Loans Held-for-Investment (Troubled Debt Restructurings) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Troubled Debt Restructurings [Line Items]
TDR Balance	$ 58	$ 85
Allowance for loan losses on TDR loans	11	9
TDR loans under fair value option	3	25
Other consumer | Residential first mortgage
Troubled Debt Restructurings [Line Items]
TDR Balance	29	33
Other consumer | Home equity
Troubled Debt Restructurings [Line Items]
TDR Balance	29	52
Performing
Troubled Debt Restructurings [Line Items]
TDR Balance	46	67
Performing | Other consumer | Residential first mortgage
Troubled Debt Restructurings [Line Items]
TDR Balance	19	22
Performing | Other consumer | Home equity
Troubled Debt Restructurings [Line Items]
TDR Balance	27	45
Nonperforming
Troubled Debt Restructurings [Line Items]
TDR Balance	12	18
Nonperforming | Other consumer | Residential first mortgage
Troubled Debt Restructurings [Line Items]
TDR Balance	10	11
Nonperforming | Other consumer | Home equity
Troubled Debt Restructurings [Line Items]
TDR Balance	$ 2	$ 7