Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013 Counterparty	Dec. 31, 2012
Derivative [Line Items]
Number of counterparties	17
Realization of gains and losses on hedges in future earnings	2014
Net gain included in accumulated other comprehensive loss, after tax	$ 118	$ 131
2013 [Member] | Derivatives Not Designated as Cash Flow Hedging Instruments [Member] | Ice Brent [Member] | Open Crude Oil Derivative Positions [Member]
Derivative [Line Items]
Derivative Non-monetary Notional Amount	4,000,000
2014 [Member] | Derivatives Not Designated as Cash Flow Hedging Instruments [Member] | Ice Brent [Member] | Open Crude Oil Derivative Positions [Member]
Derivative [Line Items]
Derivative Non-monetary Notional Amount	8,400,000
2015 [Member] | Derivatives Not Designated as Cash Flow Hedging Instruments [Member] | Ice Brent [Member] | Open Crude Oil Derivative Positions [Member]
Derivative [Line Items]
Derivative Non-monetary Notional Amount	1,500,000
Cash Flow Hedges [Member]
Derivative [Line Items]
Net gain included in accumulated other comprehensive loss, before tax applied to next twelve months	10
Net gain included in accumulated other comprehensive loss, after tax	$ 6