Supplemental Financial Statement Information - Operating Lease Information (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Fair Value of Assets (Liability), Right of use assets	$ 139.4	$ 159.3
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherNoncurrentAssetsMember	us-gaap:OtherNoncurrentAssetsMember
Fair Value of Assets (Liability), Total lease liabilities	$ 56.1	$ 62.4
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	comm:AccruedAndOtherLiabilitiesCurrent	comm:AccruedAndOtherLiabilitiesCurrent
Fair Value of Assets (Liability), Total lease liabilities	$ 101.6	$ 119.1
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	Other noncurrent liabilities	Other noncurrent liabilities
Fair Value of Assets (Liability), Total lease liabilities	$ 157.7	$ 181.5