Fair Value and Carrying Value of Long-Term Debt (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Debt Instrument [Line Items]
Estimated Fair Value	$ 1,742.7	$ 1,829.8
2012 Facility	0	0
Commercial Paper	0	0
Loan Payable	31.9	63.8
Series Two Thousand Five Dash One Notes [Member]
Debt Instrument [Line Items]
Estimated Fair Value	321.2	326.1
Notes Payable	316.3	313.8
Series Two Thousand Seven Dash One Notes [Member]
Debt Instrument [Line Items]
Estimated Fair Value	339.0	348.3
Notes Payable	300.0	300.0
Twenty Ten Senior Notes [Member]
Debt Instrument [Line Items]
Estimated Fair Value	542.9	562.8
Notes Payable	497.5	497.4
Term Loan Two Thousand Eight [Member]
Debt Instrument [Line Items]
Estimated Fair Value	31.9	63.8
Twenty Twelve Senior Notes [Member]
Debt Instrument [Line Items]
Estimated Fair Value	507.7	528.8
Notes Payable	$ 496.4	$ 496.2

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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