Loans - Consumer, Excluding Credit Card Loans, Financial Effects of Modifications and Redefaults (Details) - Consumer, excluding credit card $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) loan_payment	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Permanent Modification
Financing Receivable, Impaired [Line Items]
Weighted-average interest rate of loans with interest rate reductions – before TDR	5.51%	5.61%	5.88%
Weighted-average interest rate of loans with interest rate reductions – after TDR	2.64%	2.78%	2.92%
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – before TDR	22 years	23 years	23 years
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – after TDR	36 years	36 years	36 years
Charge-offs recognized upon permanent modification	$ 15	$ 39	$ 98
Principal deferred	85	74	203
Principal forgiven	72	207	505
Balance of loans that redefaulted within one year of permanent modification	$ 154	$ 243	$ 316
Senior lien | Permanent Modification
Financing Receivable, Impaired [Line Items]
Modifications, weighted-average remaining life	10 years
Junior lien | Permanent Modification
Financing Receivable, Impaired [Line Items]
Modifications, weighted-average remaining life	9 years
Home equity | Senior lien | Permanent Modification
Financing Receivable, Impaired [Line Items]
Weighted-average interest rate of loans with interest rate reductions – before TDR	5.69%	6.38%	6.35%
Weighted-average interest rate of loans with interest rate reductions – after TDR	2.70%	3.03%	3.23%
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – before TDR	17 years	17 years	19 years
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – after TDR	32 years	30 years	31 years
Charge-offs recognized upon permanent modification	$ 1	$ 2	$ 7
Principal deferred	13	5	7
Principal forgiven	2	14	30
Balance of loans that redefaulted within one year of permanent modification	$ 14	$ 19	$ 26
Home equity | Junior lien | Permanent Modification
Financing Receivable, Impaired [Line Items]
Weighted-average interest rate of loans with interest rate reductions – before TDR	4.93%	4.81%	5.05%
Weighted-average interest rate of loans with interest rate reductions – after TDR	2.17%	2.00%	2.14%
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – before TDR	18 years	19 years	20 years
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – after TDR	36 years	35 years	34 years
Charge-offs recognized upon permanent modification	$ 3	$ 25	$ 70
Principal deferred	14	11	24
Principal forgiven	4	21	51
Balance of loans that redefaulted within one year of permanent modification	$ 7	$ 10	$ 20
Mortgages | Prime, including option ARMs | Permanent Modification
Financing Receivable, Impaired [Line Items]
Weighted-average interest rate of loans with interest rate reductions – before TDR	5.03%	4.82%	5.28%
Weighted-average interest rate of loans with interest rate reductions – after TDR	2.55%	2.69%	2.77%
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – before TDR	25 years	25 years	25 years
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – after TDR	37 years	37 years	37 years
Charge-offs recognized upon permanent modification	$ 9	$ 9	$ 16
Principal deferred	41	39	129
Principal forgiven	34	83	206
Balance of loans that redefaulted within one year of permanent modification	$ 75	$ 121	$ 164
Mortgages | Subprime | Permanent Modification
Financing Receivable, Impaired [Line Items]
Weighted-average interest rate of loans with interest rate reductions – before TDR	6.67%	7.16%	7.33%
Weighted-average interest rate of loans with interest rate reductions – after TDR	3.15%	3.37%	3.52%
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – before TDR	24 years	24 years	24 years
Weighted-average remaining contractual term (in years) of loans with term or payment extensions – after TDR	36 years	36 years	35 years
Charge-offs recognized upon permanent modification	$ 2	$ 3	$ 5
Principal deferred	17	19	43
Principal forgiven	32	89	218
Balance of loans that redefaulted within one year of permanent modification	$ 58	$ 93	$ 106
Modifications, weighted-average remaining life	8 years
Business banking | Maximum
Financing Receivable, Impaired [Line Items]
Number of years before payment default under a modified loan	1 year
Residential real estate
Financing Receivable, Impaired [Line Items]
Number of payments past due for deemed payment | loan_payment	2
Residential real estate | Maximum
Financing Receivable, Impaired [Line Items]
Number of months before a payment redefault under modified loans	12 months
Residential real estate | Prime, including option ARMs | Permanent Modification
Financing Receivable, Impaired [Line Items]
Modifications, weighted-average remaining life	10 years