Variable Interest Entities - Narrative (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($) Entity	Sep. 30, 2017 USD ($) Entity	Sep. 30, 2018 USD ($) Entity	Sep. 30, 2017 USD ($) Entity	Dec. 31, 2017 USD ($) Entity	Dec. 31, 2016 Entity
Variable Interest Entity [Line Items]
Net fair value gains and losses on FG VIEs are expected to reverse to zero at maturity of the VIE debt	$ 0		$ 0
Reclassification adjustment for gains (losses) included in net income (loss), net of tax					$ 32,000,000
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Fair value gains (losses) on FG VIEs	5,000,000	$ 3,000,000	11,000,000	$ 25,000,000
Variable Interest Entity, Other Consolidated [Abstract]
Other consolidated VIE assets	85,000,000		85,000,000		86,000,000
Other consolidated VIE liabilities	22,000,000		22,000,000		$ 41,000,000
Variable Interest Entity, Primary Beneficiary [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Fair value gains (losses) on FG VIEs	$ 5,000,000	$ 3,000,000	$ 11,000,000	$ 25,000,000
Variable Interest Entity, Other Consolidated [Abstract]
Number of VIE that did not require consolidation | Entity	31	31	31	31	32	32
Variable Interest Entity, Not Primary Beneficiary, Aggregated Disclosure [Member]
Variable Interest Entity, Other Consolidated [Abstract]
Number of VIE that did not require consolidation | Entity	514		514		510
Residential Mortgage Backed Securities and Other Insurance Products [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Credit Risk Derivatives at Fair Value before Effect of Credit Spread Net 1 [Abstract]
Total unpaid principal balance for the VIEs' assets that were over 90 days or more past due	$ 79,000,000		$ 79,000,000		$ 99,000,000
Fair Value, Option, Loans Held as Assets, Aggregate Difference	350,000,000		350,000,000		361,000,000
Change in the instrument specific credit risk of the VIEs' assets	1,000,000	$ 8,000,000	4,000,000	$ 32,000,000
Unpaid principal for FG VIEs’ liabilities with recourse	590,000,000		590,000,000		674,000,000
Fair Value, Option, Loans Held as Liabilities, Aggregate Difference	$ 72,000,000		$ 72,000,000
Unpaid principal for FG VIEs' liabilities with and without recourse					73,000,000
Net Unrealized Gains (Losses) on FG VIE Liabilities with Recourse due to Instrument Specific Credit Risk [Member]
Variable Interest Entity [Line Items]
Reclassification adjustment for gains (losses) included in net income (loss), net of tax					33,000,000
Net Unrealized Gains (Losses) on FG VIE Liabilities with Recourse due to Instrument Specific Credit Risk [Member] | Accounting Standards Update 2016-01 [Member]
Variable Interest Entity [Line Items]
Reclassification adjustment for gains (losses) included in net income (loss), net of tax					$ 33,000,000