ACQUISITIONS AND DIVESTITURES - Narrative (Details) - USD ($) $ in Millions			3 Months Ended	6 Months Ended
	Apr. 10, 2018	Mar. 01, 2018	Jun. 30, 2018	Jun. 30, 2018	Jun. 30, 2017	Sep. 30, 2018
Business Acquisition [Line Items]
Pretax loss on sale of subsidiary			$ 790	$ 790	$ 0
Goodwill, acquired during period				614
MCCI
Business Acquisition [Line Items]
Notes receivable and revolving note, related party		$ 383
MCCI
Business Acquisition [Line Items]
Payments to acquire business		169
Goodwill, acquired during period		479
Other intangible assets acquired		80
Net tangible assets acquired		$ 27
Other intangible assets, weighted average useful life		8 years
FPG
Business Acquisition [Line Items]
Payments to acquire business	$ 185
Goodwill, acquired during period	135
Other intangible assets acquired	38
Net tangible assets acquired	$ 17
Other intangible assets, weighted average useful life	4 years 10 months 25 days
KMG America Corporation | Disposal Group, Held-for-sale, Not Discontinued Operations
Business Acquisition [Line Items]
Pretax loss on sale of subsidiary			790	790
Tax benefit on sale of subsidiary			430	430
Net loss on sale of subsidiary			360
Disposal group, revenue			93	172
Disposal group, pretax income			35	$ 53
KIC
Business Acquisition [Line Items]
Payments for reinsurance			$ 230
Forecast | Subsequent Event | KMG America Corporation | Disposal Group, Held-for-sale, Not Discontinued Operations
Business Acquisition [Line Items]
Parent company cash contributed to sale of subsidiary						$ 200
Transfer of statutory capital with sale of subsidiary						$ 150