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	$ 326	$ 322
Costs incurred	181	208
Amortization	(218)	(204)
End of period balance	289	326
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	221	187
Costs incurred	141	158
Amortization	(146)	(124)
End of period balance	$ 216	$ 221