Summary of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions			3 Months Ended	12 Months Ended
		Aug. 07, 2019	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018		Sep. 30, 2020
Summary of Significant Accounting Policies [Line Items]
Securitized restricted cash				$ 121	$ 147		$ 155
VOI purchaser funds, percentage				100.00%
Escrow deposit				$ 29	37
Capitalized interest on inventory				1	1		1
Software developed or obtained for internal use				191	193
Advertising expense				26	37		27
Asset impairments				52	27	[1]	(4)	[1]
Other Asset Impairment Charges				52	36		5
Provision for Loan, Lease, and Other Losses				415	479		456
Other (income), net				(14)	(23)		(38)
Goodwill, Impairment Loss				0	0		0
COVID-19 (Member)
Summary of Significant Accounting Policies [Line Items]
Asset impairments	[1]			57
Alliance Reservations Network | Travel and Membership
Summary of Significant Accounting Policies [Line Items]
Useful lives		10 years
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount									20.00%
Asset impairments				0
Goodwill, Impairment Loss				0
Other
Summary of Significant Accounting Policies [Line Items]
Loyalty revenue				13	15		12
Operating Expense
Summary of Significant Accounting Policies [Line Items]
Loyalty expenses				7	9		5
Operating Expense | COVID-19 (Member)
Summary of Significant Accounting Policies [Line Items]
Provision for Loan, Lease, and Other Losses				5
Asset Impairment and Operating Expenses [Member] | COVID-19 (Member)
Summary of Significant Accounting Policies [Line Items]
Asset impairments				56
Asset Impairment and Operating Expenses [Member] | Travel and Membership | COVID-19 (Member)
Summary of Significant Accounting Policies [Line Items]
Asset impairments				34
Asset Impairments [Member] | COVID-19 (Member)
Summary of Significant Accounting Policies [Line Items]
Other Asset Impairment Charges				$ 51
Asset Impairments [Member] | Travel and Membership
Summary of Significant Accounting Policies [Line Items]
Other Asset Impairment Charges			$ 6
Building and leasehold improvements
Summary of Significant Accounting Policies [Line Items]
Useful lives				30 years
Software Development
Summary of Significant Accounting Policies [Line Items]
Useful lives				10 years
Interest Expense
Summary of Significant Accounting Policies [Line Items]
Software developed or obtained for internal use				$ 1	2		$ 1
Minimum
Summary of Significant Accounting Policies [Line Items]
Average rescission period				5 days
Minimum | Furniture Fixtures And Equipment
Summary of Significant Accounting Policies [Line Items]
Useful lives				3 years
Minimum | Software Development
Summary of Significant Accounting Policies [Line Items]
Useful lives				3 years
Maximum
Summary of Significant Accounting Policies [Line Items]
Average rescission period				7 days
Maximum | Leasehold Improvements [Member]
Summary of Significant Accounting Policies [Line Items]
Useful lives				20 years
Maximum | Vacation Rental Properties
Summary of Significant Accounting Policies [Line Items]
Useful lives				30 years
Maximum | Furniture Fixtures And Equipment
Summary of Significant Accounting Policies [Line Items]
Useful lives				7 years
Maximum | Software Development
Summary of Significant Accounting Policies [Line Items]
Useful lives				5 years
Securitization restricted Cash [Member]
Summary of Significant Accounting Policies [Line Items]
Securitized restricted cash				$ 92	110
Deferred Revenue [Domain]
Summary of Significant Accounting Policies [Line Items]
Loyalty Liability				$ 15	$ 18

[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.