Quarterly report pursuant to Section 13 or 15(d)

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

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Commitments and Contingencies - Investments in Affiliates and Other Entities (Detail)
$ in Millions
45 Months Ended
Jun. 30, 2018
USD ($)
May 31, 2022
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2014
kV
substation
km
Other Commitments, Planned Oil and Gas Infrastructure Projects          
Other Commitments [Line Items]          
Outstanding capital commitment $ 15.7        
Capital for infrastructure projects          
Other Commitments [Line Items]          
Outstanding capital commitment 80.0        
Scenario, Forecast | Other Commitments, Planned Oil and Gas Infrastructure Projects          
Other Commitments [Line Items]          
Outstanding capital commitment   $ 0.9   $ 14.8  
EPC Electric Transmission Project          
Other Commitments [Line Items]          
Length of electrical transmission line to be constructed under contract | km         500
Number of substations | substation         2
Voltage of substations | kV         500
Aggregate contributions to this unconsolidated affiliate 63.9        
Proceeds from return of capital 61.6        
EPC Electric Transmission Project | Scenario, Forecast          
Other Commitments [Line Items]          
Outstanding capital commitment     $ 24.1    
Infrastructure investors partnership | Capital for infrastructure projects          
Other Commitments [Line Items]          
Outstanding capital commitment $ 1,000.0