)	(34)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	19	35
Fair value, continuous unrealized loss position for less than 12 months	3	42
Unrealized losses, continuous unrealized loss position for less than 12 months	0	(2)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	45	47
Fair value, continuous unrealized loss position for 12 months or more	73	129
Unrealized losses, continuous unrealized loss position for 12 months or more	(4)	(10)
Total unrealized losses
Total unrealized losses	(4)	(12)
CMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	8	5
Fair value, continuous unrealized loss position for less than 12 months	33	14
Unrealized losses, continuous unrealized loss position for less than 12 months	0	0
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	3	6
Fair value, continuous unrealized loss position for 12 months or more	32	52
Unrealized losses, continuous unrealized loss position for 12 months or more	(2)	(7)
Total unrealized losses
Total unrealized losses	(2)	(7)
Redeemable preferred stock
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	0	0
Fair value, continuous unrealized loss position for less than 12 months	0	0
Unrealized losses, continuous unrealized loss position for less than 12 months	0	0
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	0	0
Fair value, continuous unrealized loss position for 12 months or more	0	0
Unrealized losses, continuous unrealized loss position for 12 months or more	0	0
Total unrealized losses
Total unrealized losses	0	0
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	167	526
Fair value, continuous unrealized loss position for less than 12 months	1,275	5,272
Unrealized losses, continuous unrealized loss position for less than 12 months	(28)	(236)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	127	110
Fair value, continuous unrealized loss position for 12 months or more	989	834
Unrealized losses, continuous unrealized loss position for 12 months or more	(79)	(112)
Total unrealized losses
Total unrealized losses	(107)	(348)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	178	135
Fair value, continuous unrealized loss position for less than 12 months	800	636
Unrealized losses, continuous unrealized loss position for less than 12 months	(44)	(21)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	46	55
Fair value, continuous unrealized loss position for 12 months or more	270	326
Unrealized losses, continuous unrealized loss position for 12 months or more	(40)	(49)
Total unrealized losses
Total unrealized losses	(84)	(70)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	294	25
Fair value, continuous unrealized loss position for less than 12 months	327	80
Unrealized losses, continuous unrealized loss position for less than 12 months	(13)	(5)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	1	0
Fair value, continuous unrealized loss position for 12 months or more	6	0
Unrealized losses, continuous unrealized loss position for 12 months or more	(1)	0
Total unrealized losses
Gross unrealized losses on equity securities	$ (14)	$ (5)