Investments (Summary of fixed maturity and equity securities) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	$ 38,926	$ 38,106
Gross Unrealized Gains	5,795	4,126
Gross Unrealized Losses	77	45
Allowance for Credit Losses	40	0
Estimated Fair Value	44,604	42,187
Total fixed maturity securities trading
Debt securities, amortized cost	38,953	38,126
Total fixed maturity securities	44,631	42,207
Corporate and other bonds
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	20,792	19,789
Gross Unrealized Gains	3,578	2,292
Gross Unrealized Losses	22	32
Allowance for Credit Losses	23	0
Estimated Fair Value	24,325	22,049
Unrealized OTTI Losses (Gains)		0
Total fixed maturity securities trading
Total fixed maturity securities	25,234	22,728
States, municipalities and political subdivisions
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	9,729	9,093
Gross Unrealized Gains	1,863	1,559
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0
Estimated Fair Value	11,592	10,652
Unrealized OTTI Losses (Gains)		0
Total fixed maturity securities trading
Total fixed maturity securities	11,592	10,652
Residential mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	3,442	4,387
Gross Unrealized Gains	146	133
Gross Unrealized Losses	1	1
Allowance for Credit Losses	0
Estimated Fair Value	3,587	4,519
Unrealized OTTI Losses (Gains)		(17)
Commercial mortgage-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	1,933	2,265
Gross Unrealized Gains	93	86
Gross Unrealized Losses	42	5
Allowance for Credit Losses	17
Estimated Fair Value	1,967	2,346
Unrealized OTTI Losses (Gains)		1
Other asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	2,179	1,925
Gross Unrealized Gains	81	41
Gross Unrealized Losses	9	4
Allowance for Credit Losses	0
Estimated Fair Value	2,251	1,962
Unrealized OTTI Losses (Gains)		(3)
Asset-backed
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	7,554	8,577
Gross Unrealized Gains	320	260
Gross Unrealized Losses	52	10
Allowance for Credit Losses	17	0
Estimated Fair Value	7,805	8,827
Unrealized OTTI Losses (Gains)		(19)
Total fixed maturity securities trading
Total fixed maturity securities	7,805	8,827
U.S. Treasury and obligations of government-sponsored enterprises
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	339	146
Gross Unrealized Gains	2	1
Gross Unrealized Losses	3	2
Allowance for Credit Losses	0
Estimated Fair Value	338	145
Unrealized OTTI Losses (Gains)		0
Foreign government
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	512	491
Gross Unrealized Gains	32	14
Gross Unrealized Losses	0	1
Allowance for Credit Losses	0
Estimated Fair Value	544	504
Unrealized OTTI Losses (Gains)		0
Redeemable preferred stock
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	0	10
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Allowance for Credit Losses	0
Estimated Fair Value	0	10
Unrealized OTTI Losses (Gains)		0
Fixed maturity securities
Fixed maturity securities available-for-sale:
Cost or Amortized Cost	38,926	38,106
Gross Unrealized Gains	5,795	4,126
Gross Unrealized Losses	77	45
Allowance for Credit Losses	40
Estimated Fair Value	44,604	42,187
Unrealized OTTI Losses (Gains)		(19)
Total fixed maturity securities trading
Total fixed maturity securities trading
Cost or amortized cost, trading securities	27	20
Estimated fair value, trading securities	$ 27	$ 20

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