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Deferred Contract Costs - (Narratives) (Details) - USD ($)
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract]    
Amortization of contract costs $ 68,000,000 $ 51,000,000
Deferred contract costs impairment $ 0 $ 0