Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 49
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482785/280-10-55-49

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 18
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482810/280-10-50-18

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Operating Segments - Narrative (Details) $ in Millions	3 Months Ended	6 Months Ended
Operating Segments - Narrative (Details) $ in Millions	Jun. 30, 2024 USD ($)	Jun. 30, 2025 numberOfSegments	Jun. 30, 2024 USD ($)
Segment Reporting Information [Line Items]
Number of Major Reportable Business Segments \| numberOfSegments		2
CSBB \| Operating Segments
Segment Reporting Information [Line Items]
Net interest income segment realignment	$ (128)		$ (261)
WB \| Operating Segments
Segment Reporting Information [Line Items]
Net interest income segment realignment	$ (45)		$ (94)