Details about Accumulated Other Comprehensive Income Components (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Miscellaneous, Net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of unrecognized losses and prior service cost	[1]	$ 16	$ 13
Fuel Oil Contract | Aircraft Fuel
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassifications of losses into earnings related to fuel derivative contracts			$ 2

[1] This AOCI component is included in the computation of net periodic pension and other postretirement costs (see Note 5 to the financial statements included in this Part I, Item 1 for additional information).