Other Financial Information - Other Current Assets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid expenses	$ 40	$ 41
Contract acquisition costs	47	50
Contract fulfillment costs	28	28
Other	7	9
Total other current assets	$ 122	$ 128