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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 457	$ 398	$ 437	$ 454
Reported in Other comprehensive income (loss)	16	(2)	27	(7)
Total realized and unrealized investment gains (losses)	16	(3)	29	(4)
Purchases	78	43	154	73
Sales	0	(5)	0	(77)
Settlements	(6)	(8)	(12)	(16)
Transfers into Level 3	40	13	45	18
Transfers out of Level 3	(32)	(53)	(100)	(63)
Balance, Ending, Assets	553	385	553	385
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Net income (loss)	0	(1)	3	(3)
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Other comprehensive income (loss)	15		25
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	253	100	222	98
Reported in Other comprehensive income (loss)	12	(1)	20	(1)
Total realized and unrealized investment gains (losses)	12	(1)	20	(2)
Purchases	76	2	132	2
Sales	0	(5)	0	(5)
Settlements	(2)	(2)	(4)	(4)
Transfers into Level 3	0	0	0	5
Transfers out of Level 3	(1)	0	(32)	0
Balance, Ending, Assets	338	94	338	94
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Net income (loss)	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Other comprehensive income (loss)	10		17
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	0	1	0	1
Reported in Other comprehensive income (loss)	0	0	0	0
Total realized and unrealized investment gains (losses)	0	0	0	0
Purchases	0	0	0	0
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	0	1	0	1
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Net income (loss)	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Other comprehensive income (loss)	0		0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	184	279	197	335
Reported in Other comprehensive income (loss)	4	(1)	7	(6)
Total realized and unrealized investment gains (losses)	4	(1)	7	1
Purchases	0	41	20	71
Sales	0	0	0	(72)
Settlements	(4)	(6)	(8)	(12)
Transfers into Level 3	40	13	45	13
Transfers out of Level 3	(31)	(53)	(68)	(63)
Balance, Ending, Assets	193	273	193	273
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Net income (loss)	0	0	0	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Other comprehensive income (loss)	5		8
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	20	18	18	20
Reported in Other comprehensive income (loss)	0	0	0	0
Total realized and unrealized investment gains (losses)	0	(1)	2	(3)
Purchases	2	0	2	0
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	22	17	22	17
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Net income (loss)	0	(1)	3	(3)
Unrealized gains (losses) on Level 3 assets and liabilities held as of June 30, 2019 recognized in Other comprehensive income (loss)	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	(1)	2	3
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	(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	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	7
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	$ (1)	$ 2	$ (3)