Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018
Business And Significant Accounting Policies [Line Items]
Balance	$ 11,878.2	$ 11,643.9	$ 12,392.8	$ 12,085.5	$ 11,662.2	$ 11,276.1
Allowance for doubtful accounts	76.3		$ 65.0
Cumulative Effect, Period of Adoption, Adjustment [Member]
Business And Significant Accounting Policies [Line Items]
Balance	$ (3.1)