Basis of Presentation Basis of Presentation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Dec. 31, 2018
Basis of Presentation [Abstract]
Cash and Cash Equivalents, at Carrying Value	$ 679	$ 540	$ 686
Program cash	39	131	211
Restricted Cash and Cash Equivalents	3	5
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	721	676	900	$ 735
Net Unrealized Gain Or Loss Of Foreign Currency Transactions On Intercompany Loan Hedges	5	5
Proceeds from Sale of Equity Method Investments	64
Gain (Loss) on Sale of Equity Investments	44
Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures	53		56
Equity Securities without Readily Determinable Fair Value, Amount	8
Equity Securities without Readily Determinable Fair Value, Upward Price Adjustment, Cumulative Amount	12
Other related Revenue	32	30
Adjustments related to New Accounting Pronouncements [Line Items]
Long-term Debt, Gross	1,200
Revenues	1,753	1,920
Operating Lease, Right-of-Use Asset	2,686		2,596
Line of Credit Facility, Current Borrowing Capacity	1,800
Property leases [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Operating Lease, Right-of-Use Asset	2,686		$ 2,596
Americas [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Revenues	1,257	1,327
EMEA [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Revenues	357	433
Asia and Australasia [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Revenues	139	160
Avis [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Revenues	985	1,100
Budget [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Revenues	619	651
Other Brands [Member]
Adjustments related to New Accounting Pronouncements [Line Items]
Revenues	$ 149	$ 169