GOODWILL AND INTANGIBLE ASSETS (Components of identifiable intangible assets) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	$ 5,149.2	$ 5,058.4
Finite-Lived Intangible Assets, Accumulated Amortization	(1,755.1)	(1,716.4)
Intangible Assets, Net (Excluding Goodwill)	3,394.1	3,342.0
Customer Relationships [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	3,945.3	3,868.6
Finite-Lived Intangible Assets, Accumulated Amortization	(1,395.7)	(1,367.2)
Intangible Assets, Net (Excluding Goodwill)	2,549.6	2,501.4
Patents, Licenses And Technology [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	521.4	526.6
Finite-Lived Intangible Assets, Accumulated Amortization	(276.8)	(273.3)
Intangible Assets, Net (Excluding Goodwill)	244.6	253.3
Noncompete Agreements [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	152.4	130.3
Finite-Lived Intangible Assets, Accumulated Amortization	(65.9)	(60.4)
Intangible Assets, Net (Excluding Goodwill)	86.5	69.9
Trade Names [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	16.4	16.4
Finite-Lived Intangible Assets, Accumulated Amortization	(6.9)	(6.1)
Intangible Assets, Net (Excluding Goodwill)	9.5	10.3
Use Rights [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	3.5	3.5
Finite-Lived Intangible Assets, Accumulated Amortization	(2.8)	(2.7)
Intangible Assets, Net (Excluding Goodwill)	0.7	0.8
Canadian licenses [Member]
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	496.0	498.8
Finite-Lived Intangible Assets, Accumulated Amortization	0.0	0.0
Intangible Assets, Net (Excluding Goodwill)	496.0	498.8
In Process R&A and Media
Finite-Lived Intangible Assets [Line Items]
Intangible Assets, Gross (Excluding Goodwill)	14.2	14.2
Finite-Lived Intangible Assets, Accumulated Amortization	(7.0)	(6.7)
Intangible Assets, Net (Excluding Goodwill)	$ 7.2	$ 7.5

Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(16))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147480566/210-10-S99-1

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 350
-SubTopic 30
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482665/350-30-50-2

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 926
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147483154/926-20-50-5

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount before accumulated amortization of intangible assets, excluding goodwill.

+ References

+ Details

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

- Definition

Sum of the carrying amounts of all intangible assets, excluding goodwill, as of the balance sheet date, net of accumulated amortization and impairment charges.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph ((a)(1),(b))
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482665/350-30-50-2

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482686/350-30-45-1

+ Details

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

- Details

Name:	lh_ScheduleOfOtherIntangibleAssetsByMajorClassAxis=us-gaap_CustomerRelationshipsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	lh_ScheduleOfOtherIntangibleAssetsByMajorClassAxis=lh_PatentsLicensesAndTechnologyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	lh_ScheduleOfOtherIntangibleAssetsByMajorClassAxis=us-gaap_NoncompeteAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	lh_ScheduleOfOtherIntangibleAssetsByMajorClassAxis=us-gaap_TradeNamesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	lh_ScheduleOfOtherIntangibleAssetsByMajorClassAxis=us-gaap_UseRightsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	lh_ScheduleOfOtherIntangibleAssetsByMajorClassAxis=us-gaap_LicensingAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	lh_ScheduleOfOtherIntangibleAssetsByMajorClassAxis=lh_InProcessRAAndMediaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: