Accumulated Other Comprehensive Income (Loss) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2012	$ (640)
Reclassification from accumulated other comprehensive income (loss)	21
Balance at March 31, 2013	(619)
Interest-rate Derivatives Previously Subject to Hedge Accounting [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2012	(61)
Reclassification from accumulated other comprehensive income (loss)	2
Balance at March 31, 2013	(59)
Pension and Other Postretirement Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at December 31, 2012	(579)
Reclassification from accumulated other comprehensive income (loss)	19
Balance at March 31, 2013	$ (560)