Carrying Amounts and Estimated Fair Values of Other Financial Instruments (Detail) (Fair Value, Inputs, Level 2, USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	$ 128.9	$ 318.5
Short-term borrowings	153.5	153.8
Carrying Amount | 2.875% Senior notes due October 1, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	399.7	399.7
Carrying Amount | 3.35% Senior Notes Due December 15, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	249.9	249.8
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash equivalents	128.9	318.5
Short-term borrowings	153.5	153.8
Fair Value | 2.875% Senior notes due October 1, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	380.4	369.8
Fair Value | 3.35% Senior Notes Due December 15, 2015
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Senior notes	$ 259.4	$ 258.2