Related Party Transactions (Related Party Net Interest And Other Financial Income) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011
Related Party Transaction [Line Items]
Interest income	$ 1	$ 1
Interest capitalized			(8)
Related party net interest and other financial income	1	1	35
PFD [Member]
Related Party Transaction [Line Items]
Dividend income, PFD Preferred Stock			35
Interest expense			3
Marathon Oil Companies [Member]
Related Party Transaction [Line Items]
Interest expense			$ 5