RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Notional Principal or Quantity Information (Details) - Jun. 30, 2019 € in Millions, ¥ in Millions, £ in Millions, MMBbls in Millions, $ in Millions, $ in Millions, Bcf in Billions	CAD ($) MWh Bcf MMBbls	GBP (£) MWh Bcf MMBbls	EUR (€) MWh Bcf MMBbls	USD ($) MWh Bcf MMBbls	JPY (¥) MWh Bcf MMBbls
Foreign exchange contracts - forwards - purchase | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019				$ 878
2020				1
Foreign exchange contracts - forwards - purchase | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | €			€ 133
Foreign exchange contracts - forwards - purchase | Japanese yen
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2022 | ¥					¥ 72,500
Foreign exchange contracts - forwards - sell | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019				2,422
2020				4,893
2021				3,608
2022				2,422
2023				1,804
Thereafter				$ 1,856
Foreign exchange contracts - forwards - sell | GBP
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | £		£ 12
2020 | £		94
2021 | £		27
2022 | £		28
2023 | £		29
Thereafter | £		£ 120
Foreign exchange contracts - forwards - sell | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 | €			23
2021 | €			94
2022 | €			94
2023 | €			92
Thereafter | €			€ 606
Interest rate contracts - short-term borrowings
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019	$ 4,371
2020	6,115
2021	4,098
2022	402
2023	48
Thereafter	156
Interest rate contracts - long-term debt pay fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019	2,497
2020	3,100
2021	1,573
Equity contracts
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019	29
2020	20
2021	$ 34
Commodity contracts | Natural gas
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | Bcf	(44)	(44)	(44)	(44)	(44)
2020 | Bcf	(14)	(14)	(14)	(14)	(14)
2021 | Bcf	8	8	8	8	8
2022 | Bcf	14	14	14	14	14
2023 | Bcf	3	3	3	3	3
Commodity contracts | Crude oil
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | MMBbls	10	10	10	10	10
2020 | MMBbls	3	3	3	3	3
Commodity contracts | Power
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | MWh	98	98	98	98	98
2020 | MWh	80	80	80	80	80
2021 | MWh	(3)	(3)	(3)	(3)	(3)
2022 | MWh	(43)	(43)	(43)	(43)	(43)
2023 | MWh	(43)	(43)	(43)	(43)	(43)
Thereafter | MWh	(43)	(43)	(43)	(43)	(43)