Leases (Lessor) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lessor, Lease, Description [Line Items]
Total lease revenues	$ 2,352	$ 738	$ 3,684	$ 2,459
Avis
Lessor, Lease, Description [Line Items]
Total lease revenues	1,201	389	1,891	1,357
Budget
Lessor, Lease, Description [Line Items]
Total lease revenues	975	261	1,491	869
Other
Lessor, Lease, Description [Line Items]
Total lease revenues	176	88	302	233
Americas
Lessor, Lease, Description [Line Items]
Total lease revenues	1,972	552	3,026	1,796
Europe, Middle East and Africa
Lessor, Lease, Description [Line Items]
Total lease revenues	268	151	460	493
Asia and Australasia
Lessor, Lease, Description [Line Items]
Total lease revenues	$ 112	$ 35	$ 198	$ 170