RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Notional Principal or Quantity Information (Details) - Mar. 31, 2020 € in Millions, ¥ in Millions, £ in Millions, $ in Millions, $ in Millions	USD ($) MWh Bcf MMBbls	CAD ($) 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	$ 823
2021	500
2022	1,750
2023	0
2024	0
Thereafter	0
Derivative Notional Amount Outstanding	3,073
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	4,416
2021	5,631
2022	5,703
2023	3,784
2024	1,856
Thereafter	0
Derivative Notional Amount Outstanding	$ 21,390
Foreign exchange contracts - forwards - sell | GBP
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 | £			£ 89
2021 | £			27
2022 | £			28
2023 | £			29
2024 | £			30
Thereafter | £			90
Derivative Notional Amount Outstanding | £			£ 293
Foreign exchange contracts - forwards - sell | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 | €				€ 23
2021 | €				94
2022 | €				94
2023 | €				92
2024 | €				91
Thereafter | €				515
Derivative Notional Amount Outstanding | €				€ 909
Interest rate contracts - short-term borrowings
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020		$ 4,618
2021		4,284
2022		422
2023		50
2024		36
Thereafter		121
Derivative Notional Amount Outstanding		9,531
Interest rate contracts - long-term debt pay fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020		3,544
2021		1,619
2022		0
2023		0
2024		0
Thereafter		0
Derivative Notional Amount Outstanding		5,163
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	(38)	(38)	(38)	(38)	(38)
2021 (bcf/mmbbls) | Bcf	57	57	57	57	57
2022 (bcf/mmbbls) | Bcf	45	45	45	45	45
2023 (bcf/mmbbls) | Bcf	22	22	22	22	22
2024 (bcf/mmbbls) | Bcf	10	10	10	10	10
Thereafter (bcf/mmbbls) | Bcf	11	11	11	11	11
Derivative Nonmonetary Notional Amount Outstanding | Bcf	107	107	107	107	107
Commodity contracts | Crude oil
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 (bcf/mmbbls) | MMBbls	5	5	5	5	5
2021 (bcf/mmbbls) | MMBbls	4	4	4	4	4
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	10	10	10	10	10
Net purchase | Commodity contracts | Power
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 (MW/H) | MWh	79	79	79	79	79
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
Derivative Nonmonetary Rate Notional Amount Outstanding | MWh	16	16	16	16	16