Summary of Significant Accounting Policies - Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Revenues	$ 9,313	$ 5,402	$ 9,172
Avis
Disaggregation of Revenue [Line Items]
Revenues	4,894	2,961	5,250
Budget
Disaggregation of Revenue [Line Items]
Revenues	3,715	1,908	3,179
Other
Disaggregation of Revenue [Line Items]
Revenues	704	533	743
Americas
Disaggregation of Revenue [Line Items]
Revenues	7,557	3,965	6,352
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	1,400	1,127	2,222
Asia and Australasia
Disaggregation of Revenue [Line Items]
Revenues	$ 356	$ 310	$ 598