Financing Arrangements - Additional Information (Detail) (USD $)	1 Months Ended	9 Months Ended
	May 31, 2012	Sep. 30, 2012	Sep. 30, 2011
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity		$ 1,500,000,000
Credit facility, maturity date		Jun. 14, 2016
Credit facility interest rate above LIBOR		1.50%
Maturities of notes payable		350,000,000	0	[1]
New notes payable issued	$ 500,000,000
New notes stated coupon rate	4.00%
New notes maturity date	Jun. 01, 2022
New notes interest payment term		The new notes pay interest semi-annually on June 1 and December 1, with the initial interest payment to be made on December 1, 2012.

[1] Reclassified to conform to current presentation.