Investments (Details 11) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014 contract	Dec. 31, 2013 contract
Fixed income and equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1,273	1,554
Fair value, continuous unrealized loss position for less than 12 months	$ 12,774	$ 16,270
Unrealized losses, continuous unrealized loss position for less than 12 months	(224)	(413)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	357	319
Fair value, continuous unrealized loss position for 12 months or more	1,863	1,504
Unrealized losses, continuous unrealized loss position for 12 months or more	(145)	(194)
Total unrealized losses
Total unrealized losses	(369)	(607)
Fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	1,015	1,396
Fair value, continuous unrealized loss position for less than 12 months	11,908	15,288
Unrealized losses, continuous unrealized loss position for less than 12 months	(171)	(379)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	356	318
Fair value, continuous unrealized loss position for 12 months or more	1,852	1,504
Unrealized losses, continuous unrealized loss position for 12 months or more	(143)	(194)
Total unrealized losses
Total unrealized losses	(314)	(573)
U.S. government and agencies
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	21	22
Fair value, continuous unrealized loss position for less than 12 months	1,501	700
Unrealized losses, continuous unrealized loss position for less than 12 months	(3)	(7)
Total unrealized losses
Total unrealized losses	(3)	(7)
Municipal
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	252	315
Fair value, continuous unrealized loss position for less than 12 months	1,008	2,065
Unrealized losses, continuous unrealized loss position for less than 12 months	(9)	(41)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	19	38
Fair value, continuous unrealized loss position for 12 months or more	116	208
Unrealized losses, continuous unrealized loss position for 12 months or more	(16)	(46)
Total unrealized losses
Total unrealized losses	(25)	(87)
Corporate
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	576	796
Fair value, continuous unrealized loss position for less than 12 months	7,545	10,375
Unrealized losses, continuous unrealized loss position for less than 12 months	(147)	(308)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	119	54
Fair value, continuous unrealized loss position for 12 months or more	1,214	550
Unrealized losses, continuous unrealized loss position for 12 months or more	(93)	(79)
Total unrealized losses
Total unrealized losses	(240)	(387)
Foreign government
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	2	36
Fair value, continuous unrealized loss position for less than 12 months	13	262
Unrealized losses, continuous unrealized loss position for less than 12 months		(9)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	1	1
Fair value, continuous unrealized loss position for 12 months or more	19	18
Unrealized losses, continuous unrealized loss position for 12 months or more		(2)
Total unrealized losses
Total unrealized losses		(11)
Asset-backed securities ("ABS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	81	85
Fair value, continuous unrealized loss position for less than 12 months	1,738	1,715
Unrealized losses, continuous unrealized loss position for less than 12 months	(11)	(10)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	26	43
Fair value, continuous unrealized loss position for 12 months or more	315	429
Unrealized losses, continuous unrealized loss position for 12 months or more	(20)	(34)
Total unrealized losses
Total unrealized losses	(31)	(44)
Residential mortgage-backed securities ("RMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	75	134
Fair value, continuous unrealized loss position for less than 12 months	70	149
Unrealized losses, continuous unrealized loss position for less than 12 months	(1)	(4)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	188	175
Fair value, continuous unrealized loss position for 12 months or more	156	247
Unrealized losses, continuous unrealized loss position for 12 months or more	(12)	(26)
Total unrealized losses
Total unrealized losses	(13)	(30)
Commercial mortgage-backed securities ("CMBS")
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	8	8
Fair value, continuous unrealized loss position for less than 12 months	33	22
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	3	7
Fair value, continuous unrealized loss position for 12 months or more	32	52
Unrealized losses, continuous unrealized loss position for 12 months or more	(2)	(7)
Total unrealized losses
Total unrealized losses	(2)	(7)
Investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	754	1,217
Fair value, continuous unrealized loss position for less than 12 months	9,951	14,019
Unrealized losses, continuous unrealized loss position for less than 12 months	(71)	(340)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	281	221
Fair value, continuous unrealized loss position for 12 months or more	1,444	975
Unrealized losses, continuous unrealized loss position for 12 months or more	(87)	(116)
Total unrealized losses
Total unrealized losses	(158)	(456)
Below investment grade fixed income securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	261	179
Fair value, continuous unrealized loss position for less than 12 months	1,957	1,269
Unrealized losses, continuous unrealized loss position for less than 12 months	(100)	(39)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	75	97
Fair value, continuous unrealized loss position for 12 months or more	408	529
Unrealized losses, continuous unrealized loss position for 12 months or more	(56)	(78)
Total unrealized losses
Total unrealized losses	(156)	(117)
Equity securities
Less than 12 months
Number of issues, continuous unrealized loss position for less than 12 months	258	158
Fair value, continuous unrealized loss position for less than 12 months	866	982
Unrealized losses, continuous unrealized loss position for less than 12 months	(53)	(34)
12 months or more
Number of issues, continuous unrealized loss position for 12 months or more	1	1
Fair value, continuous unrealized loss position for 12 months or more	11
Unrealized losses, continuous unrealized loss position for 12 months or more	(2)
Total unrealized losses
Total unrealized losses	$ (55)	$ (34)