Derivative Financial Instruments and Related Hedging Programs, Offsetting of Derivative Instruments by Counterparty (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	$ 63.4	$ 58.5
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	63.4	58.5
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	2.0	2.6
Cash Collateral Received	0	0
Net Amount	61.4	55.9
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(72.0)	(66.7)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(72.0)	(66.7)
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	(2.0)	(2.6)
Cash Collateral Pledged	0	0
Net Amount	(70.0)	(64.1)
Counterparty (with Netting Agreements)
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	1.1	1.7
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	1.1	1.7
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	1.1	1.7
Cash Collateral Received	0	0
Net Amount	0	0
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(2.1)	(1.9)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(2.1)	(1.9)
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	(1.1)	(1.7)
Cash Collateral Pledged	0	0
Net Amount	(1.0)	(0.2)
Counterparty (without Netting Agreements)
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	61.4	55.9
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	61.4	55.9
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	0	0
Cash Collateral Received	0	0
Net Amount	61.4	55.9
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(68.6)	(63.8)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(68.6)	(63.8)
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	0	0
Cash Collateral Pledged	0	0
Net Amount	(68.6)	(63.8)
Counterparty (with partial Netting Agreements)
Derivative Assets and Collateral Held by Counterparty
Gross Amounts of Recognized Assets	0.9	0.9
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets Presented in the Consolidated Balance Sheets	0.9	0.9
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	0.9	0.9
Cash Collateral Received	0	0
Net Amount	0	0
Derivative Liabilities and Collateral Held by Counterparty
Gross Amounts of Recognized Liabilities	(1.3)	(1.0)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheets	(1.3)	(1.0)
Gross Amounts Not Offset in the Consolidated Balance Sheets
Financial Instruments	(0.9)	(0.9)
Cash Collateral Pledged	0	0
Net Amount	$ (0.4)	$ (0.1)

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Fair value of liability associated with derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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Fair value of the gross assets less the gross liabilities of a derivative asset or group of derivative assets.

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The amount of the obligation to return cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

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The amount of the right to reclaim cash collateral under master netting arrangements that have not been offset against net derivative instrument positions.

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Fair value of derivative asset, presented on a gross basis even when the derivative instrument is subject to master netting arrangements and qualifies for net presentation in the statement of financial position.

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The amount as of the balance sheet date of the fair value of derivative assets that in accordance with the entity's accounting policy was not offset against an obligation to return cash collateral under a master netting arrangement.

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