Loans and asset quality - Nonperforming Assets (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Financing Receivable, Impaired [Line Items]
With an allowance	$ 88	$ 68
Without an allowance	19	20
Total nonperforming loans	107	88
With an allowance, Other assets owned	0	0
Without an allowance, Other assets owned	1	1
Other assets owned	1	1
With an allowance, Total nonperforming assets	88	68
Without an allowance, Total nonperforming assets	20	21
Total nonperforming assets	108	89
Other residential mortgages
Financing Receivable, Impaired [Line Items]
With an allowance	39	57
Without an allowance	1	0
Total nonperforming loans	40	57
Wealth management loans and mortgages
Financing Receivable, Impaired [Line Items]
With an allowance	8	10
Without an allowance	18	20
Total nonperforming loans	26	30
Other
Financing Receivable, Impaired [Line Items]
With an allowance	16	0
Without an allowance	0	0
Total nonperforming loans	16	0
Commercial real estate
Financing Receivable, Impaired [Line Items]
With an allowance	25	1
Without an allowance	0	0
Total nonperforming loans	$ 25	$ 1