Loans - Summary of Past Due Status of Loans With Payment Modifications (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Financing Receivable, Past Due [Line Items]
Modified loans, past due	$ 633	$ 628
30 - 89 Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
90+ Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	167	166
Current
Financing Receivable, Past Due [Line Items]
Modified loans, past due	466	462
Commercial loans
Financing Receivable, Past Due [Line Items]
Modified loans, past due	621	616
Commercial loans | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	169	168
Commercial loans | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	409	398
Commercial loans | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	43	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	167	166
Commercial loans | 90+ Days | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	166	166
Commercial loans | 90+ Days | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
Commercial loans | 90+ Days | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	1	0
Commercial loans | Current
Financing Receivable, Past Due [Line Items]
Modified loans, past due	454	450
Commercial loans | Current | Real estate, including construction
Financing Receivable, Past Due [Line Items]
Modified loans, past due	3	2
Commercial loans | Current | Business and corporate banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	409	398
Commercial loans | Current | Global banking
Financing Receivable, Past Due [Line Items]
Modified loans, past due	42	50
Consumer loans
Financing Receivable, Past Due [Line Items]
Modified loans, past due	12	12
Consumer loans | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	12	12
Consumer loans | 30 - 89 Days
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	0
Consumer loans | 30 - 89 Days | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	0	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	12	12
Consumer loans | Current | Residential mortgages
Financing Receivable, Past Due [Line Items]
Modified loans, past due	$ 12	$ 12