Goodwill and Intangible Assets (Schedule Of Intangible Assets Subject To Amortization) (Details) - USD ($) $ in Millions	Mar. 31, 2023	Sep. 30, 2022
Finite-Lived Intangible Assets [Line Items]
Accumulated Amortization	$ (469.0)	$ (376.7)
Total intangible assets, Gross Carrying Amount	1,790.6	1,821.4
Total intangible assets, Net Carrying Amount	$ 1,321.6	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	(147.5)	(122.3)
Net Carrying Amount	$ 7.1	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	$ 74.3	105.1
Accumulated Amortization	(26.0)	(45.2)
Net Carrying Amount	48.3	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	(295.5)	(209.2)
Net Carrying Amount	$ 994.9	$ 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