Fair Value - 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, 2017	Mar. 31, 2016
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	$ 407	$ 473
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in net income (loss)	7	4
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	4	3
Purchases	44	62
Sales	(17)	(16)
Settlements	(25)	(14)
Transfers into Level 3	28	2
Transfers out of Level 3	(5)	(23)
Balance, end of year	443	491
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 recognized in Net income (loss)	0	1
Corporate and other bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	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)	1	4
Purchases	5	53
Sales	(1)	(16)
Settlements	(14)	(3)
Transfers into Level 3	0	0
Transfers out of Level 3	0	(12)
Balance, end of year	121	193
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 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 of year	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	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, end of year	1	2
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 recognized in Net income (loss)	0	0
Residential mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	129	134
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in net income (loss)	1	1
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	2	0
Purchases	0	0
Sales	0	0
Settlements	(6)	(5)
Transfers into Level 3	0	0
Transfers out of Level 3	0	(2)
Balance, end of year	126	128
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 recognized in Net income (loss)	0	0
Commercial mortgage-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	13	22
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	9
Sales	0	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	(4)
Balance, end of year	13	27
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 recognized in Net income (loss)	0	0
Other asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	57	53
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in net income (loss)	(1)	0
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	0	0
Purchases	38	0
Sales	0	0
Settlements	0	0
Transfers into Level 3	28	2
Transfers out of Level 3	(5)	(5)
Balance, end of year	117	50
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 recognized in Net income (loss)	0	0
Total asset-backed
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	199	209
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)	2	0
Purchases	38	9
Sales	0	0
Settlements	(6)	(5)
Transfers into Level 3	28	2
Transfers out of Level 3	(5)	(11)
Balance, end of year	256	205
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 recognized in Net income (loss)	0	0
Fixed maturity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	330	379
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)	3	4
Purchases	43	62
Sales	(1)	(16)
Settlements	(20)	(8)
Transfers into Level 3	28	2
Transfers out of Level 3	(5)	(23)
Balance, end of year	378	400
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 recognized in Net income (loss)	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	19	20
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)	1	(1)
Purchases	1	0
Sales	(2)	0
Settlements	0	0
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, end of year	19	19
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 recognized in Net income (loss)	0	0
Derivatives
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of year	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, end of year	0
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 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 of year	58	74
Net realized investment gains (losses) and net change in unrealized appreciation (depreciation) included in net income (loss)	6	4
Net change in unrealized appreciation (depreciation) included in Other comprehensive income (loss)	0	0
Purchases	0	0
Sales	(13)	0
Settlements	(5)	(6)
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Balance, end of year	46	72
Unrealized gains (losses) on Level 3 assets and liabilities held as of March 31, 2017 recognized in Net income (loss)	$ 0	$ 1