Fair Value Measurements Fair Value Measurements - Fair Value and Related Carrying Amount of Certain Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Estimate of Fair Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	$ 2,230.9	$ 2,171.6
Cash and Cash Equivalents, at Carrying Value	445.6	1,160.1
Checks outstanding in excess of cash balances	7.4	54.7
Reported Value Measurement [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term Debt, Fair Value	2,218.5	2,218.1
Cash and Cash Equivalents, at Carrying Value	445.6	1,160.1
Checks outstanding in excess of cash balances	$ 7.4	$ 54.7