Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	$ 42,775	$ 42,207
Equity securities:
Equity securities	859	865
Short term and other	1,334	1,741
Total assets	44,968	44,813
Other liabilities	12	7
Total liabilities	12	7
Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	23,789	22,728
States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	11,127	10,652
Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	7,859	8,827
Common Stock
Equity securities:
Equity securities	154	142
Non-redeemable preferred stock
Equity securities:
Equity securities	705	723
Level 1
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	519	175
Equity securities:
Equity securities	212	189
Short term and other	1,313	397
Total assets	2,044	761
Other liabilities	0	0
Total liabilities	0	0
Level 1 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	519	175
Level 1 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	0	0
Level 1 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	0	0
Level 1 | Common Stock
Equity securities:
Equity securities	150	135
Level 1 | Non-redeemable preferred stock
Equity securities:
Equity securities	62	54
Level 2
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	41,479	41,399
Equity securities:
Equity securities	636	658
Short term and other	21	1,344
Total assets	42,136	43,401
Other liabilities	12	7
Total liabilities	12	7
Level 2 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	22,715	22,085
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	11,127	10,652
Level 2 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	7,637	8,662
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Non-redeemable preferred stock
Equity securities:
Equity securities	636	658
Level 3
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	777	633
Equity securities:
Equity securities	11	18
Short term and other	0	0
Total assets	788	651
Other liabilities	0	0
Total liabilities	0	0
Level 3 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	555	468
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	0	0
Level 3 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,392 and $38,126, less allowance for credit loss of $51 and $-)	222	165
Level 3 | Common Stock
Equity securities:
Equity securities	4	7
Level 3 | Non-redeemable preferred stock
Equity securities:
Equity securities	$ 7	$ 11