Selected Condensed Consolidating Financial Statements of Parent, Issuer, Guarantors and Non-Guarantors - Condensed Consolidating Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2019	Jun. 30, 2018
Condensed Income Statements Captions [Line Items]
Net sales	$ 4,690.0		$ 4,137.5		$ 13,637.4	$ 12,048.5
Cost of goods sold	3,701.1		3,270.4		10,967.1	9,618.5
Selling, general and administrative, excluding intangible amortization	442.4		380.7		1,287.4	1,157.3
Selling, general and administrative intangible amortization	102.4		75.6		297.7	223.3
Loss (gain) on disposal of assets	6.5		2.7		(37.3)	6.6
Multiemployer pension withdrawals	(1.7)		4.2		(1.7)	184.2
Land and Development impairments		$ 13.0	1.7	$ 27.6	13.0	29.3
Restructuring and other costs	17.9		17.1		107.1	65.1
Operating profit (loss)	421.4		385.1		1,004.1	764.2
Interest expense, net	(111.1)		(76.7)		(317.3)	(219.8)
Gain (loss) on extinguishment of debt	(3.2)		0.9		(4.7)
Pension and other postretirement non- service (expense) income	18.9		21.3		54.9	70.5
Other (expense) income, net	3.7		9.7		(2.3)	13.3
Equity in income of unconsolidated entities	1.7		15.5		8.3	31.2
Income before income taxes	331.4		355.8		743.0	659.4
Income tax benefit (expense)	(77.6)		(84.5)		(187.5)	969.9
Consolidated net income (loss)	253.8		271.3		555.5	1,629.3
Less: Net income attributable to noncontrolling interests	(1.2)		(3.1)		(3.4)	(2.8)
Net income (loss) attributable to common stockholders	252.6		268.2		552.1	1,626.5
Comprehensive (loss) income attributable to common stockholders	282.7		35.6		552.0	1,409.5
Parent [Member]
Condensed Income Statements Captions [Line Items]
Interest expense, net			(0.6)			(0.7)
Equity in income (loss) of consolidated entities	252.6				552.1
Income before income taxes	252.6		(0.6)		552.1	(0.7)
Consolidated net income (loss)	252.6		(0.6)		552.1	(0.7)
Net income (loss) attributable to common stockholders	252.6		(0.6)		552.1	(0.7)
Comprehensive (loss) income attributable to common stockholders	282.7		(0.6)		552.0	(0.7)
Issuer [Member]
Condensed Income Statements Captions [Line Items]
Selling, general and administrative, excluding intangible amortization	(0.4)					0.4
Multiemployer pension withdrawals						6.5
Restructuring and other costs	1.4		3.0		5.3	6.3
Operating profit (loss)	(1.0)		(3.0)		(5.3)	(13.2)
Interest expense, net	(66.5)		(21.6)		(178.5)	(65.5)
Intercompany interest income (expense), net	(2.5)		8.5		1.0	20.3
Gain (loss) on extinguishment of debt	(0.8)				(2.6)	(1.6)
Other (expense) income, net			(0.3)		(4.0)	0.7
Equity in income (loss) of consolidated entities	268.2		281.7		664.9	1,676.1
Income before income taxes	197.4		265.3		475.5	1,616.8
Income tax benefit (expense)	17.9		3.5		46.9	10.4
Consolidated net income (loss)	215.3		268.8		522.4	1,627.2
Net income (loss) attributable to common stockholders	215.3		268.8		522.4	1,627.2
Comprehensive (loss) income attributable to common stockholders	244.9		36.2		522.0	1,410.2
Guarantor Subsidiaries [Member]
Condensed Income Statements Captions [Line Items]
Net sales	643.0		673.1		1,906.0	1,916.9
Cost of goods sold	475.6		529.7		1,503.3	1,489.3
Selling, general and administrative, excluding intangible amortization	26.0		20.9		53.3	70.2
Selling, general and administrative intangible amortization	26.1		26.1		78.4	78.2
Loss (gain) on disposal of assets	0.1				0.1	0.1
Multiemployer pension withdrawals						12.5
Restructuring and other costs	0.1		0.1		0.2	5.4
Operating profit (loss)	115.1		96.3		270.7	261.2
Interest expense, net	(36.9)		(43.0)		(128.8)	(130.7)
Intercompany interest income (expense), net	(33.3)		(19.7)		(87.9)	(52.0)
Gain (loss) on extinguishment of debt	(2.3)		1.0		(1.9)	1.9
Pension and other postretirement non- service (expense) income	(1.4)				(4.8)	(0.3)
Other (expense) income, net	(35.2)		(8.9)		(35.6)	(4.6)
Equity in income of unconsolidated entities			5.0			7.5
Equity in income (loss) of consolidated entities	(19.5)		159.3		397.8	1,182.4
Income before income taxes	(13.5)		190.0		409.5	1,265.4
Income tax benefit (expense)	(1.9)		(4.9)		(3.2)	119.5
Consolidated net income (loss)	(15.4)		185.1		406.3	1,384.9
Net income (loss) attributable to common stockholders	(15.4)		185.1		406.3	1,384.9
Comprehensive (loss) income attributable to common stockholders	12.0		(38.2)		406.5	1,191.3
Non-Guarantor Subsidiaries [Member]
Condensed Income Statements Captions [Line Items]
Net sales	4,676.3		4,138.2		13,648.2	12,096.2
Cost of goods sold	3,844.9		3,414.5		11,370.7	10,093.8
Selling, general and administrative, excluding intangible amortization	416.8		359.8		1,234.1	1,086.7
Selling, general and administrative intangible amortization	76.3		49.5		219.3	145.1
Loss (gain) on disposal of assets	6.4		2.7		(37.4)	6.5
Multiemployer pension withdrawals	(1.7)		4.2		(1.7)	165.2
Land and Development impairments			1.7		13.0	29.3
Restructuring and other costs	16.4		14.0		101.6	53.4
Operating profit (loss)	317.2		291.8		748.6	516.2
Interest expense, net	(7.7)		(11.5)		(10.0)	(22.9)
Intercompany interest income (expense), net	25.9		11.2		77.0	31.7
Gain (loss) on extinguishment of debt	(0.1)		(0.1)		(0.2)	(0.3)
Pension and other postretirement non- service (expense) income	20.3		21.3		59.7	70.8
Other (expense) income, net	38.9		18.9		37.3	17.2
Equity in income of unconsolidated entities	1.7		10.5		8.3	23.7
Income before income taxes	396.2		342.1		920.7	636.4
Income tax benefit (expense)	(93.6)		(83.1)		(231.2)	840.0
Consolidated net income (loss)	302.6		259.0		689.5	1,476.4
Less: Net income attributable to noncontrolling interests	(1.2)		(3.1)		(3.4)	(2.8)
Net income (loss) attributable to common stockholders	301.4		255.9		686.1	1,473.6
Comprehensive (loss) income attributable to common stockholders	332.2		23.1		686.9	1,256.7
Eliminations [Member]
Condensed Income Statements Captions [Line Items]
Net sales	(629.3)		(673.8)		(1,916.8)	(1,964.6)
Cost of goods sold	(619.4)		(673.8)		(1,906.9)	(1,964.6)
Operating profit (loss)	(9.9)				(9.9)
Intercompany interest income (expense), net	9.9				9.9
Equity in income (loss) of consolidated entities	(501.3)		(441.0)		(1,614.8)	(2,858.5)
Income before income taxes	(501.3)		(441.0)		(1,614.8)	(2,858.5)
Consolidated net income (loss)	(501.3)		(441.0)		(1,614.8)	(2,858.5)
Net income (loss) attributable to common stockholders	(501.3)		(441.0)		(1,614.8)	(2,858.5)
Comprehensive (loss) income attributable to common stockholders	$ (589.1)		$ 15.1		$ (1,615.4)	$ (2,448.0)