Revenue Recognition - Capitalized Contract Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 79	$ 64
Costs incurred	61	60
Amortization	(62)	(45)
End of period balance	78	79
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	121	84
Costs incurred	88	103
Amortization	(87)	(66)
End of period balance	$ 122	$ 121