Revenue Recognition - Summary of Effect of Adoption of ASC 606 Impact on Condensed Consolidated Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Disaggregation Of Revenue [Line Items]
Consolidated net income	$ 161.9	$ 224.5	$ 301.7	$ 1,358.0
Other assets			(128.9)	(56.0)
Inventories			(67.5)	(83.0)
Income taxes			(27.0)	$ 94.1
ASC 606 [Member] | Balances Without Adoption of ASC 606 [Member]
Disaggregation Of Revenue [Line Items]
Consolidated net income	161.5		300.6
Other assets			(131.6)
Inventories			(63.4)
Income taxes			(27.3)
ASC 606 [Member] | Impact of Adoption Increase/(Decrease) [Member]
Disaggregation Of Revenue [Line Items]
Consolidated net income	$ 0.4		1.1
Other assets			2.7
Inventories			(4.1)
Income taxes			$ 0.3