Basis of Presentation (Disaggregated Revenue in Basis of Presentation) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Revenues	$ 3,001	$ 1,534	$ 6,744	$ 4,047
Avis
Disaggregation of Revenue [Line Items]
Revenues	1,588	843	3,509	2,230
Budget
Disaggregation of Revenue [Line Items]
Revenues	1,198	539	2,707	1,425
Other
Disaggregation of Revenue [Line Items]
Revenues	215	152	528	392
Americas
Disaggregation of Revenue [Line Items]
Revenues	2,403	1,114	5,457	2,936
Europe, Middle East and Africa
Disaggregation of Revenue [Line Items]
Revenues	527	363	1,011	879
Asia and Australasia
Disaggregation of Revenue [Line Items]
Revenues	$ 71	$ 57	$ 276	$ 232