Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014 Counterparty	Sep. 30, 2013	Sep. 30, 2014 Counterparty	Sep. 30, 2013
Derivative [Line Items]
Number of counterparties	14		14
Derivatives designated as cash flow hedges	$ 273,000,000	$ (422,000,000)	$ 79,000,000	$ (275,000,000)
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivatives designated as cash flow hedges			$ 0