Subsequent Events - Additional Information (Detail) (Subsequent Event [Member], Five-year Unsecured Revolving Credit Facility [Member], USD $) In Millions, unless otherwise specified	1 Months Ended
	Oct. 31, 2013
Subsequent Event [Line Items]
Unsecured revolving credit facility available amount	$ 650
Credit Agreement term	5 years
Letters of credit sublimit under credit facility	100
Maximum amount of credit facility	$ 900
Credit Agreement due date	Oct. 23, 2018
Commitment fee percentage on undrawn balance	0.25%
Maximum [Member]
Subsequent Event [Line Items]
Operating income leverage ratio	3.0
Minimum [Member]
Subsequent Event [Line Items]
Interest coverage ratio	3.0
Base Rate [Member]
Subsequent Event [Line Items]
Applicable margin for borrowing	0.50%
Eurodollar [Member]
Subsequent Event [Line Items]
Applicable margin for borrowing	1.50%