Fee Income from Contracts with Customers - Disaggregation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Other non-fee revenue	$ 215	$ 26	$ 608	$ 475
Total other revenues	548	334	1,582	1,410
Total Fee Income
Disaggregation of Revenue [Line Items]
Total fee income from contracts with customers	333	308	974	935
Credit card fees, net
Disaggregation of Revenue [Line Items]
Total fee income from contracts with customers	14	14	45	42
Trust and investment management fees
Disaggregation of Revenue [Line Items]
Total fee income from contracts with customers	43	37	125	107
Account services
Disaggregation of Revenue [Line Items]
Total fee income from contracts with customers	84	80	243	231
Credit facilities
Disaggregation of Revenue [Line Items]
Total fee income from contracts with customers	81	69	229	243
Other fees
Disaggregation of Revenue [Line Items]
Total fee income from contracts with customers	11	8	31	29
Other fees and commissions
Disaggregation of Revenue [Line Items]
Total fee income from contracts with customers	176	157	503	503
Servicing and other fees from HSBC affiliates
Disaggregation of Revenue [Line Items]
Total fee income from contracts with customers	99	99	299	280
Insurance
Disaggregation of Revenue [Line Items]
Total fee income from contracts with customers	$ 1	$ 1	$ 2	$ 3