Long-Term Debt (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt	$ 1,641.7	$ 1,394.3
2.875% Notes Due 2016
Debt Instrument [Line Items]
Long-term debt	0.0	250.2
1.375% Notes Due 2018
Debt Instrument [Line Items]
Long-term debt	499.1	498.2
4.40% Notes Due 2021
Debt Instrument [Line Items]
Long-term debt	496.9	496.1
3.000% Notes Due 2026
Debt Instrument [Line Items]
Long-term debt	495.9	0.0
6.70% Notes Due 2026
Debt Instrument [Line Items]
Long-term debt	$ 149.8	$ 149.8