Investments (Summary of fixed maturity and equity securities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Cost or Amortized Cost	$ 37,545	$ 39,490
Gross Unrealized Gain	3,544	2,460
Gross Unrealized Loss	99	532
Estimated fair value	40,990us-gaap_AvailableForSaleSecurities	41,418us-gaap_AvailableForSaleSecurities
Corporate and other bonds [Member]
Cost or Amortized Cost	17,210	19,352
Gross Unrealized Gain	1,721	1,645
Gross Unrealized Loss	61	135
Estimated fair value	18,870	20,862
Unrealized OTTI Losses (Gains)	0	0
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	11,285	11,281
Gross Unrealized Gain	1,463	548
Gross Unrealized Loss	8	272
Estimated fair value	12,740	11,557
Unrealized OTTI Losses (Gains)	0	0
Residential mortgage-backed [Member]
Cost or Amortized Cost	5,028	4,940
Gross Unrealized Gain	218	123
Gross Unrealized Loss	13	92
Estimated fair value	5,233	4,971
Unrealized OTTI Losses (Gains)	(53)	(37)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	2,056	1,995
Gross Unrealized Gain	93	90
Gross Unrealized Loss	5	22
Estimated fair value	2,144	2,063
Unrealized OTTI Losses (Gains)	(2)	(3)
Other asset-backed [Member]
Cost or Amortized Cost	1,234	945
Gross Unrealized Gain	11	13
Gross Unrealized Loss	10	3
Estimated fair value	1,235	955
Unrealized OTTI Losses (Gains)	0	0
Total asset-backed [Member]
Cost or Amortized Cost	8,318	7,880
Gross Unrealized Gain	322	226
Gross Unrealized Loss	28	117
Estimated fair value	8,612	7,989
Unrealized OTTI Losses (Gains)	(55)	(40)
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	26	139
Gross Unrealized Gain	5	6
Gross Unrealized Loss	0	1
Estimated fair value	31	144
Unrealized OTTI Losses (Gains)	0	0
Foreign Government Debt Securities [Member]
Cost or Amortized Cost	438	531
Gross Unrealized Gain	16	15
Gross Unrealized Loss	0	3
Estimated fair value	454	543
Unrealized OTTI Losses (Gains)	0	0
Redeemable preferred stock [Member]
Cost or Amortized Cost	39	92
Gross Unrealized Gain	3	10
Gross Unrealized Loss	0	0
Estimated fair value	42	102
Unrealized OTTI Losses (Gains)	0	0
Total fixed maturity securities available-for-sale [Member]
Cost or Amortized Cost	37,316	39,275
Gross Unrealized Gain	3,530	2,450
Gross Unrealized Loss	97	528
Estimated fair value	40,749	41,197
Unrealized OTTI Losses (Gains)	(55)	(40)
Total fixed maturity securities trading [Member]
Cost or Amortized Cost, Trading Securities	19	36
Estimated Fair Value, Trading Securities	19	36
Common stock [Member]
Cost or Amortized Cost	38	36
Gross Unrealized Gain	9	9
Gross Unrealized Loss	0	0
Estimated fair value	47	45
Preferred stock [Member]
Cost or Amortized Cost	172	143
Gross Unrealized Gain	5	1
Gross Unrealized Loss	2	4
Estimated fair value	175	140
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	210	179
Gross Unrealized Gain	14	10
Gross Unrealized Loss	2	4
Estimated fair value	$ 222	$ 185

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