Allowance for credit losses - Financial effect of the modifications made to borrowers experiencing financial difficultie (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Interest Rate Reduction | Mortgages
Financing Receivable, Modifications [Line Items]
Weighted average contractual interest rate before modification	5.87%	5.70%	6.10%	5.70%
Weighted average contractual interest rate after modification	4.32%	4.20%	4.40%	4.20%
Interest Rate Reduction | Commercial | CRE non-owner occupied
Financing Receivable, Modifications [Line Items]
Weighted average contractual interest rate before modification		9.00%	10.10%	9.00%
Weighted average contractual interest rate after modification		7.20%	8.30%	7.20%
Interest Rate Reduction | Commercial | CRE owner occupied
Financing Receivable, Modifications [Line Items]
Weighted average contractual interest rate before modification	10.45%	8.40%	10.60%	8.40%
Weighted average contractual interest rate after modification	6.62%	6.60%	6.50%	6.60%
Interest Rate Reduction | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Weighted average contractual interest rate before modification	25.76%	12.50%	20.60%	14.00%
Weighted average contractual interest rate after modification	10.21%	7.60%	9.60%	7.70%
Interest Rate Reduction | Consumer | Credit card
Financing Receivable, Modifications [Line Items]
Weighted average contractual interest rate before modification	21.46%	19.60%	20.90%	18.00%
Weighted average contractual interest rate after modification	8.02%	3.60%	6.50%	4.30%
Interest Rate Reduction | Consumer | Personal loans
Financing Receivable, Modifications [Line Items]
Weighted average contractual interest rate before modification	19.47%	17.00%	19.10%	18.00%
Weighted average contractual interest rate after modification	10.35%	9.10%	10.00%	9.70%
Interest Rate Reduction | Consumer | Auto Loan
Financing Receivable, Modifications [Line Items]
Weighted average contractual interest rate before modification				12.64%
Weighted average contractual interest rate after modification				12.62%
Interest Rate Reduction | Consumer | Other
Financing Receivable, Modifications [Line Items]
Weighted average contractual interest rate before modification			18.00%	18.00%
Weighted average contractual interest rate after modification			0.00%	0.00%
Term extension | Construction
Financing Receivable, Modifications [Line Items]
Weighted average term increase	2 months		2 months	6 months
Term extension | Mortgages
Financing Receivable, Modifications [Line Items]
Weighted average term increase	12 years	11 years	12 years	11 years
Term extension | Commercial | Commercial multi-family
Financing Receivable, Modifications [Line Items]
Weighted average term increase	4 months		4 months
Term extension | Commercial | CRE non-owner occupied
Financing Receivable, Modifications [Line Items]
Weighted average term increase	7 months	28 months	9 months	19 months
Term extension | Commercial | CRE owner occupied
Financing Receivable, Modifications [Line Items]
Weighted average term increase	5 years	1 year	11 months	1 year
Term extension | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Weighted average term increase	1 year	3 years	2 years	2 years
Term extension | Consumer | Personal loans
Financing Receivable, Modifications [Line Items]
Weighted average term increase	5 years	7 years	8 years	7 years
Term extension | Consumer | Auto Loan
Financing Receivable, Modifications [Line Items]
Weighted average term increase			4 years	3 years
Principal Forgiveness | Commercial | CRE owner occupied
Financing Receivable, Modifications [Line Items]
Reduced the amortized cost basis				$ 0.1
Other-Than-Insignificant Payment Delays | Mortgages
Financing Receivable, Modifications [Line Items]
Weighted average term increase			30 months	40 months
Other-Than-Insignificant Payment Delays | Commercial | CRE non-owner occupied
Financing Receivable, Modifications [Line Items]
Weighted average term increase	14 months	7 months	14 months	12 months
Other-Than-Insignificant Payment Delays | Commercial | CRE owner occupied
Financing Receivable, Modifications [Line Items]
Weighted average term increase	7 months	10 months	10 months	8 months
Other-Than-Insignificant Payment Delays | Commercial | Commercial and industrial
Financing Receivable, Modifications [Line Items]
Weighted average term increase	7 months	7 months	7 months	8 months
Other-Than-Insignificant Payment Delays | Consumer | Credit card
Financing Receivable, Modifications [Line Items]
Weighted average term increase	16 months	29 months	18 months	26 months
Other-Than-Insignificant Payment Delays | Consumer | Other
Financing Receivable, Modifications [Line Items]
Weighted average term increase				11 months