Consolidated Statements of Comprehensive Income (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Statement of Comprehensive Income [Abstract]
Net derivative gains (losses) and other costs arising during the period, net of tax expense	$ 0.0	$ 3.5
Reclassification of (gains) into net income (loss), net of tax (expense)	$ (0.2)	$ (0.4)

Amount of tax expense (benefit) for reclassification adjustment from accumulated other comprehensive income (loss) for unrealized gain (loss) from increase (decrease) in instrument-specific credit risk, realized upon derecognition of financial liability measured under fair value option.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 825
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 6
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482736/825-10-45-6

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-12

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10A
-Subparagraph (l)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-10A

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 30
-Subparagraph (d)(4)
-SubTopic 10
-Topic 825
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482907/825-10-50-30

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration