Loans and asset quality - Information about Past Due Loans (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Past Due [Line Items]
Total past due loans	$ 64,328	$ 56,469
Total past due
Financing Receivable, Past Due [Line Items]
Total past due loans	124	105
Total past due | Wealth management loans and mortgages
Financing Receivable, Past Due [Line Items]
Total past due loans	84	55
Total past due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total past due loans	27	35
Total past due | Other residential mortgages
Financing Receivable, Past Due [Line Items]
Total past due loans	3	4
Total past due | Financial institutions
Financing Receivable, Past Due [Line Items]
Total past due loans	10	11
30 to 59 Days Past Due
Financing Receivable, Past Due [Line Items]
Total past due loans	113	87
30 to 59 Days Past Due | Wealth management loans and mortgages
Financing Receivable, Past Due [Line Items]
Total past due loans	73	54
30 to 59 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total past due loans	27	19
30 to 59 Days Past Due | Other residential mortgages
Financing Receivable, Past Due [Line Items]
Total past due loans	3	3
30 to 59 Days Past Due | Financial institutions
Financing Receivable, Past Due [Line Items]
Total past due loans	10	11
60 to 89 Days Past Due
Financing Receivable, Past Due [Line Items]
Total past due loans	11	18
60 to 89 Days Past Due | Wealth management loans and mortgages
Financing Receivable, Past Due [Line Items]
Total past due loans	11	1
60 to 89 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total past due loans	0	16
60 to 89 Days Past Due | Other residential mortgages
Financing Receivable, Past Due [Line Items]
Total past due loans	0	1
60 to 89 Days Past Due | Financial institutions
Financing Receivable, Past Due [Line Items]
Total past due loans	0	0
Equal to Greater than 90 Days Past Due
Financing Receivable, Past Due [Line Items]
Total past due loans	0	0
Equal to Greater than 90 Days Past Due | Wealth management loans and mortgages
Financing Receivable, Past Due [Line Items]
Total past due loans	0	0
Equal to Greater than 90 Days Past Due | Commercial real estate
Financing Receivable, Past Due [Line Items]
Total past due loans	0	0
Equal to Greater than 90 Days Past Due | Other residential mortgages
Financing Receivable, Past Due [Line Items]
Total past due loans	0	0
Equal to Greater than 90 Days Past Due | Financial institutions
Financing Receivable, Past Due [Line Items]
Total past due loans	$ 0	$ 0