Revenue Recognition - Contract Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Acquisition Costs
Capitalized Contract Cost [Line Items]
Beginning of period balance	$ 90	$ 91
Costs incurred	60	62
Amortization	(64)	(63)
End of period balance	86	90
Fulfillment Costs
Capitalized Contract Cost [Line Items]
Beginning of period balance	57	61
Costs incurred	39	27
Amortization	(32)	(31)
End of period balance	$ 64	$ 57