Borrowing Arrangements (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended		1 Months Ended
	Jan. 31, 2014	Jan. 31, 2013	Dec. 31, 2012 Senior Notes Senior Notes 2017	Dec. 31, 2012 Senior Notes Senior Notes 2022	Dec. 31, 2012 Senior Notes	Jan. 31, 2014 Senior Notes
Debt Disclosure [Line Items]
Debt Instrument, Face Amount			$ 400.0	$ 350.0
Debt Instrument, Interest Rate, Stated Percentage			1.95%	3.60%
Debt Instrument, Maturity Date			Dec. 15, 2017	Dec. 15, 2022
Proceeds from Debt, Net of Issuance Costs					739.3
Debt Instrument, Unamortized Discount					4.5
Debt Issuance Cost					6.1
Debt redemption percentage of principle amount (as a percent)					101.00%
Debt Instrument, Fair Value Disclosure						738.0
Unsecured revolving credit facility	400.0
Unsecured revolving credit facility, option to request an increase in the amount of the credit facility up to	100.0
Line of credit facility, expiration	May 31, 2018
Line of credit facility, outstanding borrowings	$ 0	$ 0