Revenue Recognition - Capitalized Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 300	$ 321	$ 326	$ 322
Costs incurred	45	48	130	148
Amortization	(53)	(50)	(164)	(151)
End of period balance	292	319	292	319
Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	219	207	221	187
Costs incurred	35	41	105	119
Amortization	(37)	(32)	(109)	(90)
End of period balance	$ 217	$ 216	$ 217	$ 216