Fair Value Measurements Fair Value Measurements, Assets (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash	$ 45.5	$ 8.3
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	25.4	15.7
Fair Value Assets Measured On Recurring Basis Total Assets	70.9	24.0
Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash	45.5	8.3
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	3.9	4.5
Fair Value Assets Measured On Recurring Basis Total Assets	49.4	12.8
Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash	0	0
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	6.9	5.3
Fair Value Assets Measured On Recurring Basis Total Assets	6.9	5.3
Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets Measured on Recurring Basis, Financial Statement Captions [Line Items]
Restricted Cash	0	0
Fair Value, Assets Measured on Recurring Basis, Derivative Financial Instruments, Assets	14.6	5.9
Fair Value Assets Measured On Recurring Basis Total Assets	$ 14.6	$ 5.9