Loans - Consumer, Excluding Credit Card Loan Portfolio, Financial Effects of Modifications and Redefaults (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) loan_payment	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Financing Receivable, Impaired [Line Items]
Number of years before payment default under a modified loan			1 year
Carrying value	$ 947,651	$ 909,182	$ 947,651	$ 909,182	$ 924,838
Consumer, excluding credit card
Financing Receivable, Impaired [Line Items]
Carrying value	375,958	$ 369,413	375,958	$ 369,413	372,553
Consumer, excluding credit card | In Process of Active or Suspended Foreclosure
Financing Receivable, Impaired [Line Items]
Carrying value	719		$ 719		787
Consumer, excluding credit card | Maximum
Financing Receivable, Impaired [Line Items]
Number of years before payment default under a modified loan			1 year
Consumer, excluding credit card | Total residential real estate – excluding PCI
Financing Receivable, Impaired [Line Items]
Number of payments past due for deemed payment | loan_payment			2
Carrying value	$ 260,679		$ 260,679		249,946
Consumer, excluding credit card | Total residential real estate – excluding PCI | Maximum
Financing Receivable, Impaired [Line Items]
Number of months before a payment redefault under modified loans			12 months
Consumer, excluding credit card | Total residential real estate – excluding PCI | Permanent Modification
Financing Receivable, Impaired [Line Items]
Weighted-average interest rate of loans with interest rate reductions – before TDR	5.89%	5.06%	5.39%	5.06%
Weighted-average interest rate of loans with interest rate reductions – after TDR	4.01%	2.92%	3.49%	2.79%
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – before TDR	21 years	22 years	22 years	23 years
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – after TDR	39 years	38 years	38 years	38 years
Charge-offs recognized upon permanent modification	$ 0	$ 0	$ 1	$ 2
Principal deferred	9	4	24	18
Principal forgiven	4	9	14	25
Balance of loans that redefaulted within one year of permanent modification	46	$ 49	118	$ 122
Consumer, excluding credit card | Residential mortgage
Financing Receivable, Impaired [Line Items]
Carrying value	$ 231,361		$ 231,361		216,496
Consumer, excluding credit card | Residential mortgage | Permanent Modification
Financing Receivable, Impaired [Line Items]
Weighted-average interest rate of loans with interest rate reductions – before TDR	6.13%	4.92%	5.45%	5.16%
Weighted-average interest rate of loans with interest rate reductions – after TDR	4.23%	2.89%	3.64%	2.97%
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – before TDR	22 years	24 years	24 years	24 years
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – after TDR	39 years	38 years	38 years	38 years
Charge-offs recognized upon permanent modification	$ 0	$ 0	$ 0	$ 1
Principal deferred	7	3	17	10
Principal forgiven	3	5	9	16
Balance of loans that redefaulted within one year of permanent modification	27	$ 32	$ 69	$ 86
Modifications, weighted-average remaining life			10 years
Consumer, excluding credit card | Home equity
Financing Receivable, Impaired [Line Items]
Carrying value	$ 29,318		$ 29,318		$ 33,450
Consumer, excluding credit card | Home equity | Permanent Modification
Financing Receivable, Impaired [Line Items]
Weighted-average interest rate of loans with interest rate reductions – before TDR	5.69%	5.26%	5.34%	4.92%
Weighted-average interest rate of loans with interest rate reductions – after TDR	3.83%	2.96%	3.39%	2.55%
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – before TDR	18 years	18 years	18 years	22 years
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – after TDR	39 years	38 years	39 years	39 years
Charge-offs recognized upon permanent modification	$ 0	$ 0	$ 1	$ 1
Principal deferred	2	1	7	8
Principal forgiven	1	4	5	9
Balance of loans that redefaulted within one year of permanent modification	$ 19	$ 17	$ 49	$ 36
Modifications, weighted-average remaining life			9 years