Loans - Consumer, Excluding Credit Card Loan Portfolio (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 963,665	$ 960,506	$ 965,448
Consumer, excluding credit card
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	297,731	302,127	$ 307,005
Consumer, excluding credit card | Residential real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	218,031	225,302
Consumer, excluding credit card | Auto and other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	79,700	76,825
Consumer, excluding credit card | Auto and other | Paycheck Protection Program (PPP)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Retained loans	$ 16,700	$ 19,200