Fair Value, Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis [Member] - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	$ (43)	$ (28)
Fixed Maturities Available-for-sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	44,604	42,187
Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	25,207	22,708
States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,592	10,652
Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,805	8,827
Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	42	53
Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	44,646	42,240
Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,561	1,306
Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,577	4,521
Receivables [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets		2
Level 1 [Member] | Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	(14)	(18)
Level 1 [Member] | Fixed Maturities Available-for-sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	355	175
Level 1 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	355	175
Level 1 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	355	175
Level 1 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	796	629
Level 1 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,538	3,138
Level 2 [Member] | Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	(29)	(10)
Level 2 [Member] | Fixed Maturities Available-for-sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	43,125	41,379
Level 2 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	24,082	22,065
Level 2 [Member] | States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,546	10,652
Level 2 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,497	8,662
Level 2 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	34	49
Level 2 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	43,159	41,428
Level 2 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	722	658
Level 2 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	39	1,383
Level 2 [Member] | Receivables [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets		2
Level 3 [Member] | Fixed Maturities Available-for-sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,124	633
Level 3 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	770	468
Level 3 [Member] | States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	46
Level 3 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	308	165
Level 3 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	8	4
Level 3 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,132	637
Level 3 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	$ 43	$ 19