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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Summary of Significant Accounting Policies [Line Items]
Equity method investments carrying value	$ 521,000,000				$ 482,000,000				$ 521,000,000	$ 482,000,000
Percentage of net revenues									100.00%	100.00%	100.00%
Share of equity earnings from investments in affiliates									$ 75,000,000	$ 57,000,000	$ 44,000,000
Percentage of net accounts receivable	100.00%				100.00%				100.00%	100.00%
Operating income (loss)									$ 1,971,000,000	$ 1,231,000,000	1,101,000,000
Net income	$ 609,000,000	$ 591,000,000	$ 193,000,000	$ 106,000,000	$ 265,000,000	$ 226,000,000	$ 239,000,000	$ 176,000,000	1,499,000,000	906,000,000	788,000,000
Trading equity securities gain or (loss)									8,000,000	10,000,000	(2,000,000)
Impairment charges									0	0	$ 0
Equity Securities without readily determinable fair value	25,000,000				25,000,000				25,000,000	25,000,000
Available-for-sale debt securities	12,000,000				12,000,000				12,000,000	12,000,000
Operating lease right-of-use assets	604,000,000				518,000,000				604,000,000	518,000,000
Operating lease, liability	640,000,000								640,000,000
Deferred rent adjustments												$ 50,000,000
Cumulative Effect, Period of Adoption, Adjustment
Summary of Significant Accounting Policies [Line Items]
Operating lease right-of-use assets												500,000,000
Operating lease, liability												$ 550,000,000
Other Assets
Summary of Significant Accounting Policies [Line Items]
Trading securities, equity	$ 67,000,000				$ 59,000,000				$ 67,000,000	$ 59,000,000
DIS business
Summary of Significant Accounting Policies [Line Items]
Percentage of net revenues									97.00%	96.00%	96.00%
Percentage of net accounts receivable	97.00%				95.00%				97.00%	95.00%
Operating income (loss)									$ 2,201,000,000	$ 1,298,000,000	$ 1,235,000,000
DIS business | Government payers
Summary of Significant Accounting Policies [Line Items]
Percentage of net revenues									11.00%	15.00%	16.00%
Percentage of net accounts receivable	6.00%				11.00%				6.00%	11.00%
DIS business | Patients
Summary of Significant Accounting Policies [Line Items]
Percentage of net revenues									11.00%	13.00%	13.00%
Percentage of net accounts receivable	11.00%				20.00%				11.00%	20.00%
Percentage of receivables due from patients	11.00%				20.00%				11.00%	20.00%
Minimum
Summary of Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage	20.00%								20.00%
Finite-lived intangible asset, useful life									5 years
Minimum | Laboratory Equipment and Furniture and Fixtures
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life									5 years
Minimum | Software and Software Development Costs
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life									5 years
Minimum | DIS business
Summary of Significant Accounting Policies [Line Items]
Percentage of net revenues									95.00%	95.00%	95.00%
Maximum
Summary of Significant Accounting Policies [Line Items]
Equity method investment, ownership percentage	49.00%								49.00%
Finite-lived intangible asset, useful life									20 years
Maximum | Building and Building Improvements
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life									31 years 6 months
Maximum | Laboratory Equipment and Furniture and Fixtures
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life									12 years
Maximum | Software and Software Development Costs
Summary of Significant Accounting Policies [Line Items]
Property, plant and equipment, useful life									10 years

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