Derivatives and Fair Value Measurements - Derivatives by Balance Sheet Classification (Details) - Designated as Hedging Instrument - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Asset Derivative
Derivative Asset, Fair Value, Gross Asset	$ 115.6	$ 27.4
Effect of counterparty netting	(113.0)	(16.2)
Variation margin (received) posted	(1.5)	(0.3)
Net derivatives and variation margin as classified in the balance sheets	1.1	10.9
Liability Derivative
Liability Derivative	(385.2)	(24.7)
Effect of counterparty netting	113.0	16.2
Net derivatives and variation margin as classified in the balance sheets	(56.4)	(1.7)
Gross Amount
Liability Derivative
Variation margin (received) posted	215.8	6.8
Foreign currency option contracts
Asset Derivative
Derivative Asset, Fair Value, Gross Asset	1.1	10.3
Liability Derivative
Liability Derivative	0.0	0.0
Derivative contracts related to forecasted sales
Asset Derivative
Derivative Asset, Fair Value, Gross Asset	113.0	16.7
Liability Derivative
Liability Derivative	(385.2)	(24.7)
Financial trading contracts
Asset Derivative
Derivative Asset, Fair Value, Gross Asset	1.5	0.4
Liability Derivative
Liability Derivative	$ 0.0	$ 0.0

Amount of obligation to return cash collateral under master netting arrangements offset against derivative assets.

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