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Investments in Marketable Securities - Schedule of Available-For-Sale and Trading Securities (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Available-for-Sale
Cost	$ 114.7	$ 103.2
Unrealized Gains	28.0	33.3
Unrealized Losses	(6.7)	(1.1)
Fair Value	136.0	135.4
Trading
Cost	18.5	17.9
Unrealized Gains	3.6	4.6
Unrealized Losses	0	0
Fair Value	$ 22.1	$ 22.5

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Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax

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Amount of equity securities categorized neither as held-to-maturity nor as trading.

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