Summary of Total Indebtedness (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
2012 Facility
Commercial paper
Total debt	1,707.5	1,243.8
Current portion	(95.6)	(71.3)
Total long-term debt	1,611.9	1,172.5
Series 2005-1 Notes
Debt Instrument [Line Items]
Notes Payable	318.4	311.5
Series 2007-1 Notes
Debt Instrument [Line Items]
Notes Payable	300.0	300.0
2010 Senior Notes
Debt Instrument [Line Items]
Notes Payable	497.4	497.3
2012 Senior Notes
Debt Instrument [Line Items]
Notes Payable	496.1
2008 Term Loan
Debt Instrument [Line Items]
Loan Payable	$ 95.6	$ 135.0

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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Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

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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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