Investments (Details 11) $ in Millions	Jun. 30, 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	707	2,144
Fair value, continuous unrealized loss position for less than 12 months	$ 5,620	$ 23,917
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (254)	$ (839)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	460	354
Fair value, continuous unrealized loss position for 12 months or more	$ 2,627	$ 1,654
Unrealized losses, continuous unrealized loss position for 12 months or more	(235)	(260)
Total unrealized losses
Total unrealized losses	$ (489)	$ (1,099)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	466	1,879
Fair value, continuous unrealized loss position for less than 12 months	$ 4,618	$ 22,520
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (124)	$ (732)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	405	317
Fair value, continuous unrealized loss position for 12 months or more	$ 2,467	$ 1,511
Unrealized losses, continuous unrealized loss position for 12 months or more	(200)	(228)
Total unrealized losses
Total unrealized losses	$ (324)	$ (960)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	5	53
Fair value, continuous unrealized loss position for less than 12 months	$ 528	$ 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	32	222
Fair value, continuous unrealized loss position for less than 12 months	$ 76	$ 810
Unrealized losses, continuous unrealized loss position for less than 12 months	$ 0	$ (6)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	9	9
Fair value, continuous unrealized loss position for 12 months or more	$ 28	$ 36
Unrealized losses, continuous unrealized loss position for 12 months or more	(11)	(14)
Total unrealized losses
Total unrealized losses	$ (11)	$ (20)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	296	1,361
Fair value, continuous unrealized loss position for less than 12 months	$ 3,524	$ 17,915
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (112)	$ (696)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	196	111
Fair value, continuous unrealized loss position for 12 months or more	$ 1,958	$ 1,024
Unrealized losses, continuous unrealized loss position for 12 months or more	(161)	(183)
Total unrealized losses
Total unrealized losses	$ (273)	$ (879)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1	9
Fair value, continuous unrealized loss position for less than 12 months	$ 2	$ 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	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
Asset-backed securities (“ABS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	40	133
Fair value, continuous unrealized loss position for less than 12 months	$ 371	$ 1,733
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (5)	$ (24)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	24	20
Fair value, continuous unrealized loss position for 12 months or more	$ 371	$ 324
Unrealized losses, continuous unrealized loss position for 12 months or more	(17)	(19)
Total unrealized losses
Total unrealized losses	$ (22)	$ (43)
Residential mortgage-backed securities (“RMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	78	88
Fair value, continuous unrealized loss position for less than 12 months	$ 39	$ 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	175	176
Fair value, continuous unrealized loss position for 12 months or more	$ 108	$ 125
Unrealized losses, continuous unrealized loss position for 12 months or more	(10)	(10)
Total unrealized losses
Total unrealized losses	$ (11)	$ (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	$ 78	$ 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	$ 2	$ 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	220	1,405
Fair value, continuous unrealized loss position for less than 12 months	$ 2,249	$ 17,521
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (24)	$ (362)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	256	225
Fair value, continuous unrealized loss position for 12 months or more	$ 1,331	$ 972
Unrealized losses, continuous unrealized loss position for 12 months or more	(87)	(105)
Total unrealized losses
Total unrealized losses	$ (111)	$ (467)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	246	474
Fair value, continuous unrealized loss position for less than 12 months	$ 2,369	$ 4,999
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (100)	$ (370)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	149	92
Fair value, continuous unrealized loss position for 12 months or more	$ 1,136	$ 539
Unrealized losses, continuous unrealized loss position for 12 months or more	(113)	(123)
Total unrealized losses
Total unrealized losses	$ (213)	$ (493)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	241	265
Fair value, continuous unrealized loss position for less than 12 months	$ 1,002	$ 1,397
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (130)	$ (107)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	55	37
Fair value, continuous unrealized loss position for 12 months or more	$ 160	$ 143
Unrealized losses, continuous unrealized loss position for 12 months or more	(35)	(32)
Total unrealized losses
Total unrealized losses	$ (165)	$ (139)