Loans - Consumer, Excluding Credit Card Loan Portfolio, Financial Effects of Modifications and Redefaults (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) loan_payment	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Financing Receivable, Impaired [Line Items]
Carrying value	$ 960,506	$ 945,601	$ 969,415
Consumer, excluding credit card
Financing Receivable, Impaired [Line Items]
Carrying value	$ 302,127	294,999	$ 335,776
Consumer, excluding credit card | Residential real estate
Financing Receivable, Impaired [Line Items]
Number of payments past due for deemed payment | loan_payment	2
Carrying value	$ 225,302	243,317
Consumer, excluding credit card | Residential real estate | In Process of Active or Suspended Foreclosure
Financing Receivable, Impaired [Line Items]
Carrying value	$ 846	$ 1,200
Consumer, excluding credit card | Residential real estate | Maximum
Financing Receivable, Impaired [Line Items]
Number of years before payment default under a modified loan	1 year
Number of months before a payment redefault under modified loans	12 months
Consumer, excluding credit card | Residential real estate | Permanent Modification
Financing Receivable, Impaired [Line Items]
Weighted-average interest rate of loans with interest rate reductions – before TDR	5.09%	5.68%	5.50%
Weighted-average interest rate of loans with interest rate reductions – after TDR	3.28%	3.81%	3.60%
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – before TDR	22 years	20 years	21 years
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – after TDR	39 years	39 years	38 years
Charge-offs recognized upon permanent modification	$ 5	$ 1	$ 2
Principal deferred	16	19	30
Principal forgiven	5	7	17
Balance of loans that redefaulted within one year of permanent modification	$ 199	$ 166	$ 161
Modifications, weighted-average remaining life	6 years