Revenue Recognition - Capitalized Contract Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Contract Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 13
Costs incurred	68
Amortization	(17)
End of period balance	64
Contract Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	14
Costs incurred	99
Amortization	(29)
End of period balance	$ 84