Leases (Lessor) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Lessor, Lease, Description [Line Items]
Total lease revenues	$ 1,332	$ 1,721
Avis
Lessor, Lease, Description [Line Items]
Total lease revenues	690	968
Budget
Lessor, Lease, Description [Line Items]
Total lease revenues	516	608
Other
Lessor, Lease, Description [Line Items]
Total lease revenues	126	145
Americas
Lessor, Lease, Description [Line Items]
Total lease revenues	1,054	1,244
Europe, Middle East and Africa
Lessor, Lease, Description [Line Items]
Total lease revenues	192	342
Asia and Australasia
Lessor, Lease, Description [Line Items]
Total lease revenues	$ 86	$ 135