Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Assets:
Restricted Cash	$ 2.7	$ 45.5
Derivative, Asset	17.9	20.6
Total	20.6	66.1
Liabilities:
Derivatives	0.5	9.2
Total	0.5	9.2
Fair Value, Inputs, Level 1 [Member]
Assets:
Restricted Cash	2.7	45.5
Derivative, Asset	0.9	0.3
Total	3.6	45.8
Liabilities:
Derivatives	0.5	8.2
Total	0.5	8.2
Fair Value, Inputs, Level 2 [Member]
Assets:
Restricted Cash	0	0
Derivative, Asset	12.3	14.6
Total	12.3	14.6
Liabilities:
Derivatives	0	1.0
Total	0	1.0
Fair Value, Inputs, Level 3 [Member]
Assets:
Restricted Cash	0	0
Derivative, Asset	4.7	5.7
Total	4.7	5.7
Liabilities:
Derivatives	0	0
Total	$ 0	$ 0