Loans - Loan Payment Modifications by Type of Modification (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Modified [Line Items]
Loans modified	$ 443	$ 628
% of Total Loans	0.70%	1.10%
Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	$ 438	$ 616
% of Total Loans	1.10%	1.50%
Commercial loans \| Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	$ 232	$ 168
% of Total Loans	3.50%	2.40%
Commercial loans \| Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	$ 111	$ 398
% of Total Loans	0.70%	2.50%
Commercial loans \| Global banking
Financing Receivable, Modified [Line Items]
Loans modified	$ 95	$ 50
% of Total Loans	1.00%	0.50%
Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	$ 5	$ 12
% of Total Loans	0.00%	0.10%
Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	$ 5	$ 12
% of Total Loans	0.00%	0.10%
Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans modified	$ 0	$ 21
Interest Rate Reduction \| Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	0	21
Interest Rate Reduction \| Commercial loans \| Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	0	0
Interest Rate Reduction \| Commercial loans \| Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	0	0
Interest Rate Reduction \| Commercial loans \| Global banking
Financing Receivable, Modified [Line Items]
Loans modified	0	21
Interest Rate Reduction \| Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	0	0
Interest Rate Reduction \| Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	0	0
Principal Forgiveness
Financing Receivable, Modified [Line Items]
Loans modified	32	0
Principal Forgiveness \| Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	32	0
Principal Forgiveness \| Commercial loans \| Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	32	0
Principal Forgiveness \| Commercial loans \| Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	0	0
Principal Forgiveness \| Commercial loans \| Global banking
Financing Receivable, Modified [Line Items]
Loans modified	0	0
Principal Forgiveness \| Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	0	0
Principal Forgiveness \| Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	0	0
Term Extension / Significant Payment Deferral
Financing Receivable, Modified [Line Items]
Loans modified	244	418
Term Extension / Significant Payment Deferral \| Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	241	408
Term Extension / Significant Payment Deferral \| Commercial loans \| Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	43	168
Term Extension / Significant Payment Deferral \| Commercial loans \| Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	103	211
Term Extension / Significant Payment Deferral \| Commercial loans \| Global banking
Financing Receivable, Modified [Line Items]
Loans modified	95	29
Term Extension / Significant Payment Deferral \| Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	3	10
Term Extension / Significant Payment Deferral \| Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	3	10
Combination
Financing Receivable, Modified [Line Items]
Loans modified	167	189
Combination \| Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	165	187
Combination \| Commercial loans \| Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	157	0
Combination \| Commercial loans \| Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	8	187
Combination \| Commercial loans \| Global banking
Financing Receivable, Modified [Line Items]
Loans modified	0	0
Combination \| Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	2	2
Combination \| Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	$ 2	$ 2

Amortized cost excluding accrued interest, of financing receivable modified during period for debtor experiencing financial difficulty.

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