Loans - Loan Payment Modifications by Type of Modification (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Modified [Line Items]
Loans modified		$ 57	$ 313	$ 316
% of Total Loans		0.10%	0.50%	0.50%
Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	$ 82	$ 55	$ 312	$ 305
% of Total Loans	0.20%	0.10%	0.80%	0.80%
Commercial loans | Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	$ 76	$ 2	$ 235	$ 172
% of Total Loans	1.10%	0.00%	3.50%	2.50%
Commercial loans | Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	$ 6	$ 53	$ 42	$ 128
% of Total Loans	0.00%	0.30%	0.30%	0.80%
Commercial loans | Global banking
Financing Receivable, Modified [Line Items]
Loans modified			$ 35	$ 5
% of Total Loans			0.30%	0.10%
Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified	$ 0	$ 2	$ 1	$ 11
% of Total Loans		0.00%	0.00%	0.10%
Consumer loans | Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified		$ 2	$ 1	$ 11
% of Total Loans		0.00%	0.00%	0.10%
Interest Rate Reduction
Financing Receivable, Modified [Line Items]
Loans modified		$ 0	$ 0	$ 0
Interest Rate Reduction | Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Interest Rate Reduction | Commercial loans | Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Interest Rate Reduction | Commercial loans | Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	0	0	0	0
Interest Rate Reduction | Commercial loans | Global banking
Financing Receivable, Modified [Line Items]
Loans modified			0	0
Interest Rate Reduction | Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified		0	0	0
Interest Rate Reduction | Consumer loans | Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified		0	0	0
Principal Forgiveness
Financing Receivable, Modified [Line Items]
Loans modified		0	33	0
Principal Forgiveness | Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	33	0	33	0
Principal Forgiveness | Commercial loans | Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	33	0	33	0
Principal Forgiveness | Commercial loans | Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	0	0	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	0
Principal Forgiveness | Consumer loans | Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified		0	0	0
Term Extension / Significant Payment Deferral
Financing Receivable, Modified [Line Items]
Loans modified		57	115	315
Term Extension / Significant Payment Deferral | Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	49	55	115	305
Term Extension / Significant Payment Deferral | Commercial loans | Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	43	2	43	172
Term Extension / Significant Payment Deferral | Commercial loans | Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	6	53	37	128
Term Extension / Significant Payment Deferral | Commercial loans | Global banking
Financing Receivable, Modified [Line Items]
Loans modified			35	5
Term Extension / Significant Payment Deferral | Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified		2	0	10
Term Extension / Significant Payment Deferral | Consumer loans | Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified		2	0	10
Combination
Financing Receivable, Modified [Line Items]
Loans modified		0	165	1
Combination | Commercial loans
Financing Receivable, Modified [Line Items]
Loans modified	0	0	164	0
Combination | Commercial loans | Real estate, including construction
Financing Receivable, Modified [Line Items]
Loans modified	0	0	159	0
Combination | Commercial loans | Business and corporate banking
Financing Receivable, Modified [Line Items]
Loans modified	$ 0	0	5	0
Combination | Commercial loans | Global banking
Financing Receivable, Modified [Line Items]
Loans modified			0	0
Combination | Consumer loans
Financing Receivable, Modified [Line Items]
Loans modified		0	1	1
Combination | Consumer loans | Residential mortgages
Financing Receivable, Modified [Line Items]
Loans modified		$ 0	$ 1	$ 1