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, 2022	Mar. 31, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 1,578	$ 1,151
Reported in Other comprehensive income (loss)	(108)	(51)
Total realized and unrealized investment gains (losses)	(103)	(60)
Purchases	219	72
Sales	(5)	0
Settlements	(39)	(19)
Transfers into Level 3	15	19
Transfers out of Level 3	(51)	(8)
Balance, Ending, Assets	1,614	1,155
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	3	2
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	(108)	(51)
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	937	770
Reported in Other comprehensive income (loss)	(71)	(40)
Total realized and unrealized investment gains (losses)	(72)	(53)
Purchases	67	42
Sales	(5)	0
Settlements	(22)	(2)
Transfers into Level 3	10	10
Transfers out of Level 3	0	0
Balance, Ending, Assets	915	767
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	(72)	(40)
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	56	46
Reported in Other comprehensive income (loss)	(5)	(2)
Total realized and unrealized investment gains (losses)	(5)	(2)
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	51	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	(5)	(2)
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	556	308
Reported in Other comprehensive income (loss)	(32)	(9)
Total realized and unrealized investment gains (losses)	(29)	(7)
Purchases	140	30
Sales	0	0
Settlements	(17)	(17)
Transfers into Level 3	5	9
Transfers out of Level 3	(51)	(8)
Balance, Ending, Assets	604	315
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	(31)	(9)
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	29	27
Reported in Other comprehensive income (loss)	0	0
Total realized and unrealized investment gains (losses)	3	2
Purchases	12	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	44	29
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	3	2
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	0	0
Reported in Net investment gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment gains (losses)	0	(12)
Reported in Net investment gains (losses) | Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment gains (losses)	(1)	(13)
Reported in Net investment gains (losses) | States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment gains (losses)	0	0
Reported in Net investment gains (losses) | Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment gains (losses)	2	0
Reported in Net investment gains (losses) | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment gains (losses)	(1)	1
Reported in Net investment income
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment income	5	3
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	1	2
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	$ 4	$ 1