Revenue Recognition (Contract Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Contract liabilities	$ 239	$ 283
Deferred initial franchise fee revenues
Disaggregation of Revenue [Line Items]
Contract liabilities	137	136
Deferred loyalty program revenues
Disaggregation of Revenue [Line Items]
Contract liabilities	75	86
Deferred co-branded credit card program revenues
Disaggregation of Revenue [Line Items]
Contract liabilities	6	34
Deferred hotel management fee revenues
Disaggregation of Revenue [Line Items]
Contract liabilities	1	0
Deferred other revenues
Disaggregation of Revenue [Line Items]
Contract liabilities	$ 20	$ 27