Fair Value, Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Jan. 01, 2021	Jan. 01, 2020
Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 937	$ 770	$ 770	$ 468
Included in Net Income	(10)	1
Included in OCI	(32)	43
Purchases	312	264
Sales	(3)	(3)
Settlements	(68)	(13)
Transfers into Level 3	20	10
Transfers out of Level 3	(52)
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at December 31
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss)on Level 3 Assets and Liabilities Held at December 31	(32)	43
States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	56	46	46
Included in Net Income
Included in OCI	(1)	1
Purchases	12	45
Sales
Settlements	(1)
Transfers into Level 3
Transfers out of Level 3
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at December 31
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss)on Level 3 Assets and Liabilities Held at December 31	(1)	1
Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	556	308	308	165
Included in Net Income	7	1
Included in OCI	(10)	16
Purchases	287	154
Sales	(9)	(9)
Settlements	(61)	(32)
Transfers into Level 3	109	30
Transfers out of Level 3	(75)	(17)
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at December 31
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss)on Level 3 Assets and Liabilities Held at December 31	(11)	18
Fixed maturities available-for-sale
Assets and Liabilities Measured at Fair Value [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	1,549	1,124	1,124	633
Included in Net Income	(3)	2
Included in OCI	(43)	60
Purchases	611	463
Sales	(12)	(12)
Settlements	(130)	(45)
Transfers into Level 3	129	40
Transfers out of Level 3	(127)	(17)
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at December 31	0	0
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss)on Level 3 Assets and Liabilities Held at December 31	(44)	62
Fixed maturities trading
Assets and Liabilities Measured at Fair Value [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0	8	8	4
Included in Net Income	(6)	4
Included in OCI
Purchases
Sales
Settlements	(2)
Transfers into Level 3
Transfers out of Level 3
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at December 31		4
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss)on Level 3 Assets and Liabilities Held at December 31
Total fixed maturities
Assets and Liabilities Measured at Fair Value [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	1,549	1,132	1,132	637
Included in Net Income	(9)	6
Included in OCI	(43)	60
Purchases	611	463
Sales	(12)	(12)
Settlements	(132)	(45)
Transfers into Level 3	129	40
Transfers out of Level 3	(127)	(17)
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at December 31	0	4
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss)on Level 3 Assets and Liabilities Held at December 31	(44)	62
Equity securities
Assets and Liabilities Measured at Fair Value [Abstract]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	29	43	$ 43	$ 19
Included in Net Income	(15)	(6)
Included in OCI
Purchases	11	15
Sales	(21)
Settlements
Transfers into Level 3	21	15
Transfers out of Level 3	(10)
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at December 31	(2)	(6)
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss)on Level 3 Assets and Liabilities Held at December 31
Fair Value, Recurring | Payable to brokers
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	(70)	(43)
Fair Value, Recurring | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	24,845	25,207
Fair Value, Recurring | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,943	11,592
Fair Value, Recurring | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,585	7,805
Fair Value, Recurring | Fixed maturities available-for-sale
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	44,373	44,604
Fair Value, Recurring | Fixed maturities trading
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7	42
Fair Value, Recurring | Total fixed maturities
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	44,380	44,646
Fair Value, Recurring | Equity securities
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,674	1,561
Fair Value, Recurring | Short term investments and other
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,770	4,577
Fair Value, Recurring | Level 1 | Payable to brokers
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities	(70)	(14)
Fair Value, Recurring | Level 1 | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	140	355
Fair Value, Recurring | Level 1 | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Assets
Fair Value, Recurring | Level 1 | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Assets
Fair Value, Recurring | Level 1 | Fixed maturities available-for-sale
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	140	355
Fair Value, Recurring | Level 1 | Fixed maturities trading
Assets and Liabilities Measured at Fair Value [Abstract]
Assets
Fair Value, Recurring | Level 1 | Total fixed maturities
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	140	355
Fair Value, Recurring | Level 1 | Equity securities
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	924	796
Fair Value, Recurring | Level 1 | Short term investments and other
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	4,696	4,538
Fair Value, Recurring | Level 2 | Payable to brokers
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities		(29)
Fair Value, Recurring | Level 2 | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	23,768	24,082
Fair Value, Recurring | Level 2 | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	11,887	11,546
Fair Value, Recurring | Level 2 | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7,029	7,497
Fair Value, Recurring | Level 2 | Fixed maturities available-for-sale
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	42,684	43,125
Fair Value, Recurring | Level 2 | Fixed maturities trading
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	7	34
Fair Value, Recurring | Level 2 | Total fixed maturities
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	42,691	43,159
Fair Value, Recurring | Level 2 | Equity securities
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	721	722
Fair Value, Recurring | Level 2 | Short term investments and other
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	74	39
Fair Value, Recurring | Level 3 | Payable to brokers
Assets and Liabilities Measured at Fair Value [Abstract]
Liabilities
Fair Value, Recurring | Level 3 | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	937	770
Fair Value, Recurring | Level 3 | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	56	46
Fair Value, Recurring | Level 3 | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	556	308
Fair Value, Recurring | Level 3 | Fixed maturities available-for-sale
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,549	1,124
Fair Value, Recurring | Level 3 | Fixed maturities trading
Assets and Liabilities Measured at Fair Value [Abstract]
Assets		8
Fair Value, Recurring | Level 3 | Total fixed maturities
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	1,549	1,132
Fair Value, Recurring | Level 3 | Equity securities
Assets and Liabilities Measured at Fair Value [Abstract]
Assets	29	43
Fair Value, Recurring | Level 3 | Short term investments and other
Assets and Liabilities Measured at Fair Value [Abstract]
Assets