Derivative Financial Instruments (Details 3) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Derivative Financial Instruments
Gross and net amounts presented in consolidated balance sheets, Total derivative assets	$ 27.0	$ 74.3
Gross and net amounts presented in consolidated balance sheets, Total derivative liabilities	23.3
Gross and net amounts presented in consolidated balance sheets, Net assets	3.7	74.3
Gross amounts not offset in consolidated balance sheets
Financial instruments, Total derivative assets	11.9	0.2
Financial instruments, Total derivative liabilities	11.9
Financial instruments, Net assets (liabilities)		0.2
Net Amount, Total derivative assets	15.1	74.1
Net Amount, Total derivative liabilities	11.4
Net Amount, Net assets (liabilities)	3.7	74.1
Exposure to credit loss from nonperformance by counterparties to derivative instruments	$ 3.7	$ 74.1