Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Cost or Amortized Cost	$ 37,453	$ 37,444
Gross Unrealized Gain	3,275	2,717
Gross Unrealized Loss	287	392
Estimated fair value	40,441	39,769
Corporate and other bonds [Member]
Cost or Amortized Cost	17,076	17,080
Gross Unrealized Gain	1,255	1,019
Gross Unrealized Loss	224	342
Estimated fair value	18,107	17,757
Unrealized OTTI Losses (Gains)	0	0
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	11,478	11,729
Gross Unrealized Gain	1,704	1,453
Gross Unrealized Loss	3	8
Estimated fair value	13,179	13,174
Unrealized OTTI Losses (Gains)	(15)	(4)
Residential mortgage-backed [Member]
Cost or Amortized Cost	5,028	4,935
Gross Unrealized Gain	197	154
Gross Unrealized Loss	19	17
Estimated fair value	5,206	5,072
Unrealized OTTI Losses (Gains)	(33)	(37)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	2,137	2,154
Gross Unrealized Gain	78	55
Gross Unrealized Loss	16	12
Estimated fair value	2,199	2,197
Unrealized OTTI Losses (Gains)	0	0
Other asset-backed [Member]
Cost or Amortized Cost	937	923
Gross Unrealized Gain	4	6
Gross Unrealized Loss	20	8
Estimated fair value	921	921
Unrealized OTTI Losses (Gains)	0	0
Total asset-backed [Member]
Cost or Amortized Cost	8,102	8,012
Gross Unrealized Gain	279	215
Gross Unrealized Loss	55	37
Estimated fair value	8,326	8,190
Unrealized OTTI Losses (Gains)	(33)	(37)
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	133	62
Gross Unrealized Gain	7	5
Gross Unrealized Loss	0	0
Estimated fair value	140	67
Unrealized OTTI Losses (Gains)	0	0
Foreign Government Debt Securities [Member]
Cost or Amortized Cost	447	334
Gross Unrealized Gain	17	13
Gross Unrealized Loss	1	1
Estimated fair value	463	346
Unrealized OTTI Losses (Gains)	0	0
Redeemable preferred stock [Member]
Cost or Amortized Cost	33	33
Gross Unrealized Gain	2	2
Gross Unrealized Loss	0	0
Estimated fair value	35	35
Unrealized OTTI Losses (Gains)	0	0
Total fixed maturity securities available-for-sale [Member]
Cost or Amortized Cost	37,269	37,250
Gross Unrealized Gain	3,264	2,707
Gross Unrealized Loss	283	388
Estimated fair value	40,250	39,569
Unrealized OTTI Losses (Gains)	(48)	(41)
Total fixed maturity securities trading [Member]
Cost or Amortized Cost, Trading Securities	2	3
Estimated Fair Value, Trading Securities	2	3
Common stock [Member]
Cost or Amortized Cost	37	46
Gross Unrealized Gain	6	3
Gross Unrealized Loss	2	1
Estimated fair value	41	48
Preferred stock [Member]
Cost or Amortized Cost	145	145
Gross Unrealized Gain	5	7
Gross Unrealized Loss	2	3
Estimated fair value	148	149
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	182	191
Gross Unrealized Gain	11	10
Gross Unrealized Loss	4	4
Estimated fair value	$ 189	$ 197