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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 788	$ 553	$ 651	$ 437
Reported in Other comprehensive income (loss)	14	15	45	42
Total realized and unrealized investment gains (losses)	14	15	38	44
Purchases	206	101	357	255
Sales	0	0	(9)	0
Settlements	(17)	(7)	(31)	(19)
Transfers into Level 3	8	0	8	45
Transfers out of Level 3	(2)	(16)	(17)	(116)
Balance, Ending, Assets	997	646	997	646
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 recognized in Net income (loss) in the period	0	0	(7)	2
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 recognized in Other comprehensive income (loss) in the period	13	16	48	38
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	555	338	468	222
Reported in Other comprehensive income (loss)	5	14	27	34
Total realized and unrealized investment gains (losses)	5	14	27	34
Purchases	129	79	200	211
Sales	0	0	0	0
Settlements	(3)	(3)	(9)	(7)
Transfers into Level 3	8	0	8	0
Transfers out of Level 3	0	0	0	(32)
Balance, Ending, Assets	694	428	694	428
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 recognized in Net income (loss) in the period	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 recognized in Other comprehensive income (loss) in the period	5	14	29	29
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)	0		0
Total realized and unrealized investment gains (losses)	0		0
Purchases	45		45
Sales	0		0
Settlements	0		0
Transfers into Level 3	0		0
Transfers out of Level 3	0		0
Balance, Ending, Assets	45		45
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 recognized in Net income (loss) in the period	0		0
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 recognized in Other comprehensive income (loss) in the period	0		0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	222	193	165	197
Reported in Other comprehensive income (loss)	9	1	18	8
Total realized and unrealized investment gains (losses)	9	1	18	8
Purchases	20	22	100	42
Sales	0	0	(9)	0
Settlements	(14)	(4)	(22)	(12)
Transfers into Level 3	0	0	0	45
Transfers out of Level 3	(2)	(16)	(17)	(84)
Balance, Ending, Assets	235	196	235	196
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 recognized in Net income (loss) in the period	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 recognized in Other comprehensive income (loss) in the period	8	2	19	9
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	11	22	18	18
Reported in Other comprehensive income (loss)	0	0	0	0
Total realized and unrealized investment gains (losses)	0	0	(7)	2
Purchases	12	0	12	2
Sales	0	0	0	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	23	22	23	22
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 recognized in Net income (loss) in the period	0	0	(7)	2
Unrealized gains (losses) on Level 3 assets and liabilities held as of September 30, 2020 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)	0	0	(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)	0	0	0	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)	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	0	(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	(3)	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	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	0	0	0	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	$ (3)	$ 0