RISK MANAGEMENT ACTIVITIES AND FAIR VALUE MEASUREMENTS - ADDITIONAL INFORMATION (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Dec. 31, 2018	Jun. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term Debt, Fair Value	$ 24,602	$ 23,402
Long Term Debt, Current Maturities Measured at Fair Value	2,301	1,769
U.S. Government Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	1,601	2,003
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost	3,657	3,659
Corporate Bond Securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, within One Year, Amortized Cost	1,525	1,291
Debt Securities, Available-for-sale, Maturity, Allocated and Single Maturity Date, after One Through Five Years, Amortized Cost	1,760	2,503
Derivatives in Fair Value Hedging Relationships | Underlying, Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Underlying Debt Obligation, Carrying Amount	4,623	4,639
Derivatives in Net Investment Hedging Relationships | Underlying, Other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Underlying Debt Obligation, Carrying Amount	$ 17,092	$ 15,012