Loans - Gross Charge-Offs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 3	$ 11
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	0
Three years prior to current year	0	0
Four years prior to current year	0	0
Prior	0	2
Revolving loans	1	3
Revolving Loans Converted to Term Loans	0	0
Total	1	5
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	0
Three years prior to current year	0	0
Four years prior to current year	0	0
Prior	0	2
Revolving loans	1	3
Revolving Loans Converted to Term Loans	0	0
Total	1	5
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	0	4
Revolving loans	2	2
Total	2	6
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		3
Revolving loans		0
Total		3
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
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	2	2
Total	$ 2	$ 2