Reconciliation of Adjusted EBITDA to Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Acquired Indefinite-lived Intangible Assets [Line Items]
Non-vehicle depreciation and amortization	$ 286	$ 263	$ 256
COVID-19 Charges	122
Charges for legal matter	8
Non-operational charges related to shareholder activist activity	4	2	9
Equity Method Investment, Realized Gain (Loss) on Disposal		(44)
Acquisition-related Costs [Member]
Acquired Indefinite-lived Intangible Assets [Line Items]
Non-vehicle depreciation and amortization	$ 66	$ 56	$ 61