XML 28 R125.htm IDEA: XBRL DOCUMENT v3.19.3.a.u2
Financial instruments - Summary of Commodity Volumes Associated with Derivative Contracts (Detail)
Dec. 31, 2019
MMBTU
Derivative [Line Items]  
Commodity volumes, Gas 4,784,739
Swap  
Derivative [Line Items]  
Commodity volumes, Gas 2,134,739
Options  
Derivative [Line Items]  
Commodity volumes, Gas 150,000
Forward contracts  
Derivative [Line Items]  
Commodity volumes, Gas 2,500,000