Financial Results by Quarter (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
Quarterly Financial Data [Abstract]
Net sales	$ 4,471.5	$ 4,236.3	$ 4,447.3	$ 4,423.7	$ 4,651.6	$ 4,690.0	$ 4,620.0	$ 4,327.4	$ 17,578.8	$ 18,289.0	$ 16,285.1
Gross profit	813.4	770.0	804.8	809.0	1,078.7	988.9	899.6	781.8	3,197.2	3,749.0	3,362.0
(Gain) loss on disposal of assets	(10.4)	1.0	(5.6)	(1.3)	(3.9)	6.5		(43.8)	(16.3)	(41.2)	10.1
Multiemployer pension withdrawal (income) expense		(2.0)	0.9		(4.6)	(1.7)			(1.1)	(6.3)	184.2
Land and Development impairments							13.0			13.0	31.9
Restructuring and other costs	56.5	9.7	16.4	30.1	66.6	17.9	34.8	54.4	112.7	173.7	105.4
Goodwill impairment	1,333.2								1,333.2
(Loss) gain on extinguishment of debt	(0.4)	(0.6)	(0.5)		(0.4)	(3.2)	0.4	(1.9)	(1.5)	(5.1)	(0.1)
Income tax (expense) benefit	(40.0)	(19.2)	(57.8)	(46.5)	(89.3)	(77.6)	(47.2)	(62.7)	(163.5)	(276.8)	874.5
Consolidated net income (loss)	(1,154.5)	180.0	148.9	139.5	312.4	253.8	161.9	139.8	(686.1)	867.9	1,909.3
Net income (loss) attributable to common stockholders	$ (1,156.0)	$ 178.5	$ 148.1	$ 138.5	$ 310.8	$ 252.6	$ 160.4	$ 139.1	$ (690.9)	$ 862.9	$ 1,906.1
Basic earnings (loss) per share attributable to common stockholders	$ (4.45)	$ 0.69	$ 0.57	$ 0.54	$ 1.21	$ 0.98	$ 0.63	$ 0.55	$ (2.67)	$ 3.36	$ 7.46
Diluted earnings (loss) per share attributable to common stockholders	$ (4.45)	$ 0.69	$ 0.57	$ 0.53	$ 1.20	$ 0.98	$ 0.62	$ 0.54	$ (2.67)	$ 3.33	$ 7.34