Fair Value Measurements, Available-for-sale Securities (Details) (USD $) In Millions	Dec. 31, 2010	Dec. 31, 2009
Schedule of Available-for-sale Securities [Line Items]
Market Value	$ 36.6	$ 36.6
Cost Basis	31.4	32.9
Gross Unrealized Gains	5.9	4.3
Gross Unrealized Losses	0.7	0.6
Trading Securities	4.3	1.7
Mutual Fund and Unit Trust Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	32.0	31.2
Cost Basis	26.1	26.9
Gross Unrealized Gains	5.9	4.3
Gross Unrealized Losses	0	0
Auction Rate Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Market Value	4.6	5.4
Cost Basis	5.3	6.0
Gross Unrealized Gains	0	0
Gross Unrealized Losses	$ 0.7	$ 0.6

For an unclassified balance sheet, this item represents investments in debt and equity securities which are categorized neither as held-to-maturity nor trading. Such securities are reported at fair value, with unrealized gains and losses excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale Security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain or loss of an Available-for-sale Security that is designated as being hedged in a fair value hedge shall be recognized in earnings during the period of the hedge, as should other than temporary declines in fair value below costs basis.

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The total of financial instruments that are bought and held principally for the purpose of selling them in the near term (thus held for only a short period of time, usually less than one year or the normal operating cycle, whichever is longer) or for debt and equity securities formerly categorized as available-for-sale or held-to-maturity which the entity held as of the date it opted to account for such securities at fair value. An enterprise may also categorize such a security as trading without the intent to sell it in the near term assuming the decision to categorize the security as trading occurred at acquisition; this is the reason why the trading category of investments in debt and equity securities are bought and sold "principally" for sale in the near term. Transfers into and out of the trading category should be rare. Such financial instruments that are held as of the reporting date are measured at fair value with unrealized holding gains and losses (the difference between fair value and the previously reported carrying amount) included in earnings.

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