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Summary of Significant Accounting Policies Asset Retirement Obligation (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Entity Information [Line Items]      
Asset Retirement Obligation $ 8 $ 10 $ 11
Accretion Expense, Including Asset Retirement Obligations 1 1  
Asset Retirement Obligation, Liabilities Incurred (2) (1)  
Asset Retirement Obligation, Liabilities Settled 0 (1)  
Advertising Expense $ 24 $ 20 $ 28