Fair Value, Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis [Member] - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	$ (96)	$ (43)
Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	44,900	44,604
Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	25,058	25,207
States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,866	11,592
Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,976	7,805
Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	10	42
Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	44,910	44,646
Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,663	1,561
Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,698	4,577
Level 1 [Member] | Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	(94)	(14)
Level 1 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	158	355
Level 1 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	158	355
Level 1 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	158	355
Level 1 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	884	796
Level 1 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,661	4,538
Level 2 [Member] | Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	(2)	(29)
Level 2 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	43,392	43,125
Level 2 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	24,017	24,082
Level 2 [Member] | States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,809	11,546
Level 2 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,566	7,497
Level 2 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	10	34
Level 2 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	43,402	43,159
Level 2 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	743	722
Level 2 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	37	39
Level 3 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,350	1,124
Level 3 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	883	770
Level 3 [Member] | States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	57	46
Level 3 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	410	308
Level 3 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets		8
Level 3 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,350	1,132
Level 3 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	$ 36	$ 43