Allowance for credit losses - Troubled debt restructurings loan count by type of modification (Details) - loans	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Financing Receivable
Reduction In Interest Rate	483	388	735	674
Extension of Maturity Date	32	63	78	127
Combination Interest Rate Reduction Maturity Date Extension	14	137	167	299
Other Modifications	143	57	158	123
Mortgages
Financing Receivable
Reduction In Interest Rate	0	25	2	31
Extension of Maturity Date	0	28	26	55
Combination Interest Rate Reduction Maturity Date Extension	14	130	161	287
Other Modifications	72	2	72	2
Commercial | Commercial multi-family
Financing Receivable
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	1	1	1	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	1	2	2	3
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	1	0	1
Extension of Maturity Date	13	5	19	15
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	0	1	0
Extension of Maturity Date	15	18	26	34
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	404	161	552	283
Extension of Maturity Date	0	0	0	0
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	1
Other Modifications	52	54	65	120
Consumer | Home equity lines of credit
Financing Receivable
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	1	6	1	12
Combination Interest Rate Reduction Maturity Date Extension	0	5	1	9
Other Modifications	0	0	0	0
Consumer | Personal loans
Financing Receivable
Reduction In Interest Rate	78	192	178	344
Extension of Maturity Date	1	1	2	3
Combination Interest Rate Reduction Maturity Date Extension	0	0	0	0
Other Modifications	0	1	1	1
Consumer | Auto Loan
Financing Receivable
Reduction In Interest Rate	0	0	0	0
Extension of Maturity Date	0	2	1	4
Combination Interest Rate Reduction Maturity Date Extension	0	1	2	1
Other Modifications	8	0	8	0
Consumer | Other
Financing Receivable
Reduction In Interest Rate	1	9	2	15
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	0	0	0
Combination Interest Rate Reduction Maturity Date Extension	0	1	3	1
Other Modifications	11	0	11	0