Fair Value Measurements Fair Value on a Nonrecurring Basis (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Level 1
Fair value assets and liabilities measured on recurring and nonrecurring basis
Total Long-term Debt, Fair Value	$ 0
Level 2
Fair value assets and liabilities measured on recurring and nonrecurring basis
Total Long-term Debt, Fair Value	1,542.4
Level 3
Fair value assets and liabilities measured on recurring and nonrecurring basis
Total Long-term Debt, Fair Value	64.5
Fair Value, Total
Fair value assets and liabilities measured on recurring and nonrecurring basis
Total Long-term Debt, Fair Value	$ 1,606.9