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
	Mar. 31, 2019	Mar. 31, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 437	$ 454
Total realized and unrealized investment gains (losses)	11	(5)
Total realized and unrealized investment gains (losses)	13	(1)
Purchases	76	30
Sales	0	(72)
Settlements	(6)	(8)
Transfers into Level 3	5	5
Transfers out of Level 3	(68)	(10)
Balance, Ending, Assets	457	398
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Net income (loss)	2	(2)
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Other comprehensive income (loss)	10
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	222	98
Total realized and unrealized investment gains (losses)	8	0
Total realized and unrealized investment gains (losses)	8	(1)
Purchases	56	0
Sales	0	0
Settlements	(2)	(2)
Transfers into Level 3	0	5
Transfers out of Level 3	(31)	0
Balance, Ending, Assets	253	100
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Net income (loss)	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Other comprehensive income (loss)	7
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	0	1
Total realized and unrealized investment gains (losses)	0	0
Total realized and unrealized investment gains (losses)	0	0
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	0	1
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Net income (loss)	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Other comprehensive income (loss)	0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	197	335
Total realized and unrealized investment gains (losses)	3	(5)
Total realized and unrealized investment gains (losses)	3	2
Purchases	20	30
Sales	0	(72)
Settlements	(4)	(6)
Transfers into Level 3	5	0
Transfers out of Level 3	(37)	(10)
Balance, Ending, Assets	184	279
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Net income (loss)	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Other comprehensive income (loss)	3
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	18	20
Total realized and unrealized investment gains (losses)	0	0
Total realized and unrealized investment gains (losses)	2	(2)
Purchases	0	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	20	18
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Net income (loss)	2	(2)
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2019 recognized in Other comprehensive income (loss)	0
Reported in Net investment gains (losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)	2	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 Other comprehensive income (loss)	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 Other comprehensive income (loss)	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 Other comprehensive income (loss)	0	7
Reported in Net investment gains (losses) | Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Reported in Other comprehensive income (loss)	$ 2	$ (2)