PENSION AND POSTRETIREMENT PLANS Defined Contribution Plans (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Non Elective Contribution	3.00%
Defined Contribution Plan, Cost	$ 24.2	$ 16.1
Discretionary Contribution Percentage Mininum	1.00%
Discretionary Contribution Percentage Maximum	3.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	4.50%
Covance [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Cost	$ 19.9	$ 18.9

The maximum discretionary contribution % by the company for eligible employees based on service.

No definition available.

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- Definition

The minimum discretionary contribution % by the company for eligible employees based on service.

+ References

No definition available.

+ Details

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Namespace Prefix:	lh_
Data Type:	num:percentItemType
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Period Type:	duration

- Definition

The minimum non-elective contribution % by the company to all employees eligible for the defined contribution retirement plan. Contributions are concurrent with each payroll period and are non-forfeitable and vest immediately.

+ References

No definition available.

+ Details

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Namespace Prefix:	lh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- 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

No definition available.

+ Details

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- Definition

Amount of cost for defined contribution plan.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 70
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Percentage employer matches of the employee's percentage contribution matched.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Details

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