Fair Value, Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis [Member] - USD ($) $ in Millions	Mar. 31, 2021		Dec. 31, 2020
Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	$ (73)	[1]	$ (43)
Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	43,545		44,604
Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	24,329		25,207
States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,600		11,592
Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,616		7,805
Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	39		42
Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	43,584		44,646
Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,580		1,561
Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,176	[1]	4,577
Level 1 [Member] | Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	(71)	[1]	(14)
Level 1 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	152		355
Level 1 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	152		355
Level 1 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	152		355
Level 1 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	824		796
Level 1 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,140	[1]	4,538
Level 2 [Member] | Payable to Brokers [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	(2)	[1]	(29)
Level 2 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	42,267		43,125
Level 2 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	23,410		24,082
Level 2 [Member] | States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,556		11,546
Level 2 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,301		7,497
Level 2 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	34		34
Level 2 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	42,301		43,159
Level 2 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	711		722
Level 2 [Member] | Short Term and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	36	[1]	39
Level 3 [Member] | Fixed Maturities Available-for-Sale [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,126		1,124
Level 3 [Member] | Corporate Bonds and Other [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	767		770
Level 3 [Member] | States, Municipalities and Political Subdivisions [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	44		46
Level 3 [Member] | Asset-Backed [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	315		308
Level 3 [Member] | Fixed Maturities Trading [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	5		8
Level 3 [Member] | Total Fixed Maturities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,131		1,132
Level 3 [Member] | Equity Securities [Member]
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	$ 45		$ 43

[1] As of March 31, 2021, Short term and other and Payable to brokers exclude amounts classified as held for sale. See Note 2 for further discussion.