Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	$ 38,081	$ 38,212
Gross Unrealized Gains	1,982
Gross Unrealized Losses	521
Estimated Fair Value	39,542	41,484
Total fixed maturity securities trading
Estimated fair value, trading securities	39,546	41,487
Equity securities available-for-sale:
Cost or Amortized Cost		659
Estimated Fair Value		695
Debt securities, amortized cost	38,085
Debt securities	39,546	41,487
Marketable securities, amortized cost		38,874
Gross Unrealized Gains		3,397
Gross Unrealized Losses		89
Marketable securities		42,182
Corporate and other bonds
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	18,764	17,210
Gross Unrealized Gains	791	1,625
Gross Unrealized Losses	395	28
Estimated Fair Value	19,160	18,807
Equity securities available-for-sale:
Debt securities	19,814	19,374
Unrealized OTTI Losses (Gains)	0	0
States, municipalities and political subdivisions
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	9,681	12,478
Gross Unrealized Gains	1,076	1,551
Gross Unrealized Losses	9	2
Estimated Fair Value	10,748	14,027
Equity securities available-for-sale:
Debt securities	10,748	14,027
Unrealized OTTI Losses (Gains)	0	(11)
Residential mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	4,815	5,043
Gross Unrealized Gains	68	109
Gross Unrealized Losses	57	32
Estimated Fair Value	4,826	5,120
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	(20)	(27)
Commercial mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	2,200	1,840
Gross Unrealized Gains	28	46
Gross Unrealized Losses	32	14
Estimated Fair Value	2,196	1,872
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	0	0
Other asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	1,975	1,083
Gross Unrealized Gains	11	16
Gross Unrealized Losses	24	5
Estimated Fair Value	1,962	1,094
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	0	0
Asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	8,990	7,966
Gross Unrealized Gains	107	171
Gross Unrealized Losses	113	51
Estimated Fair Value	8,984	8,086
Equity securities available-for-sale:
Debt securities	8,984	8,086
Unrealized OTTI Losses (Gains)	(20)	(27)
U.S. Treasury and obligations of government-sponsored enterprises
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	156	111
Gross Unrealized Gains	3	2
Gross Unrealized Losses	0	4
Estimated Fair Value	159	109
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	0	0
Foreign government
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	480	437
Gross Unrealized Gains	5	9
Gross Unrealized Losses	4	2
Estimated Fair Value	481	444
Equity securities available-for-sale:
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	1
Gross Unrealized Losses	0	0
Estimated Fair Value	10	11
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	0	0
Fixed maturity securities
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	38,081	38,212
Gross Unrealized Gains	1,982	3,359
Gross Unrealized Losses	521	87
Estimated Fair Value	39,542	41,484
Equity securities available-for-sale:
Unrealized OTTI Losses (Gains)	(20)	(38)
Total fixed maturity securities trading
Total fixed maturity securities trading
Cost or amortized cost, trading securities	4	3
Gross unrealized gains, trading securities	0	0
Gross unrealized losses, trading securities	0	0
Estimated fair value, trading securities	$ 4	3
Common Stock
Equity securities available-for-sale:
Cost or Amortized Cost		21
Gross Unrealized Gains		7
Gross Unrealized Losses		1
Estimated Fair Value		27
Preferred stock
Equity securities available-for-sale:
Cost or Amortized Cost		638
Gross Unrealized Gains		31
Gross Unrealized Losses		1
Estimated Fair Value		668
Equity securities
Equity securities available-for-sale:
Cost or Amortized Cost		659
Gross Unrealized Gains		38
Gross Unrealized Losses		2
Estimated Fair Value		$ 695

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