Financial Risk Management Activities - Additional Information (Detail) bbl in Millions, $ in Millions	1 Months Ended	12 Months Ended
	Sep. 30, 2020 bbl	Dec. 31, 2020 USD ($) bbl / d vlcc $ / bbl bbl	Mar. 31, 2021 bbl	Mar. 01, 2021 bbl / d $ / bbl	Dec. 31, 2019 USD ($)
Derivative Instruments, Gain (Loss) [Line Items]
Number of VLCCs | vlcc		3
Crude oil in transit (in barrels of oil) | bbl		6.3
Crude oil sold (in barrels of oil) | bbl	2.1
Accumulated other comprehensive income (loss)		$ (755)			$ (699)
Liability for deferred unrealized losses		55			1
Subsequent Event
Derivative Instruments, Gain (Loss) [Line Items]
Crude oil in transit (in barrels of oil) | bbl			4.2
Derivative Contracts Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Liability for deferred unrealized losses		$ 54			0
Very Large Crude Carriers (VLCCs)
Derivative Instruments, Gain (Loss) [Line Items]
Number of VLCCs | vlcc		3
Crude oil in transit (in barrels of oil) | bbl		6.3
Swap | Derivative Contracts Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Liability for deferred unrealized losses		$ 54
Swap | Brent | Derivative Contracts Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated other comprehensive income (loss)		16
Liability for deferred unrealized losses		54
Put Option | Derivative Contracts Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Liability for deferred unrealized losses		$ 0			$ 0
Put Option | West Texas Intermediate
Derivative Instruments, Gain (Loss) [Line Items]
Average monthly floor price | $ / bbl		45
Commodity - crude oil (millions of barrels) | bbl / d		75,000
Put Option | West Texas Intermediate | Derivative Activity - Changed Price
Derivative Instruments, Gain (Loss) [Line Items]
Average monthly floor price | $ / bbl		45
Put Option | West Texas Intermediate | Subsequent Event
Derivative Instruments, Gain (Loss) [Line Items]
Average monthly floor price | $ / bbl				50
Commodity - crude oil (millions of barrels) | bbl / d				120,000
Put Option | West Texas Intermediate | Subsequent Event | Derivative Activity - Purchased Additional
Derivative Instruments, Gain (Loss) [Line Items]
Average monthly floor price | $ / bbl				50
Commodity - crude oil (millions of barrels) | bbl / d				45,000
Put Option | West Texas Intermediate | Subsequent Event | Derivative Activity - Changed Price
Derivative Instruments, Gain (Loss) [Line Items]
Average monthly floor price | $ / bbl				50
Commodity - crude oil (millions of barrels) | bbl / d				75,000
Put Option | West Texas Intermediate | Very Large Crude Carriers (VLCCs) | Derivative Contracts Designated as Hedging Instruments
Derivative Instruments, Gain (Loss) [Line Items]
Accumulated other comprehensive income (loss)		$ 40
Put Option | Brent | Subsequent Event
Derivative Instruments, Gain (Loss) [Line Items]
Average monthly floor price | $ / bbl				55
Commodity - crude oil (millions of barrels) | bbl / d				30,000
Put Option | Brent | Subsequent Event | Derivative Activity - Purchased Additional
Derivative Instruments, Gain (Loss) [Line Items]
Average monthly floor price | $ / bbl				55
Commodity - crude oil (millions of barrels) | bbl / d				30,000