Operating Revenue by Principle Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total revenues	$ 9,052	$ 9,913	$ 9,396	$ 8,195	$ 9,036	$ 10,306	$ 9,914	$ 8,608	$ 36,556	$ 37,864	$ 38,901
Domestic (U.S. and Canada)
Segment Reporting Information [Line Items]
Total revenues									22,202	21,931	22,320
Pacific
Segment Reporting Information [Line Items]
Total revenues									4,959	5,498	5,767
Atlantic
Segment Reporting Information [Line Items]
Total revenues									6,157	7,068	7,321
Latin America
Segment Reporting Information [Line Items]
Total revenues									$ 3,238	$ 3,367	$ 3,493