Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Fixed maturity securities:
Total fixed maturity securities	$ 43,579	$ 44,631
Equity securities:
Equity securities	984	992
Short term and other	1,203	1,789
Total assets	45,766	47,412
Other liabilities	2	19
Total liabilities	2	19
Corporate and other bonds
Fixed maturity securities:
Total fixed maturity securities	24,363	25,234
States, municipalities and political subdivisions
Fixed maturity securities:
Total fixed maturity securities	11,600	11,592
Asset-backed
Fixed maturity securities:
Total fixed maturity securities	7,616	7,805
Common Stock
Equity securities:
Equity securities	198	195
Non-redeemable preferred stock
Equity securities:
Equity securities	786	797
Level 1
Fixed maturity securities:
Total fixed maturity securities	152	355
Equity securities:
Equity securities	244	243
Short term and other	1,178	1,761
Total assets	1,574	2,359
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Total fixed maturity securities	152	355
Level 1 | States, municipalities and political subdivisions
Fixed maturity securities:
Total fixed maturity securities	0	0
Level 1 | Asset-backed
Fixed maturity securities:
Total fixed maturity securities	0	0
Level 1 | Common Stock
Equity securities:
Equity securities	177	175
Level 1 | Non-redeemable preferred stock
Equity securities:
Equity securities	67	68
Level 2
Fixed maturity securities:
Total fixed maturity securities	42,301	43,152
Equity securities:
Equity securities	711	722
Short term and other	25	28
Total assets	43,037	43,902
Other liabilities	2	19
Total liabilities	2	19
Level 2 | Corporate and other bonds
Fixed maturity securities:
Total fixed maturity securities	23,444	24,109
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Total fixed maturity securities	11,556	11,546
Level 2 | Asset-backed
Fixed maturity securities:
Total fixed maturity securities	7,301	7,497
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Non-redeemable preferred stock
Equity securities:
Equity securities	711	722
Level 3
Fixed maturity securities:
Total fixed maturity securities	1,126	1,124
Equity securities:
Equity securities	29	27
Short term and other	0	0
Total assets	1,155	1,151
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Total fixed maturity securities	767	770
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Total fixed maturity securities	44	46
Level 3 | Asset-backed
Fixed maturity securities:
Total fixed maturity securities	315	308
Level 3 | Common Stock
Equity securities:
Equity securities	21	20
Level 3 | Non-redeemable preferred stock
Equity securities:
Equity securities	$ 8	$ 7