Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Period to recover call premiums on reacquisition of long-term debt	15-year
Carrying value of notes receivable, inclusive of any accrued interest and net of impairment reserves	$ 2.1	$ 10.9
Error corrections and prior period adjustment, description		The fair value table in Note 18 of the financial statements in the 2010 Form 10-K excluded the estimated fair value of a long-term debt instrument. The chart above now includes the amount and reflects an increase in the estimated fair value of long-term debt of approximately $73.9 million. This change in the disclosed fair value of long-term debt had no effect on the carrying value of debt included in the consolidated balance sheet.
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	1,622.3	1,715.9
Short-term borrowings	227.1	118.3
Cash and cash equivalents	8.6	10.4
Estimated Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt	1,804.4	1,841.2
Short-term borrowings	227.1	118.3
Cash and cash equivalents	$ 8.6	$ 10.4

This element represents the portion of the balance sheet assertion valued at fair value by the entity whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission. This item includes currency on hand as well as demand deposits with banks or financial institutions. It also includes other kinds of accounts that have the general characteristics of demand deposits in that the Company may deposit additional funds at any time and also effectively may withdraw funds at any time without prior notice or penalty. Cash equivalents, excluding items classified as marketable securities, include short-term, highly liquid investments that are both readily convertible to known amounts of cash, and so near their maturity that they present minimal risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three years ago does not become a cash equivalent when its remaining maturity is three months.

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Description of a prior period adjustment to previously issued financial statements, including an adjustment that is a correction of an error. At a minimum, the description may include the nature and reasons for the adjustment and the periods affected by the adjustment, as well as (1) the effect of the correction on each financial statement line item and any per-share amounts affected for each prior period presented (2) the cumulative effect of the change on retained earnings or other appropriate components of equity or net assets in the statement of financial position, as of the beginning of the earliest period presented, and (3) the effect of the prior period adjustment (both gross and net of applicable income tax) on the net income of each prior period presented in the entity's annual report for the year in which the adjustments are made.

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