Credit Facility - Additional Information (Detail) (Five-year Unsecured Revolving Credit Facility [Member], USD $)	0 Months Ended	1 Months Ended	6 Months Ended
	Dec. 31, 2014	Oct. 31, 2013	Dec. 31, 2014
Line of Credit Facility [Line Items]
Unsecured revolving credit facility available amount		$ 650,000,000
Credit Agreement term		5 years
Letters of credit sublimit under credit facility		100,000,000
Maximum amount of credit facility		$ 900,000,000
Credit Agreement due date			Oct. 23, 2018
Interest on borrowings, description			Either (a) a Eurodollar Rate formula or (b) the Base Rate formula, each as set forth in the Credit Agreement.
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