Fair Value Measurement - Condensed Consolidated Balance Sheets for Derivative Financial Instruments (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Current Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Ending balance	$ 1	$ 8	$ 4	$ 14
Net realized and unrealized gains (losses) included in earnings	(1)	7	(1)	7
Transfers out of Level 3	0	(8)	0	(7)
Settlements	0	2	(3)	(9)
Ending balance	0	5	0	5
Net unrealized gains (losses) on derivatives still held included in earnings	0	3	(2)	5
Long- Term Assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Ending balance	0	2	0	2
Net realized and unrealized gains (losses) included in earnings	4	(1)	8	(1)
Transfers out of Level 3	0	0	(4)	0
Settlements	0	0	0	0
Ending balance	4	1	4	1
Net unrealized gains (losses) on derivatives still held included in earnings	4	(1)	4	1
Current Liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers out of Level 3	(2)
Settlements	(1)	1
Net unrealized gains (losses) on derivatives still held included in earnings	1	0	(1)	(1)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	3	1	(1)	0
Net realized and unrealized (losses) gains included in earnings	(1)	1	8	0
Transfers out of Level 3		0	0	0
Settlements			(8)	(1)
Ending balance	1	1	1	1
Long- Term Liabilities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Transfers out of Level 3	0
Settlements	0	0
Net unrealized gains (losses) on derivatives still held included in earnings	3	(5)	1	(5)
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	4	0	(3)	(2)
Net realized and unrealized (losses) gains included in earnings	3	(5)	2	(6)
Transfers out of Level 3		0	0	3
Settlements			0	0
Ending balance	$ 1	$ 5	$ 1	$ 5