Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Narrative) (Details)

v3.10.0.1
Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Jan. 01, 2019
Dec. 31, 2015
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Accumulated foreign currency translation adjustments, before tax $ (4) $ 6      
Accumulated foreign currency translation adjustments, net of tax 4 (5)      
Cash flow hedge loss, before tax 5        
Cash flow hedge loss, after tax 4 0 $ 0    
Cumulative effect of change in accounting standard - increase (decrease)   (15)      
Total cash, cash equivalents and restricted cash 366 59 30   $ 40
Cash and cash equivalents 366 57      
Other current assets          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Restricted cash 0 2      
Accounting Standards Update 2016-16 | Retained Earnings          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of change in accounting standard - increase (decrease)   15      
New Revenue Standard Adjustments | Accounting Standards Update 2014-09 | Retained Earnings          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Cumulative effect of change in accounting standard - increase (decrease)     $ (29)    
Deferred loyalty program revenue          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Loyalty Program Liability $ 89 $ 60      
Subsequent Event | Accounting Standards Update 2016-02          
New Accounting Pronouncements or Change in Accounting Principle [Line Items]          
Operating right-of-use asset       $ 12  
Operating lease liability       $ 12