Credit Lines - Additional Information (Detail) (USD $) In Billions, unless otherwise specified	1 Months Ended
	Nov. 30, 2011	Nov. 01, 2011
New Credit Facilities
Line of Credit Facility [Line Items]
Revolving credit facility, borrowing capacity		$ 1
Revolving credit facility, optional maximum borrowing capacity		1.5
Revolving credit facility, optional extension period	1 year
New Credit Facilities | Before Extension
Line of Credit Facility [Line Items]
Revolving credit facility, maturity period	November 2016
New Credit Facilities | After Extension | Maximum
Line of Credit Facility [Line Items]
Revolving credit facility, maturity period	2018-11-01
Old Credit Facilities
Line of Credit Facility [Line Items]
Revolving credit facility, borrowing capacity		$ 1
Revolving credit facility, maturity period	December 2012