Revenue - Performance Obligation (Detail) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01 $ in Billions	12 Months Ended
	Dec. 31, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation	$ 2.2
Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Percentage of revenue recognized on remaining performance obligation	40.00%
Revenue over the remaining lives of the contracts	12 months
Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Percentage of revenue recognized on remaining performance obligation	84.00%
Revenue over the remaining lives of the contracts	36 months