RISK MANAGEMENT ACTIVITIES AND FAIR VALUE MEASUREMENTS - NOTIONAL AMOUNTS AND FAIR VALUES OF QUALIFYING AND NON-QUALIFYING FINANCIAL INSTRUMENTS USED IN HEDGING TRANSACTIONS - ADDITIONAL INFORMATION (Details) (Details) - Underlying, Other - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2018	Jun. 30, 2018
Derivatives in Fair Value Hedging Relationships
Derivative [Line Items]
Underlying Debt Obligation, Carrying Amount	$ 4,623	$ 4,639
Derivatives in Net Investment Hedging Relationships
Derivative [Line Items]
Underlying Debt Obligation, Carrying Amount	$ 17,092	$ 15,012