Segment Information - Changes in Carrying Amount of Goodwill (Details) $ in Millions	9 Months Ended
	Jun. 30, 2022 USD ($)
Goodwill [Line Items]
Balance at beginning of period	$ 5,959.2
Goodwill acquired	3.2
Translation adjustments	(33.6)
Balance at end of period	5,928.8
Legacy Reportable Corrugated Packaging Segment [Member]
Goodwill [Line Items]
Balance at beginning of period	3,663.3
Segment recasting	(3,663.3)	[1]
Legacy Reportable Consumer Packaging Segment [Member]
Goodwill [Line Items]
Balance at beginning of period	2,295.9
Segment recasting	(2,295.9)	[1]
New Reportable Corrugated Packaging Segment [Member]
Goodwill [Line Items]
Segment recasting	2,834.8	[1]
Goodwill acquired	3.2
Translation adjustments	(19.2)
Balance at end of period	2,818.8
New Reportable Consumer Packaging Segment [Member]
Goodwill [Line Items]
Segment recasting	1,603.3	[1]
Translation adjustments	(5.9)
Balance at end of period	1,597.4
New Reportable Global Paper Segment [Member]
Goodwill [Line Items]
Segment recasting	1,382.0	[1]
Translation adjustments	(7.7)
Balance at end of period	1,374.3
New Reportable Distribution Segment [Member]
Goodwill [Line Items]
Segment recasting	139.1	[1]
Translation adjustments	(0.8)
Balance at end of period	$ 138.3

[1] Represents reallocation of goodwill as a result of changes in segments on October 1, 2021.