Investments (Details 11) $ in Millions	Mar. 31, 2017 USD ($) contract	Dec. 31, 2016 USD ($) security contract
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,989	2,590
Fair value, continuous unrealized loss position for less than 12 months	$ 14,971	$ 18,572
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (284)	$ (407)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	287	334
Fair value, continuous unrealized loss position for 12 months or more	$ 747	$ 1,087
Unrealized losses, continuous unrealized loss position for 12 months or more	(103)	(125)
Total unrealized losses
Total unrealized losses	$ (387)	$ (532)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,856	2,395
Fair value, continuous unrealized loss position for less than 12 months	$ 14,495	$ 17,918
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (243)	$ (351)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	266	288
Fair value, continuous unrealized loss position for 12 months or more	$ 649	$ 922
Unrealized losses, continuous unrealized loss position for 12 months or more	(89)	(96)
Total unrealized losses
Total unrealized losses	$ (332)	$ (447)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	45	46
Fair value, continuous unrealized loss position for less than 12 months	$ 1,411	$ 943
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (4)	$ (9)
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	$ (4)	$ (9)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	963	1,310
Fair value, continuous unrealized loss position for less than 12 months	$ 2,000	$ 3,073
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (47)	$ (76)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	8	8
Fair value, continuous unrealized loss position for 12 months or more	$ 30	$ 29
Unrealized losses, continuous unrealized loss position for 12 months or more	(10)	(11)
Total unrealized losses
Total unrealized losses	$ (57)	$ (87)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	714	862
Fair value, continuous unrealized loss position for less than 12 months	$ 10,634	$ 13,343
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (186)	$ (256)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	51	83
Fair value, continuous unrealized loss position for 12 months or more	$ 462	$ 678
Unrealized losses, continuous unrealized loss position for 12 months or more	(56)	(63)
Total unrealized losses
Total unrealized losses	$ (242)	$ (319)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	33	41
Fair value, continuous unrealized loss position for less than 12 months	$ 166	$ 225
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)
Asset-backed securities (“ABS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	30	31
Fair value, continuous unrealized loss position for less than 12 months	$ 219	$ 222
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	13	14
Fair value, continuous unrealized loss position for 12 months or more	$ 61	$ 109
Unrealized losses, continuous unrealized loss position for 12 months or more	(11)	(10)
Total unrealized losses
Total unrealized losses	$ (12)	$ (11)
Residential mortgage-backed securities (“RMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	63	89
Fair value, continuous unrealized loss position for less than 12 months	$ 44	$ 53
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	187	179
Fair value, continuous unrealized loss position for 12 months or more	$ 77	$ 91
Unrealized losses, continuous unrealized loss position for 12 months or more	(5)	(7)
Total unrealized losses
Total unrealized losses	$ (6)	$ (8)
Commercial mortgage-backed securities (“CMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	8	15
Fair value, continuous unrealized loss position for less than 12 months	$ 21	$ 59
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	7	4
Fair value, continuous unrealized loss position for 12 months or more	$ 19	$ 15
Unrealized losses, continuous unrealized loss position for 12 months or more	(7)	(5)
Total unrealized losses
Total unrealized losses	$ (9)	$ (9)
Redeemable preferred stock
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security		1
Fair value, continuous unrealized loss position for less than 12 months		$ 0
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 | security		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
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,697	2,202
Fair value, continuous unrealized loss position for less than 12 months	$ 12,905	$ 15,678
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (211)	$ (293)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	194	201
Fair value, continuous unrealized loss position for 12 months or more	$ 340	$ 493
Unrealized losses, continuous unrealized loss position for 12 months or more	(47)	(51)
Total unrealized losses
Total unrealized losses	$ (258)	$ (344)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	159	193
Fair value, continuous unrealized loss position for less than 12 months	$ 1,590	$ 2,240
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (32)	$ (58)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	72	87
Fair value, continuous unrealized loss position for 12 months or more	$ 309	$ 429
Unrealized losses, continuous unrealized loss position for 12 months or more	(42)	(45)
Total unrealized losses
Total unrealized losses	$ (74)	$ (103)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	133	195
Fair value, continuous unrealized loss position for less than 12 months	$ 476	$ 654
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (41)	$ (56)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	21	46
Fair value, continuous unrealized loss position for 12 months or more	$ 98	$ 165
Unrealized losses, continuous unrealized loss position for 12 months or more	(14)	(29)
Total unrealized losses
Total unrealized losses	$ (55)	$ (85)