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	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 651	$ 437
Reported in Other comprehensive income (loss)	60	41
Total realized and unrealized investment gains (losses)	56	39
Purchases	478	306
Sales	(12)	0
Settlements	(45)	(27)
Transfers into Level 3	40	45
Transfers out of Level 3	(17)	(149)
Balance, Ending, Assets	1,151	651
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 recognized in Net income (loss) in the period	(6)	(2)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 recognized in Other comprehensive income (loss) in the period	62	35
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	468	222
Reported in Other comprehensive income (loss)	43	33
Total realized and unrealized investment gains (losses)	44	33
Purchases	264	256
Sales	(3)	0
Settlements	(13)	(11)
Transfers into Level 3	10	0
Transfers out of Level 3	0	(32)
Balance, Ending, Assets	770	468
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 recognized in Net income (loss) in the period	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 recognized in Other comprehensive income (loss) in the period	43	28
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	0	0
Reported in Other comprehensive income (loss)	1	0
Total realized and unrealized investment gains (losses)	1	0
Purchases	45	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	46	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 recognized in Net income (loss) in the period	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 recognized in Other comprehensive income (loss) in the period	1	0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	165	197
Reported in Other comprehensive income (loss)	16	8
Total realized and unrealized investment gains (losses)	17	8
Purchases	154	48
Sales	(9)	0
Settlements	(32)	(16)
Transfers into Level 3	30	45
Transfers out of Level 3	(17)	(117)
Balance, Ending, Assets	308	165
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 recognized in Net income (loss) in the period	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 recognized in Other comprehensive income (loss) in the period	18	7
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	18	18
Reported in Other comprehensive income (loss)	0	0
Total realized and unrealized investment gains (losses)	(6)	(2)
Purchases	15	2
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	27	18
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 recognized in Net income (loss) in the period	(6)	(2)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2020 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)	(4)	(2)
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
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)	(1)	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)	(4)	(2)
Reported in Net investment income
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 | 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	2	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	$ (2)	$ 0