Debt - Additional Information (Detail) (USD $) Share data in Millions, unless otherwise specified	1 Months Ended	12 Months Ended			1 Months Ended											12 Months Ended
	Sep. 09, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 20, 2010	Dec. 15, 2010 Accelerated Share Repurchase Agreement	Dec. 15, 2010 Common Stock	Dec. 15, 2010 Additional Paid-in Capital	Sep. 09, 2011 Retained Earnings	Dec. 15, 2010 Retained Earnings	Dec. 31, 2012 2.875% Notes Due 2016	Dec. 20, 2010 2.875% Notes Due 2016	Dec. 31, 2012 4.40% Notes Due 2021	Dec. 20, 2010 4.40% Notes Due 2021	Dec. 31, 2012 1.375% Notes Due 2018	Oct. 30, 2012 1.375% Notes Due 2018	Dec. 31, 2012 Five-Year Credit Facility Expiring In October 2016	Dec. 31, 2012 6.70% Notes Due 2026
Debt Disclosure [Line Items]
Senior unsecured notes - aggregate principal amount				$ 750,000,000							$ 250,000,000		$ 500,000,000		$ 500,000,000
Debt instrument interest rate										2.875%	2.875%	4.40%	4.40%	1.375%	1.375%		6.70%
Debt instrument maturity date										2016	2016	2021	2021	2018	2018		2026
Net proceeds from offering		495,400,000
Debt offering expenses		4,000,000
Debt issuance discount		600,000
ASR agreement with the bank to repurchase outstanding common stock					750,000,000
Shares received upon initial settlement under the ASR transaction					8.1
Decrease to shareholder's investment						2,000,000	10,200,000	69,100,000	737,800,000
Cash remitted to bank counterparty upon final settlement under the ASR agreement	58,900,000
Increase of capital in excess of par value	10,200,000
Line of credit facility, borrowing capacity																600,000,000
Line of credit facility, term, in years																5 years
Line of credit facility, expiration date																2016-10
Commercial paper			$ 304,500,000
Weighted-average effective interest rate			0.30%