Financial Risk Management - Gross and Net Fair Values of Corporate and Trading Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015
Accounts Receivable [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	$ 73
Derivative contracts not designated as hedging instruments	46
Gross fair value of derivative contracts	119
Master netting arrangements	(14)
Net fair value of derivative contracts	105
Accounts Receivable [Member] | Commodity [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	69
Derivative contracts not designated as hedging instruments	12
Accounts Receivable [Member] | Interest Rate and Other [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	4
Accounts Receivable [Member] | Foreign Exchange [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	34
Accounts Payable [Member]
Derivatives Fair Value [Line Items]
Gross fair value of derivative contracts	(18)
Master netting arrangements	14
Net fair value of derivative contracts	(4)
Derivative contracts designated as hedging instruments	(1)
Derivative contracts not designated as hedging instruments	(17)
Accounts Payable [Member] | Commodity [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	(15)
Accounts Payable [Member] | Interest Rate and Other [Member]
Derivatives Fair Value [Line Items]
Derivative contracts designated as hedging instruments	(1)
Accounts Payable [Member] | Foreign Exchange [Member]
Derivatives Fair Value [Line Items]
Derivative contracts not designated as hedging instruments	$ (2)