Annual report pursuant to Section 13 and 15(d)

Summary of Significant Accounting Policies (Narrative) (Details)

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Summary of Significant Accounting Policies (Narrative) (Details) - USD ($)
Jan. 01, 2020
Dec. 31, 2019
Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Accrued expenses and other current liabilities   $ 279,000,000 $ 502,000,000
Other Liabilities, Noncurrent   220,000,000 182,000,000
Cumulative effect of change in accounting standard - increase (decrease)     (15,000,000)
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)     15,000,000
Deferred loyalty program revenue      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Loyalty Program Liability   90,000,000 89,000,000
Accrued expenses and other current liabilities   56,000,000 54,000,000
Other Liabilities, Noncurrent   $ 34,000,000 $ 35,000,000
Scenario, Forecast | Minimum | Accounting Standards Update 2016-13 | Retained Earnings      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Cumulative effect of change in accounting standard - increase (decrease) $ 8,000,000    
Scenario, Forecast | Maximum | Accounting Standards Update 2016-13 | Retained Earnings      
New Accounting Pronouncements or Change in Accounting Principle [Line Items]      
Cumulative effect of change in accounting standard - increase (decrease) $ 12,000,000