Investments (Details 11) $ in Millions	Mar. 31, 2016 USD ($) contract	Dec. 31, 2015 USD ($) contract
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,196	2,144
Fair value, continuous unrealized loss position for less than 12 months	$ 9,963	$ 23,917
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (479)	$ (839)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	372	354
Fair value, continuous unrealized loss position for 12 months or more	$ 1,762	$ 1,654
Unrealized losses, continuous unrealized loss position for 12 months or more	(251)	(260)
Total unrealized losses
Total unrealized losses	$ (730)	$ (1,099)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	954	1,879
Fair value, continuous unrealized loss position for less than 12 months	$ 8,798	$ 22,520
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (358)	$ (732)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	329	317
Fair value, continuous unrealized loss position for 12 months or more	$ 1,603	$ 1,511
Unrealized losses, continuous unrealized loss position for 12 months or more	(222)	(228)
Total unrealized losses
Total unrealized losses	$ (580)	$ (960)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	10	53
Fair value, continuous unrealized loss position for less than 12 months	$ 307	$ 1,874
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 | contract	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	$ (4)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	132	222
Fair value, continuous unrealized loss position for less than 12 months	$ 351	$ 810
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (3)	$ (6)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	7	9
Fair value, continuous unrealized loss position for 12 months or more	$ 32	$ 36
Unrealized losses, continuous unrealized loss position for 12 months or more	(12)	(14)
Total unrealized losses
Total unrealized losses	$ (15)	$ (20)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	632	1,361
Fair value, continuous unrealized loss position for less than 12 months	$ 7,101	$ 17,915
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (332)	$ (696)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	124	111
Fair value, continuous unrealized loss position for 12 months or more	$ 1,126	$ 1,024
Unrealized losses, continuous unrealized loss position for 12 months or more	(175)	(183)
Total unrealized losses
Total unrealized losses	$ (507)	$ (879)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	11	9
Fair value, continuous unrealized loss position for less than 12 months	$ 29	$ 44
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 | contract	1	0
Fair value, continuous unrealized loss position for 12 months or more	$ 3	$ 0
Unrealized losses, continuous unrealized loss position for 12 months or more	0	0
Total unrealized losses
Total unrealized losses	$ 0	$ 0
Asset-backed securities (“ABS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	76	133
Fair value, continuous unrealized loss position for less than 12 months	$ 836	$ 1,733
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (16)	$ (24)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	22	20
Fair value, continuous unrealized loss position for 12 months or more	$ 320	$ 324
Unrealized losses, continuous unrealized loss position for 12 months or more	(23)	(19)
Total unrealized losses
Total unrealized losses	$ (39)	$ (43)
Residential mortgage-backed securities (“RMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	79	88
Fair value, continuous unrealized loss position for less than 12 months	$ 54	$ 69
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (1)	$ 0
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	174	176
Fair value, continuous unrealized loss position for 12 months or more	$ 119	$ 125
Unrealized losses, continuous unrealized loss position for 12 months or more	(11)	(10)
Total unrealized losses
Total unrealized losses	$ (12)	$ (10)
Commercial mortgage-backed securities (“CMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	14	13
Fair value, continuous unrealized loss position for less than 12 months	$ 120	$ 75
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (6)	$ (2)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	1	1
Fair value, continuous unrealized loss position for 12 months or more	$ 3	$ 2
Unrealized losses, continuous unrealized loss position for 12 months or more	(1)	(2)
Total unrealized losses
Total unrealized losses	$ (7)	$ (4)
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	620	1,405
Fair value, continuous unrealized loss position for less than 12 months	$ 5,727	$ 17,521
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (131)	$ (362)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	223	225
Fair value, continuous unrealized loss position for 12 months or more	$ 979	$ 972
Unrealized losses, continuous unrealized loss position for 12 months or more	(93)	(105)
Total unrealized losses
Total unrealized losses	$ (224)	$ (467)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	334	474
Fair value, continuous unrealized loss position for less than 12 months	$ 3,071	$ 4,999
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (227)	$ (370)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	106	92
Fair value, continuous unrealized loss position for 12 months or more	$ 624	$ 539
Unrealized losses, continuous unrealized loss position for 12 months or more	(129)	(123)
Total unrealized losses
Total unrealized losses	$ (356)	$ (493)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	242	265
Fair value, continuous unrealized loss position for less than 12 months	$ 1,165	$ 1,397
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (121)	$ (107)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	43	37
Fair value, continuous unrealized loss position for 12 months or more	$ 159	$ 143
Unrealized losses, continuous unrealized loss position for 12 months or more	(29)	(32)
Total unrealized losses
Total unrealized losses	$ (150)	$ (139)