Property, Plant and Equipment - Downstream Businesses - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended		1 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Jul. 31, 2013 Discontinued Downstream Businesses [Member] Energy Marketing Business [Member]	Nov. 30, 2013 Discontinued Downstream Businesses [Member] Energy Marketing Business [Member] Subsequent Events [Member]	Oct. 31, 2013 Discontinued Downstream Businesses [Member] U.S. East Coast terminal network and St. Lucia terminal [Member] Subsequent Events [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash proceeds from asset sales	$ 3,802	$ 656	$ 1,200	$ 1,200	$ 850