Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Loss Contingencies [Line Items]
Litigation reserves	$ 22		$ 28
Receivables	1
Range of possible loss up to, portion not accrued	$ 64
Percentage of Cendant's contingent and other corporate liabilities and associated costs	37.50%
Hotel Group [Member]
Loss Contingencies [Line Items]
Annual cap	$ 27
Amount of liability in guarantees	21		23
Guarantor offsetting asset carrying value	11		12
Amortization expense, contingent asset (less than)	1	$ 1
Guarantees subject to recapture provisions	46		41
Hotel Group [Member] | Other Non Current Liabilities [Member]
Loss Contingencies [Line Items]
Amount of liability in guarantees	16		16
Hotel Group [Member] | Accrued Liabilities [Member]
Loss Contingencies [Line Items]
Amount of liability in guarantees	5		7
Hotel Group [Member] | Other Non Current Assets [Member]
Loss Contingencies [Line Items]
Guarantor offsetting asset carrying value	10		1
Guarantees subject to recapture provisions	43
Hotel Group [Member] | Other Current Assets [Member]
Loss Contingencies [Line Items]
Guarantor offsetting asset carrying value	1		$ 11
Guarantees subject to recapture provisions	$ 3
Hotel Group [Member] | Minimum [Member]
Loss Contingencies [Line Items]
Guarantor obligations, term	8 years
Guarantees, remaining life (in years)	5 years
Hotel Group [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Guarantor obligations, term	10 years
Annual cap	$ 110
Guarantees, remaining life (in years)	7 years
Hotel Group [Member] | Weighted Average [Member]
Loss Contingencies [Line Items]
Guarantor obligations, term	5 years