Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Cost or Amortized Cost	$ 37,407	$ 37,545
Gross Unrealized Gain	2,819	3,544
Gross Unrealized Loss	161	99
Estimated fair value	40,065	40,990
Corporate and other bonds [Member]
Cost or Amortized Cost	16,863	17,210
Gross Unrealized Gain	1,337	1,721
Gross Unrealized Loss	88	61
Estimated fair value	18,112	18,870
Unrealized OTTI Losses (Gains)	0	0
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	11,707	11,285
Gross Unrealized Gain	1,186	1,463
Gross Unrealized Loss	40	8
Estimated fair value	12,853	12,740
Unrealized OTTI Losses (Gains)	0	0
Residential mortgage-backed [Member]
Cost or Amortized Cost	4,940	5,028
Gross Unrealized Gain	175	218
Gross Unrealized Loss	15	13
Estimated fair value	5,100	5,233
Unrealized OTTI Losses (Gains)	(46)	(53)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	2,186	2,056
Gross Unrealized Gain	77	93
Gross Unrealized Loss	12	5
Estimated fair value	2,251	2,144
Unrealized OTTI Losses (Gains)	(2)	(2)
Other asset-backed [Member]
Cost or Amortized Cost	1,044	1,234
Gross Unrealized Gain	12	11
Gross Unrealized Loss	1	10
Estimated fair value	1,055	1,235
Unrealized OTTI Losses (Gains)	0	0
Total asset-backed [Member]
Cost or Amortized Cost	8,170	8,318
Gross Unrealized Gain	264	322
Gross Unrealized Loss	28	28
Estimated fair value	8,406	8,612
Unrealized OTTI Losses (Gains)	(48)	(55)
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	24	26
Gross Unrealized Gain	5	5
Gross Unrealized Loss	0	0
Estimated fair value	29	31
Unrealized OTTI Losses (Gains)	0	0
Foreign Government Debt Securities [Member]
Cost or Amortized Cost	387	438
Gross Unrealized Gain	13	16
Gross Unrealized Loss	1	0
Estimated fair value	399	454
Unrealized OTTI Losses (Gains)	0	0
Redeemable preferred stock [Member]
Cost or Amortized Cost	33	39
Gross Unrealized Gain	2	3
Gross Unrealized Loss	0	0
Estimated fair value	35	42
Unrealized OTTI Losses (Gains)	0	0
Total fixed maturity securities available-for-sale [Member]
Cost or Amortized Cost	37,184	37,316
Gross Unrealized Gain	2,807	3,530
Gross Unrealized Loss	157	97
Estimated fair value	39,834	40,749
Unrealized OTTI Losses (Gains)	(48)	(55)
Total fixed maturity securities trading [Member]
Cost or Amortized Cost, Trading Securities	15	19
Estimated Fair Value, Trading Securities	15	19
Common Stock [Member]
Cost or Amortized Cost	54	38
Gross Unrealized Gain	8	9
Gross Unrealized Loss	2	0
Estimated fair value	60	47
Preferred stock [Member]
Cost or Amortized Cost	154	172
Gross Unrealized Gain	4	5
Gross Unrealized Loss	2	2
Estimated fair value	156	175
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	208	210
Gross Unrealized Gain	12	14
Gross Unrealized Loss	4	2
Estimated fair value	$ 216	$ 222