RISK MANAGEMENT ACTIVITIES AND FAIR VALUE MEASUREMENTS - GAIN (LOSS) ON DERIVATIVE INSTRUMENTS (EFFECTIVE PORTION) (Details) - USD ($) $ in Millions		Sep. 30, 2018	Sep. 30, 2017
Foreign Exchange Contract | Derivatives in Net Investment Hedging Relationships
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated Other Comprehensive Income, Amount of Gain (Loss) Recognized on Derivatives	[1],[2]	$ (43)	$ (184)

[1] For the derivatives in net investment hedging relationships, the amount of gain/(loss) excluded from effectiveness testing, which was recognized in earnings, was $14 and $31 for the three months ended September 30, 2018 and 2017, respectively.

[2] In addition to the foreign currency derivative contracts designated as net investment hedges, certain of our foreign currency denominated debt instruments are designated as net investment hedges. The amount of gain/(loss) recognized in AOCI for such instruments was $207 and $248, as of September 30, 2018 and 2017, respectively.