Debt (Details 3) (Revolving Loans, USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	May 31, 2011
Revolving loans
Total Amount Committed by Lenders	$ 484.4
Outstanding Borrowings	112.5
Outstanding Letters of Credit	136.8	150.3
Total Amount Available	235.1
US Dollar revolving loans under the Amended Credit Agreement
Revolving loans
Weighted Average Interest Rate (as a percent)	1.30%
Total Amount Committed by Lenders	250.0		250.0
Outstanding Borrowings	112.5
Outstanding Letters of Credit	6.6
Total Amount Available	130.9
Other revolving lines of credit
Revolving loans
Total Amount Committed by Lenders	234.4
Outstanding Letters of Credit	130.2
Total Amount Available	$ 104.2