Allowance for credit losses - Troubled debt restructurings loan count by type of modification (Details) - loans	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Financing Receivable
Reduction In Interest Rate	252	286
Extension of Maturity Date	46	64
Combination Interest Rate Reduction Maturity Date Extension	153	162
Other Modifications	15	66
Mortgages
Financing Receivable
Reduction In Interest Rate	2	6
Extension of Maturity Date	26	27
Combination Interest Rate Reduction Maturity Date Extension	147	157
Other Modifications	0	0
Commercial | CRE non-owner occupied
Financing Receivable
Reduction In Interest Rate	0	0
Extension of Maturity Date	1	1
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	0	0
Commercial | CRE owner occupied
Financing Receivable
Reduction In Interest Rate	0	0
Extension of Maturity Date	6	10
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	0	0
Commercial | Commercial and Industrial
Financing Receivable
Reduction In Interest Rate	1	0
Extension of Maturity Date	11	16
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	1	0
Consumer | Credit cards
Financing Receivable
Reduction In Interest Rate	148	122
Extension of Maturity Date	0	0
Combination Interest Rate Reduction Maturity Date Extension	0	1
Other Modifications	13	66
Consumer | Home equity lines of credit
Financing Receivable
Reduction In Interest Rate	0	0
Extension of Maturity Date	0	6
Combination Interest Rate Reduction Maturity Date Extension	1	4
Other Modifications	0	0
Consumer | Personal loans
Financing Receivable
Reduction In Interest Rate	100	152
Extension of Maturity Date	1	2
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	1	0
Consumer | Auto Loan
Financing Receivable
Reduction In Interest Rate	0	0
Extension of Maturity Date	1	2
Combination Interest Rate Reduction Maturity Date Extension	2	0
Other Modifications	0	0
Consumer | Other
Financing Receivable
Reduction In Interest Rate	1	6
Extension of Maturity Date	0	0
Combination Interest Rate Reduction Maturity Date Extension	0	0
Other Modifications	0	0
Leasing
Financing Receivable
Reduction In Interest Rate	0
Extension of Maturity Date	0
Combination Interest Rate Reduction Maturity Date Extension	3
Other Modifications	0