RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - NOTIONAL PRINCIPAL OR QUANTITY INFORMATION (Details) - Mar. 31, 2018 € in Millions, ¥ in Millions, £ 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 | €				€ 35
Foreign exchange contracts - forwards - purchase | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018		$ 544
2019		2
2020		1
2021		0
Foreign exchange contracts - forwards - purchase | GBP
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | £			£ 0
2019 | £			0
Foreign exchange contracts - forwards - purchase | Euro
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | €				264
2019 | €				375
2020 | €				0
Foreign exchange contracts - forwards - purchase | Japanese yen
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2019 | ¥					¥ 32,662
2020 | ¥					0
2022 | ¥					20,000
Thereafter | ¥					¥ 0
Foreign exchange contracts - forwards - sell | United States dollar
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018		3,215
2019		3,247
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 | €				169
2022 | €				169
Thereafter | €				€ 889
Interest rate contracts - short-term borrowings
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	$ 3,749
2019	2,100
2020	527
2021	109
2022	93
Thereafter	203
Interest rate contracts - long-term receive fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	728
2019	580
2020	553
2021	188
2022	102
Thereafter	0
Interest rate contracts - long-term debt pay fixed rate
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	2,242
2019	800
2020	447
Equity contracts
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018	40
2019	37
2020	$ 8
Commodity contracts | Natural gas
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | Bcf	(16)	(16)	(16)	(16)	(16)
2019 | Bcf	(57)	(57)	(57)	(57)	(57)
2020 | Bcf	(23)	(23)	(23)	(23)	(23)
2021 | Bcf	(2)	(2)	(2)	(2)	(2)
2022 | Bcf	14	14	14	14	14
Thereafter | Bcf	2	2	2	2	2
Commodity contracts | Crude oil
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | MMBbls	1	1	1	1	1
2019 | MMBbls	2	2	2	2	2
Commodity contracts | NGL
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | MMBbls	(10)	(10)	(10)	(10)	(10)
2019 | MMBbls	(1)	(1)	(1)	(1)	(1)
Commodity contracts | Power
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS
2018 | MWh	60	60	60	60	60
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)