Acquisitions (Pro Forma Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues	$ 3,765	$ 3,051	$ 10,604	$ 8,346
Pro forma revenues		3,277		9,000
Pretax income	$ 943	816	$ 2,309	1,907
Pro forma pretax income		759		1,714
Impact of fair value mark-ups/useful life changes on depreciation
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income		(26)		(76)
Impact of the fair value mark-up of acquired fleet on cost of rental equipment sales
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income		(4)		(26)
Intangible asset amortization
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income		(20)		(59)
Interest expense
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income		(27)		(77)
Elimination of historic interest
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income		15		42
Elimination of historic legal and financing costs
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income		4		8
United Rentals and Ahern Rentals
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pretax income		817		1,902
United Rentals
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues		3,051		8,346
Pretax income		816		1,907
Ahern Rentals
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues		226		654
Pretax income		$ 1		$ (5)