Income Taxes - Tabular Reconciliation of Total Amounts of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Balance at January 1	$ 685.5	$ 626.8	$ 649.3
Increases related to business combinations		4.5	70.2
Increases related to prior periods	24.7	34.6	172.8
Decreases related to prior periods	(35.6)	(14.4)	(262.2)
Increases related to current period	133.2	41.9	24.8
Decreases related to settlements with taxing authorities	(60.2)	(3.8)	(21.7)
Decreases related to lapse of statute of limitations	(5.8)	(4.1)	(6.4)
Balance at December 31	741.8	685.5	626.8
Amounts impacting effective tax rate, if recognized balance at December 31	$ 599.2	$ 549.1	$ 499.6

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Amount of unrecognized tax benefits.

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