Revenue Recognition - Capitalized Contract Costs (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Contract Acquisition Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	$ 321	$ 287	$ 322	$ 268
Costs incurred	48	53	148	152
Amortization	(50)	(44)	(151)	(124)
End of period balance	319	296	319	296
Contract Fulfillment Costs
Capitalized Contract Cost [Roll Forward]
Beginning of period balance	207	161	187	133
Costs incurred	41	46	119	104
Amortization	(32)	(34)	(90)	(64)
End of period balance	$ 216	$ 173	$ 216	$ 173