Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Fixed maturity securities:
Debt Securities	$ 44,631	$ 42,207
Equity securities:
Equity securities	992	865
Short term and other	1,789	1,741
Total assets	47,412	44,813
Other liabilities	19	7
Total liabilities	19	7
Corporate and other bonds
Fixed maturity securities:
Debt Securities	25,234	22,728
States, municipalities and political subdivisions
Fixed maturity securities:
Debt Securities	11,592	10,652
Asset-backed
Fixed maturity securities:
Debt Securities	7,805	8,827
Common Stock
Equity securities:
Equity securities	195	142
Non-redeemable preferred stock
Equity securities:
Equity securities	797	723
Level 1
Fixed maturity securities:
Debt Securities	355	175
Equity securities:
Equity securities	243	189
Short term and other	1,761	397
Total assets	2,359	761
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Debt Securities	355	175
Level 1 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt Securities	0	0
Level 1 | Asset-backed
Fixed maturity securities:
Debt Securities	0	0
Level 1 | Common Stock
Equity securities:
Equity securities	175	135
Level 1 | Non-redeemable preferred stock
Equity securities:
Equity securities	68	54
Level 2
Fixed maturity securities:
Debt Securities	43,152	41,399
Equity securities:
Equity securities	722	658
Short term and other	28	1,344
Total assets	43,902	43,401
Other liabilities	19	7
Total liabilities	19	7
Level 2 | Corporate and other bonds
Fixed maturity securities:
Debt Securities	24,109	22,085
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt Securities	11,546	10,652
Level 2 | Asset-backed
Fixed maturity securities:
Debt Securities	7,497	8,662
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Non-redeemable preferred stock
Equity securities:
Equity securities	722	658
Level 3
Fixed maturity securities:
Debt Securities	1,124	633
Equity securities:
Equity securities	27	18
Short term and other	0	0
Total assets	1,151	651
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Debt Securities	770	468
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Debt Securities	46	0
Level 3 | Asset-backed
Fixed maturity securities:
Debt Securities	308	165
Level 3 | Common Stock
Equity securities:
Equity securities	20	7
Level 3 | Non-redeemable preferred stock
Equity securities:
Equity securities	$ 7	$ 11