Fair Value Measurements Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash	$ 17.9	$ 45.5
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	2.7	0.3
Fair Value Assets Measured on Recurring Basis Total Assets	20.6	45.8
Fair Value, Liabilities Measured on Recurring Basis, Derivative Financial Instruments, Liabilities	0.5	8.2
Fair Value Liabilities Measured on Recurring Basis Total Liabilities	0.5	8.2
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	12.1	14.6
Fair Value Assets Measured on Recurring Basis Total Assets	12.1	14.6
Fair Value, Liabilities Measured on Recurring Basis, Derivative Financial Instruments, Liabilities	7.5	1.0
Fair Value Liabilities Measured on Recurring Basis Total Liabilities	7.5	1.0
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	9.9	5.7
Fair Value Assets Measured on Recurring Basis Total Assets	9.9	5.7
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	17.9	45.5
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	24.7	20.6
Fair Value Assets Measured on Recurring Basis Total Assets	42.6	66.1
Fair Value, Liabilities Measured on Recurring Basis, Derivative Financial Instruments, Liabilities	8.0	9.2
Fair Value Liabilities Measured on Recurring Basis Total Liabilities	$ 8.0	$ 9.2