Investments (Details 10) $ in Millions	Dec. 31, 2016 USD ($) security	Dec. 31, 2015 USD ($) security
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	888	1,385
Fair value, continuous unrealized loss position for less than 12 months	$ 5,270	$ 7,310
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (145)	$ (346)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | security	188	172
Fair value, continuous unrealized loss position for 12 months or more	$ 641	$ 858
Unrealized losses, continuous unrealized loss position for 12 months or more	(90)	(176)
Total unrealized losses
Total unrealized losses	$ (235)	$ (522)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	721	1,106
Fair value, continuous unrealized loss position for less than 12 months	$ 5,070	$ 6,767
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (126)	$ (297)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | security	126	140
Fair value, continuous unrealized loss position for 12 months or more	$ 561	$ 802
Unrealized losses, continuous unrealized loss position for 12 months or more	(74)	(165)
Total unrealized losses
Gross unrealized losses	$ (200)	$ (462)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	6	6
Fair value, continuous unrealized loss position for less than 12 months	$ 104	$ 91
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (2)	$ 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	$ (2)	$ 0
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	8	15
Fair value, continuous unrealized loss position for less than 12 months	$ 44	$ 125
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 | security	3	5
Fair value, continuous unrealized loss position for 12 months or more	$ 18	$ 25
Unrealized losses, continuous unrealized loss position for 12 months or more	(6)	(9)
Total unrealized losses
Total unrealized losses	$ (7)	$ (12)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	629	953
Fair value, continuous unrealized loss position for less than 12 months	$ 4,767	$ 5,315
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (118)	$ (281)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | security	56	78
Fair value, continuous unrealized loss position for 12 months or more	$ 414	$ 568
Unrealized losses, continuous unrealized loss position for 12 months or more	(51)	(133)
Total unrealized losses
Total unrealized losses	$ (169)	$ (414)
Foreign government
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		$ 2
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
ABS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	18	81
Fair value, continuous unrealized loss position for less than 12 months	$ 95	$ 1,152
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (1)	$ (11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | security	13	16
Fair value, continuous unrealized loss position for 12 months or more	$ 76	$ 154
Unrealized losses, continuous unrealized loss position for 12 months or more	(9)	(17)
Total unrealized losses
Total unrealized losses	$ (10)	$ (28)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	47	38
Fair value, continuous unrealized loss position for less than 12 months	$ 3	$ 7
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	50	40
Fair value, continuous unrealized loss position for 12 months or more	$ 38	$ 53
Unrealized losses, continuous unrealized loss position for 12 months or more	(3)	(4)
Total unrealized losses
Total unrealized losses	$ (3)	$ (4)
CMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	12	12
Fair value, continuous unrealized loss position for less than 12 months	$ 57	$ 75
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (4)	$ (2)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | security	4	1
Fair value, continuous unrealized loss position for 12 months or more	$ 15	$ 2
Unrealized losses, continuous unrealized loss position for 12 months or more	(5)	(2)
Total unrealized losses
Total unrealized losses	$ (9)	$ (4)
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 | security	559	780
Fair value, continuous unrealized loss position for less than 12 months	$ 4,348	$ 5,429
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (100)	$ (175)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | security	75	82
Fair value, continuous unrealized loss position for 12 months or more	$ 350	$ 503
Unrealized losses, continuous unrealized loss position for 12 months or more	(47)	(90)
Total unrealized losses
Total unrealized losses	$ (147)	$ (265)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	162	326
Fair value, continuous unrealized loss position for less than 12 months	$ 722	$ 1,338
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (26)	$ (122)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | security	51	58
Fair value, continuous unrealized loss position for 12 months or more	$ 211	$ 299
Unrealized losses, continuous unrealized loss position for 12 months or more	(27)	(75)
Total unrealized losses
Total unrealized losses	$ (53)	$ (197)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	167	279
Fair value, continuous unrealized loss position for less than 12 months	$ 200	$ 543
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (19)	$ (49)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more | security	62	32
Fair value, continuous unrealized loss position for 12 months or more	$ 80	$ 56
Unrealized losses, continuous unrealized loss position for 12 months or more	(16)	(11)
Total unrealized losses
Gross unrealized losses on equity securities	$ (35)	$ (60)