Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Cost or Amortized Cost	$ 38,348	$ 37,444
Gross Unrealized Gain	4,154	2,717
Gross Unrealized Loss	65	392
Estimated fair value	42,437	39,769
Corporate and other bonds [Member]
Cost or Amortized Cost	17,985	17,080
Gross Unrealized Gain	1,867	1,019
Gross Unrealized Loss	36	342
Estimated fair value	19,816	17,757
Unrealized OTTI Losses (Gains)	(1)	0
States, municipalities and political subdivisions [Member]
Cost or Amortized Cost	11,566	11,729
Gross Unrealized Gain	1,937	1,453
Gross Unrealized Loss	2	8
Estimated fair value	13,501	13,174
Unrealized OTTI Losses (Gains)	(27)	(4)
Residential mortgage-backed [Member]
Cost or Amortized Cost	5,174	4,935
Gross Unrealized Gain	206	154
Gross Unrealized Loss	15	17
Estimated fair value	5,365	5,072
Unrealized OTTI Losses (Gains)	(24)	(37)
Commercial mortgage-backed [Member]
Cost or Amortized Cost	2,064	2,154
Gross Unrealized Gain	88	55
Gross Unrealized Loss	8	12
Estimated fair value	2,144	2,197
Unrealized OTTI Losses (Gains)	0	0
Other asset-backed [Member]
Cost or Amortized Cost	948	923
Gross Unrealized Gain	12	6
Gross Unrealized Loss	1	8
Estimated fair value	959	921
Unrealized OTTI Losses (Gains)	0	0
Total asset-backed [Member]
Cost or Amortized Cost	8,186	8,012
Gross Unrealized Gain	306	215
Gross Unrealized Loss	24	37
Estimated fair value	8,468	8,190
Unrealized OTTI Losses (Gains)	(24)	(37)
U.S. Treasury and obligations of government-sponsored enterprises [Member]
Cost or Amortized Cost	68	62
Gross Unrealized Gain	8	5
Gross Unrealized Loss	0	0
Estimated fair value	76	67
Unrealized OTTI Losses (Gains)	0	0
Foreign Government Debt Securities [Member]
Cost or Amortized Cost	415	334
Gross Unrealized Gain	23	13
Gross Unrealized Loss	0	1
Estimated fair value	438	346
Unrealized OTTI Losses (Gains)	0	0
Redeemable preferred stock [Member]
Cost or Amortized Cost	18	33
Gross Unrealized Gain	2	2
Gross Unrealized Loss	0	0
Estimated fair value	20	35
Unrealized OTTI Losses (Gains)	0	0
Total fixed maturity securities available-for-sale [Member]
Cost or Amortized Cost	38,238	37,250
Gross Unrealized Gain	4,143	2,707
Gross Unrealized Loss	62	388
Estimated fair value	42,319	39,569
Unrealized OTTI Losses (Gains)	(52)	(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	15	46
Gross Unrealized Gain	6	3
Gross Unrealized Loss	1	1
Estimated fair value	20	48
Preferred stock [Member]
Cost or Amortized Cost	93	145
Gross Unrealized Gain	5	7
Gross Unrealized Loss	2	3
Estimated fair value	96	149
Total equity securities available-for-sale [Member]
Cost or Amortized Cost	108	191
Gross Unrealized Gain	11	10
Gross Unrealized Loss	3	4
Estimated fair value	$ 116	$ 197