Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Cost or Amortized Cost	$ 37,444	$ 37,545
Gross Unrealized Gain	2,717	3,544
Gross Unrealized Loss	392	99
Estimated fair value	39,769	40,990
Corporate and other bonds [Member]
Cost or Amortized Cost	17,080	17,210
Gross Unrealized Gain	1,019	1,721
Gross Unrealized Loss	342	61
Estimated fair value	17,757	18,870
Unrealized OTTI Losses (Gains)	0	0
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	11,729	11,285
Gross Unrealized Gain	1,453	1,463
Gross Unrealized Loss	8	8
Estimated fair value	13,174	12,740
Unrealized OTTI Losses (Gains)	(4)	0
Residential mortgage-backed [Member]
Cost or Amortized Cost	4,935	5,028
Gross Unrealized Gain	154	218
Gross Unrealized Loss	17	13
Estimated fair value	5,072	5,233
Unrealized OTTI Losses (Gains)	(37)	(53)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	2,154	2,056
Gross Unrealized Gain	55	93
Gross Unrealized Loss	12	5
Estimated fair value	2,197	2,144
Unrealized OTTI Losses (Gains)	0	(2)
Other asset-backed [Member]
Cost or Amortized Cost	923	1,234
Gross Unrealized Gain	6	11
Gross Unrealized Loss	8	10
Estimated fair value	921	1,235
Unrealized OTTI Losses (Gains)	0	0
Total asset-backed [Member]
Cost or Amortized Cost	8,012	8,318
Gross Unrealized Gain	215	322
Gross Unrealized Loss	37	28
Estimated fair value	8,190	8,612
Unrealized OTTI Losses (Gains)	(37)	(55)
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	62	26
Gross Unrealized Gain	5	5
Gross Unrealized Loss	0	0
Estimated fair value	67	31
Unrealized OTTI Losses (Gains)	0	0
Foreign Government Debt Securities [Member]
Cost or Amortized Cost	334	438
Gross Unrealized Gain	13	16
Gross Unrealized Loss	1	0
Estimated fair value	346	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	37,250	37,316
Gross Unrealized Gain	2,707	3,530
Gross Unrealized Loss	388	97
Estimated fair value	39,569	40,749
Unrealized OTTI Losses (Gains)	(41)	(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	46	38
Gross Unrealized Gain	3	9
Gross Unrealized Loss	1	0
Estimated fair value	48	47
Preferred stock [Member]
Cost or Amortized Cost	145	172
Gross Unrealized Gain	7	5
Gross Unrealized Loss	3	2
Estimated fair value	149	175
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	191	210
Gross Unrealized Gain	10	14
Gross Unrealized Loss	4	2
Estimated fair value	$ 197	$ 222