ACQUISITIONS AND DIVESTITURES - Transaction, Reorganization, and Separation (TRS) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Transaction, reorganization, and separation	$ 50	$ 28	$ 16
Employee benefits	26
Employee Termination
Business Acquisition [Line Items]
Transaction, reorganization, and separation	2
Employee Termination and Office Closures
Business Acquisition [Line Items]
Employee benefits	15
Consulting Fees
Business Acquisition [Line Items]
Transaction, reorganization, and separation	$ 7		11
Consulting and Legal Fees
Business Acquisition [Line Items]
Transaction, reorganization, and separation		22
Employee Separation, Consolidation Of Office Space and Other Reorganization Efforts
Business Acquisition [Line Items]
Transaction, reorganization, and separation		$ 6	$ 5