Revenue (Details) $ in Millions	12 Months Ended
Dec. 31, 2019 CAD ($)
Canadian Coal
Disclosure of disaggregation of revenue from contracts with customers [line items]
Transaction price allocated to remaining performance obligations	$ 452
Canadian Gas
Disclosure of disaggregation of revenue from contracts with customers [line items]
Transaction price allocated to remaining performance obligations	18
Australian Gas
Disclosure of disaggregation of revenue from contracts with customers [line items]
Transaction price allocated to remaining performance obligations	2,095
Wind and Solar
Disclosure of disaggregation of revenue from contracts with customers [line items]
Transaction price allocated to remaining performance obligations	8
Hydro
Disclosure of disaggregation of revenue from contracts with customers [line items]
Transaction price allocated to remaining performance obligations	72
Later than one year \| Canadian Coal
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	116
2023 \| Australian Gas
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	223
Minimum \| Canadian Gas
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	4
Minimum \| Australian Gas
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	80
Minimum \| Wind and Solar
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	1
Minimum \| 2024 \| Canadian Coal
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	5
Minimum \| More than five years \| Canadian Coal
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	40
Maximum \| Canadian Gas
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	6
Maximum \| Australian Gas
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	110
Maximum \| Wind and Solar
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	2
Maximum \| 2024 \| Canadian Coal
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	10
Maximum \| More than five years \| Canadian Coal
Disclosure of disaggregation of revenue from contracts with customers [line items]
Revenue from performance obligations satisfied or partially satisfied in previous periods	$ 45

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

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The amount of revenue from performance obligations satisfied (or partially satisfied) in previous periods. [Refer: Performance obligations [member]; Revenue]

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