Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Summary Of Significant Accounting policies [Line Items]
Deferred Revenue under POC	$ 657,000,000	$ 615,000,000
Net change in revenues deferred under POC	(20,000,000)	(8,000,000)	$ (16,000,000)
Cash desposited in reserve account	106,000,000	90,000,000
Escrow deposit	67,000,000	59,000,000
Loyalty points liability	90,000,000	77,000,000
Capitalized interest on inventory (less than $1 million in 2017)	1,000,000	1,000,000	3,000,000
Advertising expense	86,000,000	108,000,000	111,000,000
Software developed or obtained for internal use	271,000,000	221,000,000
Other income, net	$ 27,000,000	21,000,000	16,000,000
Minimum [Member]
Summary Of Significant Accounting policies [Line Items]
Rescission period	3 days
Maximum [Member]
Summary Of Significant Accounting policies [Line Items]
Rescission period	15 days
Buildings and leasehold improvements
Summary Of Significant Accounting policies [Line Items]
Property and equipment useful life, average (in years)	30 years
Leasehold Improvements [Member]
Summary Of Significant Accounting policies [Line Items]
Property and equipment useful life, average (in years)	20 years
Vacation Rental Properties [Member] | Minimum [Member]
Summary Of Significant Accounting policies [Line Items]
Property and equipment useful life, average (in years)	15 years
Vacation Rental Properties [Member] | Maximum [Member]
Summary Of Significant Accounting policies [Line Items]
Property and equipment useful life, average (in years)	30 years
Furniture Fixtures And Equipment [Member] | Minimum [Member]
Summary Of Significant Accounting policies [Line Items]
Property and equipment useful life, average (in years)	3 years
Furniture Fixtures And Equipment [Member] | Maximum [Member]
Summary Of Significant Accounting policies [Line Items]
Property and equipment useful life, average (in years)	7 years
Software Development [Member]
Summary Of Significant Accounting policies [Line Items]
Property and equipment useful life, average (in years)	10 years
Software Development [Member] | Minimum [Member]
Summary Of Significant Accounting policies [Line Items]
Property and equipment useful life, average (in years)	3 years
Software Development [Member] | Maximum [Member]
Summary Of Significant Accounting policies [Line Items]
Property and equipment useful life, average (in years)	5 years
Interest Expense [Member]
Summary Of Significant Accounting policies [Line Items]
Software developed or obtained for internal use	$ 1,000,000	4,000,000	4,000,000
Loyalty Programs [Member]
Summary Of Significant Accounting policies [Line Items]
Loyalty revenue	172,000,000	159,000,000	152,000,000
Loyalty expenses	131,000,000	134,000,000	119,000,000
Other Current Assets [Member]
Summary Of Significant Accounting policies [Line Items]
Cash desposited in reserve account	75,000,000	75,000,000
Non Current Assets [Member]
Summary Of Significant Accounting policies [Line Items]
Cash desposited in reserve account	$ 31,000,000	15,000,000
Hotel Group [Member]
Summary Of Significant Accounting policies [Line Items]
Standard management agreement, maximum	25 years
Management fee revenues	$ 25,000,000	22,000,000	23,000,000
Revenue related to payroll costs	264,000,000	271,000,000	273,000,000
Destination Network [Member]
Summary Of Significant Accounting policies [Line Items]
Other income, net	26,000,000
Vacation Ownership [Member]
Summary Of Significant Accounting policies [Line Items]
Management fee revenues	$ 300,000,000	287,000,000	275,000,000
Percentage of minimum down payment to meet initial investment criteria	10.00%
Deferred Revenue under POC	$ 0	0
Net change in revenues deferred under POC			(13,000,000)
Maximum number of days before payments begin under financing contracts	45 days
Property management revenues	$ 692,000,000	660,000,000	615,000,000
Reimbursable revenues	392,000,000	373,000,000	340,000,000
Payment for exchange services	$ 29,000,000	26,000,000	24,000,000
Other income, net		$ 20,000,000	$ 15,000,000