Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	$ 38,253	$ 38,081
Gross Unrealized Gains	4,251	1,982
Gross Unrealized Losses	50	521
Estimated Fair Value	42,454	39,542
Total fixed maturity securities trading
Debt securities, amortized cost	38,258	38,085
Debt securities	42,459	39,546
Corporate and other bonds
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	19,806	18,764
Gross Unrealized Gains	2,263	791
Gross Unrealized Losses	42	395
Estimated Fair Value	22,027	19,160
Total fixed maturity securities trading
Debt securities	22,684	19,814
Unrealized OTTI Losses (Gains)	0	0
States, municipalities and political subdivisions
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	9,154	9,681
Gross Unrealized Gains	1,641	1,076
Gross Unrealized Losses	0	9
Estimated Fair Value	10,795	10,748
Total fixed maturity securities trading
Debt securities	10,795	10,748
Unrealized OTTI Losses (Gains)	0	0
Residential mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	4,718	4,815
Gross Unrealized Gains	157	68
Gross Unrealized Losses	1	57
Estimated Fair Value	4,874	4,826
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	(23)	(20)
Commercial mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	2,066	2,200
Gross Unrealized Gains	117	28
Gross Unrealized Losses	3	32
Estimated Fair Value	2,180	2,196
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	1	0
Other asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	1,884	1,975
Gross Unrealized Gains	46	11
Gross Unrealized Losses	4	24
Estimated Fair Value	1,926	1,962
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	(3)	0
Asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	8,668	8,990
Gross Unrealized Gains	320	107
Gross Unrealized Losses	8	113
Estimated Fair Value	8,980	8,984
Total fixed maturity securities trading
Debt securities	8,980	8,984
Unrealized OTTI Losses (Gains)	(25)	(20)
U.S. Treasury and obligations of government-sponsored enterprises
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	124	156
Gross Unrealized Gains	7	3
Gross Unrealized Losses	0	0
Estimated Fair Value	131	159
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	0	0
Foreign government
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	491	480
Gross Unrealized Gains	20	5
Gross Unrealized Losses	0	4
Estimated Fair Value	511	481
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	0	0
Redeemable preferred stock
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	10	10
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	10	10
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	0	0
Fixed maturity securities
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	38,253	38,081
Gross Unrealized Gains	4,251	1,982
Gross Unrealized Losses	50	521
Estimated Fair Value	42,454	39,542
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	(25)	(20)
Total fixed maturity securities trading
Total fixed maturity securities trading
Cost or amortized cost, trading securities	5	4
Estimated fair value, trading securities	$ 5	$ 4

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