Loans - Wholesale Loan Portfolio - Real Estate Class of Loans (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 943,841	$ 969,415	$ 925,611
Wholesale
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 433,611	$ 439,162	$ 412,020
% of total criticized exposure to total retained loans	1.55%	1.33%
% of criticized nonaccrual loans to total real estate retained loans	0.36%	0.26%
Wholesale | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 1,570	$ 1,150
Wholesale | Real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 116,173	$ 115,737
% of total criticized exposure to total retained loans	0.79%	0.65%
% of criticized nonaccrual loans to total real estate retained loans	0.10%	0.12%
Wholesale | Real estate | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 79,263	$ 79,184
% of total criticized exposure to total retained loans	0.63%	0.49%
% of criticized nonaccrual loans to total real estate retained loans	0.05%	0.07%
Wholesale | Real estate | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 36,910	$ 36,553
% of total criticized exposure to total retained loans	1.13%	1.00%
% of criticized nonaccrual loans to total real estate retained loans	0.19%	0.21%
Wholesale | Real estate | Criticized exposure
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 919	$ 754
Wholesale | Real estate | Criticized exposure | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	501	388
Wholesale | Real estate | Criticized exposure | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	418	366
Wholesale | Real estate | Criticized nonaccrual
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	111	134
Wholesale | Real estate | Criticized nonaccrual | Multifamily
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	42	57
Wholesale | Real estate | Criticized nonaccrual | Other commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 69	$ 77