Loans - Purchased, Sold and Reclassified to Held-for-Sale (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	$ 846	$ 1,190	$ 4,079	$ 3,634
Sales	5,986	4,014	17,490	10,191
Retained loans reclassified to held-for-sale	666	367	1,962	7,301
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Purchases	561	711	2,164	2,277
Sales	1,789	672	4,661	2,025
Retained loans reclassified to held-for-sale	0	0	36	6,340
Excluded retained loans purchased from correspondents that were originated in accordance with the Firm's underwriting standards	5,600	6,900	14,500	18,200
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	285	479	1,915	1,357
Sales	4,197	3,342	12,829	8,166
Retained loans reclassified to held-for-sale	$ 666	$ 367	$ 1,926	$ 961