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, 2019	Dec. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 437	$ 454
Reported in Other comprehensive income (loss)	41	(12)
Total realized and unrealized investment gains (losses)	39	(10)
Purchases	306	279
Sales	0	(77)
Settlements	(27)	(74)
Transfers into Level 3	45	77
Transfers out of Level 3	(149)	(212)
Balance, Ending, Assets	651	437
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 recognized in Net income (loss) in the period	(2)	(4)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 recognized in Other comprehensive income (loss) in the period	35	(9)
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	222	98
Reported in Other comprehensive income (loss)	33	(4)
Total realized and unrealized investment gains (losses)	33	(5)
Purchases	256	117
Sales	0	(5)
Settlements	(11)	(9)
Transfers into Level 3	0	35
Transfers out of Level 3	(32)	(9)
Balance, Ending, Assets	468	222
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 recognized in Net income (loss) in the period	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 recognized in Other comprehensive income (loss) in the period	28	(5)
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	0	1
Reported in Other comprehensive income (loss)	0	0
Total realized and unrealized investment gains (losses)	0	0
Purchases	0	0
Sales	0	0
Settlements	0	(1)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 recognized in Net income (loss) in the period	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 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	197	335
Reported in Other comprehensive income (loss)	8	(8)
Total realized and unrealized investment gains (losses)	8	(3)
Purchases	48	162
Sales	0	(72)
Settlements	(16)	(64)
Transfers into Level 3	45	42
Transfers out of Level 3	(117)	(203)
Balance, Ending, Assets	165	197
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 recognized in Net income (loss) in the period	0	(2)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 recognized in Other comprehensive income (loss) in the period	7	(4)
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	18	20
Reported in Other comprehensive income (loss)	0	0
Total realized and unrealized investment gains (losses)	(2)	(2)
Purchases	2	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	18	18
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 recognized in Net income (loss) in the period	(2)	(2)
Unrealized gains (losses) on Level 3 assets and liabilities held as of December 31, 2019 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)	(2)	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	(1)
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	5
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)	(2)	(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	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