The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

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Amount of right to receive cash collateral under master netting arrangements that have not been offset against derivative liabilities.

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Cap rate on a foreign currency derivative for example, but not limited to, a cap or a collar.

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The net amount as of the balance sheet date of the fair value of derivative assets and derivative liabilities that in accordance with the entity's accounting policy were offset against collateral under a master netting arrangement.

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Nominal mass used to calculate payments on a derivative instrument.

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Amount receivable from broker-dealers and clearing organizations, including, but not limited to, securities failed-to-deliver, certain deposits for securities borrowed, open transactions, good faith and margin deposits, commissions and floor brokerage receivables.

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Derivatives and Fair Value Measurements - Narrative (Details) t in Millions, $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2020 AUD ($) t	Dec. 31, 2020 t $ / $	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Derivatives, Fair Value [Line Items]
Additional collateral			$ 0.1	$ 0.1
Foreign currency option contracts
Derivatives, Fair Value [Line Items]
Notional amount	$ 600,000,000.0
Coal trading contracts
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) \| t	1.1
Diesel Fuel Hedge Contracts
Derivatives, Fair Value [Line Items]
Notional amount	$ 0
Forecast \| Foreign currency option contracts
Derivatives, Fair Value [Line Items]
Derivative, exchange rate floor (in dollars per share) \| $ / $		0.70
Derivative, exchange rate cap (in dollars per share) \| $ / $		0.76
Forecast \| Coal trading contracts
Derivatives, Fair Value [Line Items]
Derivative notional amount (in tonnes) \| t		0.8
Coal Trading
Derivatives, Fair Value [Line Items]
Derivative, initial margin posted			3.0	7.9
Derivatives, amount posted in excess of initial margin requirements			0.8	1.3
Derivative, variation margin			$ 11.1	$ 22.1