Financial Risk Management and Trading Activities - Gross and Net Fair Values of Corporate and Trading Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Derivatives Fair Value [Line Items]
Cash collateral (received) posted	$ 0	$ 31
Accounts Receivable [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	98	47
Derivative contracts not designated as hedging instruments	3,127	3,090
Gross fair value of derivative contracts	3,225	3,137
Master netting arrangements	(2,861)	(2,083)
Cash collateral (received) posted	(33)	(79)
Net fair value of derivative contracts	331	975
Accounts Receivable [Member] | Commodity [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	69	11
Derivative contracts not designated as hedging instruments	3,068	3,075
Accounts Receivable [Member] | Interest Rate and Other [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	29	36
Accounts Receivable [Member] | Foreign Exchange [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	49	2
Accounts Receivable [Member] | Equity and Other [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	10
Accounts Receivable [Member] | Other [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments		13
Accounts Payable [Member]
Derivatives Fair Value [Line Items]
Gross fair value of derivative contracts	(3,220)	(3,224)
Master netting arrangements	2,861	2,083
Cash collateral (received) posted	98	168
Net fair value of derivative contracts	(261)	(973)
Derivative contracts designated as hedging instruments	(4)	(4)
Derivative contracts not designated as hedging instruments	(3,216)	(3,220)
Accounts Payable [Member] | Commodity [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments		(3)
Derivative contracts not designated as hedging instruments	(3,207)	(3,209)
Accounts Payable [Member] | Interest Rate and Other [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	(4)	(1)
Accounts Payable [Member] | Foreign Exchange [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	(1)	(3)
Accounts Payable [Member] | Equity and Other [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	(8)
Accounts Payable [Member] | Other [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments		$ (8)