Financial Risk Management Activities - Fair Value Measurements - Additional Information (Detail) $ in Millions	Dec. 31, 2020 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total long-term debt	$ 8,296
Carrying value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total long-term debt	8,296
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total long-term debt fair value	$ 9,647