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Loans - Loan Payment Modifications by Type of Modification (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Financing Receivable, Modified [Line Items]
Loans modified	$ 167	$ 223	$ 177	$ 282
% of Total Loans	0.30%	0.40%	0.30%	0.50%
Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	$ 129	$ 222	$ 139	$ 281
% of Total Loans	0.30%	0.50%	0.30%	0.70%
Commercial loans \| Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified		$ 161		$ 161
% of Total Loans		2.40%		2.40%
Commercial loans \| Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	$ 129	$ 61	$ 139	$ 120
% of Total Loans	0.50%	0.20%	0.50%	0.40%
Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	$ 38	$ 1	$ 38	$ 1
% of Total Loans	0.20%	0.00%	0.20%	0.00%
Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	$ 38	$ 1	$ 38	$ 1
% of Total Loans	0.20%	0.00%	0.20%	0.00%
Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans modified	$ 23	$ 0	$ 23	$ 0
Interest Rate Reduction \| Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	23	0	23	0
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	23	0	23	0
Interest Rate Reduction \| Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Interest Rate Reduction \| Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Principal Forgiveness
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Principal Forgiveness \| Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Principal Forgiveness \| Commercial loans \| Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified		0		0
Principal Forgiveness \| Commercial loans \| Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Principal Forgiveness \| Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Principal Forgiveness \| Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Term Extension / Significant Payment Deferral
Financing Receivable, Modified [Line Items]
Loans modified	139	54	149	113
Term Extension / Significant Payment Deferral \| Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	103	54	113	113
Term Extension / Significant Payment Deferral \| Commercial loans \| Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified		0		0
Term Extension / Significant Payment Deferral \| Commercial loans \| Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	103	54	113	113
Term Extension / Significant Payment Deferral \| Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	36	0	36	0
Term Extension / Significant Payment Deferral \| Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	36	0	36	0
Combination
Financing Receivable, Modified [Line Items]
Loans modified	5	169	5	169
Combination \| Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	3	168	3	168
Combination \| Commercial loans \| Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified		161		161
Combination \| Commercial loans \| Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	3	7	3	7
Combination \| Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	2	1	2	1
Combination \| Consumer loans \| Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified	$ 2	$ 1	$ 2	$ 1