Debt (Details 2) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	May 31, 2011	Feb. 29, 2008
Revolving Loans
Revolving loans
Total Amount Committed by Lenders	$ 427.2
Outstanding Borrowings	55.0
Outstanding Letters of Credit	119.2
Total Amount Available	253.0
U.S. Dollar revolving loans under the Amended Credit Agreement
Revolving loans
Weighted Average Interest Rate (as a percent)	1.40%
Total Amount Committed by Lenders	250.0	250.0	230.0
Outstanding Borrowings	55.0
Outstanding Letters of Credit	1.2
Total Amount Available	193.8
Other revolving loans
Revolving loans
Total Amount Committed by Lenders	177.2
Outstanding Letters of Credit	118.0
Total Amount Available	$ 59.2