Acquisitions (Details) $ in Millions			3 Months Ended		9 Months Ended		12 Months Ended
	Aug. 03, 2015 USD ($) item	Mar. 11, 2015 USD ($) Plant	Sep. 30, 2015 USD ($) employee	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($) employee	Sep. 30, 2014 USD ($)	Aug. 31, 2014 USD ($)	Dec. 31, 2014 USD ($)
Business Acquisition [Line Items]
Net sales			$ 1,436.7	$ 1,460.3	$ 4,215.8	$ 4,300.1
Number of people | employee			11,900		11,900
Preliminary purchase price allocation
Goodwill			$ 601.0		$ 601.0			$ 478.0
Penford
Business Acquisition [Line Items]
Total purchase consideration		$ 332.0
Extinguishment of debt in conjunction with the acquisition		$ 93.0
Net sales							$ 444.0
Number of Plants | Plant		6
Preliminary purchase price allocation
Working capital (excluding cash)		$ 68.0
Property, plant and equipment		86.0
Other assets		9.0
Identifiable intangible assets		121.0
Goodwill		119.0
Non-current liabilities assumed		(71.0)
Total preliminary purchase price		$ 332.0
Kerr
Business Acquisition [Line Items]
Total purchase consideration	$ 102.0
Number of people | item	80
Preliminary purchase price allocation
Working capital (excluding cash)	$ 38.0
Property, plant and equipment	8.0
Identifiable intangible assets	29.0
Goodwill	27.0
Total preliminary purchase price	$ 102.0