Separation-Related Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Related Party Transaction [Line Items]
Separation-related	$ 51	$ 0	$ 0
Spin-Off, Hotel Group Business [Member]
Related Party Transaction [Line Items]
Separation-related	51
European vacation rentals business [Member]
Related Party Transaction [Line Items]
Separation-related	$ 15