Accumulated Other Comprehensive Loss (Schedule Of Components Of Other Comprehensive Loss) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ (63)	$ (106)	$ (138)
Current year change	15	43	32
Ending Balance	(48)	(63)	(106)
Commodity Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(29)	(78)	(99)
Current year change	23	49	21
Ending Balance	(6)	(29)	(78)
Treasury Lock [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(10)	(11)	(22)
Current year change		1	11
Ending Balance	(10)	(10)	(11)
Other [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(24)	(17)	(17)
Current year change	(8)	(7)
Ending Balance	$ (32)	$ (24)	$ (17)