Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	$ 43,901	$ 42,207
Equity securities:
Equity securities	919	865
Short term and other	1,326	1,741
Total assets	46,146	44,813
Other liabilities	16	7
Total liabilities	16	7
Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	24,525	22,728
States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	11,224	10,652
Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	8,152	8,827
Common Stock
Equity securities:
Equity securities	173	142
Non-redeemable preferred stock
Equity securities:
Equity securities	746	723
Level 1
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	372	175
Equity securities:
Equity securities	222	189
Short term and other	1,301	397
Total assets	1,895	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 $38,969 and $38,126, less allowance for credit loss of $47 and $-)	372	175
Level 1 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	0	0
Level 1 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	0	0
Level 1 | Common Stock
Equity securities:
Equity securities	157	135
Level 1 | Non-redeemable preferred stock
Equity securities:
Equity securities	65	54
Level 2
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	42,555	41,399
Equity securities:
Equity securities	674	658
Short term and other	25	1,344
Total assets	43,254	43,401
Other liabilities	16	7
Total liabilities	16	7
Level 2 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	23,459	22,085
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	11,179	10,652
Level 2 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	7,917	8,662
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Non-redeemable preferred stock
Equity securities:
Equity securities	674	658
Level 3
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	974	633
Equity securities:
Equity securities	23	18
Short term and other	0	0
Total assets	997	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 $38,969 and $38,126, less allowance for credit loss of $47 and $-)	694	468
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	45	0
Level 3 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,969 and $38,126, less allowance for credit loss of $47 and $-)	235	165
Level 3 | Common Stock
Equity securities:
Equity securities	16	7
Level 3 | Non-redeemable preferred stock
Equity securities:
Equity securities	$ 7	$ 11