Fair Value (Assets and liabilities measured at fair value on a recurring basis) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	$ 40,098	$ 42,207
Equity securities:
Equity securities	799	865
Short term and other	500	1,741
Total assets	41,397	44,813
Other liabilities	1	7
Total liabilities	1	7
Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	21,376	22,728
States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	10,491	10,652
Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	8,231	8,827
Common Stock
Equity securities:
Equity securities	191	142
Non-redeemable preferred stock
Equity securities:
Equity securities	608	723
Level 1
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	175	175
Equity securities:
Equity securities	246	189
Short term and other	135	397
Total assets	556	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 $38,034 and $38,126, less allowance for credit loss of $49 and $-)	175	175
Level 1 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	0	0
Level 1 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	0	0
Level 1 | Common Stock
Equity securities:
Equity securities	187	135
Level 1 | Non-redeemable preferred stock
Equity securities:
Equity securities	59	54
Level 2
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	39,230	41,399
Equity securities:
Equity securities	538	658
Short term and other	365	1,344
Total assets	40,133	43,401
Other liabilities	1	7
Total liabilities	1	7
Level 2 | Corporate and other bonds
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	20,705	22,085
Level 2 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	10,491	10,652
Level 2 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	8,034	8,662
Level 2 | Common Stock
Equity securities:
Equity securities	0	0
Level 2 | Non-redeemable preferred stock
Equity securities:
Equity securities	538	658
Level 3
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	693	633
Equity securities:
Equity securities	15	18
Short term and other	0	0
Total assets	708	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 $38,034 and $38,126, less allowance for credit loss of $49 and $-)	496	468
Level 3 | States, municipalities and political subdivisions
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	0	0
Level 3 | Asset-backed
Fixed maturity securities:
Fixed maturity securities at fair value (amortized cost of $38,034 and $38,126, less allowance for credit loss of $49 and $-)	197	165
Level 3 | Common Stock
Equity securities:
Equity securities	4	7
Level 3 | Non-redeemable preferred stock
Equity securities:
Equity securities	$ 11	$ 11