Loans - Summary of Past Due Status of Loans With Payment Modifications (Details) $ in Millions	Jun. 30, 2023 USD ($)
Financing Receivable, Past Due [Line Items]
Modified loans, past due	$ 357
30 - 89 Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
90+ Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	64
Current
Financing Receivable, Past Due [Line Items]
Modified loans, past due	293
Commercial loans
Financing Receivable, Past Due [Line Items]
Modified loans, past due	349
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	235
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	109
Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	5
Commercial loans | 30 - 89 Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Commercial loans | 30 - 89 Days | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Commercial loans | 30 - 89 Days | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Commercial loans | 30 - 89 Days | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Commercial loans | 90+ Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	64
Commercial loans | 90+ Days | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	64
Commercial loans | 90+ Days | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Commercial loans | 90+ Days | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Commercial loans | Current
Financing Receivable, Past Due [Line Items]
Modified loans, past due	285
Commercial loans | Current | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	171
Commercial loans | Current | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	109
Commercial loans | Current | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	5
Consumer loans
Financing Receivable, Past Due [Line Items]
Modified loans, past due	8
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	8
Consumer loans | 30 - 89 Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Consumer loans | 30 - 89 Days | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Consumer loans | 90+ Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Consumer loans | 90+ Days | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0
Consumer loans | Current
Financing Receivable, Past Due [Line Items]
Modified loans, past due	8
Consumer loans | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	$ 8