Loans - Wholesale Loan Portfolio - Real Estate Class of Loans (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 947,651	$ 924,838	$ 909,182
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 423,837	$ 402,898	$ 398,569
% of total criticized exposure to total retained loans	1.27%	1.71%
% of criticized nonaccrual loans to total real estate retained loans	0.23%	0.43%
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 994	$ 1,734
Wholesale | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 115,296	$ 113,648
% of total criticized exposure to total retained loans	0.64%	0.74%
% of criticized nonaccrual loans to total real estate retained loans	0.11%	0.12%
Wholesale | Real estate | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 79,112	$ 77,597
% of total criticized exposure to total retained loans	0.48%	0.63%
% of criticized nonaccrual loans to total real estate retained loans	0.06%	0.06%
Wholesale | Real estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 36,184	$ 36,051
% of total criticized exposure to total retained loans	0.97%	0.98%
% of criticized nonaccrual loans to total real estate retained loans	0.23%	0.26%
Wholesale | Real estate | Criticized exposure
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 734	$ 846
Wholesale | Real estate | Criticized exposure | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	383	491
Wholesale | Real estate | Criticized exposure | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	351	355
Wholesale | Real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	130	136
Wholesale | Real estate | Criticized nonaccrual | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	47	44
Wholesale | Real estate | Criticized nonaccrual | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 83	$ 92