Revenue Recognition - Capitalized Contract Costs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 322	$ 268
Costs incurred	208	226
Amortization	(204)	(172)
End of period balance	326	322
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	187	133
Costs incurred	158	146
Amortization	(124)	(92)
End of period balance	$ 221	$ 187