Loans - Gross Charge-Offs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 87	$ 62	$ 26
Commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	4	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	41	11
Revolving loans	1	20
Revolving Loans Converted to Term Loans	0	0
Total	78	48
Commercial loans | Real estate, including construction
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	17
Revolving loans	0
Revolving Loans Converted to Term Loans	0
Total	17	0	3
Commercial loans | Business and corporate banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year	4	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	11
Revolving loans	1	20
Revolving Loans Converted to Term Loans	0	0
Total	58	48	9
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	3	0	9
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	8	8
Total	9	14
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	1	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	8	8
Total	8	8	1
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	$ 1	$ 1