Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Cost or Amortized Cost	$ 37,955	$ 37,444
Gross Unrealized Gain	4,158	2,717
Gross Unrealized Loss	133	392
Estimated fair value	41,980	39,769
Corporate and other bonds [Member]
Cost or Amortized Cost	17,613	17,080
Gross Unrealized Gain	1,684	1,019
Gross Unrealized Loss	93	342
Estimated fair value	19,204	17,757
Unrealized OTTI Losses (Gains)	(1)	0
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	11,661	11,729
Gross Unrealized Gain	2,114	1,453
Gross Unrealized Loss	2	8
Estimated fair value	13,773	13,174
Unrealized OTTI Losses (Gains)	(25)	(4)
Residential mortgage-backed [Member]
Cost or Amortized Cost	4,994	4,935
Gross Unrealized Gain	215	154
Gross Unrealized Loss	20	17
Estimated fair value	5,189	5,072
Unrealized OTTI Losses (Gains)	(21)	(37)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	2,080	2,154
Gross Unrealized Gain	91	55
Gross Unrealized Loss	8	12
Estimated fair value	2,163	2,197
Unrealized OTTI Losses (Gains)	0	0
Other asset-backed [Member]
Cost or Amortized Cost	928	923
Gross Unrealized Gain	8	6
Gross Unrealized Loss	5	8
Estimated fair value	931	921
Unrealized OTTI Losses (Gains)	0	0
Total asset-backed [Member]
Cost or Amortized Cost	8,002	8,012
Gross Unrealized Gain	314	215
Gross Unrealized Loss	33	37
Estimated fair value	8,283	8,190
Unrealized OTTI Losses (Gains)	(21)	(37)
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	81	62
Gross Unrealized Gain	11	5
Gross Unrealized Loss	0	0
Estimated fair value	92	67
Unrealized OTTI Losses (Gains)	0	0
Foreign Government Debt Securities [Member]
Cost or Amortized Cost	438	334
Gross Unrealized Gain	22	13
Gross Unrealized Loss	0	1
Estimated fair value	460	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	37,828	37,250
Gross Unrealized Gain	4,147	2,707
Gross Unrealized Loss	128	388
Estimated fair value	41,847	39,569
Unrealized OTTI Losses (Gains)	(47)	(41)
Total fixed maturity securities trading [Member]
Cost or Amortized Cost, Trading Securities	10	3
Estimated Fair Value, Trading Securities	10	3
Common stock [Member]
Cost or Amortized Cost	20	46
Gross Unrealized Gain	5	3
Gross Unrealized Loss	2	1
Estimated fair value	23	48
Preferred stock [Member]
Cost or Amortized Cost	97	145
Gross Unrealized Gain	6	7
Gross Unrealized Loss	3	3
Estimated fair value	100	149
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	117	191
Gross Unrealized Gain	11	10
Gross Unrealized Loss	5	4
Estimated fair value	$ 123	$ 197