Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Cost or Amortized Cost	$ 37,775	$ 37,545
Gross Unrealized Gain	2,891	3,544
Gross Unrealized Loss	253	99
Estimated fair value	40,413	40,990
Corporate and other bonds [Member]
Cost or Amortized Cost	17,155	17,210
Gross Unrealized Gain	1,237	1,721
Gross Unrealized Loss	207	61
Estimated fair value	18,185	18,870
Unrealized OTTI Losses (Gains)	0	0
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	11,978	11,285
Gross Unrealized Gain	1,336	1,463
Gross Unrealized Loss	17	8
Estimated fair value	13,297	12,740
Unrealized OTTI Losses (Gains)	(5)	0
Residential mortgage-backed [Member]
Cost or Amortized Cost	4,850	5,028
Gross Unrealized Gain	204	218
Gross Unrealized Loss	13	13
Estimated fair value	5,041	5,233
Unrealized OTTI Losses (Gains)	(46)	(53)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	2,183	2,056
Gross Unrealized Gain	77	93
Gross Unrealized Loss	9	5
Estimated fair value	2,251	2,144
Unrealized OTTI Losses (Gains)	0	(2)
Other asset-backed [Member]
Cost or Amortized Cost	1,009	1,234
Gross Unrealized Gain	11	11
Gross Unrealized Loss	4	10
Estimated fair value	1,016	1,235
Unrealized OTTI Losses (Gains)	0	0
Total asset-backed [Member]
Cost or Amortized Cost	8,042	8,318
Gross Unrealized Gain	292	322
Gross Unrealized Loss	26	28
Estimated fair value	8,308	8,612
Unrealized OTTI Losses (Gains)	(46)	(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	333	438
Gross Unrealized Gain	12	16
Gross Unrealized Loss	1	0
Estimated fair value	344	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	37,565	37,316
Gross Unrealized Gain	2,884	3,530
Gross Unrealized Loss	251	97
Estimated fair value	40,198	40,749
Unrealized OTTI Losses (Gains)	(51)	(55)
Total fixed maturity securities trading [Member]
Cost or Amortized Cost, Trading Securities	3	19
Estimated Fair Value, Trading Securities	3	19
Common Stock [Member]
Cost or Amortized Cost	62	38
Gross Unrealized Gain	3	9
Gross Unrealized Loss	0	0
Estimated fair value	65	47
Preferred stock [Member]
Cost or Amortized Cost	145	172
Gross Unrealized Gain	4	5
Gross Unrealized Loss	2	2
Estimated fair value	147	175
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	207	210
Gross Unrealized Gain	7	14
Gross Unrealized Loss	2	2
Estimated fair value	$ 212	$ 222