Derivative Instruments and Hedging Activities - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Assets:
Total Derivative assets	$ 3	$ 33
Liabilities:
Total Derivative liabilities	216	116
Recurring [Member] | Significant Other Inputs (Level 2) [Member]
Assets:
Derivatives designated as cash flow hedges	11	48
Derivatives not designated as cash flow hedges	14
Total Derivative assets	25
Liabilities:
Derivatives designated as cash flow hedges	8	51
Derivatives not designated as cash flow hedges	230	80
Total Derivative liabilities	238	131
Recurring [Member] | Total Fair Value [Member]
Assets:
Derivatives designated as cash flow hedges	11	48
Derivatives not designated as cash flow hedges	14
Total Derivative assets	25
Liabilities:
Derivatives designated as cash flow hedges	8	51
Derivatives not designated as cash flow hedges	230	80
Total Derivative liabilities	238	131
Recurring [Member] | Netting [Member]
Assets:
Derivatives designated as cash flow hedges		(15)
Total Derivative assets	(22)
Liabilities:
Total Derivative liabilities	(22)	(15)
Recurring [Member] | Carrying Amount [Member]
Assets:
Derivatives designated as cash flow hedges		33
Total Derivative assets	3
Liabilities:
Total Derivative liabilities	$ 216	$ 116