Summary of Significant Accounting Policies (Revenue Recognition) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Owned equipment rentals									$ 4,928	$ 4,273	$ 4,288
Re-rent revenue									106	93	89
Ancillary and other rental revenues:
Delivery and pick-up									389	340	337
Other									292	235	235
Total ancillary and other rental revenues									681	575	572
Equipment rentals									5,715	4,941	4,949
Service and other revenues									118	102	94
Total revenues	$ 1,922	$ 1,766	$ 1,597	$ 1,356	$ 1,523	$ 1,508	$ 1,421	$ 1,310	6,641	5,762	5,817
Deferred revenue	$ 38				$ 33				38	33
Topic 840
Revenues:
Owned equipment rentals									4,928	4,273	4,288
Re-rent revenue									106	93	89
Ancillary and other rental revenues:
Delivery and pick-up									0	0	0
Other									228	186	187
Total ancillary and other rental revenues									228	186	187
Equipment rentals									5,262	4,552	4,564
Service and other revenues									0	0	0
Total revenues									5,262	4,552	4,564
Topic 605
Revenues:
Owned equipment rentals									0	0	0
Re-rent revenue									0	0	0
Ancillary and other rental revenues:
Delivery and pick-up									389	340	337
Other									64	49	48
Total ancillary and other rental revenues									453	389	385
Equipment rentals									453	389	385
Service and other revenues									118	102	94
Total revenues									1,379	1,210	1,253
Rental Equipment
Ancillary and other rental revenues:
Sales revenue									550	496	538
Rental Equipment | Topic 840
Ancillary and other rental revenues:
Sales revenue									0	0	0
Rental Equipment | Topic 605
Ancillary and other rental revenues:
Sales revenue									550	496	538
New Equipment
Ancillary and other rental revenues:
Sales revenue									178	144	157
New Equipment | Topic 840
Ancillary and other rental revenues:
Sales revenue									0	0	0
New Equipment | Topic 605
Ancillary and other rental revenues:
Sales revenue									178	144	157
Contractor Supplies
Ancillary and other rental revenues:
Sales revenue									80	79	79
Contractor Supplies | Topic 840
Ancillary and other rental revenues:
Sales revenue									0	0	0
Contractor Supplies | Topic 605
Ancillary and other rental revenues:
Sales revenue									$ 80	$ 79	$ 79