Derivative Financial Instruments and Related Hedging Programs, Offsetting of Derivative Instruments by Counterparty (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	$ 0.3	$ 85.7
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	0.3	85.7
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0.3	0.8
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Received	0.0	0.0
Net Amount	0.0	84.9
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(19.3)	(96.8)
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(19.3)	(96.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(0.3)	(0.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	0.0	0.0
Net Amount	(19.0)	(96.0)
Counterparty (with Netting Agreements)
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	0.3	0.9
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	0.3	0.9
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0.3	0.8
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Received	0.0	0.0
Net Amount	0.0	0.1
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(10.9)	(8.0)
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(10.9)	(8.0)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(0.3)	(0.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	0.0	0.0
Net Amount	(10.6)	(7.2)
Counterparty (without Netting Agreements)
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets		84.8
Gross Amounts Offset in the Consolidated Balance Sheets		0.0
Net Amounts of Assets Presented in the Consolidated Balance Sheets		84.8
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments		0.0
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Received		0.0
Net Amount		84.8
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(0.5)	(85.0)
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(0.5)	(85.0)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0.0	0.0
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	0.0	0.0
Net Amount	(0.5)	(85.0)
Counterparty (with partial Netting Agreements)
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(7.9)	(3.8)
Gross Amounts Offset in the Consolidated Balance Sheets	0.0	0.0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(7.9)	(3.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0.0	0.0
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	0.0	0.0
Net Amount	$ (7.9)	$ (3.8)