Business Segment Information - Financial Segment Information (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2012 Canada [Member] Operating Segments [Member]	Mar. 31, 2012 Canada [Member] Operating Segments [Member]	Jun. 30, 2013 Argentina [Member] Operating Segments [Member]
Segment Reporting Information [Line Items]
Write-down of oil and gas properties	$ 648	$ 65	$ 1,169	$ 641	$ 521	$ 65