Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended								12 Months Ended
	Aug. 31, 2021	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Selected Quarterly Financial Information [Abstract]
Revenues		$ 2,776	$ 2,596	$ 2,287	$ 2,057	$ 2,279	$ 2,187	$ 1,939	$ 2,125	$ 9,716	$ 8,530	$ 9,351
Gross profit		1,161	1,103	875	714	869	886	701	727	3,853	3,183	3,670
Operating income		745	679	481	372	510	551	381	358	2,277	1,800	2,152
Net income		$ 481	$ 409	$ 293	$ 203	$ 297	$ 208	$ 212	$ 173	$ 1,386	$ 890	$ 1,174
Earnings per share - basic (in dollars per share)		$ 6.65	$ 5.65	$ 4.03	$ 2.81	$ 4.11	$ 2.88	$ 2.94	$ 2.33	$ 19.14	$ 12.24	$ 15.18
Earnings per share - diluted (in dollars per share)		6.61	5.63	4.02	2.80	4.09	2.87	2.93	2.33	$ 19.04	$ 12.20	$ 15.11
Effect of Fourth Quarter Events [Line Items]
Loss on extinguishment of debt	$ 30									$ 30	$ 183	$ 61
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Merger related costs (in dollars per share)		0	0	(0.03)	0					$ (0.03)
Merger related intangible asset amortization (in dollars per share)		(0.47)	(0.53)	(0.48)	(0.50)	(0.52)	(0.55)	(0.59)	(0.59)	(1.98)	$ (2.22)
Impact on depreciation related to acquired fleet and property and equipment (in dollars per share)		(0.13)	(0.01)	(0.01)	(0.02)	0.04	(0.06)	(0.02)	(0.03)	(0.16)	(0.08)
Impact of the fair value mark-up of acquired fleet (in dollars per share)		(0.10)	(0.08)	(0.08)	(0.12)	(0.16)	(0.12)	(0.10)	(0.12)	(0.38)	(0.51)
Restructuring charge (in dollars per share)		0	0	0	(0.01)	(0.06)	(0.06)	(0.04)	(0.02)	(0.02)	(0.18)
Asset impairment charge (in dollars per share)		(0.08)	(0.02)	(0.04)	0	0	(0.10)	0	(0.26)	(0.14)	(0.37)
Loss on repurchase/redemption of debt securities (in dollars per share)		$ 0	$ (0.31)	$ 0	$ 0	$ (0.25)	$ (1.64)	$ 0	$ 0	$ (0.31)	$ (1.88)
Acquisition company revenue prior to acquisition		$ 200								$ 200
Senior notes | 4 5/8 Senior Notes due 2025
Effect of Fourth Quarter Events [Line Items]
Loss on extinguishment of debt						$ 24
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Stated interest rate		4.625%								4.625%