FINANCIAL INFORMATION FOR SUBSIDIARY GUARANTORS AND NON-GUARANTORS - Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 30, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Condensed Statement of Income Captions [Line Items]
Net income (loss)	$ (146.9)	$ 82.8	$ 149.0	$ (21.2)	$ (33.4)	$ 151.9	$ 165.2	$ (64.9)	$ 63.7	$ 218.8	$ 314.8
Net foreign currency translation adjustment									9.0	28.2	(6.2)
Net change in derivatives									6.2	6.7	4.3
Net change in pension and other post-retirement benefits									8.0	13.2	(8.2)
Total other comprehensive income (loss)									23.2	48.1	(10.1)
Comprehensive income									86.9	266.9	304.7
Comprehensive (income) loss attributable to noncontrolling interest									0.0	(0.9)	0.5
Comprehensive income attributable to controlling interest									86.9	266.0	305.2
Reportable Legal Entities | Parent
Condensed Statement of Income Captions [Line Items]
Net income (loss)									65.1	219.8	317.0
Net foreign currency translation adjustment									9.0	28.2	(6.2)
Net change in derivatives									6.2	6.7	4.3
Net change in pension and other post-retirement benefits									8.0	13.2	(8.2)
Total other comprehensive income (loss)									23.2	48.1	(10.1)
Comprehensive income									88.3	267.9	306.9
Comprehensive (income) loss attributable to noncontrolling interest									0.0	0.0	0.0
Comprehensive income attributable to controlling interest									88.3	267.9	306.9
Reportable Legal Entities | Subsidiary Guarantors
Condensed Statement of Income Captions [Line Items]
Net income (loss)									145.4	235.6	338.7
Net foreign currency translation adjustment									0.0	0.0	0.0
Net change in derivatives									3.5	2.8	0.3
Net change in pension and other post-retirement benefits									2.8	3.7	0.4
Total other comprehensive income (loss)									6.3	6.5	0.7
Comprehensive income									151.7	242.1	339.4
Comprehensive (income) loss attributable to noncontrolling interest									0.0	0.0	0.0
Comprehensive income attributable to controlling interest									151.7	242.1	339.4
Reportable Legal Entities | Non- Guarantors
Condensed Statement of Income Captions [Line Items]
Net income (loss)									(53.4)	31.1	17.2
Net foreign currency translation adjustment									9.0	28.2	(6.2)
Net change in derivatives									0.0	0.0	0.0
Net change in pension and other post-retirement benefits									5.2	9.5	(8.6)
Total other comprehensive income (loss)									14.2	37.7	(14.8)
Comprehensive income									(39.2)	68.8	2.4
Comprehensive (income) loss attributable to noncontrolling interest									0.0	0.0	0.0
Comprehensive income attributable to controlling interest									(39.2)	68.8	2.4
Eliminations/ Consolidations
Condensed Statement of Income Captions [Line Items]
Net income (loss)									(93.4)	(267.7)	(358.1)
Net foreign currency translation adjustment									(9.0)	(28.2)	6.2
Net change in derivatives									(3.5)	(2.8)	(0.3)
Net change in pension and other post-retirement benefits									(8.0)	(13.2)	8.2
Total other comprehensive income (loss)									(20.5)	(44.2)	14.1
Comprehensive income									(113.9)	(311.9)	(344.0)
Comprehensive (income) loss attributable to noncontrolling interest									0.0	(0.9)	0.5
Comprehensive income attributable to controlling interest									$ (113.9)	$ (312.8)	$ (343.5)