Loans - Gross Charge-Offs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 8	$ 36	$ 64	$ 52
Commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0	0
One year prior to current year			0	0
Two years prior to current year			0	17
Three years prior to current year			32	0
Four years prior to current year			0	0
Prior			24	9
Revolving loans			1	14
Revolving Loans Converted to Term Loans			0	0
Total			57	40
Commercial loans | Business and corporate banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0	0
One year prior to current year			0	0
Two years prior to current year			0	17
Three years prior to current year			32	0
Four years prior to current year			0	0
Prior			21	9
Revolving loans			1	14
Revolving Loans Converted to Term Loans			0	0
Total	5	34	54	40
Commercial loans | Global banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0
One year prior to current year			0
Two years prior to current year			0
Three years prior to current year			0
Four years prior to current year			0
Prior			3
Revolving loans			0
Revolving Loans Converted to Term Loans			0
Total	0	0	3	0
Consumer loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0	0
One year prior to current year			0	0
Two years prior to current year			0	0
Three years prior to current year			0	0
Four years prior to current year			0	0
Prior			1	6
Revolving loans			6	6
Total			7	12
Consumer loans | Residential mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year				0
One year prior to current year				0
Two years prior to current year				0
Three years prior to current year				0
Four years prior to current year				0
Prior				4
Revolving loans				0
Total				4
Consumer loans | Home equity mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Current year				0
One year prior to current year				0
Two years prior to current year				0
Three years prior to current year				0
Four years prior to current year				0
Prior				1
Revolving loans				0
Total	0	0	0	1
Consumer loans | Credit cards
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0	0
One year prior to current year			0	0
Two years prior to current year			0	0
Three years prior to current year			0	0
Four years prior to current year			0	0
Prior			0	0
Revolving loans			6	6
Total	2	2	6	6
Consumer loans | Other consumer
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0	0
One year prior to current year			0	0
Two years prior to current year			0	0
Three years prior to current year			0	0
Four years prior to current year			0	0
Prior			1	1
Revolving loans			0	0
Total	$ 1	$ 0	$ 1	$ 1