Equity (Detail) - Share Repurchase Program and Share Repurchase Activity - USD ($)		1 Months Ended	3 Months Ended
	Apr. 05, 2017	Jan. 31, 2016	Mar. 31, 2017	Mar. 31, 2016
Class of Stock [Line Items]
Stock repurchase program, authorized amount			$ 1,200,000,000.0
Stock repurchase program, remaining authorized repurchase amount			$ 1,100,000,000
Number of shares repurchased (in shares)			218,752	466,823
Cash paid for repurchased shares during the quarter		$ 7,200,000	$ 21,978,000	$ 45,487,000
Treasury stock, average price paid per share (in dollars per share)			$ 100.47	$ 82.02
CEB | Subsequent Event
Class of Stock [Line Items]
Business acquisition, equity interest issued, number of shares (in shares)	7,400,000