Investments (Details 11) $ in Millions	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Fixed income and equity securities
Less than 12 months
Number of issues | security	2,590	2,144
Fair value	$ 18,572	$ 23,917
Unrealized losses	$ (407)	$ (839)
12 months or more
Number of issues | security	334	354
Fair value	$ 1,087	$ 1,654
Unrealized losses	(125)	(260)
Total unrealized losses
Total unrealized losses	$ (532)	$ (1,099)
Fixed income securities
Less than 12 months
Number of issues | security	2,395	1,879
Fair value	$ 17,918	$ 22,520
Unrealized losses	$ (351)	$ (732)
12 months or more
Number of issues | security	288	317
Fair value	$ 922	$ 1,511
Unrealized losses	(96)	(228)
Total unrealized losses
Total unrealized losses	$ (447)	$ (960)
U.S. government and agencies
Less than 12 months
Number of issues | security	46	53
Fair value	$ 943	$ 1,874
Unrealized losses	$ (9)	$ (4)
12 months or more
Number of issues | security	0	0
Fair value	$ 0	$ 0
Unrealized losses	0	0
Total unrealized losses
Total unrealized losses	$ (9)	$ (4)
Municipal
Less than 12 months
Number of issues | security	1,310	222
Fair value	$ 3,073	$ 810
Unrealized losses	$ (76)	$ (6)
12 months or more
Number of issues | security	8	9
Fair value	$ 29	$ 36
Unrealized losses	(11)	(14)
Total unrealized losses
Total unrealized losses	$ (87)	$ (20)
Corporate
Less than 12 months
Number of issues | security	862	1,361
Fair value	$ 13,343	$ 17,915
Unrealized losses	$ (256)	$ (696)
12 months or more
Number of issues | security	83	111
Fair value	$ 678	$ 1,024
Unrealized losses	(63)	(183)
Total unrealized losses
Total unrealized losses	$ (319)	$ (879)
Foreign government
Less than 12 months
Number of issues | security	41	9
Fair value	$ 225	$ 44
Unrealized losses	$ (4)	$ 0
12 months or more
Number of issues | security	0	0
Fair value	$ 0	$ 0
Unrealized losses	0	0
Total unrealized losses
Total unrealized losses	$ (4)	$ 0
ABS
Less than 12 months
Number of issues | security	31	133
Fair value	$ 222	$ 1,733
Unrealized losses	$ (1)	$ (24)
12 months or more
Number of issues | security	14	20
Fair value	$ 109	$ 324
Unrealized losses	(10)	(19)
Total unrealized losses
Total unrealized losses	$ (11)	$ (43)
RMBS
Less than 12 months
Number of issues | security	89	88
Fair value	$ 53	$ 69
Unrealized losses	$ (1)	$ 0
12 months or more
Number of issues | security	179	176
Fair value	$ 91	$ 125
Unrealized losses	(7)	(10)
Total unrealized losses
Total unrealized losses	$ (8)	$ (10)
CMBS
Less than 12 months
Number of issues | security	15	13
Fair value	$ 59	$ 75
Unrealized losses	$ (4)	$ (2)
12 months or more
Number of issues | security	4	1
Fair value	$ 15	$ 2
Unrealized losses	(5)	(2)
Total unrealized losses
Total unrealized losses	$ (9)	$ (4)
Redeemable preferred stock
Less than 12 months
Number of issues | security	1
Fair value	$ 0
Unrealized losses	$ 0
12 months or more
Number of issues | security	0
Fair value	$ 0
Unrealized losses	0
Total unrealized losses
Total unrealized losses	$ 0
Equity securities
Less than 12 months
Number of issues | security	195	265
Fair value	$ 654	$ 1,397
Unrealized losses	$ (56)	$ (107)
12 months or more
Number of issues | security	46	37
Fair value	$ 165	$ 143
Unrealized losses	(29)	(32)
Total unrealized losses
Total unrealized losses	$ (85)	$ (139)
Investment grade fixed income securities
Less than 12 months
Number of issues | security	2,202	1,405
Fair value	$ 15,678	$ 17,521
Unrealized losses	$ (293)	$ (362)
12 months or more
Number of issues | security	201	225
Fair value	$ 493	$ 972
Unrealized losses	(51)	(105)
Total unrealized losses
Total unrealized losses	$ (344)	$ (467)
Below investment grade fixed income securities
Less than 12 months
Number of issues | security	193	474
Fair value	$ 2,240	$ 4,999
Unrealized losses	$ (58)	$ (370)
12 months or more
Number of issues | security	87	92
Fair value	$ 429	$ 539
Unrealized losses	(45)	(123)
Total unrealized losses
Total unrealized losses	$ (103)	$ (493)