Financial Risk Management and Trading Activities - Net Realized and Unrealized Pre-Tax Gains (Losses) on Derivative Contracts Used in Corporate Risk Management Activities and Not Designated as Hedges (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Derivative Instruments Gain Loss [Line Items]
Net realized and unrealized pre-tax gains (losses) on derivative contracts used in Corporate Risk Management activities and not designated as hedges	$ 85	$ 4	$ 75	$ (36)
Foreign Exchange [Member]
Derivative Instruments Gain Loss [Line Items]
Net realized and unrealized pre-tax gains (losses) on derivative contracts used in Corporate Risk Management activities and not designated as hedges	81	4	68	(36)
Commodity [Member]
Derivative Instruments Gain Loss [Line Items]
Net realized and unrealized pre-tax gains (losses) on derivative contracts used in Corporate Risk Management activities and not designated as hedges	$ 4		$ 7