Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	$ 37,912	$ 38,081
Gross Unrealized Gains	2,753	1,982
Gross Unrealized Losses	140	521
Estimated Fair Value	40,525	39,542
Total fixed maturity securities trading
Debt securities, amortized cost	37,940	38,085
Debt securities	40,553	39,546
Corporate and other bonds
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	19,296	18,764
Gross Unrealized Gains	1,269	791
Gross Unrealized Losses	99	395
Estimated Fair Value	20,466	19,160
Total fixed maturity securities trading
Debt securities	21,163	19,814
Unrealized OTTI Losses (Gains)	0	0
States, municipalities and political subdivisions
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	9,279	9,681
Gross Unrealized Gains	1,299	1,076
Gross Unrealized Losses	0	9
Estimated Fair Value	10,578	10,748
Total fixed maturity securities trading
Debt securities	10,596	10,748
Unrealized OTTI Losses (Gains)	0	0
Residential mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	4,760	4,815
Gross Unrealized Gains	92	68
Gross Unrealized Losses	20	57
Estimated Fair Value	4,832	4,826
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	(22)	(20)
Commercial mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	2,026	2,200
Gross Unrealized Gains	53	28
Gross Unrealized Losses	7	32
Estimated Fair Value	2,072	2,196
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	0	0
Other asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	1,877	1,975
Gross Unrealized Gains	25	11
Gross Unrealized Losses	12	24
Estimated Fair Value	1,890	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	8,663	8,990
Gross Unrealized Gains	170	107
Gross Unrealized Losses	39	113
Estimated Fair Value	8,794	8,984
Total fixed maturity securities trading
Debt securities	8,794	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	162	156
Gross Unrealized Gains	3	3
Gross Unrealized Losses	1	0
Estimated Fair Value	164	159
Total fixed maturity securities trading
Unrealized OTTI Losses (Gains)	0	0
Foreign government
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	502	480
Gross Unrealized Gains	12	5
Gross Unrealized Losses	1	4
Estimated Fair Value	513	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	37,912	38,081
Gross Unrealized Gains	2,753	1,982
Gross Unrealized Losses	140	521
Estimated Fair Value	40,525	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	28	4
Estimated fair value, trading securities	$ 28	$ 4

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