RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - NOTIONAL PRINCIPAL OR QUANTITY INFORMATION (Details) - Sep. 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 | €				€ 23
Foreign exchange contracts - forwards - purchase | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018		$ 591
2019		3
2020		1
Foreign exchange contracts - forwards - purchase | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | €				42
2019 | €				208
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		1,592
2019		3,262
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 | €				94
2022 | €				94
Thereafter | €				€ 698
Interest rate contracts - short-term borrowings
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	$ 1,251
2019	3,590
2020	1,093
2021	121
2022	93
Thereafter	203
Interest rate contracts - long-term receive fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	145
2019	582
2020	555
2021	188
2022	102
Interest rate contracts - long-term debt pay fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	1,894
2019	600
2020	573
Equity contracts
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	40
2019	35
2020	$ 20
Commodity contracts | Natural gas
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | Bcf	(7)	(7)	(7)	(7)	(7)
2019 | Bcf	(58)	(58)	(58)	(58)	(58)
2020 | Bcf	(18)	(18)	(18)	(18)	(18)
2021 | Bcf	(5)	(5)	(5)	(5)	(5)
2022 | Bcf	8	8	8	8	8
Thereafter | Bcf	1	1	1	1	1
Commodity contracts | Crude oil
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | MMBbls	4	4	4	4	4
2019 | MMBbls	4	4	4	4	4
Commodity contracts | NGL
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | MMBbls	(1)	(1)	(1)	(1)	(1)
Commodity contracts | Power
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | MWh	57	57	57	57	57
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)