Investments (Details 11) $ in Millions	Sep. 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	825	2,144
Fair value, continuous unrealized loss position for less than 12 months	$ 6,962	$ 23,917
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (132)	$ (839)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	366	354
Fair value, continuous unrealized loss position for 12 months or more	$ 1,444	$ 1,654
Unrealized losses, continuous unrealized loss position for 12 months or more	(140)	(260)
Total unrealized losses
Total unrealized losses	$ (272)	$ (1,099)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	635	1,879
Fair value, continuous unrealized loss position for less than 12 months	$ 6,273	$ 22,520
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (50)	$ (732)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	324	317
Fair value, continuous unrealized loss position for 12 months or more	$ 1,323	$ 1,511
Unrealized losses, continuous unrealized loss position for 12 months or more	(118)	(228)
Total unrealized losses
Total unrealized losses	$ (168)	$ (960)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	17	53
Fair value, continuous unrealized loss position for less than 12 months	$ 1,530	$ 1,874
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (2)	$ (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	$ (2)	$ (4)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	302	222
Fair value, continuous unrealized loss position for less than 12 months	$ 785	$ 810
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (2)	$ (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	$ (13)	$ (20)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	226	1,361
Fair value, continuous unrealized loss position for less than 12 months	$ 3,733	$ 17,915
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (38)	$ (696)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	112	111
Fair value, continuous unrealized loss position for 12 months or more	$ 882	$ 1,024
Unrealized losses, continuous unrealized loss position for 12 months or more	(83)	(183)
Total unrealized losses
Total unrealized losses	$ (121)	$ (879)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract		9
Fair value, continuous unrealized loss position for less than 12 months		$ 44
Unrealized losses, continuous unrealized loss position for less than 12 months		$ 0
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract		0
Fair value, continuous unrealized loss position for 12 months or more		$ 0
Unrealized losses, continuous unrealized loss position for 12 months or more		0
Total unrealized losses
Total unrealized losses		$ 0
Asset-backed securities (“ABS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	12	133
Fair value, continuous unrealized loss position for less than 12 months	$ 102	$ 1,733
Unrealized losses, continuous unrealized loss position for less than 12 months	$ 0	$ (24)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	23	20
Fair value, continuous unrealized loss position for 12 months or more	$ 308	$ 324
Unrealized losses, continuous unrealized loss position for 12 months or more	(15)	(19)
Total unrealized losses
Total unrealized losses	$ (15)	$ (43)
Residential mortgage-backed securities (“RMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	61	88
Fair value, continuous unrealized loss position for less than 12 months	$ 30	$ 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	177	176
Fair value, continuous unrealized loss position for 12 months or more	$ 97	$ 125
Unrealized losses, continuous unrealized loss position for 12 months or more	(7)	(10)
Total unrealized losses
Total unrealized losses	$ (8)	$ (10)
Commercial mortgage-backed securities (“CMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	17	13
Fair value, continuous unrealized loss position for less than 12 months	$ 93	$ 75
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (7)	$ (2)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	3	1
Fair value, continuous unrealized loss position for 12 months or more	$ 8	$ 2
Unrealized losses, continuous unrealized loss position for 12 months or more	(2)	(2)
Total unrealized losses
Total unrealized losses	$ (9)	$ (4)
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	525	1,405
Fair value, continuous unrealized loss position for less than 12 months	$ 5,095	$ 17,521
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (17)	$ (362)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	220	225
Fair value, continuous unrealized loss position for 12 months or more	$ 808	$ 972
Unrealized losses, continuous unrealized loss position for 12 months or more	(61)	(105)
Total unrealized losses
Total unrealized losses	$ (78)	$ (467)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	110	474
Fair value, continuous unrealized loss position for less than 12 months	$ 1,178	$ 4,999
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (33)	$ (370)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	104	92
Fair value, continuous unrealized loss position for 12 months or more	$ 515	$ 539
Unrealized losses, continuous unrealized loss position for 12 months or more	(57)	(123)
Total unrealized losses
Total unrealized losses	$ (90)	$ (493)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	190	265
Fair value, continuous unrealized loss position for less than 12 months	$ 689	$ 1,397
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (82)	$ (107)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	42	37
Fair value, continuous unrealized loss position for 12 months or more	$ 121	$ 143
Unrealized losses, continuous unrealized loss position for 12 months or more	(22)	(32)
Total unrealized losses
Total unrealized losses	$ (104)	$ (139)