Operating Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Contract Acquisition Costs
Revenue other than customer contracts (as a percent)	1.00%	1.00%
Deferred contract costs	$ 136
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	$ 107
Selling, General and Administrative Expenses [Member]
Contract Acquisition Costs
Deferred contract costs amortization	6
Reduction to Sales [Member]
Contract Acquisition Costs
Deferred contract costs amortization	$ 10
Minimum [Member]
Contract Acquisition Costs
Contract amortization period	5 years
Maximum [Member]
Contract Acquisition Costs
Contract amortization period	13 years