Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies (Investments in Affiliates and Other Entities) - Additional Information (Detail)

v3.7.0.1
Commitments and Contingencies (Investments in Affiliates and Other Entities) - Additional Information (Detail)
$ in Millions
30 Months Ended
Mar. 31, 2017
USD ($)
km
May 31, 2022
USD ($)
Jun. 30, 2017
USD ($)
Other Commitments, Planned Oil and Gas Infrastructure Projects [Member]      
Other Commitments [Line Items]      
Outstanding capital commitment $ 17.9    
Scenario Forecast [Member] | Other Commitments, Planned Oil and Gas Infrastructure Projects [Member]      
Other Commitments [Line Items]      
Outstanding capital commitment   $ 16.7 $ 1.2
Alberta Power Line [Member]      
Other Commitments [Line Items]      
Length of electrical transmission line to be constructed under contract | km 500    
Aggregate contributions to this unconsolidated affiliate $ 16.9    
Proceeds from return of capital $ 2.9