Special Charges and Mark-to-Market Adjustments - Additional Information (Detail) technician in Thousands	1 Months Ended	3 Months Ended			9 Months Ended
	May 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2017 USD ($) technician	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)
Special Charges [Line Items]
Impairment of assets		$ 11,000,000	$ 15,000,000		$ 145,000,000	$ 15,000,000
Severance and benefits costs		9,000,000	23,000,000		34,000,000	101,000,000
Gain (loss) on other special items		3,000,000	(12,000,000)		(7,000,000)	(29,000,000)
Gain (loss) on other special items, net of tax		2,000,000			(5,000,000)
Gain (loss) from equity method investments		29,000,000			(61,000,000)
Gain (loss) from equity method investments, net of tax		23,000,000			(47,000,000)
Tropical Storms
Special Charges [Line Items]
Loss on unusual item			12,000,000			17,000,000
Loss on unusual item, net of tax			7,000,000			11,000,000
International Brotherhood of Teamsters
Special Charges [Line Items]
Severance and benefits costs		5,000,000			19,000,000
Severance and benefits costs net of tax		4,000,000			15,000,000
Maintenance service agreement
Special Charges [Line Items]
Intangible asset impairment			15,000,000
Intangible asset impairment, net of tax			10,000,000
Voluntary early out program
Special Charges [Line Items]
Severance and benefits costs			16,000,000			73,000,000
Severance and benefits costs net of tax			10,000,000			47,000,000
Voluntary early out program | International Brotherhood of Teamsters
Special Charges [Line Items]
Number of positions eliminated | technician				1
Voluntary early out program | International Brotherhood of Teamsters | Maximum
Special Charges [Line Items]
Severance payment per participant				$ 100,000
Management reorganization initiative
Special Charges [Line Items]
Severance and benefits costs		4,000,000	7,000,000		15,000,000	28,000,000
Severance and benefits costs net of tax		3,000,000	$ 5,000,000		12,000,000	$ 18,000,000
Certain Fleet Types and Certain International Slots
Special Charges [Line Items]
Impairment of assets		11,000,000			40,000,000
Impairment of assets, net of tax		$ 9,000,000			$ 31,000,000
Brazil Routes
Special Charges [Line Items]
Intangible asset impairment	$ 105,000,000
Intangible asset impairment, net of tax	$ 82,000,000