Loans - Gross Charge-Offs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Total	$ 41	$ 8	$ 112	$ 64
Commercial loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0	0
One year prior to current year			1	0
Two years prior to current year			18	0
Three years prior to current year			0	32
Four years prior to current year			2	0
Prior			30	24
Revolving loans			55	1
Revolving Loans Converted to Term Loans			0	0
Total			106	57
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			2
Prior			27
Revolving loans			0
Revolving Loans Converted to Term Loans			0
Total	2	0	29	0
Commercial loans | Business and corporate banking
Financing Receivable, Credit Quality Indicator [Line Items]
Current year			0	0
One year prior to current year			1	0
Two years prior to current year			18	0
Three years prior to current year			0	32
Four years prior to current year			0	0
Prior			3	24
Revolving loans			55	1
Revolving Loans Converted to Term Loans			0	0
Total	37	5	77	57
Commercial loans | Other commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0	0	0	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	1
Revolving loans			5	6
Total			6	7
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			1
Revolving loans			0
Total			1
Consumer loans | Home equity mortgages
Financing Receivable, Credit Quality Indicator [Line Items]
Total	0	0	0	0
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			5	6
Total	1	2	5	6
Consumer loans | Other consumer
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	$ 0	$ 1