Goodwill and Other Intangibles - Goodwill by Reportable Segment (Details) $ in Millions	9 Months Ended
	Jun. 30, 2016 USD ($)
Successor
Goodwill
Balance at September 30, 2015	$ 0.0
Business Combination	695.6
Foreign currency translation	(2.2)
Balance at June 8, 2016	693.4
Successor | Chemicals
Goodwill
Balance at September 30, 2015	0.0
Business Combination	335.3
Foreign currency translation	(0.1)
Balance at June 8, 2016	335.2
Successor | Plastics
Goodwill
Balance at September 30, 2015	0.0
Business Combination	295.0
Foreign currency translation	(2.1)
Balance at June 8, 2016	292.9
Successor | Other
Goodwill
Balance at September 30, 2015	0.0
Business Combination	65.3
Foreign currency translation	0.0
Balance at June 8, 2016	65.3
Predecessor
Goodwill
Balance at September 30, 2015	373.7
Predecessor | Chemicals
Goodwill
Balance at September 30, 2015	269.7
Predecessor | Plastics
Goodwill
Balance at September 30, 2015	91.5
Predecessor | Other
Goodwill
Balance at September 30, 2015	$ 12.5