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		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 1,375	$ 788	$ 1,151	$ 651
Reported in Other comprehensive income (loss)	2	14	(27)	45
Total realized and unrealized investment gains (losses)	2	14	(32)	38
Purchases	139	206	429	357
Sales	(20)	0	(27)	(9)
Settlements	(22)	(17)	(74)	(31)
Transfers into Level 3	52	8	92	8
Transfers out of Level 3	(90)	(2)	(103)	(17)
Balance, Ending, Assets	1,436	997	1,436	997
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	(3)	0	(1)	(7)
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	2	13	(27)	48
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	883	555	770	468
Reported in Other comprehensive income (loss)	1	5	(23)	27
Total realized and unrealized investment gains (losses)	2	5	(32)	27
Purchases	55	129	219	200
Sales	0	0	(3)	0
Settlements	(11)	(3)	(35)	(9)
Transfers into Level 3	0	8	10	8
Transfers out of Level 3	(52)	0	(52)	0
Balance, Ending, Assets	877	694	877	694
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	2	5	(22)	29
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	57	0	46	0
Reported in Other comprehensive income (loss)	0	0	0	0
Total realized and unrealized investment gains (losses)	0	0	0	0
Purchases	0	45	12	45
Sales	0	0	0	0
Settlements	0	0	(1)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, Ending, Assets	57	45	57	45
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	0	0	0	0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	410	222	308	165
Reported in Other comprehensive income (loss)	1	9	(4)	18
Total realized and unrealized investment gains (losses)	2	9	0	18
Purchases	83	20	197	100
Sales	(9)	0	(9)	(9)
Settlements	(11)	(14)	(38)	(22)
Transfers into Level 3	41	0	71	0
Transfers out of Level 3	(38)	(2)	(51)	(17)
Balance, Ending, Assets	478	235	478	235
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	0	8	(5)	19
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	25	11	27	18
Reported in Other comprehensive income (loss)	0	0	0	0
Total realized and unrealized investment gains (losses)	(2)	0	0	(7)
Purchases	1	12	1	12
Sales	(11)	0	(15)	0
Settlements	0	0	0	0
Transfers into Level 3	11	0	11	0
Transfers out of Level 3	0	0	0	0
Balance, Ending, Assets	24	23	24	23
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	(3)	0	(1)	(7)
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	0	0	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)	(2)	0	(11)	(4)
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	0	(9)	0
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	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)	0	0	0	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)	(3)	0	(2)	(4)
Reported in Net investment income
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment income	2	0	6	(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	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	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	0	4	0
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	$ 1	$ 0	$ 2	$ (3)