Loans - Consumer, Excluding Credit Card Loan Portfolio (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	$ 960,506	$ 945,601	$ 969,415
Consumer, excluding credit card
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	302,127	294,999	$ 335,776
Consumer, excluding credit card | Residential real estate
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	225,302	243,317
Consumer, excluding credit card | Auto and other
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	76,825	$ 51,682
Consumer, excluding credit card | Auto and other | Paycheck Protection Program (PPP)
Loans and Leases Receivable Disclosure [Line Items]
Retained loans	$ 19,200