RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Notional Principal or Quantity Information (Details) - Sep. 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				$ 1,049
2020				1
2021				0
2022				0
2023				0
Thereafter				0
Foreign exchange contracts - forwards - purchase | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019	$ 51
2020	0
2021	0
2022	0
2023	0
Thereafter	0
Foreign exchange contracts - forwards - purchase | Japanese yen
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | ¥					¥ 0
2020 | ¥					0
2021 | ¥					0
2022 | ¥					72,500
2023 | ¥					0
Thereafter | ¥					¥ 0
Foreign exchange contracts - forwards - sell | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019				1,218
2020				5,355
2021				4,946
2022				5,182
2023				1,804
Thereafter				$ 1,856
Foreign exchange contracts - forwards - sell | GBP
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | £		£ 6
2020 | £		94
2021 | £		27
2022 | £		28
2023 | £		29
Thereafter | £		£ 120
Foreign exchange contracts - forwards - sell | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | €			€ 0
2020 | €			23
2021 | €			94
2022 | €			94
2023 | €			92
Thereafter | €			€ 606
Interest rate contracts - short-term borrowings
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019	2,204
2020	6,152
2021	4,124
2022	405
2023	48
Thereafter	156
Interest rate contracts - long-term debt pay fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019	1,509
2020	3,125
2021	1,579
2022	0
2023	0
Thereafter	0
Equity contracts
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019	29
2020	20
2021	34
2022	0
2023	0
Thereafter	$ 0
Commodity contracts | Natural gas
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 (bcf/mmbbls) | Bcf	(3)	(3)	(3)	(3)	(3)
2020 (bcf/mmbbls) | Bcf	(26)	(26)	(26)	(26)	(26)
2021 (bcf/mmbbls) | Bcf	3	3	3	3	3
2022 (bcf/mmbbls) | Bcf	21	21	21	21	21
2023 (bcf/mmbbls) | Bcf	4	4	4	4	4
Thereafter (bcf/mmbbls) | Bcf	0	0	0	0	0
Commodity contracts | Crude oil
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 (bcf/mmbbls) | MMBbls	7	7	7	7	7
2020 (bcf/mmbbls) | MMBbls	1	1	1	1	1
2021 (bcf/mmbbls) | MMBbls	0	0	0	0	0
2022 (bcf/mmbbls) | MMBbls	0	0	0	0	0
2023 (bcf/mmbbls) | MMBbls	0	0	0	0	0
Thereafter (bcf/mmbbls) | MMBbls	0	0	0	0	0
Commodity contracts | Power
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 (MW/H) | MWh	90	90	90	90	90
2020 (MW/H) | MWh	80	80	80	80	80
2021 (MW/H) | MWh	(3)	(3)	(3)	(3)	(3)
2022 (MW/H) | MWh	(43)	(43)	(43)	(43)	(43)
2023 (MW/H) | MWh	(43)	(43)	(43)	(43)	(43)
Thereafter (MW/H) | MWh	(43)	(43)	(43)	(43)	(43)