Recently Issued Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Recently Issued Accounting Pronouncements [Line Items]
Operating Income	$ 158.7	$ 191.1	$ 592.7	$ 609.0
Other non-operating items, net	$ (3.3)	$ 8.1	(18.1)	$ 9.2
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