Investments (Details 11) $ in Millions	Dec. 31, 2015 USD ($) security	Dec. 31, 2014 USD ($) security
Fixed income and equity securities
Less than 12 months
Number of issues | security	2,144	1,273
Fair value	$ 23,917	$ 12,774
Unrealized losses	$ (839)	$ (224)
12 months or more
Number of issues | security	354	357
Fair value	$ 1,654	$ 1,863
Unrealized losses	(260)	(145)
Total unrealized losses
Total unrealized losses	$ (1,099)	$ (369)
Fixed income securities
Less than 12 months
Number of issues | security	1,879	1,015
Fair value	$ 22,520	$ 11,908
Unrealized losses	$ (732)	$ (171)
12 months or more
Number of issues | security	317	356
Fair value	$ 1,511	$ 1,852
Unrealized losses	(228)	(143)
Total unrealized losses
Total unrealized losses	$ (960)	$ (314)
U.S. government and agencies
Less than 12 months
Number of issues | security	53	21
Fair value	$ 1,874	$ 1,501
Unrealized losses	$ (4)	$ (3)
12 months or more
Number of issues | security	0	0
Fair value	$ 0	$ 0
Unrealized losses	0	0
Total unrealized losses
Total unrealized losses	$ (4)	$ (3)
Municipal
Less than 12 months
Number of issues | security	222	252
Fair value	$ 810	$ 1,008
Unrealized losses	$ (6)	$ (9)
12 months or more
Number of issues | security	9	19
Fair value	$ 36	$ 116
Unrealized losses	(14)	(16)
Total unrealized losses
Total unrealized losses	$ (20)	$ (25)
Corporate
Less than 12 months
Number of issues | security	1,361	576
Fair value	$ 17,915	$ 7,545
Unrealized losses	$ (696)	$ (147)
12 months or more
Number of issues | security	111	119
Fair value	$ 1,024	$ 1,214
Unrealized losses	(183)	(93)
Total unrealized losses
Total unrealized losses	$ (879)	$ (240)
Foreign government
Less than 12 months
Number of issues | security	9	2
Fair value	$ 44	$ 13
Unrealized losses	$ 0	$ 0
12 months or more
Number of issues | security	0	1
Fair value	$ 0	$ 19
Unrealized losses	0	0
Total unrealized losses
Total unrealized losses	$ 0	$ 0
ABS
Less than 12 months
Number of issues | security	133	81
Fair value	$ 1,733	$ 1,738
Unrealized losses	$ (24)	$ (11)
12 months or more
Number of issues | security	20	26
Fair value	$ 324	$ 315
Unrealized losses	(19)	(20)
Total unrealized losses
Total unrealized losses	$ (43)	$ (31)
RMBS
Less than 12 months
Number of issues | security	88	75
Fair value	$ 69	$ 70
Unrealized losses	$ 0	$ (1)
12 months or more
Number of issues | security	176	188
Fair value	$ 125	$ 156
Unrealized losses	(10)	(12)
Total unrealized losses
Total unrealized losses	$ (10)	$ (13)
CMBS
Less than 12 months
Number of issues | security	13	8
Fair value	$ 75	$ 33
Unrealized losses	$ (2)	$ 0
12 months or more
Number of issues | security	1	3
Fair value	$ 2	$ 32
Unrealized losses	(2)	(2)
Total unrealized losses
Total unrealized losses	$ (4)	$ (2)
Equity securities
Less than 12 months
Number of issues | security	265	258
Fair value	$ 1,397	$ 866
Unrealized losses	$ (107)	$ (53)
12 months or more
Number of issues | security	37	1
Fair value	$ 143	$ 11
Unrealized losses	(32)	(2)
Total unrealized losses
Total unrealized losses	$ (139)	$ (55)
Investment grade fixed income securities
Less than 12 months
Number of issues | security	1,405	754
Fair value	$ 17,521	$ 9,951
Unrealized losses	$ (362)	$ (71)
12 months or more
Number of issues | security	225	281
Fair value	$ 972	$ 1,444
Unrealized losses	(105)	(87)
Total unrealized losses
Total unrealized losses	$ (467)	$ (158)
Below investment grade fixed income securities
Less than 12 months
Number of issues | security	474	261
Fair value	$ 4,999	$ 1,957
Unrealized losses	$ (370)	$ (100)
12 months or more
Number of issues | security	92	75
Fair value	$ 539	$ 408
Unrealized losses	(123)	(56)
Total unrealized losses
Total unrealized losses	$ (493)	$ (156)