Fair Value Measurements (Changes in Fair Value of Level 3) (Details) - Level 3 - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Summary of net changes in fair value of the company's level 3 financial assets and liabilities
Beginning Balance at January 1,	$ 19.8	$ (10.4)
Realized gain on derivative instruments	(35.1)	(3.6)
Unrealized gain (loss) on derivative instruments	(26.1)	30.2
Settlements	(35.1)	(3.6)
Ending Balance at December 31,	(6.3)	19.8
Total gain (loss) included in net loss attributable to changes in unrealized gain (loss)	$ (26.1)	$ 30.2

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of gain (loss) recognized in income from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value on recurring basis using unobservable input (level 3).

+ References

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- Definition

Amount of gain (loss) recognized in other comprehensive income from derivative asset (liability) after deduction of derivative liability (asset), measured at fair value on recurring basis using unobservable input (level 3).

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- Definition

Amount of settlements of financial instrument classified as a derivative asset (liability) after deduction of derivative liability, measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of unrealized gain (loss) related to derivatives designated as cash flow hedging instruments, recorded in results of operations to the extent that the cash flow hedge is determined to be ineffective.

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