Acquisitions, Divestitures, and Assets Held for Sale - Acquisitions (Detail) shares in Millions, $ in Billions	9 Months Ended
	Sep. 30, 2016 USD ($) shares
Property, Plant, and Equipment [Line Items]
Common stock issued during the period | shares	40.5
Oil and Gas Assets in the Gulf of Mexico [Member]
Property, Plant, and Equipment [Line Items]
Purchase price | $	$ 2.0