Goodwill and Intangible Assets (Schedule Of Intangible Assets Subject To Amortization) (Details) - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ (518.8)	$ (376.7)
Total intangible assets, Gross Carrying Amount	1,788.4	1,821.4
Total intangible assets, Net Carrying Amount	$ 1,269.6	1,444.7
Customer relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (Years)	2 years 3 months 18 days
Finite-Lived Intangible Assets, Gross	$ 154.6	154.6
Accumulated Amortization	(151.0)	(122.3)
Net Carrying Amount	$ 3.6	32.3
Computer Software, Intangible Asset [Member]
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (Years)	2 years 8 months 12 days
Finite-Lived Intangible Assets, Gross	$ 72.1	105.1
Accumulated Amortization	(30.3)	(45.2)
Net Carrying Amount	41.8	59.9
In Process Research and Development [Member]
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	0.0	0.0
Indefinite-lived Intangible Assets (Excluding Goodwill)	$ 271.3	280.8
Developed Technology Rights
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (Years)	6 years 1 month 6 days
Finite-Lived Intangible Assets, Gross	$ 1,290.4	1,280.9
Accumulated Amortization	(337.5)	(209.2)
Net Carrying Amount	$ 952.9	$ 1,071.7
Developed Technology Rights | Silicon Labs Industrial and Automotive Business
Finite-Lived Intangible Assets [Line Items]
Weighted Average Amortization Period (Years)	12 years