Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2012	$ (640)
Reclassifications from accumulated other comprehensive income (loss)	41
Balance at June 30, 2013	(599)
Interest-rate Derivatives Previously Subject to Hedge Accounting [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2012	(61)
Reclassifications from accumulated other comprehensive income (loss)	3
Balance at June 30, 2013	(58)
Pension and Other Postretirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2012	(579)
Reclassifications from accumulated other comprehensive income (loss)	38
Balance at June 30, 2013	$ (541)