GOODWILL AND OTHER INTANGIBLE ASSETS - Intangible Assets Included in Other Long-Term Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	9 years 2 months 12 days
Cost	$ 1,098	$ 1,069
Accumulated Amortization	755	740
Net	$ 343	329
Customer contracts/ relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	9 years 4 months 24 days
Cost	$ 873	849
Accumulated Amortization	584	572
Net	$ 289	277
Trade names and technology
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	6 years 10 months 24 days
Cost	$ 124	122
Accumulated Amortization	90	89
Net	$ 34	33
Provider contracts
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	11 years 9 months 18 days
Cost	$ 69	69
Accumulated Amortization	52	50
Net	$ 17	19
Noncompetes and other
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	7 years 1 month 6 days
Cost	$ 32	29
Accumulated Amortization	29	29
Net	$ 3	$ 0