Receivables Held for Sale - Receivables Sold to Third Party Investors (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Aggregate cash consideration received			$ 4,863	$ 4,667
Gain (loss) on sale of real estate secured receivables	$ (2)	$ 423	615	423
Real Estate Secured Receivables Held for Sale [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance at the time of sale	621	4,722	4,984	4,722
Aggregate cash consideration received	556	4,667	4,863	4,667
Aggregate carrying value at the time of sale	554	4,219	4,219	4,219
Transaction costs	4	25	29	25
Gain (loss) on sale of real estate secured receivables	$ (2)	$ 423	$ 615	$ 423