ACQUISITIONS AND DIVESTITURES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Business Acquisition [Line Items]
Goodwill, acquired during period				$ 25
MCCI Holdings, LLC
Business Acquisition [Line Items]
Payments to acquire business			$ 169
Goodwill, acquired during period			483
Other intangible assets acquired			80
Net tangible assets acquired			$ 24
Other intangible assets, weighted average useful life			8 years
Family Physicians Group
Business Acquisition [Line Items]
Payments to acquire business		$ 185
Goodwill, acquired during period		133
Other intangible assets acquired		38
Net tangible assets acquired		$ 14			$ 14
Other intangible assets, weighted average useful life		4 years 10 months 24 days
MCCI Holdings, LLC
Business Acquisition [Line Items]
Notes receivable and revolving note, related party			$ 383
Kanawah Insurance Company KIC
Business Acquisition [Line Items]
Payments for reinsurance	$ 245
KMG America Corporation | Disposed of by Sale
Business Acquisition [Line Items]
Parent company cash contributed to sale of subsidiary	190
Transfer of statutory capital with sale of subsidiary	160
Pretax loss on sale of subsidiary	786
Tax benefit on sale of subsidiary	$ 452
Disposal group, revenues		$ 93			172
Disposal group, pretax income		$ 35			$ 53