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, 2017	Dec. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	$ 407	$ 473
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in Net income (loss)	9	5
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	9	(4)
Purchases	126	296
Sales	(68)	(61)
Settlements	(102)	(157)
Transfers into Level 3	169	61
Transfers out of Level 3	(96)	(206)
Balance, Ending, Assets	454	407
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0	(5)
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	130	168
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in Net income (loss)	0	1
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	3	1
Purchases	18	163
Sales	(5)	(36)
Settlements	(54)	(103)
Transfers into Level 3	16	0
Transfers out of Level 3	(10)	(64)
Balance, Ending, Assets	98	130
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0	0
States, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	1	2
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in Net income (loss)	0	0
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	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	1	1
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0	0
Asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	199	209
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in Net income (loss)	2	0
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	3	(5)
Purchases	107	133
Sales	0	(25)
Settlements	(43)	(32)
Transfers into Level 3	153	61
Transfers out of Level 3	(86)	(142)
Balance, Ending, Assets	335	199
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	19	20
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in Net income (loss)	0	(1)
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	3	0
Purchases	1	0
Sales	(3)	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	20	19
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0	(2)
Derivative financial instruments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	0
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in Net income (loss)	1
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	0
Purchases	0
Sales	(1)
Settlements	0
Transfers into Level 3	0
Transfers out of Level 3	0
Balance, Ending, Assets	0	0
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	0
Life settlement contracts, included in Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, Beginning, Assets	58	74
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in Net income (loss)	6	5
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	0	0
Purchases	0	0
Sales	(59)	0
Settlements	(5)	(21)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, Ending, Assets	0	58
Unrealized gains (losses) on Level 3 assets and liabilities recognized in Net income (loss)	$ 0	$ (3)