RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Notional Principal or Quantity Information (Details) - Jun. 30, 2020 € in Millions, ¥ in Millions, £ in Millions, $ in Millions, $ in Millions	CAD ($) MWh Bcf MMBbls	USD ($) MWh Bcf MMBbls	GBP (£) MWh Bcf MMBbls	EUR (€) MWh Bcf MMBbls	JPY (¥) MWh Bcf MMBbls
Foreign exchange contracts - forwards - purchase | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020		$ 973
2021		500
2022		1,750
2023		0
2024		0
Thereafter		0
Derivative Notional Amount Outstanding		3,223
Foreign exchange contracts - forwards - purchase | Japanese yen
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 | ¥					¥ 0
2021 | ¥					0
2022 | ¥					72,500
2023 | ¥					0
2024 | ¥					0
Thereafter | ¥					0
Derivative Notional Amount Outstanding | ¥					¥ 72,500
Foreign exchange contracts - forwards - sell | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020		3,027
2021		5,631
2022		5,703
2023		3,784
2024		1,856
Thereafter		0
Derivative Notional Amount Outstanding		$ 20,001
Foreign exchange contracts - forwards - sell | GBP
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 | £			£ 76
2021 | £			27
2022 | £			28
2023 | £			29
2024 | £			30
Thereafter | £			90
Derivative Notional Amount Outstanding | £			£ 280
Foreign exchange contracts - forwards - sell | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 | €				€ 23
2021 | €				94
2022 | €				94
2023 | €				92
2024 | €				90
Thereafter | €				515
Derivative Notional Amount Outstanding | €				€ 908
Interest rate contracts - short-term borrowings
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020	$ 2,984
2021	4,190
2022	411
2023	49
2024	35
Thereafter	121
Derivative Notional Amount Outstanding	7,790
Interest rate contracts - long-term debt pay fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020	3,452
2021	1,595
2022	0
2023	0
2024	0
Thereafter	0
Derivative Notional Amount Outstanding	5,047
Equity contracts
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020	16
2021	34
2022	0
2023	0
2024	0
Thereafter	0
Derivative Notional Amount Outstanding	$ 50
Commodity contracts | Natural gas
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 (bcf/mmbbls) | Bcf	45	45	45	45	45
2021 (bcf/mmbbls) | Bcf	55	55	55	55	55
2022 (bcf/mmbbls) | Bcf	22	22	22	22	22
2023 (bcf/mmbbls) | Bcf	17	17	17	17	17
2024 (bcf/mmbbls) | Bcf	10	10	10	10	10
Thereafter (bcf/mmbbls) | Bcf	11	11	11	11	11
Derivative Nonmonetary Notional Amount Outstanding | Bcf	160	160	160	160	160
Commodity contracts | Crude oil
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 (bcf/mmbbls) | MMBbls	8	8	8	8	8
2021 (bcf/mmbbls) | MMBbls	9	9	9	9	9
2022 (bcf/mmbbls) | MMBbls	1	1	1	1	1
2023 (bcf/mmbbls) | MMBbls	0	0	0	0	0
2024 (bcf/mmbbls) | MMBbls	0	0	0	0	0
Thereafter (bcf/mmbbls) | MMBbls	0	0	0	0	0
Derivative Nonmonetary Notional Amount Outstanding | MMBbls	18	18	18	18	18
Net purchase | Commodity contracts | Power
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 (MW/H) | MWh	70	70	70	70	70
Net sell | Commodity contracts | Power
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
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
2024 (MW/H) | MWh	43	43	43	43	43
Thereafter (MW/H) | MWh	43	43	43	43	43
Total (MW/H) | MWh	18	18	18	18	18