Other Financial Information (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Prepaid Expense and Other Assets, Current [Abstract]
Prepaid expenses	$ 62	$ 42
Deferred commissions	47	0
Deferred activation and installation charges	104	49
Other	4	7
Total other current assets	217	98
Accounts Payable, Current [Abstract]
Capital expenditures incurred and included in accounts payable	$ 51	$ 86