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Business Segment Information - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2020 USD ($)	Sep. 30, 2021 USD ($) segment	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)
Segment Reporting Information [Line Items]
Number of operating segments \| segment		3
Gain (loss) related to litigation settlement	$ 70.0
Identifiable assets		$ 10,701.6	$ 7,264.7	$ 6,113.0
Sales		6,997.4	6,329.8	6,694.8
Intelligent Devices
Segment Reporting Information [Line Items]
Identifiable assets		2,143.3	1,585.0	1,550.0
Sales		3,311.9	2,956.0
U.S. Plans
Segment Reporting Information [Line Items]
Sales		$ 3,740.2	$ 3,425.1	$ 3,640.2
Customer Concentration Risk \| Revenue from Contract with Customer Benchmark \| Systems And Services
Segment Reporting Information [Line Items]
Portion of total sales from individual segment		10.00%	10.00%	10.00%
Corporate
Segment Reporting Information [Line Items]
Identifiable assets		$ 2,433.6	$ 2,692.0	$ 2,557.0
Corporate \| Shared by segments and used in operating activities
Segment Reporting Information [Line Items]
Identifiable assets		$ 275.8	$ 247.3	$ 230.3