Common Stock - Schedule of Additional Information on Compensation Costs and Income Tax Benefits and Excess Tax Benefits Related to Stock-Based Compensation Awards (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Compensation costs	$ 13.5	$ 12.0	$ 9.1
Income tax benefits	5.2	4.6	3.5
Excess tax benefits	$ 0	$ 2.6	$ 1.7