Investments (Details 11) $ in Millions	Jun. 30, 2017 USD ($) security contract	Dec. 31, 2016 USD ($) security contract
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,895	2,590
Fair value, continuous unrealized loss position for less than 12 months	$ 13,809	$ 18,572
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (180)	$ (407)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	255	334
Fair value, continuous unrealized loss position for 12 months or more	$ 534	$ 1,087
Unrealized losses, continuous unrealized loss position for 12 months or more	(69)	(125)
Total unrealized losses
Total unrealized losses	$ (249)	$ (532)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,758	2,395
Fair value, continuous unrealized loss position for less than 12 months	$ 13,262	$ 17,918
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (146)	$ (351)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	242	288
Fair value, continuous unrealized loss position for 12 months or more	$ 491	$ 922
Unrealized losses, continuous unrealized loss position for 12 months or more	(62)	(96)
Total unrealized losses
Total unrealized losses	$ (208)	$ (447)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	62	46
Fair value, continuous unrealized loss position for less than 12 months	$ 1,840	$ 943
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (7)	$ (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	$ (7)	$ (9)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	903	1,310
Fair value, continuous unrealized loss position for less than 12 months	$ 1,842	$ 3,073
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (20)	$ (76)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	4	8
Fair value, continuous unrealized loss position for 12 months or more	$ 14	$ 29
Unrealized losses, continuous unrealized loss position for 12 months or more	(4)	(11)
Total unrealized losses
Total unrealized losses	$ (24)	$ (87)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	615	862
Fair value, continuous unrealized loss position for less than 12 months	$ 8,649	$ 13,343
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (109)	$ (256)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	44	83
Fair value, continuous unrealized loss position for 12 months or more	$ 358	$ 678
Unrealized losses, continuous unrealized loss position for 12 months or more	(41)	(63)
Total unrealized losses
Total unrealized losses	$ (150)	$ (319)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	57	41
Fair value, continuous unrealized loss position for less than 12 months	$ 625	$ 225
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (6)	$ (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	$ (6)	$ (4)
Asset-backed securities (“ABS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	35	31
Fair value, continuous unrealized loss position for less than 12 months	$ 242	$ 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	10	14
Fair value, continuous unrealized loss position for 12 months or more	$ 39	$ 109
Unrealized losses, continuous unrealized loss position for 12 months or more	(9)	(10)
Total unrealized losses
Total unrealized losses	$ (10)	$ (11)
Residential mortgage-backed securities (“RMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	79	89
Fair value, continuous unrealized loss position for less than 12 months	$ 41	$ 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	179	179
Fair value, continuous unrealized loss position for 12 months or more	$ 66	$ 91
Unrealized losses, continuous unrealized loss position for 12 months or more	(3)	(7)
Total unrealized losses
Total unrealized losses	$ (4)	$ (8)
Commercial mortgage-backed securities (“CMBS”)
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	6	15
Fair value, continuous unrealized loss position for less than 12 months	$ 23	$ 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	5	4
Fair value, continuous unrealized loss position for 12 months or more	$ 14	$ 15
Unrealized losses, continuous unrealized loss position for 12 months or more	(5)	(5)
Total unrealized losses
Total unrealized losses	$ (7)	$ (9)
Redeemable preferred stock
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	1	1
Fair value, continuous unrealized loss position for less than 12 months	$ 0	$ 0
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 | security	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
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	1,655	2,202
Fair value, continuous unrealized loss position for less than 12 months	$ 12,373	$ 15,678
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (124)	$ (293)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	183	201
Fair value, continuous unrealized loss position for 12 months or more	$ 295	$ 493
Unrealized losses, continuous unrealized loss position for 12 months or more	(31)	(51)
Total unrealized losses
Total unrealized losses	$ (155)	$ (344)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	103	193
Fair value, continuous unrealized loss position for less than 12 months	$ 889	$ 2,240
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (22)	$ (58)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	59	87
Fair value, continuous unrealized loss position for 12 months or more	$ 196	$ 429
Unrealized losses, continuous unrealized loss position for 12 months or more	(31)	(45)
Total unrealized losses
Total unrealized losses	$ (53)	$ (103)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | contract	137	195
Fair value, continuous unrealized loss position for less than 12 months	$ 547	$ 654
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (34)	$ (56)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | contract	13	46
Fair value, continuous unrealized loss position for 12 months or more	$ 43	$ 165
Unrealized losses, continuous unrealized loss position for 12 months or more	(7)	(29)
Total unrealized losses
Total unrealized losses	$ (41)	$ (85)