Unrecognized tax benefits (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax [Abstract]
Balance at Beginning of Year	$ 19.8	$ 18.4	$ 17.5
Additions to Tax Positions Taken During Prior Years	0.0	1.7	5.7
Settlements with Tax Authorities	(19.0)	(0.6)	(4.8)
Tax Positions Taken During Current Year	0.0	0.3	0.0
Balance at End of Year	0.8	19.8	18.4
Less Tax Attributable to Temporary Items Included Above	0.0	(10.4)	(10.2)
Total Unrecognized Tax Benefits that if Recognized Would Affect the Effective Tax Rate	$ 0.8	$ 9.4	$ 8.2