Segment Information - Certain Operating Data for Segments (Details) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net sales	$ 4,423.7	$ 4,327.4
Gain on sale of certain closed facilities	0.5	50.5
Restructuring and other costs	(30.1)	(54.4)
Interest expense, net	(93.5)	(94.4)
Loss on extinguishment of debt		(1.9)
Other expense, net	(3.7)	(2.7)
Income before income taxes	186.0	202.5
Depreciation, depletion and amortization	381.2	359.1
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	4,465.3	4,366.5
Segment income	331.0	324.4
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales	(41.6)	(39.1)
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Non-allocated expenses	(18.2)	(19.0)
Interest expense, net	(93.5)	(94.4)
Loss on extinguishment of debt		(1.9)
Other expense, net	(3.7)	(2.7)
Corrugated Packaging [Member]
Segment Reporting Information [Line Items]
Net sales	2,909.5	2,733.8
Depreciation, depletion and amortization	244.3	218.5
Corrugated Packaging [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	2,909.5	2,733.8
Segment income	283.4	246.8
Corrugated Packaging [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales	(18.3)	(18.0)
Corrugated Packaging [Member] \| Unaffiliated Customers [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	2,891.2	2,715.8
Consumer Packaging [Member]
Segment Reporting Information [Line Items]
Net sales	1,536.9	1,618.8
Depreciation, depletion and amortization	135.3	138.6
Consumer Packaging [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	1,536.9	1,618.8
Segment income	46.2	76.9
Consumer Packaging [Member] \| Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Net sales	(23.3)	(21.1)
Consumer Packaging [Member] \| Unaffiliated Customers [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	1,513.6	1,597.7
Land and Development [Member]
Segment Reporting Information [Line Items]
Net sales	18.9	13.9
Land and Development [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	18.9	13.9
Segment income	1.4	0.7
Land and Development [Member] \| Unaffiliated Customers [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales	18.9	13.9
Corporate Segment [Member]
Segment Reporting Information [Line Items]
Depreciation, depletion and amortization	$ 1.6	$ 2.0

The aggregate expense recognized in the current period that allocates the cost of tangible assets, intangible assets, or depleting assets to periods that benefit from use of the assets.

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