Investments- Portfolio Monitoring (Details 11) $ in Millions	Mar. 31, 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	709	888
Fair value, continuous unrealized loss position for less than 12 months	$ 4,471	$ 5,270
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (106)	$ (145)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	171	188
Fair value, continuous unrealized loss position for 12 months or more	$ 517	$ 641
Unrealized losses, continuous unrealized loss position for 12 months or more	(82)	(90)
Total unrealized losses
Total unrealized losses	$ (188)	$ (235)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	598	721
Fair value, continuous unrealized loss position for less than 12 months	$ 4,349	$ 5,070
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (94)	$ (126)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	122	126
Fair value, continuous unrealized loss position for 12 months or more	$ 455	$ 561
Unrealized losses, continuous unrealized loss position for 12 months or more	(72)	(74)
Total unrealized losses
Gross unrealized losses	$ (166)	$ (200)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	5	6
Fair value, continuous unrealized loss position for less than 12 months	$ 64	$ 104
Unrealized losses, continuous unrealized loss position for less than 12 months	$ 0	$ (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	$ 0	$ (2)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	7	8
Fair value, continuous unrealized loss position for less than 12 months	$ 30	$ 44
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	3	3
Fair value, continuous unrealized loss position for 12 months or more	$ 19	$ 18
Unrealized losses, continuous unrealized loss position for 12 months or more	(5)	(6)
Total unrealized losses
Gross unrealized losses	$ (6)	$ (7)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	537	629
Fair value, continuous unrealized loss position for less than 12 months	$ 4,115	$ 4,767
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (90)	$ (118)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	40	56
Fair value, continuous unrealized loss position for 12 months or more	$ 330	$ 414
Unrealized losses, continuous unrealized loss position for 12 months or more	(49)	(51)
Total unrealized losses
Gross unrealized losses	$ (139)	$ (169)
ABS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	19	18
Fair value, continuous unrealized loss position for less than 12 months	$ 115	$ 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	13	13
Fair value, continuous unrealized loss position for 12 months or more	$ 57	$ 76
Unrealized losses, continuous unrealized loss position for 12 months or more	(8)	(9)
Total unrealized losses
Gross unrealized losses	$ (9)	$ (10)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	23	47
Fair value, continuous unrealized loss position for less than 12 months	$ 4	$ 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	59	50
Fair value, continuous unrealized loss position for 12 months or more	$ 30	$ 38
Unrealized losses, continuous unrealized loss position for 12 months or more	(3)	(3)
Total unrealized losses
Gross unrealized losses	$ (3)	$ (3)
CMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	7	12
Fair value, continuous unrealized loss position for less than 12 months	$ 21	$ 57
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 (in Security) | security	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
Gross 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 (in Security) | 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
Gross unrealized losses		$ 0
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	111	167
Fair value, continuous unrealized loss position for less than 12 months	$ 122	$ 200
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (12)	$ (19)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	49	62
Fair value, continuous unrealized loss position for 12 months or more	$ 62	$ 80
Unrealized losses, continuous unrealized loss position for 12 months or more	(10)	(16)
Total unrealized losses
Gross unrealized losses on equity securities	$ (22)	$ (35)
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	471	559
Fair value, continuous unrealized loss position for less than 12 months	$ 3,816	$ 4,348
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (79)	$ (100)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	78	75
Fair value, continuous unrealized loss position for 12 months or more	$ 287	$ 350
Unrealized losses, continuous unrealized loss position for 12 months or more	(45)	(47)
Total unrealized losses
Total unrealized losses	$ (124)	$ (147)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	127	162
Fair value, continuous unrealized loss position for less than 12 months	$ 533	$ 722
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (15)	$ (26)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	44	51
Fair value, continuous unrealized loss position for 12 months or more	$ 168	$ 211
Unrealized losses, continuous unrealized loss position for 12 months or more	(27)	(27)
Total unrealized losses
Total unrealized losses	$ (42)	$ (53)