Segment Information (Summary of Segment Assets) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2025	Dec. 31, 2024
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment additions	$ 34	$ 202
Assets exclusive of assets under vehicle programs	9,830	9,668
Assets under vehicle programs	19,214	19,373
Net long-lived assets	2,375	2,369
Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment additions	14	109
Assets exclusive of assets under vehicle programs	6,876	6,785
Assets under vehicle programs	15,851	16,058
Net long-lived assets	1,458	1,474
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment additions	6	40
Assets exclusive of assets under vehicle programs	2,608	2,539
Assets under vehicle programs	3,363	3,315
Net long-lived assets	753	733
Unallocated Assets
Revenues from External Customers and Long-Lived Assets [Line Items]
Property and equipment additions	14	53
Assets exclusive of assets under vehicle programs	346	344
Assets under vehicle programs	0	0
Net long-lived assets	$ 164	$ 162