Fair Value, Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis [Member] - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	$ (79)	$ (28)
Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	42,770	42,187
Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	23,784	22,708
States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,127	10,652
Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,859	8,827
Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	29	53
Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	42,799	42,240
Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,305	1,306
Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,409	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	(46)	(18)
Level 1 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	519	175
Level 1 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	519	175
Level 1 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	519	175
Level 1 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	642	629
Level 1 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,349	3,138
Level 2 [Member] | Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	(33)	(10)
Level 2 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	41,474	41,379
Level 2 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	22,710	22,065
Level 2 [Member] | States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,127	10,652
Level 2 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,637	8,662
Level 2 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	25	49
Level 2 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	41,499	41,428
Level 2 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	636	658
Level 2 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	60	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	777	633
Level 3 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	555	468
Level 3 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	222	165
Level 3 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4	4
Level 3 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	781	637
Level 3 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	$ 27	$ 19