Derivative Financial Instruments (Details) In Millions, unless otherwise specified	Mar. 31, 2015 Exchange-Traded Derivatives Long item	Mar. 31, 2015 Exchange-Traded Derivatives Short item	Mar. 31, 2015 OTC Derivatives (Petroleum/Ethanol) Long item	Mar. 31, 2015 OTC Derivatives (Petroleum/Ethanol) Short item	Mar. 31, 2015 OTC Derivatives (Natural Gas) Long item	Mar. 31, 2015 OTC Derivatives (Natural Gas) Short item	Mar. 31, 2015 Interest rate swaps USD ($)	Mar. 31, 2015 Interest rate cap USD ($)	Mar. 31, 2015 Open Forward Exchange Contracts USD ($)	Mar. 31, 2015 Open Forward Exchange Contracts CAD
Volume of activity related to derivative financial instruments
Nonmonetary units	46,736,000	(50,292,000)	13,318,000	(10,167,000)	10,607,000	(10,661,000)
Monetary units							$ 200.0	$ 100.0	$ 4.7	6.0
Forward rate of CAD to USD									1.2662	1.2662