GOODWILL AND OTHER INTANGIBLE ASSETS - Intangible Assets Included in Other Long-Term Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	8 years 8 months 12 days
Cost	$ 829	$ 827
Accumulated Amortization	618	582
Net	$ 211	245
Customer contracts/ relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	8 years 8 months 12 days
Cost	$ 647	646
Accumulated Amortization	465	434
Net	$ 182	212
Trade names and technology
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	6 years 4 months 24 days
Cost	$ 84	84
Accumulated Amortization	84	83
Net	$ 0	1
Provider contracts
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	11 years 9 months 18 days
Cost	$ 69	68
Accumulated Amortization	41	37
Net	$ 28	31
Noncompetes and other
Acquired Finite-Lived Intangible Assets [Line Items]
Weighted Average Life	7 years 3 months 18 days
Cost	$ 29	29
Accumulated Amortization	28	28
Net	$ 1	$ 1