Accumulated Other Comprehensive Loss (Schedule Of Income Tax Expense (Benefit) Allocated To Accumulated Other Comprehensive Income Loss) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended				9 Months Ended
	Sep. 30, 2012		Sep. 30, 2011		Sep. 30, 2012		Sep. 30, 2011
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense related to other comprehensive income	$ 4	[1]	$ 6	[1]	$ 12	[2]	$ 24	[2]
Tax expense for losses reclassified to income	2		7		13		25
Commodity Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense related to other comprehensive income	2	[1]	7	[1]	13	[2]	26	[2]
Treasury Lock [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense related to other comprehensive income	1	[1]	1	[1]	1	[2]	1	[2]
Pension And Other Postretirement Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income tax expense related to other comprehensive income	$ 1	[1]	$ (2)	[1]	$ (2)	[2]	$ (3)	[2]

[1] Includes tax expense for losses reclassified to income during the three months ended September 30, 2012 and 2011 of $2 million and $7 million, respectively.

[2] Includes tax expense for losses reclassified to income during the nine months ended September 30, 2012 and 2011 of $13 million and $25 million, respectively.