Investments-Portfolio Monitoring (Details 11) $ in Millions	Mar. 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	802	1,385
Fair value, continuous unrealized loss position for less than 12 months	$ 3,497	$ 7,310
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (191)	$ (346)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	205	172
Fair value, continuous unrealized loss position for 12 months or more	$ 895	$ 858
Unrealized losses, continuous unrealized loss position for 12 months or more	(181)	(176)
Total unrealized losses
Total unrealized losses	$ (372)	$ (522)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	542	1,106
Fair value, continuous unrealized loss position for less than 12 months	$ 3,041	$ 6,767
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (140)	$ (297)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	153	140
Fair value, continuous unrealized loss position for 12 months or more	$ 823	$ 802
Unrealized losses, continuous unrealized loss position for 12 months or more	(168)	(165)
Total unrealized losses
Gross unrealized losses	$ (308)	$ (462)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	2	6
Fair value, continuous unrealized loss position for less than 12 months	$ 230	$ 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	8	15
Fair value, continuous unrealized loss position for less than 12 months	$ 30	$ 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 (in Security) | security	5	5
Fair value, continuous unrealized loss position for 12 months or more	$ 25	$ 25
Unrealized losses, continuous unrealized loss position for 12 months or more	(8)	(9)
Total unrealized losses
Total unrealized losses	$ (9)	$ (12)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	424	953
Fair value, continuous unrealized loss position for less than 12 months	$ 2,132	$ 5,315
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (126)	$ (281)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	88	78
Fair value, continuous unrealized loss position for 12 months or more	$ 595	$ 568
Unrealized losses, continuous unrealized loss position for 12 months or more	(135)	(133)
Total unrealized losses
Total unrealized losses	$ (261)	$ (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	53	81
Fair value, continuous unrealized loss position for less than 12 months	$ 502	$ 1,152
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (7)	$ (11)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	18	16
Fair value, continuous unrealized loss position for 12 months or more	$ 152	$ 154
Unrealized losses, continuous unrealized loss position for 12 months or more	(19)	(17)
Total unrealized losses
Total unrealized losses	$ (26)	$ (28)
RMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	42	38
Fair value, continuous unrealized loss position for less than 12 months	$ 27	$ 7
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (1)	$ 0
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	41	40
Fair value, continuous unrealized loss position for 12 months or more	$ 49	$ 53
Unrealized losses, continuous unrealized loss position for 12 months or more	(4)	(4)
Total unrealized losses
Total unrealized losses	$ (5)	$ (4)
CMBS
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	13	12
Fair value, continuous unrealized loss position for less than 12 months	$ 120	$ 75
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (5)	$ (2)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	1	1
Fair value, continuous unrealized loss position for 12 months or more	$ 2	$ 2
Unrealized losses, continuous unrealized loss position for 12 months or more	(2)	(2)
Total unrealized losses
Total unrealized losses	$ (7)	$ (4)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	260	279
Fair value, continuous unrealized loss position for less than 12 months	$ 456	$ 543
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (51)	$ (49)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	52	32
Fair value, continuous unrealized loss position for 12 months or more	$ 72	$ 56
Unrealized losses, continuous unrealized loss position for 12 months or more	(13)	(11)
Total unrealized losses
Gross unrealized losses on equity securities	$ (64)	$ (60)
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	314	780
Fair value, continuous unrealized loss position for less than 12 months	$ 2,049	$ 5,429
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (61)	$ (175)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	78	82
Fair value, continuous unrealized loss position for 12 months or more	$ 489	$ 503
Unrealized losses, continuous unrealized loss position for 12 months or more	(84)	(90)
Total unrealized losses
Total unrealized losses	$ (145)	$ (265)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months | security	228	326
Fair value, continuous unrealized loss position for less than 12 months	$ 992	$ 1,338
Unrealized losses, continuous unrealized loss position for less than 12 months	$ (79)	$ (122)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more (in Security) | security	75	58
Fair value, continuous unrealized loss position for 12 months or more	$ 334	$ 299
Unrealized losses, continuous unrealized loss position for 12 months or more	(84)	(75)
Total unrealized losses
Total unrealized losses	$ (163)	$ (197)