Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income	$ 5,243	$ 9,028
Lessee, Lease, Description [Line Items]
Vehicle Lease Charges	$ 195	255	$ 253
Supplemental balance sheet information related to leases [Line Items]
Document Period End Date	Dec. 31, 2020
Operating Lease, Residual Value of Leased Asset	$ 202	314
Operating Lease, Right-of-Use Asset	2,560	2,596
Operating Lease, Liability, Noncurrent	2,078	2,140
Americas [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income	3,864	6,303
EMEA [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income	1,080	2,141
Asia and Australasia [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income	299	584
Avis [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income	2,851	5,163
Budget [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income	1,878	3,129
Other Brands [Member]
Disaggregation of Revenue [Line Items]
Operating Lease, Lease Income	514	736
Property leases [Member]
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	575	722
Variable Lease, Cost	152	274
Sublease Income	(6)	(8)
Lease, Cost	$ 721	$ 988
Supplemental balance sheet information related to leases [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	8 years 4 months 24 days	8 years 10 months 24 days
Operating Lease, Right-of-Use Asset	$ 2,560	$ 2,596
Operating Lease, Liability, Current	514	479
Operating Lease, Liability, Noncurrent	2,078	2,140
Operating Lease, Liability	$ 2,592	$ 2,619
Operating Lease, Weighted Average Discount Rate, Percent	3.86%	4.31%
Supplemental cash flow information related to leases [Line Items]
Operating Lease, Payments	$ 740	$ 733
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	666	531
Maturities of lease liabilities [Line Items]
Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months	602
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	475
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	416
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	296
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	223
Lessee, Operating Lease, Liability, Payments, Due after Rolling Year Five	1,081
Lessee, Operating Lease, Liability, Payments, Due	3,093
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	501
Vehicle leases [Member]
Lessee, Lease, Description [Line Items]
Lease, Cost	231	301
Finance Lease, Right-of-Use Asset, Amortization	33	42
Finance Lease, Interest Expense	$ 3	$ 4
Supplemental balance sheet information related to leases [Line Items]
Operating Lease, Weighted Average Remaining Lease Term	1 year 6 months	1 year 9 months 18 days
Operating Lease, Right-of-Use Asset	$ 113	$ 195
Operating Lease, Liability, Current	82	124
Operating Lease, Liability, Noncurrent	31	71
Operating Lease, Liability	$ 113	$ 195
Operating Lease, Weighted Average Discount Rate, Percent	2.90%	3.08%
Finance Lease, Right-of-Use Asset, Gross	$ 304	$ 337
Finance Lease, Right-of-Use Asset, Accumulated Amortization	(42)	(56)
Finance Lease, Right-of-Use Asset	262	281
Finance Lease, Liability, Current	86	95
Finance Lease, Liability, Noncurrent	140	157
Finance Lease, Liability	$ 226	$ 252
Finance Lease, Weighted Average Remaining Lease Term	1 year 9 months 18 days	2 years
Finance Lease, Weighted Average Discount Rate, Percent	1.99%	1.67%
Supplemental cash flow information related to leases [Line Items]
Operating Lease, Payments	$ 196	$ 248
Finance Lease, Interest Payment on Liability	3	4
Finance Lease, Principal Payments	294	266
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	111	262
Right-of-Use Asset Obtained in Exchange for Finance Lease Liability	257	$ 304
Maturities of lease liabilities [Line Items]
Lessee, Operating Lease, Liability, Payments, Due Next Rolling Twelve Months	84
Finance Lease, Liability, Payments, Due in Next Rolling Twelve Months	86
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Two	23
Finance Lease, Liability, Payments, Due in Rolling Year Two	49
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Three	8
Finance Lease, Liability, Payments, Due in Rolling Year Three	91
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Four	1
Finance Lease, Liability, Payments, Due in Rolling Year Four	0
Lessee, Operating Lease, Liability, Payments, Due in Rolling Year Five	0
Finance Lease, Liability, Payments, Due in Rolling Year Five	0
Lessee, Operating Lease, Liability, Payments, Due after Rolling Year Five	0
Finance Lease, Liability, Payments, Due in Rolling after Year Five	0
Lessee, Operating Lease, Liability, Payments, Due	116
Finance Lease, Liability, Payment, Due	226
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	3
Finance Lease, Liability, Undiscounted Excess Amount	$ 0