ACQUISITIONS AND DIVESTITURES - Narrative (Details) - USD ($) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 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
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				$ 190
Transfer of statutory capital with sale of subsidiary	160				160
Pretax loss on sale of subsidiary	786
Tax benefit on sale of subsidiary	$ 452
Disposal group, revenues					182
Disposal group, pretax income					$ 47