Goodwill and Other Intangibles - Changes in Goodwill (Detail) $ in Millions	9 Months Ended
Sep. 30, 2021 USD ($)
Goodwill [Line Items]
Balance at January 1, 2021	$ 2,414.0
Acquisitions	198.7
Goodwill allocated to assets held for sale	(2.1)
Balance at September 30, 2021	2,610.6
East Group
Goodwill [Line Items]
Balance at January 1, 2021	572.5
Acquisitions	185.9
Balance at September 30, 2021	758.4
West Group
Goodwill [Line Items]
Balance at January 1, 2021	1,841.5
Acquisitions	12.8
Goodwill allocated to assets held for sale	(2.1)
Balance at September 30, 2021	$ 1,852.2

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10)(1))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=120320667&loc=SL49117168-202975

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant