Recently Issued Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Recently Issued Accounting Pronouncements [Line Items]
Operating Income	$ 217.6	$ 205.2
Other non-operating items, net	(9.5)	$ (1.2)
Minimum | Accounting Standard Update 2017-07, Statement of Net Income Classification of Operating Income | Restatement Adjustment
Recently Issued Accounting Pronouncements [Line Items]
Operating Income	(5.0)
Other non-operating items, net	5.0
Maximum | Accounting Standard Update 2017-07, Statement of Net Income Classification of Operating Income | Restatement Adjustment
Recently Issued Accounting Pronouncements [Line Items]
Operating Income	(7.0)
Other non-operating items, net	$ 7.0