Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Assets:
Restricted Cash	$ 45.5	$ 8.3
Derivative, Asset	20.6	15.7
Total	66.1	24.0
Liabilities:
Derivatives	9.2	11.6
Total	9.2	11.6
Fair Value, Inputs, Level 1 [Member]
Assets:
Restricted Cash	45.5	8.3
Derivative, Asset	0.3	4.5
Total	45.8	12.8
Liabilities:
Derivatives	8.2	6.1
Total	8.2	6.1
Fair Value, Inputs, Level 2 [Member]
Assets:
Restricted Cash	0	0
Derivative, Asset	14.6	5.3
Total	14.6	5.3
Liabilities:
Derivatives	1.0	5.5
Total	1.0	5.5
Fair Value, Inputs, Level 3 [Member]
Assets:
Restricted Cash	0	0
Derivative, Asset	5.7	5.9
Total	5.7	5.9
Liabilities:
Derivatives	0	0
Total	$ 0	$ 0