Derivative Instruments and Hedging Activities - Additional Information (Detail) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2013	Oct. 31, 2013	Mar. 31, 2013 USD ($) Counterparty
Derivative Instruments And Hedging Activities Disclosure [Abstract]
Number of counterparties				16
Realization of gains and losses on hedges in future earnings	Mid-2014
Gigajoule deliver per day of natural gas		50,000	50,000
Fixed prices of sales contracts	3.42
Net gain included in accumulated other comprehensive loss, before tax applied to next twelve months				$ 13
Net gain included in accumulated other comprehensive loss, after tax				$ 8