Long-Term Debt -Fair Value of Long-Term Debt (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Fair Value [Line Items]
Debt, short-term and long-term	$ 3,268.3	$ 3,177.0
Debt, Long-term and Short-term, Combined Amount		3,192.4
Fair Value, Inputs, Level 2 [Member]
Fair Value [Line Items]
Long-term Debt, fair value disclosures	3,316.4	3,208.7
Reported Value Measurement [Member]
Fair Value [Line Items]
Debt, short-term and long-term		$ 3,192.4
Debt, Long-term and Short-term, Combined Amount	$ 3,295.8