Allowance for credit losses - Troubled debt restructurings loan count by type of modification (Details) - loans	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Financing Receivable
Loan count	705	672	1,292	1,138
Reduction in interest rate
Financing Receivable
Loan count	114	483	241	735
Extension of maturity date
Financing Receivable
Loan count	105	32	186	78
Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	463	14	828	167
Other
Financing Receivable
Loan count	23	143	37	158
Mortgages
Financing Receivable
Loan count	511	86	919	261
Mortgages | Reduction in interest rate
Financing Receivable
Loan count	14	0	22	2
Mortgages | Extension of maturity date
Financing Receivable
Loan count	39	0	79	26
Mortgages | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	458	14	818	161
Mortgages | Other
Financing Receivable
Loan count	0	72	0	72
Commercial | Commercial multi-family
Financing Receivable
Loan count	1	1	2	1
Commercial | Commercial multi-family | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Commercial | Commercial multi-family | Extension of maturity date
Financing Receivable
Loan count	0	1	1	1
Commercial | Commercial multi-family | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	1	0	1	0
Commercial | Commercial multi-family | Other
Financing Receivable
Loan count	0	0	0	0
Commercial | CRE non-owner occupied
Financing Receivable
Loan count		1	9	3
Commercial | CRE non-owner occupied | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Commercial | CRE non-owner occupied | Extension of maturity date
Financing Receivable
Loan count	0	1	9	2
Commercial | CRE non-owner occupied | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Commercial | CRE non-owner occupied | Other
Financing Receivable
Loan count	0	0	0	1
Commercial | CRE owner occupied
Financing Receivable
Loan count	9	13	31	19
Commercial | CRE owner occupied | Reduction in interest rate
Financing Receivable
Loan count	1	0	3	0
Commercial | CRE owner occupied | Extension of maturity date
Financing Receivable
Loan count	3	13	23	19
Commercial | CRE owner occupied | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	3	0	3	0
Commercial | CRE owner occupied | Other
Financing Receivable
Loan count	2	0	2	0
Commercial | Commercial and Industrial
Financing Receivable
Loan count	7	15	15	27
Commercial | Commercial and Industrial | Reduction in interest rate
Financing Receivable
Loan count	1	0	1	1
Commercial | Commercial and Industrial | Extension of maturity date
Financing Receivable
Loan count	0	15	8	26
Commercial | Commercial and Industrial | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Commercial | Commercial and Industrial | Other
Financing Receivable
Loan count	6	0	6	0
Consumer | Credit card
Financing Receivable
Loan count	51	456	117	617
Consumer | Credit card | Reduction in interest rate
Financing Receivable
Loan count	37	404	89	552
Consumer | Credit card | Extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Consumer | Credit card | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	1	0	1	0
Consumer | Credit card | Other
Financing Receivable
Loan count	13	52	27	65
Consumer | Home equity lines of credit
Financing Receivable
Loan count	1	1	2	2
Consumer | Home equity lines of credit | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Consumer | Home equity lines of credit | Extension of maturity date
Financing Receivable
Loan count	1	1	1	1
Consumer | Home equity lines of credit | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	1	1
Consumer | Home equity lines of credit | Other
Financing Receivable
Loan count	0	0	0	0
Consumer | Personal loans
Financing Receivable
Loan count	122	79	186	181
Consumer | Personal loans | Reduction in interest rate
Financing Receivable
Loan count	59	78	120	178
Consumer | Personal loans | Extension of maturity date
Financing Receivable
Loan count	61	1	63	2
Consumer | Personal loans | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	1	0
Consumer | Personal loans | Other
Financing Receivable
Loan count	2	0	2	1
Consumer | Auto Loan
Financing Receivable
Loan count	1	8	4	11
Consumer | Auto Loan | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Consumer | Auto Loan | Extension of maturity date
Financing Receivable
Loan count	1	0	2	1
Consumer | Auto Loan | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	2	2
Consumer | Auto Loan | Other
Financing Receivable
Loan count	0	8	0	8
Consumer | Other
Financing Receivable
Loan count	2	1	6	2
Consumer | Other | Reduction in interest rate
Financing Receivable
Loan count	2	1	6	2
Consumer | Other | Extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Consumer | Other | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Consumer | Other | Other
Financing Receivable
Loan count	0	0	0	0
Leasing
Financing Receivable
Loan count		11	1	14
Leasing | Reduction in interest rate
Financing Receivable
Loan count	0	0	0	0
Leasing | Extension of maturity date
Financing Receivable
Loan count	0	0	0	0
Leasing | Combination of reduction in interest rate and extension of maturity date
Financing Receivable
Loan count	0	0	1	3
Leasing | Other
Financing Receivable
Loan count	0	11	0	11