Operating Revenues (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Sep. 30, 2017
Contract Acquisition Costs
Revenue other than customer contracts (as a percent)		1.00%	1.00%
Deferred contract costs	$ 141	$ 141
Long-term revenue contracts (as a percent)		30.00%
Weighted average remaining contract term		4 years
Deferred Sales Incentives [Member]
Contract Acquisition Costs
Deferred contract costs	109	$ 109
Selling, General and Administrative Expenses [Member]
Contract Acquisition Costs
Deferred contract costs amortization	6	17
Reduction to Sales [Member]
Contract Acquisition Costs
Deferred contract costs amortization	$ 8	$ 27
Minimum [Member]
Contract Acquisition Costs
Deferred revenue recognition period		1 month
Contract amortization period		5 years
Maximum [Member]
Contract Acquisition Costs
Deferred revenue recognition period		3 months
Contract amortization period		13 years