Selected Condensed Consolidating Financial Statements of Parent, Issuer, Guarantors and Non-Guarantors - Condensed Consolidating Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Mar. 31, 2018
Condensed Income Statements Captions [Line Items]
Net sales	$ 4,620.0	$ 4,017.0		$ 8,947.4	$ 7,911.0
Cost of goods sold	3,720.4	3,227.6		7,266.0	6,348.1
Selling, general and administrative, excluding intangible amortization	444.1	395.8		845.0	776.6
Selling, general and administrative intangible amortization	102.4	75.2		195.3	147.7
Loss (gain) on disposal of assets		2.8		(43.8)	3.9
Multiemployer pension withdrawals					180.0
Land and Development impairments	13.0		$ 27.6	13.0	27.6
Restructuring and other costs	34.8	31.7		89.2	48.0
Operating profit (loss)	305.3	283.9		582.7	379.1
Interest expense, net	(111.8)	(78.3)		(206.2)	(143.1)
Gain (loss) on extinguishment of debt	0.4	0.1		(1.5)	(0.9)
Pension and other postretirement non- service (expense) income	18.7	24.6		36.0	49.2
Other (expense) income, net	(3.3)	1.1		(6.0)	3.6
Equity in income of unconsolidated entities	(0.2)	11.9		6.6	15.7
Income before income taxes	209.1	243.3		411.6	303.6
Income tax benefit (expense)	(47.2)	(18.8)		(109.9)	1,054.4
Consolidated net income	161.9	224.5		301.7	1,358.0
Less: Net (income) loss attributable to noncontrolling interests	(1.5)	(1.3)		(2.2)	0.3
Net income attributable to common stockholders	160.4	223.2		299.5	1,358.3
Comprehensive income (loss) attributable to common stockholders	189.7	279.1		269.3	1,373.9
Parent [Member]
Condensed Income Statements Captions [Line Items]
Interest expense, net		(0.1)			(0.1)
Equity in income of consolidated entities	160.4			299.5
Income before income taxes	160.4	(0.1)		299.5	(0.1)
Consolidated net income	160.4	(0.1)		299.5	(0.1)
Net income attributable to common stockholders	160.4	(0.1)		299.5	(0.1)
Comprehensive income (loss) attributable to common stockholders	189.7	(0.1)		269.3	(0.1)
Issuer [Member]
Condensed Income Statements Captions [Line Items]
Selling, general and administrative, excluding intangible amortization	0.3	0.4		0.4	0.4
Multiemployer pension withdrawals					6.5
Restructuring and other costs	3.9	2.5		3.9	3.3
Operating profit (loss)	(4.2)	(2.9)		(4.3)	(10.2)
Interest expense, net	(65.0)	(28.6)		(112.0)	(43.9)
Intercompany interest income (expense), net	0.5	6.2		3.5	11.8
Gain (loss) on extinguishment of debt		(0.7)		(1.8)	(1.6)
Other (expense) income, net	(3.4)	0.6		(4.0)	1.0
Equity in income of consolidated entities	196.9	242.4		396.7	1,394.4
Income before income taxes	124.8	217.0		278.1	1,351.5
Income tax benefit (expense)	14.1	6.3		29.0	6.9
Consolidated net income	138.9	223.3		307.1	1,358.4
Net income attributable to common stockholders	138.9	223.3		307.1	1,358.4
Comprehensive income (loss) attributable to common stockholders	168.3	279.2		277.1	1,374.0
Guarantor Subsidiaries [Member]
Condensed Income Statements Captions [Line Items]
Net sales	639.2	633.7		1,263.0	1,243.8
Cost of goods sold	526.8	512.1		1,027.7	959.6
Selling, general and administrative, excluding intangible amortization	14.2	24.9		27.3	49.3
Selling, general and administrative intangible amortization	26.3	26.1		52.3	52.1
Loss (gain) on disposal of assets		0.1			0.1
Multiemployer pension withdrawals					12.5
Restructuring and other costs		4.2		0.1	5.3
Operating profit (loss)	71.9	66.3		155.6	164.9
Interest expense, net	(42.0)	(43.5)		(91.9)	(87.7)
Intercompany interest income (expense), net	(27.5)	(16.5)		(54.6)	(32.3)
Gain (loss) on extinguishment of debt	0.4	0.9		0.4	0.9
Pension and other postretirement non- service (expense) income	(1.7)	(0.2)		(3.4)	(0.3)
Other (expense) income, net	(1.0)	2.6		(0.4)	4.3
Equity in income of unconsolidated entities					2.5
Equity in income of consolidated entities	168.8	129.5		417.3	1,023.1
Income before income taxes	168.9	139.1		423.0	1,075.4
Income tax benefit (expense)	0.6	(0.1)		(1.3)	124.4
Consolidated net income	169.5	139.0		421.7	1,199.8
Net income attributable to common stockholders	169.5	139.0		421.7	1,199.8
Comprehensive income (loss) attributable to common stockholders	201.6	213.9		394.5	1,229.5
Non-Guarantor Subsidiaries [Member]
Condensed Income Statements Captions [Line Items]
Net sales	4,638.1	4,034.3		8,971.9	7,958.0
Cost of goods sold	3,850.9	3,366.5		7,525.8	6,679.3
Selling, general and administrative, excluding intangible amortization	429.6	370.5		817.3	726.9
Selling, general and administrative intangible amortization	76.1	49.1		143.0	95.6
Loss (gain) on disposal of assets		2.7		(43.8)	3.8
Multiemployer pension withdrawals					161.0
Land and Development impairments	13.0			13.0	27.6
Restructuring and other costs	30.9	25.0		85.2	39.4
Operating profit (loss)	237.6	220.5		431.4	224.4
Interest expense, net	(4.8)	(6.1)		(2.3)	(11.4)
Intercompany interest income (expense), net	27.0	10.3		51.1	20.5
Gain (loss) on extinguishment of debt		(0.1)		(0.1)	(0.2)
Pension and other postretirement non- service (expense) income	20.4	24.8		39.4	49.5
Other (expense) income, net	1.1	(2.1)		(1.6)	(1.7)
Equity in income of unconsolidated entities	(0.2)	11.9		6.6	13.2
Income before income taxes	281.1	259.2		524.5	294.3
Income tax benefit (expense)	(61.9)	(25.0)		(137.6)	923.1
Consolidated net income	219.2	234.2		386.9	1,217.4
Less: Net (income) loss attributable to noncontrolling interests	(1.5)	(1.3)		(2.2)	0.3
Net income attributable to common stockholders	217.7	232.9		384.7	1,217.7
Comprehensive income (loss) attributable to common stockholders	247.0	288.8		354.7	1,233.6
Eliminations [Member]
Condensed Income Statements Captions [Line Items]
Net sales	(657.3)	(651.0)		(1,287.5)	(1,290.8)
Cost of goods sold	(657.3)	(651.0)		(1,287.5)	(1,290.8)
Equity in income of consolidated entities	(526.1)	(371.9)		(1,113.5)	(2,417.5)
Income before income taxes	(526.1)	(371.9)		(1,113.5)	(2,417.5)
Consolidated net income	(526.1)	(371.9)		(1,113.5)	(2,417.5)
Net income attributable to common stockholders	(526.1)	(371.9)		(1,113.5)	(2,417.5)
Comprehensive income (loss) attributable to common stockholders	$ (616.9)	$ (502.7)		$ (1,026.3)	$ (2,463.1)