RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Notional Principal or Quantity Information (Details) - Sep. 30, 2020 € in Millions, ¥ in Millions, £ in Millions, $ in Millions, $ in Millions	USD ($) MWh Bcf MMBbls	GBP (£) MWh Bcf MMBbls	EUR (€) MWh Bcf MMBbls	JPY (¥) MWh Bcf MMBbls	CAD ($) MWh Bcf MMBbls
Foreign exchange contracts - forwards - purchase | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020	$ 1,117
2021	500
2022	1,750
2023	0
2024	0
Thereafter	0
Derivative Notional Amount Outstanding	3,367
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	1,593
2021	5,631
2022	5,703
2023	3,784
2024	1,856
Thereafter	0
Derivative Notional Amount Outstanding	$ 18,567
Foreign exchange contracts - forwards - sell | GBP
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 | £		£ 70
2021 | £		27
2022 | £		28
2023 | £		29
2024 | £		30
Thereafter | £		90
Derivative Notional Amount Outstanding | £		£ 274
Foreign exchange contracts - forwards - sell | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 | €			€ 23
2021 | €			94
2022 | €			94
2023 | €			92
2024 | €			91
Thereafter | €			514
Derivative Notional Amount Outstanding | €			€ 908
Interest rate contracts - short-term borrowings
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020					$ 1,265
2021					4,129
2022					407
2023					48
2024					35
Thereafter					121
Derivative Notional Amount Outstanding					6,005
Interest rate contracts - long-term debt pay fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020					508
2021					1,584
2022					2,035
2023					1,368
2024					0
Thereafter					0
Derivative Notional Amount Outstanding					5,495
Equity contracts
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020					19
2021					44
2022					7
2023					11
2024					0
Thereafter					0
Derivative Notional Amount Outstanding					$ 81
Commodity contracts | Natural gas
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 (bcf/mmbbls) | Bcf	25	25	25	25	25
2021 (bcf/mmbbls) | Bcf	60	60	60	60	60
2022 (bcf/mmbbls) | Bcf	31	31	31	31	31
2023 (bcf/mmbbls) | Bcf	18	18	18	18	18
2024 (bcf/mmbbls) | Bcf	10	10	10	10	10
Thereafter (bcf/mmbbls) | Bcf	10	10	10	10	10
Derivative Nonmonetary Notional Amount Outstanding | Bcf	154	154	154	154	154
Commodity contracts | Crude oil
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 (bcf/mmbbls) | MMBbls	4	4	4	4	4
2021 (bcf/mmbbls) | MMBbls	12	12	12	12	12
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	17	17	17	17	17
Net purchase | Commodity contracts | Power
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2020 (MW/H) | MWh	65	65	65	65	65
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	30	30	30	30	30