Fair Value, Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis [Member] - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Assets and Liabilities Measured at Fair Value [Abstract]
Payable to brokers	$ (119)	$ (43)
Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	45,060	44,604
Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	25,209	25,207
States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	11,979	11,592
Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	7,872	7,805
Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	9	42
Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	45,069	44,646
Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	1,660	1,561
Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	4,063	4,577
Level 1 [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Payable to brokers	(118)	(14)
Level 1 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	146	355
Level 1 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	146	355
Level 1 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	146	355
Level 1 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	890	796
Level 1 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	4,063	4,538
Level 2 [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Payable to brokers	(1)	(29)
Level 2 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	43,502	43,125
Level 2 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	24,186	24,082
Level 2 [Member] | States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	11,922	11,546
Level 2 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	7,394	7,497
Level 2 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	9	34
Level 2 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	43,511	43,159
Level 2 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	745	722
Level 2 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments		39
Level 3 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	1,412	1,124
Level 3 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	877	770
Level 3 [Member] | States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	57	46
Level 3 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	478	308
Level 3 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments		8
Level 3 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	1,412	1,132
Level 3 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Investments	$ 25	$ 43