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Income Taxes - Summary of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	$ 22.8	$ 39.8	$ 15.6
Decreases related to prior year tax positions			(8.4)
Increases related to current year tax positions	3.4	3.3	32.6
Decreases related to prior year tax positions	(0.3)	(14.9)
Decrease related to Tax Cuts and Jobs Act of 2017		(5.4)
Ending Balance	$ 25.9	$ 22.8	$ 39.8

X

- Definition

Unrecognized Tax Benefits, Decrease Resulting from Tax Cuts And Jobs Act Of 2017

+ References

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- Definition

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

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- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 45
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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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