Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	May 31, 2013	May 31, 2012
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	$ 17.4	$ 30.7
Derivative liabilities at fair value	45.1	60.7
Foreign Exchange Contract [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	10.7	23.8
Derivative liabilities at fair value	38.6	36.7
Commodity Contract (MMbtu) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	5.0	5.8
Derivative liabilities at fair value	6.1	23.5
Freight Contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	1.7	1.1
Derivative liabilities at fair value	0.4	0.5
Fair Value Inputs Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	8.7	20.5
Derivative liabilities at fair value	4.3	0.3
Fair Value Inputs Level 1 [Member] | Foreign Exchange Contract [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	8.7	20.1
Derivative liabilities at fair value	4.3	0.3
Fair Value Inputs Level 1 [Member] | Commodity Contract (MMbtu) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	0	0.4
Derivative liabilities at fair value	0	0
Fair Value Inputs Level 1 [Member] | Freight Contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	0	0
Derivative liabilities at fair value	0	0
Fair Value Inputs Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	7.0	9.1
Derivative liabilities at fair value	40.4	59.9
Fair Value Inputs Level 2 [Member] | Foreign Exchange Contract [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	2.0	3.7
Derivative liabilities at fair value	34.3	36.4
Fair Value Inputs Level 2 [Member] | Commodity Contract (MMbtu) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	5.0	5.4
Derivative liabilities at fair value	6.1	23.5
Fair Value Inputs Level 2 [Member] | Freight Contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	0	0
Derivative liabilities at fair value	0	0
Fair Value Inputs Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	1.7	1.1
Derivative liabilities at fair value	0.4	0.5
Fair Value Inputs Level 3 [Member] | Foreign Exchange Contract [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	0	0
Derivative liabilities at fair value	0	0
Fair Value Inputs Level 3 [Member] | Commodity Contract (MMbtu) [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	0	0
Derivative liabilities at fair value	0	0
Fair Value Inputs Level 3 [Member] | Freight Contracts [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Abstract]
Derivative assets at fair value	1.7	1.1
Derivative liabilities at fair value	$ 0.4	$ 0.5