RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - NOTIONAL PRINCIPAL OR QUANTITY INFORMATION (Details) - Jun. 30, 2018 € in Millions, ¥ in Millions, £ in Millions, MMBbls in Millions, $ in Millions, $ in Millions, Bcf in Billions	CAD ($) MWh Bcf MMBbls	USD ($) MWh Bcf MMBbls	GBP (£) MWh Bcf MMBbls	EUR (€) MWh Bcf MMBbls	JPY (¥) MWh Bcf MMBbls
Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 | €				€ 35
Foreign exchange contracts - forwards - purchase | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018		$ 572
2019		3
2020		1
Foreign exchange contracts - forwards - purchase | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | €				147
2019 | €				375
Foreign exchange contracts - forwards - purchase | Japanese yen
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | ¥					¥ 32,662
2022 | ¥					¥ 20,000
Foreign exchange contracts - forwards - sell | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018		2,610
2019		3,249
2020		3,258
2021		1,689
2022		1,676
Thereafter		$ 3,489
Foreign exchange contracts - forwards - sell | GBP
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | £			£ 89
2020 | £			25
2021 | £			27
2022 | £			28
Thereafter | £			£ 149
Foreign exchange contracts - forwards - sell | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2021 | €				169
2022 | €				169
Thereafter | €				€ 889
Interest rate contracts - short-term borrowings
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	$ 2,530
2019	2,766
2020	547
2021	111
2022	94
Thereafter	204
Interest rate contracts - long-term receive fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	434
2019	592
2020	565
2021	191
2022	104
Interest rate contracts - long-term debt pay fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	1,907
2019	400
2020	454
Equity contracts
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	40
2019	35
2020	$ 20
Commodity contracts | Natural gas
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | Bcf	(2)	(2)	(2)	(2)	(2)
2019 | Bcf	(35)	(35)	(35)	(35)	(35)
2020 | Bcf	(22)	(22)	(22)	(22)	(22)
2021 | Bcf	(9)	(9)	(9)	(9)	(9)
2022 | Bcf	17	17	17	17	17
Thereafter | Bcf	2	2	2	2	2
Commodity contracts | Crude oil
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | MMBbls	6	6	6	6	6
2019 | MMBbls	1	1	1	1	1
Commodity contracts | NGL
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | MMBbls	(10)	(10)	(10)	(10)	(10)
2019 | MMBbls	(1)	(1)	(1)	(1)	(1)
Commodity contracts | Power
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | MWh	63	63	63	63	63
2019 | MWh	64	64	64	64	64
2020 | MWh	66	66	66	66	66
2021 | MWh	(3)	(3)	(3)	(3)	(3)
2022 | MWh	(43)	(43)	(43)	(43)	(43)
Thereafter | MWh	(43)	(43)	(43)	(43)	(43)