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		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 1,155	$ 708	$ 1,151	$ 651
Reported in Other comprehensive income (loss)	22	77	(29)	32
Total realized and unrealized investment gains (losses)	26	73	(34)	25
Purchases	218	39	290	151
Sales	(7)	(9)	(7)	(9)
Settlements	(33)	(9)	(52)	(15)
Transfers into Level 3	21	0	40	0
Transfers out of Level 3	(5)	(14)	(13)	(15)
Balance, Ending, Assets	1,375	788	1,375	788
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	0	(4)	2	(7)
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Other comprehensive income (loss) in the period	22	76	(29)	34
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	767	496	770	468
Reported in Other comprehensive income (loss)	16	59	(24)	22
Total realized and unrealized investment gains (losses)	19	59	(34)	22
Purchases	122	4	164	71
Sales	(3)	0	(3)	0
Settlements	(22)	(4)	(24)	(6)
Transfers into Level 3	0	0	10	0
Transfers out of Level 3	0	0	0	0
Balance, Ending, Assets	883	555	883	555
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	16	58	(24)	24
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	44	0	46	0
Reported in Other comprehensive income (loss)	2	0	0	0
Total realized and unrealized investment gains (losses)	2	0	0	0
Purchases	12	0	12	0
Sales	0	0	0	0
Settlements	(1)	0	(1)	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, Ending, Assets	57	0	57	0
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	0	0	0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	315	197	308	165
Reported in Other comprehensive income (loss)	4	18	(5)	10
Total realized and unrealized investment gains (losses)	5	18	(2)	10
Purchases	84	35	114	80
Sales	0	(9)	0	(9)
Settlements	(10)	(5)	(27)	(9)
Transfers into Level 3	21	0	30	0
Transfers out of Level 3	(5)	(14)	(13)	(15)
Balance, Ending, Assets	410	222	410	222
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	4	18	(5)	10
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	29	15	27	18
Reported in Other comprehensive income (loss)	0	0	0	0
Total realized and unrealized investment gains (losses)	0	(4)	2	(7)
Purchases	0	0	0	0
Sales	(4)	0	(4)	0
Settlements	0	0	0	0
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	0	0	0
Balance, Ending, Assets	25	11	25	11
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss) in the period	0	(4)	2	(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)	3	(4)	(9)	(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)	3	0	(10)	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)	0	(4)	1	(4)
Reported in Net investment income
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Net investment income	1	0	4	(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	3	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	$ 0	$ 0	$ 1	$ (3)