Loans and asset quality - Loan Modifications (Details) - USD ($) $ in Millions	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Sep. 30, 2020
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, CARES Act	$ 23	$ 3	$ 106
Unpaid principal balance	$ 94
Commercial real estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Financing receivable, modifications, CARES Act			$ 56