Acquisitions (Pro Forma Information) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues	$ 3,728	$ 3,765	$ 3,554	$ 3,285	$ 3,296	$ 3,051	$ 2,771	$ 2,524	$ 14,332	$ 11,642	$ 9,716
Pro forma revenues										12,469
Pretax income									$ 3,211	2,802	$ 1,846
Pro forma pretax income										2,572
Impact of fair value mark-ups/useful life changes on depreciation
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income										(94)
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										(28)
Intangible asset amortization
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income										(78)
Interest expense
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income										(96)
Elimination of historic interest
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income										53
Elimination of historic legal and financing costs
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pro forma pretax income										11
United Rentals and Ahern Rentals
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Pretax income										2,804
United Rentals
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues										11,642
Pretax income										2,802
Ahern Rentals
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Revenues										827
Pretax income										$ 2