Credit Facility - Additional Information (Detail) (Five-year Unsecured Revolving Credit Facility [Member], USD $) In Millions, unless otherwise specified	0 Months Ended	1 Months Ended
	Mar. 31, 2014	Oct. 31, 2013
Line of Credit Facility [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%
Base Rate [Member]
Line of Credit Facility [Line Items]
Applicable margin for borrowing	0.50%
Eurodollar [Member]
Line of Credit Facility [Line Items]
Applicable margin for borrowing	1.50%
Maximum [Member]
Line of Credit Facility [Line Items]
Operating income leverage ratio		3.0
Minimum [Member]
Line of Credit Facility [Line Items]
Interest coverage ratio		3.0