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Stock-based Compensation (Stock-Based Compensation Expense) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Share-based Payment Arrangement, Expense $ 131 $ 133 $ 116
Site Rental Cost of Operations [Member]      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Share-based Payment Arrangement, Expense 14 16 19
Services and Other Costs of Operations [Member]      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Share-based Payment Arrangement, Expense 8 8 7
Selling, General and Administrative Expenses [Member]      
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]      
Share-based Payment Arrangement, Expense $ 109 $ 109 $ 90