Goodwill and Other Intangible Assets - goodwill rollforward (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Goodwill [Line Items]
Goodwill, Beginning Balance	$ 15,251
Foreign exchange translation	59
Goodwill, Ending Balance	15,310
Expedia
Goodwill [Line Items]
Goodwill, Beginning Balance	15,194
Foreign exchange translation	59
Goodwill, Ending Balance	15,253
Corporate and Other
Goodwill [Line Items]
Goodwill, Beginning Balance	57
Goodwill, Ending Balance	$ 57