FAIR VALUE MEASUREMENTS (Details) $ in Millions	3 Months Ended
	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Number of Measurement Funds Available For Participant Election	16
Noncontrolling interest puts	$ 16.4	$ 16.3
Foreign Currency Contracts, Liability, Fair Value Disclosure	36.7
Fair market value of senior notes	5,444.5	5,841.1
Cash Surrender Value, Fair Value Disclosure	102.0	106.4
Fair Value Liabilities Measured On Recurring Basis Deferred Compensation Liability	103.5	104.4
Equity Securities, FV-NI	5.9	10.9
Contingent Consideration Classified as Equity, Fair Value Disclosure	105.2	21.9
lh_BusinessCombinationContingentConsiderationArrangementsPayments	(4.4)
Foreign Currency Contract, Asset, Fair Value Disclosure		32.8
Fair Value Hedges, Net	31.3	2.9
Contingent consideration adjustment	(2.3)
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	90.0
Tax effect of adjustments	0.0
Level 1 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Noncontrolling interest puts	0.0	0.0
Cash Surrender Value, Fair Value Disclosure	0.0	0.0
Fair Value Liabilities Measured On Recurring Basis Deferred Compensation Liability	0.0	0.0
Equity Securities, FV-NI	5.9	10.9
Contingent Consideration Classified as Equity, Fair Value Disclosure	0.0	0.0
Foreign Currency Contract, Asset, Fair Value Disclosure	0.0	0.0
Fair Value Hedges, Net	0.0	0.0
Fair Value, Inputs, Level 2 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Noncontrolling interest puts	16.4	16.3
Foreign Currency Contracts, Liability, Fair Value Disclosure	36.7
Cash Surrender Value, Fair Value Disclosure	102.0	106.4
Fair Value Liabilities Measured On Recurring Basis Deferred Compensation Liability	103.5	104.4
Equity Securities, FV-NI	0.0	0.0
Contingent Consideration Classified as Equity, Fair Value Disclosure	0.0	0.0
Foreign Currency Contract, Asset, Fair Value Disclosure		32.8
Fair Value Hedges, Net	31.3	2.9
Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Noncontrolling interest puts	0.0	0.0
Cash Surrender Value, Fair Value Disclosure	0.0	0.0
Fair Value Liabilities Measured On Recurring Basis Deferred Compensation Liability	0.0	0.0
Equity Securities, FV-NI	0.0	0.0
Contingent Consideration Classified as Equity, Fair Value Disclosure	105.2	21.9
Foreign Currency Contract, Asset, Fair Value Disclosure	0.0	0.0
Fair Value Hedges, Net	$ 0.0	$ 0.0