SEGMENT INFORMATION - Net Sales, Profit (Loss), and Total Assets by Segment (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 28, 2020 USD ($)	Mar. 30, 2019 USD ($)	Mar. 28, 2020 USD ($) segment	Mar. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)
Segment Reporting [Abstract]
Number of reportable segments | segment			3
Segment Reporting Information [Line Items]
Net sales	$ 1,382.8	$ 1,189.9	$ 1,748.6	$ 1,488.0
Impairment, restructuring and other	0.3	0.2	(2.2)	3.7
Equity in income of unconsolidated affiliates	0.0	2.0	0.0	3.3
Costs related to refinancing	0.0	0.0	(15.1)	0.0
Interest expense	(22.7)	(28.9)	(42.7)	(54.1)
Other non-operating income, net	2.8	260.1	5.4	262.9
Total assets:
Total assets	4,135.7	3,956.5	4,135.7	3,956.5	$ 3,028.7
Continuing Operations
Segment Reporting Information [Line Items]
Segment profit (loss)	333.8	523.4	238.7	417.5
Intangible asset amortization	(8.1)	(8.4)	(15.8)	(16.8)
Impairment, restructuring and other	3.7	1.2	1.4	7.2
Equity in income of unconsolidated affiliates	0.0	2.0	0.0	3.3
Costs related to refinancing	0.0	0.0	(15.1)	0.0
Interest expense	(22.7)	(28.9)	(42.7)	(54.1)
Other non-operating income, net	2.8	260.1	5.4	262.9
Continuing Operations | Operating Segments
Segment Reporting Information [Line Items]
Segment profit (loss)	402.4	334.1	371.3	291.5
Continuing Operations | Corporate
Segment Reporting Information [Line Items]
Segment profit (loss)	(36.9)	(34.3)	(63.0)	(62.1)
U.S. Consumer
Segment Reporting Information [Line Items]
Net sales	1,102.7	993.5	1,250.1	1,130.4
U.S. Consumer | Continuing Operations | Operating Segments
Segment Reporting Information [Line Items]
Segment profit (loss)	372.9	320.0	331.5	277.0
Hawthorne
Segment Reporting Information [Line Items]
Net sales	230.0	144.1	428.8	284.8
Hawthorne | Continuing Operations | Operating Segments
Segment Reporting Information [Line Items]
Segment profit (loss)	25.5	10.3	39.4	14.7
Other
Segment Reporting Information [Line Items]
Net sales	50.1	52.3	69.7	72.8
Other | Continuing Operations | Operating Segments
Segment Reporting Information [Line Items]
Segment profit (loss)	$ 4.0	$ 3.8	$ 0.4	$ (0.2)