Loans - Wholesale Loan Portfolio - Real Estate Class of Loans (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 940,440	$ 924,838	$ 899,576
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 420,632	$ 402,898	$ 394,426
% of total criticized exposure to total retained loans	1.24%	1.71%
% of criticized nonaccrual loans to total real estate retained loans	0.27%	0.43%
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 1,156	$ 1,734
Wholesale | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 113,340	$ 113,648
% of total criticized exposure to total retained loans	0.62%	0.74%
% of criticized nonaccrual loans to total real estate retained loans	0.12%	0.12%
Wholesale | Real estate | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 78,093	$ 77,597
% of total criticized exposure to total retained loans	0.56%	0.63%
% of criticized nonaccrual loans to total real estate retained loans	0.07%	0.06%
Wholesale | Real estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 35,247	$ 36,051
% of total criticized exposure to total retained loans	0.76%	0.98%
% of criticized nonaccrual loans to total real estate retained loans	0.24%	0.26%
Wholesale | Real estate | Criticized exposure
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 704	$ 846
Wholesale | Real estate | Criticized exposure | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	437	491
Wholesale | Real estate | Criticized exposure | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	267	355
Wholesale | Real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	138	136
Wholesale | Real estate | Criticized nonaccrual | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	53	44
Wholesale | Real estate | Criticized nonaccrual | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 85	$ 92