Receivables Held for Sale - Receivables Sold to Third Party Investors (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Aggregate cash consideration received			$ 6,059	$ 5,382
Gain (loss) on sale of real estate secured receivables	$ 139	$ (5)	754	418
Real Estate Secured Receivables Held for Sale [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Unpaid principal balance at the time of sale	1,244	930	6,228	5,652
Aggregate cash consideration received	1,196	715	6,059	5,382
Aggregate carrying value at the time of sale	1,048	714	5,267	4,933
Transaction costs	9	6	38	31
Gain (loss) on sale of real estate secured receivables	$ 139	$ (5)	$ 754	$ 418