Shareholder's Equity - Additional Information (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Shareholders Equity
Common stock, shares authorized	426.0	426.0
Common stock, par value (per share)	$ 0.01	$ 0.01
Common stock shares repurchased, shares		3.1
Common stock amount repurchased		$ 200.0
Dividends payable amount per share	0.35
ApprovedNotDeclaredlDividends	$ 1.38
Dividends payable	$ 61.8	$ 59.6
Dividends paid per common share	$ 1.34	$ 1.28	$ 1.10
September 2012 Share Repurchase Program [Member]
Shareholders Equity
Authorized amount to repurchase shares of common stock					$ 400.0
October 2012 Share Repurchase Program [Member]
Shareholders Equity
Authorized amount to repurchase shares of common stock				$ 800.0
December 2013 Share Repurchase Program
Shareholders Equity
Authorized amount to repurchase shares of common stock				$ 1,000.0
December 2014 Share Repurchase Program [Member] [Domain]
Shareholders Equity
Authorized amount to repurchase shares of common stock			$ 1,000.0
Remaining authorized repurchase amount		$ 800.0
Treasury Stock [Member]
Shareholders Equity
Treasury Stock, Shares, Retired		19.1
Treasury Stock, Retired, Cost Method, Amount		$ 1,210.9