Investments (Details 11) $ in Millions	Sep. 30, 2015 USD ($) contract	Dec. 31, 2014 USD ($) contract
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,758	1,273
Fair value, continuous unrealized loss position for less than 12 months	$ 15,705	$ 12,774
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (724)	$ (224)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	315	357
Fair value, continuous unrealized loss position for 12 months or more	$ 1,349	$ 1,863
Unrealized losses, continuous unrealized loss position for 12 months or more	(195)	(145)
Total unrealized losses
Total unrealized losses	$ (919)	$ (369)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,404	1,015
Fair value, continuous unrealized loss position for less than 12 months	$ 14,086	$ 11,908
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (587)	$ (171)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	290	356
Fair value, continuous unrealized loss position for 12 months or more	$ 1,265	$ 1,852
Unrealized losses, continuous unrealized loss position for 12 months or more	(171)	(143)
Total unrealized losses
Total unrealized losses	$ (758)	$ (314)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	5	21
Fair value, continuous unrealized loss position for less than 12 months	$ 364	$ 1,501
Unrealized losses, continuous unrealized loss position for less than 12 months	$ 0	$ (3)
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	$ (3)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	171	252
Fair value, continuous unrealized loss position for less than 12 months	$ 495	$ 1,008
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (5)	$ (9)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	9	19
Fair value, continuous unrealized loss position for 12 months or more	$ 48	$ 116
Unrealized losses, continuous unrealized loss position for 12 months or more	(14)	(16)
Total unrealized losses
Total unrealized losses	$ (19)	$ (25)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,078	576
Fair value, continuous unrealized loss position for less than 12 months	$ 12,371	$ 7,545
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (563)	$ (147)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	82	119
Fair value, continuous unrealized loss position for 12 months or more	$ 800	$ 1,214
Unrealized losses, continuous unrealized loss position for 12 months or more	(127)	(93)
Total unrealized losses
Total unrealized losses	$ (690)	$ (240)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	14	2
Fair value, continuous unrealized loss position for less than 12 months	$ 73	$ 13
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	0	1
Fair value, continuous unrealized loss position for 12 months or more	$ 0	$ 19
Unrealized losses, continuous unrealized loss position for 12 months or more	0	0
Total unrealized losses
Total unrealized losses	$ (1)	$ 0
Asset-backed securities (“ABS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	53	81
Fair value, continuous unrealized loss position for less than 12 months	$ 738	$ 1,738
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (17)	$ (11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	21	26
Fair value, continuous unrealized loss position for 12 months or more	$ 281	$ 315
Unrealized losses, continuous unrealized loss position for 12 months or more	(18)	(20)
Total unrealized losses
Total unrealized losses	$ (35)	$ (31)
Residential mortgage-backed securities (“RMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	76	75
Fair value, continuous unrealized loss position for less than 12 months	$ 13	$ 70
Unrealized losses, continuous unrealized loss position for less than 12 months	$ 0	$ (1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	176	188
Fair value, continuous unrealized loss position for 12 months or more	$ 132	$ 156
Unrealized losses, continuous unrealized loss position for 12 months or more	(10)	(12)
Total unrealized losses
Total unrealized losses	$ (10)	$ (13)
Commercial mortgage-backed securities (“CMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	7	8
Fair value, continuous unrealized loss position for less than 12 months	$ 32	$ 33
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	2	3
Fair value, continuous unrealized loss position for 12 months or more	$ 4	$ 32
Unrealized losses, continuous unrealized loss position for 12 months or more	(2)	(2)
Total unrealized losses
Total unrealized losses	$ (3)	$ (2)
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	906	754
Fair value, continuous unrealized loss position for less than 12 months	$ 9,147	$ 9,951
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (217)	$ (71)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	212	281
Fair value, continuous unrealized loss position for 12 months or more	$ 762	$ 1,444
Unrealized losses, continuous unrealized loss position for 12 months or more	(80)	(87)
Total unrealized losses
Total unrealized losses	$ (297)	$ (158)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	498	261
Fair value, continuous unrealized loss position for less than 12 months	$ 4,939	$ 1,957
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (370)	$ (100)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	78	75
Fair value, continuous unrealized loss position for 12 months or more	$ 503	$ 408
Unrealized losses, continuous unrealized loss position for 12 months or more	(91)	(56)
Total unrealized losses
Total unrealized losses	$ (461)	$ (156)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	354	258
Fair value, continuous unrealized loss position for less than 12 months	$ 1,619	$ 866
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (137)	$ (53)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	25	1
Fair value, continuous unrealized loss position for 12 months or more	$ 84	$ 11
Unrealized losses, continuous unrealized loss position for 12 months or more	(24)	(2)
Total unrealized losses
Total unrealized losses	$ (161)	$ (55)