Fair Value Measurements Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash	$ 0	$ 2.7
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	7.0	2.2
Fair Value Assets Measured on Recurring Basis Total Assets	7.0	4.9
Fair Value, Liabilities Measured on Recurring Basis, Derivative Financial Instruments, Liabilities	0	1.9
Fair Value Liabilities Measured on Recurring Basis Total Liabilities	0	1.9
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash	0	0
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	3.3	12.3
Fair Value Assets Measured on Recurring Basis Total Assets	3.3	12.3
Fair Value, Liabilities Measured on Recurring Basis, Derivative Financial Instruments, Liabilities	0.3	0
Fair Value Liabilities Measured on Recurring Basis Total Liabilities	0.3	0
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash	0	0
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	1.6	4.7
Fair Value Assets Measured on Recurring Basis Total Assets	1.6	4.7
Fair Value, Liabilities Measured on Recurring Basis, Derivative Financial Instruments, Liabilities	0	0
Fair Value Liabilities Measured on Recurring Basis Total Liabilities	0	0
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash	0	2.7
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	11.9	19.2
Fair Value Assets Measured on Recurring Basis Total Assets	11.9	21.9
Fair Value, Liabilities Measured on Recurring Basis, Derivative Financial Instruments, Liabilities	0.3	1.9
Fair Value Liabilities Measured on Recurring Basis Total Liabilities	$ 0.3	$ 1.9