Shareholder's Equity - Additional Information (Detail) - USD ($)			12 Months Ended
	May 08, 2018	Dec. 06, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Sep. 19, 2017	Dec. 31, 2014
Shareholders Equity
Common stock, shares authorized			426,000,000	426,000,000
Common stock, par value (per share)			$ 0.01	$ 0.01
Common stock shares repurchased, shares			10,200,000
Stock Repurchased During Period, Value			$ 500,000,000		$ 200,000,000
Dividends payable amount per share						$ 0.18
ApprovedNotDeclaredlDividends		$ 0.72
Dividends payable			$ 30,800,000	$ 63,100,000
Dividends paid per common share			$ 1.05	$ 1.38	$ 1.34
December 2014 Share Repurchase Program [Member] [Domain]
Shareholders Equity
Authorized amount to repurchase shares of common stock							$ 1,000,000,000
May 2018 Share Repurchase Program [Member]
Shareholders Equity
Authorized amount to repurchase shares of common stock	$ 750,000,000.0
Stock Repurchase Program Expiration Date	May 31, 2021
Common stock shares repurchased, shares			8,000,000
Stock Repurchased During Period, Value			$ 350,000,000
Remaining authorized repurchase amount			$ 400,000,120
December 2014 Share Repurchase Program [Member]
Shareholders Equity
Common stock shares repurchased, shares			2,200,000	3,000,000
Stock Repurchased During Period, Value			$ 150,000,000	$ 200,000,000