Fair Value (Table of reconciliation for assets and liabilities measured at fair value on a recurring basis using significant unobservable inputs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 2,014	$ 1,676
Reported in Net investment gains (losses)	$ (4)	$ 0
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net investment losses	Net investment losses
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other comprehensive income	Other comprehensive income
Reported in Other comprehensive income (loss)	$ (18)	$ 32
Total realized and unrealized investment gains (losses)	(10)	31
Purchases	92	136
Sales	(28)	0
Settlements	(53)	(12)
Transfers into Level 3	11	23
Transfers out of Level 3	(19)	(10)
Balance, Ending, Assets	2,007	1,844
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	1	(6)
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	(20)	32
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	1,045	810
Reported in Net investment gains (losses)	0	0
Reported in Other comprehensive income (loss)	(12)	24
Total realized and unrealized investment gains (losses)	(12)	24
Purchases	74	81
Sales	0	0
Settlements	(36)	(3)
Transfers into Level 3	11	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	1,082	912
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	0	0
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	(14)	24
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	44	43
Reported in Net investment gains (losses)	0	0
Reported in Other comprehensive income (loss)	(1)	1
Total realized and unrealized investment gains (losses)	(1)	1
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	43	44
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	0	0
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	(1)	1
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	901	788
Reported in Net investment gains (losses)	(4)	0
Reported in Other comprehensive income (loss)	(5)	7
Total realized and unrealized investment gains (losses)	(3)	12
Purchases	18	55
Sales	(9)	0
Settlements	(17)	(9)
Transfers into Level 3	0	23
Transfers out of Level 3	(19)	(10)
Balance, Ending, Assets	871	859
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	0	0
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	(5)	7
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	24	35
Reported in Net investment gains (losses)	0	0
Reported in Other comprehensive income (loss)	0	0
Total realized and unrealized investment gains (losses)	6	(6)
Purchases	0	0
Sales	(19)	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	11	29
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	1	(6)
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	0	0
Reported in Net investment income
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment income	12	(1)
Reported in Net investment income | Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment income	0	0
Reported in Net investment income | States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment income	0	0
Reported in Net investment income | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment income	6	5
Reported in Net investment income | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment income	$ 6	$ (6)