Acquisitions (Narrative) (Details) $ / shares in Units, $ in Millions			1 Months Ended	3 Months Ended		12 Months Ended
	Aug. 07, 2020 USD ($) $ / shares shares	Aug. 07, 2019 USD ($) $ / shares shares	Jan. 31, 2018 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)		Dec. 31, 2018 USD ($) Acquisition
Acquisitions [Line Items]
Payments to acquire businesses, net of cash acquired						$ 0	$ 51		$ 5
Payment for Contingent Consideration Liability, Financing Activities						11	0		0
Goodwill, Impairment Loss						0	0		0
Asset impairments						52	$ 27	[1]	(4)	[1]
Alliance Reservations Network | Travel and Membership
Acquisitions [Line Items]
Acquisition price		$ 102
Business combination, consideration transferred, net of cash acquired		97
Payments to acquire businesses, net of cash acquired		48
Stock value		$ 10
Business Acquisition, Equity Interest Issued or Issuable, Number of Shares | shares	468,100	253,350
Business acquisition, Equity issued or issuable, price per share | $ / shares	$ 28.84	$ 39.29
Business Combination, Liabilities Arising from Contingencies, Amount Recognized		$ 21
Payment for Contingent Consideration Liability, Financing Activities	$ 11
Payment for Contingent Consideration Liability, Financing Activities		10
Value of additional shares	$ 14
Developed software		$ 27
Developed software weighted average useful life		10 years
Goodwill, Acquired During Period		$ 38
Definite-lived intangibles		$ 35
Finite-Lived Intangible Asset, Useful Life		12 years
Finite-lived assets, purchase price adjustments				$ 7
Goodwill, Purchase Accounting Adjustments				$ (7)
Goodwill, Impairment Loss						0
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				20.00%
Asset impairments						$ 0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable		$ 4
La Quinta Holdings Inc.
Acquisitions [Line Items]
Payments to acquire businesses			$ 1,950
Other Acquisitions | Travel and Membership
Acquisitions [Line Items]
Payments to acquire businesses, net of cash acquired									5
Goodwill, Acquired During Period									1
Definite-lived intangibles									$ 4
Finite-Lived Intangible Asset, Useful Life									21 years
Number of businesses acquired | Acquisition									1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets									$ 1
Liabilities assumed									$ 1
Other Acquisitions | Vacation Ownership
Acquisitions [Line Items]
Acquisition price					$ 13
Business combination, consideration transferred, net of cash acquired					10
Inventory					4
Definite-lived intangibles					7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable					$ 1

[1] Includes $5 million of bad debt expense related to a note receivable for the year ended December 31, 2020, included in Operating Expenses on the Consolidated Statements of (Loss)/Income.