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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 708	$ 457	$ 651	$ 437
Reported in Other comprehensive income (loss)	77	16	32	27
Total realized and unrealized investment gains (losses)	73	16	25	29
Purchases	39	78	151	154
Sales	(9)	0	(9)	0
Settlements	(9)	(6)	(15)	(12)
Transfers into Level 3	0	40	0	45
Transfers out of Level 3	(14)	(32)	(15)	(100)
Balance, Ending, Assets	788	553	788	553
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2020 recognized in Net income (loss) in the period	(4)	0	(7)	3
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2020 recognized in Other comprehensive income (loss) in the period	76	15	34	25
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	496	253	468	222
Reported in Other comprehensive income (loss)	59	12	22	20
Total realized and unrealized investment gains (losses)	59	12	22	20
Purchases	4	76	71	132
Sales	0	0	0	0
Settlements	(4)	(2)	(6)	(4)
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	0	(1)	0	(32)
Balance, Ending, Assets	555	338	555	338
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 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 June 30, 2020 recognized in Other comprehensive income (loss) in the period	58	10		17
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	197	184	165	197
Reported in Other comprehensive income (loss)	18	4	10	7
Total realized and unrealized investment gains (losses)	18	4	10	7
Purchases	35	0	80	20
Sales	(9)	0	(9)	0
Settlements	(5)	(4)	(9)	(8)
Transfers into Level 3	0	40	0	45
Transfers out of Level 3	(14)	(31)	(15)	(68)
Balance, Ending, Assets	222	193	222	193
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 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 June 30, 2020 recognized in Other comprehensive income (loss) in the period	18	5	10	8
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	15	20	18	18
Reported in Other comprehensive income (loss)	0	0	0	0
Total realized and unrealized investment gains (losses)	(4)	0	(7)	2
Purchases	0	2	0	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	11	22	11	22
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2020 recognized in Net income (loss) in the period	(4)	0	(7)	3
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 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)	(4)	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) | 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)	(4)	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 | 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