Loans - Purchased, Sold and Reclassified to Held-for-Sale (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	$ 1,064	$ 1,220	$ 3,233	$ 2,444
Sales	7,334	3,140	11,504	6,177
Retained loans reclassified to held-for-sale	392	338	1,296	7,108
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	532	626	1,603	1,566
Sales	2,391	763	2,872	1,353
Retained loans reclassified to held-for-sale	0	31	36	6,340
Excluded retained loans purchased from correspondents that were originated in accordance with the Firm's underwriting standards	5,300	5,900	8,900	11,300
Credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	0	0	0	0
Sales	0	0	0	0
Retained loans reclassified to held-for-sale	0	0	0	0
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	532	594	1,630	878
Sales	4,943	2,377	8,632	4,824
Retained loans reclassified to held-for-sale	$ 392	$ 307	$ 1,260	$ 768