Derivatives - Open Commodity Derivative Contracts (Detail)	6 Months Ended
	Jun. 30, 2014
Crude Oil Exchange-Traded
Derivative [Line Items]
Percentage of derivative contracts expiring in the period	100.00%
Derivative contract expiration date	Sep. 30, 2014
Crude Oil Exchange-Traded | Long
Derivative [Line Items]
Notional Contracts (in thousands of Total Barrels)	14,775,000	[1]
Crude Oil Exchange-Traded | Short
Derivative [Line Items]
Notional Contracts (in thousands of Total Barrels)	33,812,000	[1]
Refined Products Exchange-Traded
Derivative [Line Items]
Percentage of derivative contracts expiring in the period	100.00%
Derivative contract expiration date	Sep. 30, 2014
Refined Products Exchange-Traded | Long
Derivative [Line Items]
Notional Contracts (in thousands of Total Barrels)	4,618,000
Refined Products Exchange-Traded | Short
Derivative [Line Items]
Notional Contracts (in thousands of Total Barrels)	2,541,000

[1] 100 percent of these contracts expire in the third quarter of 2014.