GOODWILL AND INTANGIBLE ASSETS - COMPONENTS OF IDENTIFIABLE INTANGIBLE ASSETS (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount	$ 5,515.9	$ 5,566.2
Accumulated Amortization	(1,604.8)	(1,400.1)
Net Carrying Amount	3,911.1	4,166.1
Customer Relationships [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount		4,118.1
Accumulated Amortization		(992.8)
Net Carrying Amount		3,125.3
Patents, licenses and technology [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount		457.9
Accumulated Amortization		(188.6)
Net Carrying Amount		269.3
Non-compete agreements [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount		75.8
Accumulated Amortization		(48.3)
Net Carrying Amount		27.5
Trade names [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount		407.9
Accumulated Amortization		(167.9)
Net Carrying Amount		240.0
Canadian licenses [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount		495.7
Accumulated Amortization		0.0
Net Carrying Amount		495.7
Patents, licenses and technology [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount	447.3
Accumulated Amortization	(211.2)
Net Carrying Amount	236.1
Customer Relationships [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount	4,119.4
Accumulated Amortization	(1,146.7)
Net Carrying Amount	2,972.7
Use Rights [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount	10.8	10.8
Accumulated Amortization	(4.1)	(2.5)
Net Carrying Amount	6.7	$ 8.3
Trade names [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount	404.0
Accumulated Amortization	(189.1)
Net Carrying Amount	214.9
Non-compete agreements [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount	76.8
Accumulated Amortization	(53.7)
Net Carrying Amount	23.1
Canadian licenses [Member]
Finite-Lived Intangible Assets [Abstract]
Gross Carrying Amount	457.6
Accumulated Amortization	0.0
Net Carrying Amount	$ 457.6

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

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

- References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetsNetAbstract
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

No definition available.

+ 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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph ((a)(1),(b))
-URI http://asc.fasb.org/extlink&oid=66006027&loc=d3e16323-109275

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388964&loc=d3e16212-109274

+ Details

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

- Details

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

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=lh_PatentsLicensesAndTechnologyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_LicensingAgreementsMember
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_CustomerRelationshipsMember
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_TradeNamesMember
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_LicensingAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: