Income Taxes - Tabular Reconciliation of Total Amounts of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Balance at January 1	$ 741.8	$ 685.5	$ 626.8
Increases related to business combinations			4.5
Increases related to prior periods	75.3	24.7	34.6
Decreases related to prior periods	(158.3)	(35.6)	(14.4)
Increases related to current period	3.4	133.2	41.9
Decreases related to settlements with taxing authorities	(14.6)	(60.2)	(3.8)
Decreases related to lapse of statute of limitations	(28.2)	(5.8)	(4.1)
Balance at December 31	619.4	741.8	685.5
Amounts impacting effective tax rate, if recognized balance at December 31	$ 473.9	$ 599.2	$ 549.1

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Amount of unrecognized tax benefits.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from acquisitions.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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