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Fair Value Measurements - Assets and Liabilities Measured on a Recurring Basis (Details) - Fair Value Measured on a Recurring Basis - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Financial Assets
Investments in marketable securities	$ 68.2	$ 59.4
Derivative financial instruments	2.6	7.9
Financial Liabilities
Affiliate equity repurchase obligations	69.9	19.8
Derivative financial instruments	4.0	1.0
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets
Investments in marketable securities	27.5	24.4
Derivative financial instruments	0.0	0.0
Financial Liabilities
Affiliate equity repurchase obligations	0.0	0.0
Derivative financial instruments	0.0	0.0
Significant Other Observable Inputs (Level 2)
Financial Assets
Investments in marketable securities	40.7	35.0
Derivative financial instruments	2.6	7.9
Financial Liabilities
Affiliate equity repurchase obligations	0.0	0.0
Derivative financial instruments	4.0	1.0
Significant Unobservable Inputs (Level 3)
Financial Assets
Investments in marketable securities	0.0	0.0
Derivative financial instruments	0.0	0.0
Financial Liabilities
Affiliate equity repurchase obligations	69.9	19.8
Derivative financial instruments	$ 0.0	$ 0.0

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