Financial Instruments, Derivatives and Hedging Activities - Additional Information (Detail) (Installment Notes, Lehman Brothers Holdings Inc, USD $) In Millions, unless otherwise specified	1 Months Ended	6 Months Ended
	Apr. 30, 2012	Jun. 30, 2012
Installment Notes | Lehman Brothers Holdings Inc
Fair Value Measurements [Line Items]
Distribution received from Lehman bankruptcy	$ 50	$ 50