Investments (Details 11) $ in Millions	Jun. 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	1,848	1,273
Fair value, continuous unrealized loss position for less than 12 months	$ 15,712	$ 12,774
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (371)	$ (224)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	275	357
Fair value, continuous unrealized loss position for 12 months or more	$ 1,091	$ 1,863
Unrealized losses, continuous unrealized loss position for 12 months or more	(129)	(145)
Total unrealized losses
Total unrealized losses	$ (500)	$ (369)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,597	1,015
Fair value, continuous unrealized loss position for less than 12 months	$ 14,959	$ 11,908
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (310)	$ (171)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	274	356
Fair value, continuous unrealized loss position for 12 months or more	$ 1,078	$ 1,852
Unrealized losses, continuous unrealized loss position for 12 months or more	(128)	(143)
Total unrealized losses
Total unrealized losses	$ (438)	$ (314)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	16	21
Fair value, continuous unrealized loss position for less than 12 months	$ 761	$ 1,501
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (1)	$ (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	$ (1)	$ (3)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	473	252
Fair value, continuous unrealized loss position for less than 12 months	$ 1,472	$ 1,008
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (23)	$ (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	$ 60	$ 116
Unrealized losses, continuous unrealized loss position for 12 months or more	(13)	(16)
Total unrealized losses
Total unrealized losses	$ (36)	$ (25)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	954	576
Fair value, continuous unrealized loss position for less than 12 months	$ 11,790	$ 7,545
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (274)	$ (147)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	65	119
Fair value, continuous unrealized loss position for 12 months or more	$ 616	$ 1,214
Unrealized losses, continuous unrealized loss position for 12 months or more	(86)	(93)
Total unrealized losses
Total unrealized losses	$ (360)	$ (240)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	10	2
Fair value, continuous unrealized loss position for less than 12 months	$ 53	$ 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	56	81
Fair value, continuous unrealized loss position for less than 12 months	$ 801	$ 1,738
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (10)	$ (11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	22	26
Fair value, continuous unrealized loss position for 12 months or more	$ 253	$ 315
Unrealized losses, continuous unrealized loss position for 12 months or more	(16)	(20)
Total unrealized losses
Total unrealized losses	$ (26)	$ (31)
Residential mortgage-backed securities (“RMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	81	75
Fair value, continuous unrealized loss position for less than 12 months	$ 51	$ 70
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (1)	$ (1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	177	188
Fair value, continuous unrealized loss position for 12 months or more	$ 146	$ 156
Unrealized losses, continuous unrealized loss position for 12 months or more	(11)	(12)
Total unrealized losses
Total unrealized losses	$ (12)	$ (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	$ 31	$ 33
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	3
Fair value, continuous unrealized loss position for 12 months or more	$ 3	$ 32
Unrealized losses, continuous unrealized loss position for 12 months or more	(2)	(2)
Total unrealized losses
Total unrealized losses	$ (2)	$ (2)
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,225	754
Fair value, continuous unrealized loss position for less than 12 months	$ 10,917	$ 9,951
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (158)	$ (71)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	206	281
Fair value, continuous unrealized loss position for 12 months or more	$ 670	$ 1,444
Unrealized losses, continuous unrealized loss position for 12 months or more	(69)	(87)
Total unrealized losses
Total unrealized losses	$ (227)	$ (158)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	372	261
Fair value, continuous unrealized loss position for less than 12 months	$ 4,042	$ 1,957
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (152)	$ (100)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	68	75
Fair value, continuous unrealized loss position for 12 months or more	$ 408	$ 408
Unrealized losses, continuous unrealized loss position for 12 months or more	(59)	(56)
Total unrealized losses
Total unrealized losses	$ (211)	$ (156)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	251	258
Fair value, continuous unrealized loss position for less than 12 months	$ 753	$ 866
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (61)	$ (53)
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	$ 13	$ 11
Unrealized losses, continuous unrealized loss position for 12 months or more	(1)	(2)
Total unrealized losses
Total unrealized losses	$ (62)	$ (55)