Financial Risk Management Activities - Additional Information (Detail) - Commodity derivative contracts MMBbls in Millions	Jun. 30, 2020 bbl / d MMBbls $ / bbl	Dec. 31, 2019 MMBbls
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of crude oil | MMBbls	27.6	54.9
West Texas Intermediate | Designated as Cash Flow Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Average monthly floor price (US dollar per barrel) | $ / bbl	55
Notional amount of crude oil | bbl / d	130,000
Brent | Designated as Cash Flow Hedges
Derivative Instruments, Gain (Loss) [Line Items]
Average monthly floor price (US dollar per barrel) | $ / bbl	60
Notional amount of crude oil | bbl / d	20,000