Derivative Financial Instruments and Related Hedging Programs, Offsetting of Derivative Instruments by Counterparty (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	$ 95.1	$ 85.7
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	95.1	85.7
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0.2	0.8
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Received	0	0
Net Amount	94.9	84.9
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(110.7)	(96.8)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(110.7)	(96.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(0.2)	(0.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	0	0
Net Amount	(110.5)	(96.0)
Counterparty (with Netting Agreements)
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	0.1	0.9
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	0.1	0.9
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0.1	0.8
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Received	0	0
Net Amount	0	0.1
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(8.4)	(8.0)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(8.4)	(8.0)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(0.1)	(0.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	0	0
Net Amount	(8.3)	(7.2)
Counterparty (without Netting Agreements)
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	94.9	84.8
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	94.9	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	94.9	84.8
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(96.9)	(85.0)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(96.9)	(85.0)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0	0
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	0	0
Net Amount	(96.9)	(85.0)
Counterparty (with partial Netting Agreements)
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	0.1
Gross Amounts Offset in the Consolidated Balance Sheets	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	0.1
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	0.1
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Received	0
Net Amount	0
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(5.4)	(3.8)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(5.4)	(3.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets - Financial Instruments	(0.1)	0
Gross Amounts Not Offset in the Consolidated Balance Sheets - Cash Collateral Pledged	0	0
Net Amount	$ (5.3)	$ (3.8)