Investments-Portfolio Monitoring (Details 11) $ in Millions	Sep. 30, 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	424	1,385
Fair value, continuous unrealized loss position for less than 12 months	$ 1,816	$ 7,310
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (53)	$ (346)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	207	172
Fair value, continuous unrealized loss position for 12 months or more	$ 722	$ 858
Unrealized losses, continuous unrealized loss position for 12 months or more	(101)	(176)
Total unrealized losses
Total unrealized losses	$ (154)	$ (522)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	241	1,106
Fair value, continuous unrealized loss position for less than 12 months	$ 1,561	$ 6,767
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (24)	$ (297)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	146	140
Fair value, continuous unrealized loss position for 12 months or more	$ 651	$ 802
Unrealized losses, continuous unrealized loss position for 12 months or more	(88)	(165)
Total unrealized losses
Gross unrealized losses	$ (112)	$ (462)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	10	6
Fair value, continuous unrealized loss position for less than 12 months	$ 258	$ 91
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
Total unrealized losses	$ 0	$ 0
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	2	15
Fair value, continuous unrealized loss position for less than 12 months	$ 0	$ 125
Unrealized losses, continuous unrealized loss position for less than 12 months	$ 0	$ (3)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | 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	$ (6)	$ (12)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	172	953
Fair value, continuous unrealized loss position for less than 12 months	$ 1,141	$ 5,315
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (17)	$ (281)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	75	78
Fair value, continuous unrealized loss position for 12 months or more	$ 493	$ 568
Unrealized losses, continuous unrealized loss position for 12 months or more	(65)	(133)
Total unrealized losses
Total unrealized losses	$ (82)	$ (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 (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
Total unrealized losses		$ 0
ABS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	9	81
Fair value, continuous unrealized loss position for less than 12 months	$ 68	$ 1,152
Unrealized losses, continuous unrealized loss position for less than 12 months	$ 0	$ (11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	16	16
Fair value, continuous unrealized loss position for 12 months or more	$ 92	$ 154
Unrealized losses, continuous unrealized loss position for 12 months or more	(13)	(17)
Total unrealized losses
Total unrealized losses	$ (13)	$ (28)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	32	38
Fair value, continuous unrealized loss position for less than 12 months	$ 1	$ 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 (in Security) | security	49	40
Fair value, continuous unrealized loss position for 12 months or more	$ 40	$ 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	16	12
Fair value, continuous unrealized loss position for less than 12 months	$ 93	$ 75
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (7)	$ (2)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	3	1
Fair value, continuous unrealized loss position for 12 months or more	$ 8	$ 2
Unrealized losses, continuous unrealized loss position for 12 months or more	(1)	(2)
Total unrealized losses
Total unrealized losses	$ (8)	$ (4)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	183	279
Fair value, continuous unrealized loss position for less than 12 months	$ 255	$ 543
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (29)	$ (49)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	61	32
Fair value, continuous unrealized loss position for 12 months or more	$ 71	$ 56
Unrealized losses, continuous unrealized loss position for 12 months or more	(13)	(11)
Total unrealized losses
Gross unrealized losses on equity securities	$ (42)	$ (60)
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	150	780
Fair value, continuous unrealized loss position for less than 12 months	$ 1,126	$ 5,429
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (7)	$ (175)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	79	82
Fair value, continuous unrealized loss position for 12 months or more	$ 389	$ 503
Unrealized losses, continuous unrealized loss position for 12 months or more	(56)	(90)
Total unrealized losses
Total unrealized losses	$ (63)	$ (265)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	91	326
Fair value, continuous unrealized loss position for less than 12 months	$ 435	$ 1,338
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (17)	$ (122)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	67	58
Fair value, continuous unrealized loss position for 12 months or more	$ 262	$ 299
Unrealized losses, continuous unrealized loss position for 12 months or more	(32)	(75)
Total unrealized losses
Total unrealized losses	$ (49)	$ (197)