Basis of Presentation - Additional Information 1 (Details) - Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date: 2018-03-31 $ in Billions	9 Months Ended
	Sep. 30, 2018 USD ($)
New Accounting Pronouncement Early Adoption [Line Items]
Unearned revenue	$ 1.9
Unearned revenue expect to recognize period	1 year
Unearned revenue expect to recognize description	Approximately $1.9 billion of the September 30, 2018 unearned revenue is expected to be recognized within the next twelve months and the remaining amount will be recognized thereafter.