Revenue and Contract Costs - Additional Information (Detail)	3 Months Ended
	Mar. 31, 2018 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract assets	$ 0
Contract with customer, contract duration	1 year
Deferred revenue recognized	$ 58,000,000
Revenue expected to be recognized	$ 254,000,000
Minimum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Advisory services period	1 hour
Consulting services period	two weeks
Performance obligation, revenue expected to be recognized	12 months
Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Advisory services period	2 days
Consulting services period	three months
Contract with customer, expected payment term	one year
Performance obligation, revenue expected to be recognized	24 months