Revenue Recognition - Capitalized Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 289	$ 326
Costs incurred	44	49
Amortization	(54)	(55)
End of period balance	279	320
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	216	221
Costs incurred	37	36
Amortization	(37)	(37)
End of period balance	$ 216	$ 220