Financing Arrangements - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2011
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity	$ 1,500,000,000
Credit facility, maturity date	2016-06-30
Uncommitted Credit Facility
Line of Credit Facility [Line Items]
Credit facility maximum borrowing capacity	$ 400,000,000