Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014 Counterparty	Jun. 30, 2013	Jun. 30, 2014 Counterparty	Jun. 30, 2013
Derivative [Line Items]
Number of counterparties	14		14
Derivatives designated as cash flow hedges	$ (174,000,000)	$ 247,000,000	$ (194,000,000)	$ 147,000,000
Cash Flow Hedging [Member]
Derivative [Line Items]
Derivatives designated as cash flow hedges			$ 0