Financing Arrangements- Additional Information (Detail) (USD $)	12 Months Ended						12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Feb. 28, 2010 Private Placement Notes	Dec. 31, 2012 Tranche A Unsecured Senior Notes	Dec. 31, 2012 Tranche B Unsecured Senior Notes	Dec. 31, 2012 Tranche C Unsecured Senior Notes	Dec. 31, 2012 Commercial Paper [Member]	Dec. 31, 2011 Commercial Paper [Member]
Debt Instrument [Line Items]
Credit facilities, maximum borrowing capacity							$ 500,000,000
Short-term debt							45,000,000	266,800,000
Short-term debt, average outstanding amount	248,318,000	225,498,000					267,100,000
Short term debt, weighted average interest rates	0.60%	0.80%
Total unused lines of credit	527,400,000
Floating rate senior term loan	1,472,913,000	1,491,419,000
Debt instrument issued			$ 250,000,000	$ 250,000,000	$ 300,000,000	$ 450,000,000