FAIR VALUE MEASUREMENTS (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)	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	16
Noncontrolling interest puts	$ 15.0	$ 15.0	$ 16.3
Foreign Currency Contracts, Liability, Fair Value Disclosure	8.1	8.1
Fair market value of senior notes	4,921.2	4,921.2	5,841.1
Cash Surrender Value, Fair Value Disclosure	95.5	95.5	106.4
Fair Value Liabilities Measured On Recurring Basis Deferred Compensation Liability	93.7	93.7	104.4
Equity Securities, FV-NI			10.9
Contingent Consideration Classified as Equity, Fair Value Disclosure	62.0	62.0	21.9
lh_BusinessCombinationContingentConsiderationArrangementsPayments		(10.4)
Foreign Currency Contract, Asset, Fair Value Disclosure			32.8
Fair Value Hedges, Net	82.5	82.5	2.9
Contingent consideration adjustment		(2.4)
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability		52.9
Tax effect of adjustments		0.0
Long-term Debt, Excluding Current Maturities	5,334.3	5,334.3	5,416.5
Fair Value Hedge Liabilities	82.5	82.5
Senior notes due 2027 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Long-term Debt, Excluding Current Maturities	600.0	600.0
Senior notes due 2022 [Member] | 2018 Swap Agreements
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative, Notional Amount	300.0	300.0
Gain (Loss) on Hedging Activity	0.9
Senior notes due 2024 | 2022 Swap Agreements
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Derivative, Notional Amount	300.0	300.0
Level 1 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Noncontrolling interest puts	0.0	0.0	0.0
Cash Surrender Value, Fair Value Disclosure	0.0	0.0	0.0
Fair Value Liabilities Measured On Recurring Basis Deferred Compensation Liability	0.0	0.0	0.0
Equity Securities, FV-NI			10.9
Contingent Consideration Classified as Equity, Fair Value Disclosure	0.0	0.0	0.0
Foreign Currency Contract, Asset, Fair Value Disclosure	0.0	0.0	0.0
Fair Value Hedges, Net	0.0	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	15.0	15.0	16.3
Foreign Currency Contracts, Liability, Fair Value Disclosure	8.1	8.1
Cash Surrender Value, Fair Value Disclosure	95.5	95.5	106.4
Fair Value Liabilities Measured On Recurring Basis Deferred Compensation Liability	93.7	93.7	104.4
Equity Securities, FV-NI			0.0
Contingent Consideration Classified as Equity, Fair Value Disclosure	0.0	0.0	0.0
Foreign Currency Contract, Asset, Fair Value Disclosure			32.8
Fair Value Hedges, Net	82.5	82.5	2.9
Level 3 [Member]
Fair Value, Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Noncontrolling interest puts	0.0	0.0	0.0
Cash Surrender Value, Fair Value Disclosure	0.0	0.0	0.0
Fair Value Liabilities Measured On Recurring Basis Deferred Compensation Liability	0.0	0.0	0.0
Equity Securities, FV-NI			0.0
Contingent Consideration Classified as Equity, Fair Value Disclosure	62.0	62.0	21.9
Foreign Currency Contract, Asset, Fair Value Disclosure	0.0	0.0	0.0
Fair Value Hedges, Net	$ 0.0	$ 0.0	$ 0.0