Segment Reporting and Geographic Information - Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue	$ 3,636	$ 3,659	$ 3,639	$ 3,620	$ 3,599	$ 3,518	$ 3,488	$ 3,411	$ 14,554	$ 14,016	$ 12,151
Long-Lived Assets	42,281				43,810				42,281	43,810	43,141
Leased vehicles, net	42,100				43,559				42,100	43,559	42,900
U.S. [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									12,672	12,158	10,424
Long-Lived Assets	39,509				41,320				39,509	41,320	40,674
Non-US [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenue									1,882	1,858	1,727
Long-Lived Assets	$ 2,772				$ 2,490				$ 2,772	$ 2,490	$ 2,467