Allowance for credit losses - Troubled debt restructurings loan count by type of modification (Details) - loans	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Financing Receivable
Reduction In Interest Rate	161	305	896	979
Extension of Maturity Date	49	62	127	189
Combination Interest Rate Reduction Maturity Date Extension	70	211	237	510
Other Modifications	267	44	425	167
Construction
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
Mortgages
Financing Receivable
Reduction In Interest Rate	0	2	2	33
Extension of Maturity Date	24	43	50	98
Combination Interest Rate Reduction Maturity Date Extension	70	207	231	494
Other Modifications	254	3	326	5
Commercial | Commercial multi-family
Financing Receivable
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	1	0	2	1
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	0	0
Commercial | CRE non-owner occupied
Financing Receivable
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	2	3	4	6
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	1	0
Commercial | CRE owner occupied
Financing Receivable
Reduction In Interest Rate	0	0	0	1
Extension of Maturity Date	7	4	26	19
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	0	0
Commercial | Commercial and Industrial
Financing Receivable
Reduction In Interest Rate	0	2	1	2
Extension of Maturity Date	12	7	38	41
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	0	0
Consumer | Credit cards
Financing Receivable
Reduction In Interest Rate	69	111	621	394
Extension of Maturity Date	0	0	0	0
Combination Interest Rate Reduction Maturity Date Extension	0	1	0	2
Other Modifications	13	41	78	161
Consumer | Home equity lines of credit
Financing Receivable
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	0	2	1	14
Combination Interest Rate Reduction Maturity Date Extension	0	2	1	11
Other Modifications	0	0	0	0
Consumer | Personal loans
Financing Receivable
Reduction In Interest Rate	91	183	269	527
Extension of Maturity Date	1	1	3	4
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	1	1
Consumer | Auto Loan
Financing Receivable
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	1	1	2	5
Combination Interest Rate Reduction Maturity Date Extension	0	0	2	1
Other Modifications	0	0	8	0
Consumer | Other
Financing Receivable
Reduction In Interest Rate	1	7	3	22
Extension of Maturity Date	0	0	0	0
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	0	0	0
Leasing
Financing Receivable
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	0	1	0	1
Combination Interest Rate Reduction Maturity Date Extension	0	1	3	2
Other Modifications	0	0	11	0