Loans - Summary of Past Due Status of Loans With Payment Modifications (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Past Due [Line Items]
Modified loans, past due	$ 443	$ 628
30 - 89 Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	1	0
90+ Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	29	166
Current
Financing Receivable, Past Due [Line Items]
Modified loans, past due	413	462
Commercial loans
Financing Receivable, Past Due [Line Items]
Modified loans, past due	438	616
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	232	168
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	111	398
Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	95	50
Commercial loans | 30 - 89 Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
Commercial loans | 30 - 89 Days | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
Commercial loans | 30 - 89 Days | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
Commercial loans | 30 - 89 Days | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
Commercial loans | 90+ Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	29	166
Commercial loans | 90+ Days | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	166
Commercial loans | 90+ Days | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	29	0
Commercial loans | 90+ Days | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
Commercial loans | Current
Financing Receivable, Past Due [Line Items]
Modified loans, past due	409	450
Commercial loans | Current | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	232	2
Commercial loans | Current | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	82	398
Commercial loans | Current | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	95	50
Consumer loans
Financing Receivable, Past Due [Line Items]
Modified loans, past due	5	12
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	5	12
Consumer loans | 30 - 89 Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	1	0
Consumer loans | 30 - 89 Days | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	1	0
Consumer loans | 90+ Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
Consumer loans | 90+ Days | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
Consumer loans | Current
Financing Receivable, Past Due [Line Items]
Modified loans, past due	4	12
Consumer loans | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	$ 4	$ 12