Revenue Recognition - Additional Information (Details) $ in Billions	3 Months Ended
	Mar. 31, 2018 USD ($)
Revenue from Contract with Customer [Abstract]
Remaining performance obligation	$ 7.5
Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract term	1 year
Average expected contract term	10 years
Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract term	5 years
Average expected contract term	20 years
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-04-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, percentage	56.00%
Remaining performance obligation, timing of satisfaction	1 year 9 months
Contract Acquisition and Fulfillment Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Average expected contract term	30 months
Contract Acquisition and Fulfillment Costs | Minimum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Amortization period	12 months
Contract Acquisition and Fulfillment Costs | Maximum
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Amortization period	60 months