Investments- Portfolio Monitoring (Details 11) $ in Millions	Jun. 30, 2017 USD ($) security	Dec. 31, 2016 USD ($) security
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	623	888
Fair value, continuous unrealized loss position for less than 12 months	$ 3,581	$ 5,270
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (70)	$ (145)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	121	188
Fair value, continuous unrealized loss position for 12 months or more	$ 338	$ 641
Unrealized losses, continuous unrealized loss position for 12 months or more	(50)	(90)
Total unrealized losses
Total unrealized losses	$ (120)	$ (235)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	516	721
Fair value, continuous unrealized loss position for less than 12 months	$ 3,448	$ 5,070
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (59)	$ (126)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	86	126
Fair value, continuous unrealized loss position for 12 months or more	$ 298	$ 561
Unrealized losses, continuous unrealized loss position for 12 months or more	(43)	(74)
Total unrealized losses
Gross unrealized losses	$ (102)	$ (200)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	13	6
Fair value, continuous unrealized loss position for less than 12 months	$ 177	$ 104
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (1)	$ (2)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | 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
Gross unrealized losses	$ (1)	$ (2)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	5	8
Fair value, continuous unrealized loss position for less than 12 months	$ 22	$ 44
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (2)	$ (1)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	1	3
Fair value, continuous unrealized loss position for 12 months or more	$ 10	$ 18
Unrealized losses, continuous unrealized loss position for 12 months or more	(3)	(6)
Total unrealized losses
Gross unrealized losses	$ (5)	$ (7)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	421	629
Fair value, continuous unrealized loss position for less than 12 months	$ 3,063	$ 4,767
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (52)	$ (118)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	29	56
Fair value, continuous unrealized loss position for 12 months or more	$ 224	$ 414
Unrealized losses, continuous unrealized loss position for 12 months or more	(28)	(51)
Total unrealized losses
Gross unrealized losses	$ (80)	$ (169)
ABS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	27	18
Fair value, continuous unrealized loss position for less than 12 months	$ 161	$ 95
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 (in Security) | security	8	13
Fair value, continuous unrealized loss position for 12 months or more	$ 23	$ 76
Unrealized losses, continuous unrealized loss position for 12 months or more	(7)	(9)
Total unrealized losses
Gross unrealized losses	$ (8)	$ (10)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	44	47
Fair value, continuous unrealized loss position for less than 12 months	$ 2	$ 3
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 (in Security) | security	44	50
Fair value, continuous unrealized loss position for 12 months or more	$ 28	$ 38
Unrealized losses, continuous unrealized loss position for 12 months or more	(1)	(3)
Total unrealized losses
Gross unrealized losses	$ (1)	$ (3)
CMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	5	12
Fair value, continuous unrealized loss position for less than 12 months	$ 23	$ 57
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (3)	$ (4)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	4	4
Fair value, continuous unrealized loss position for 12 months or more	$ 13	$ 15
Unrealized losses, continuous unrealized loss position for 12 months or more	(4)	(5)
Total unrealized losses
Gross 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 (in Security) | 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
Gross unrealized losses	$ 0	$ 0
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	107	167
Fair value, continuous unrealized loss position for less than 12 months	$ 133	$ 200
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (11)	$ (19)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	35	62
Fair value, continuous unrealized loss position for 12 months or more	$ 40	$ 80
Unrealized losses, continuous unrealized loss position for 12 months or more	(7)	(16)
Total unrealized losses
Gross unrealized losses on equity securities	$ (18)	$ (35)
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	417	559
Fair value, continuous unrealized loss position for less than 12 months	$ 3,122	$ 4,348
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (47)	$ (100)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	59	75
Fair value, continuous unrealized loss position for 12 months or more	$ 206	$ 350
Unrealized losses, continuous unrealized loss position for 12 months or more	(27)	(47)
Total unrealized losses
Total unrealized losses	$ (74)	$ (147)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	99	162
Fair value, continuous unrealized loss position for less than 12 months	$ 326	$ 722
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (12)	$ (26)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	27	51
Fair value, continuous unrealized loss position for 12 months or more	$ 92	$ 211
Unrealized losses, continuous unrealized loss position for 12 months or more	(16)	(27)
Total unrealized losses
Total unrealized losses	$ (28)	$ (53)