Fair Value Measurements - Schedule of Financial Instruments Measured at Fair Value on Recurring and Nonrecurring Basis (Detail) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Carrying Amount [Member]
Measured at fair value on recurring basis
Forward contracts, asset	[1]	$ 106
Forward contracts, liability	[1]		$ (39)
Not measured at fair value on recurring basis
Debt and finance lease obligations	[2]	3,639	(3,633)
Fair value [Member]
Measured at fair value on recurring basis
Forward contracts, asset	[1]	106
Forward contracts, liability	[1]		(39)
Not measured at fair value on recurring basis
Debt and finance lease obligations	[2]	1,895	(3,287)
Level 2 [Member]
Measured at fair value on recurring basis
Forward contracts, asset	[1]	106
Forward contracts, liability	[1]		(39)
Not measured at fair value on recurring basis
Debt and finance lease obligations	[2]	1,782	(3,197)
Level 3 [Member]
Not measured at fair value on recurring basis
Debt and finance lease obligations	[2]	$ 113	$ (90)

[1] The fair value of forward contracts is classified as Level 2 within the fair value hierarchy and is valued using observable market parameters for similar instruments traded in active markets. Where quoted prices are not available, the income approach is used to value forward contracts. This approach discounts future cash flows based on current market expectations and credit risk.

[2] Our debt instruments are generally valued using a market approach based on quoted prices for similar instruments traded in active markets and are classified as Level 2 within the fair value hierarchy. Quoted prices were not available for the NO 105 construction financing, structured equipment financing or finance leases. Therefore, these instruments were valued based on the present value of future cash flows discounted at estimated borrowing rates for similar debt instruments or on estimated prices based on current yields for debt issues of similar quality and terms and are classified as Level 3 within the fair value hierarchy.