Quarterly Financial Information (Unaudited) (Details) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Nov. 30, 2019
Selected Quarterly Financial Information [Abstract]
Revenues	$ 2,279,000,000	$ 2,187,000,000	$ 1,939,000,000	$ 2,125,000,000	$ 2,456,000,000	$ 2,488,000,000	$ 2,290,000,000	$ 2,117,000,000	$ 8,530,000,000	$ 9,351,000,000	$ 8,047,000,000
Gross profit	869,000,000	886,000,000	701,000,000	727,000,000	965,000,000	1,033,000,000	911,000,000	761,000,000	3,183,000,000	3,670,000,000	3,364,000,000
Operating income	510,000,000	551,000,000	381,000,000	358,000,000	599,000,000	656,000,000	529,000,000	368,000,000	1,800,000,000	2,152,000,000	1,951,000,000
Net income	$ 297,000,000	$ 208,000,000	$ 212,000,000	$ 173,000,000	$ 338,000,000	$ 391,000,000	$ 270,000,000	$ 175,000,000	$ 890,000,000	$ 1,174,000,000	$ 1,096,000,000
Earnings per share - basic (in dollars per share)	$ 4.11	$ 2.88	$ 2.94	$ 2.33	$ 4.51	$ 5.10	$ 3.45	$ 2.21	$ 12.24	$ 15.18	$ 13.26
Earnings per share - diluted (in dollars per share)	4.09	2.87	2.93	2.33	4.49	5.08	3.44	2.19	$ 12.20	$ 15.11	$ 13.12
Effect of Fourth Quarter Events [Line Items]
Loss on extinguishment of debt									$ 183,000,000	$ 61,000,000	$ 0
Earnings Per Share, Diluted, Other Disclosures [Abstract]
Merger related costs (in dollars per share)					0	0	0	(0.01)		$ (0.01)
Merger related intangible asset amortization (in dollars per share)	(0.52)	(0.55)	(0.59)	(0.59)	(0.60)	(0.63)	(0.64)	(0.64)	$ (2.22)	(2.48)
Impact on depreciation related to acquired fleet and property and equipment (in dollars per share)	0.04	(0.06)	(0.02)	(0.03)	(0.05)	(0.07)	(0.12)	(0.14)	(0.08)	(0.39)
Impact of the fair value mark-up of acquired fleet (in dollars per share)	(0.16)	(0.12)	(0.10)	(0.12)	(0.16)	(0.14)	(0.15)	(0.25)	(0.51)	(0.72)
Restructuring charge (in dollars per share)	(0.06)	(0.06)	(0.04)	(0.02)	(0.03)	(0.02)	(0.06)	(0.07)	(0.18)	(0.18)
Asset impairment charge (in dollars per share)	0	(0.10)	0	(0.26)	0.01	(0.02)	(0.03)	(0.01)	(0.37)	(0.05)
Loss on extinguishment of debt securities and amendment of ABL facility (in dollars per share)	$ (0.25)	$ (1.64)	$ 0	$ 0	$ (0.28)	$ 0	$ (0.30)	$ 0	$ (1.88)	$ (0.58)
Senior notes | 4 5/8 Senior Notes due 2025
Effect of Fourth Quarter Events [Line Items]
Loss on extinguishment of debt	$ 24,000,000								$ 24,000,000
Senior notes | 3 7/8 percent Senior Secured Notes due 2027
Effect of Fourth Quarter Events [Line Items]
Loss on extinguishment of debt					$ 29,000,000
Senior notes | 3 7/8 percent Senior Secured Notes due 2027 | Subsidiaries
Effect of Fourth Quarter Events [Line Items]
Debt instrument, face amount					$ 750,000,000					$ 750,000,000		$ 750,000,000