Financial Risk Management - Gross and Net Fair Values of Corporate and Trading Derivative Instruments (Detail) $ in Millions	Jun. 30, 2015 USD ($)
Derivatives Fair Value [Line Items]
Gross Amounts, Assets	$ 40
Gross Amounts, Liabilities	(21)
Commodity [Member]
Derivatives Fair Value [Line Items]
Gross Amounts, Assets	33
Gross Amounts, Liabilities	(11)
Interest Rate and Other [Member]
Derivatives Fair Value [Line Items]
Gross Amounts, Assets	7
Accounts Receivable [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	27
Derivative contracts not designated as hedging instruments	13
Gross Amounts, Assets	40
Master netting arrangements	(12)
Net fair value of derivative contracts	28
Accounts Receivable [Member] | Commodity [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	25
Derivative contracts not designated as hedging instruments	8
Accounts Receivable [Member] | Interest Rate and Other [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	2
Accounts Receivable [Member] | Foreign Exchange [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	5
Accounts Payable [Member]
Derivatives Fair Value [Line Items]
Master netting arrangements	12
Net fair value of derivative contracts	(9)
Derivative contracts not designated as hedging instruments	(21)
Gross Amounts, Liabilities	(21)
Accounts Payable [Member] | Commodity [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	(11)
Accounts Payable [Member] | Foreign Exchange [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	$ (10)