Derivatives (Open Commodity Derivative Contracts) (Detail) gal in Thousands, bbl in Thousands	12 Months Ended
	Dec. 31, 2018 bbl gal
Exchange Traded | Crude oil
Derivative [Line Items]
Percentage of derivative contracts expiring next quarter	71.50%
Exchange Traded | Crude oil | Long
Derivative [Line Items]
Notional contracts (contract volumes)	40,257	[1]
Exchange Traded | Crude oil | Long | Spread contracts
Derivative [Line Items]
Notional contracts (contract volumes)	7,470
Exchange Traded | Crude oil | Short
Derivative [Line Items]
Notional contracts (contract volumes) | gal	44,709	[1]
Exchange Traded | Crude oil | Short | Spread contracts
Derivative [Line Items]
Notional contracts (contract volumes)	6,800
Exchange Traded | Refined products
Derivative [Line Items]
Percentage of derivative contracts expiring next quarter	75.90%
Exchange Traded | Refined products | Long
Derivative [Line Items]
Notional contracts (contract volumes)	10,210	[1]
Exchange Traded | Refined products | Long | Spread contracts
Derivative [Line Items]
Notional contracts (contract volumes)	450
Exchange Traded | Refined products | Short
Derivative [Line Items]
Notional contracts (contract volumes) | gal	11,149	[1]
Exchange Traded | Refined products | Short | Spread contracts
Derivative [Line Items]
Notional contracts (contract volumes)	450
Exchange Traded | Blending products
Derivative [Line Items]
Percentage of derivative contracts expiring next quarter	70.30%
Exchange Traded | Blending products | Long
Derivative [Line Items]
Notional contracts (contract volumes)	5,194	[1]
Exchange Traded | Blending products | Long | Spread contracts
Derivative [Line Items]
Notional contracts (contract volumes)	2,678
Exchange Traded | Blending products | Short
Derivative [Line Items]
Notional contracts (contract volumes) | gal	7,356	[1]
Exchange Traded | Blending products | Short | Spread contracts
Derivative [Line Items]
Notional contracts (contract volumes)	2,767
OTC | Crude oil
Derivative [Line Items]
Percentage of derivative contracts expiring next quarter	0.00%
OTC | Crude oil | Long
Derivative [Line Items]
Notional contracts (contract volumes)	880
OTC | Crude oil | Short
Derivative [Line Items]
Notional contracts (contract volumes)	0
OTC | Blending products
Derivative [Line Items]
Percentage of derivative contracts expiring next quarter	24.10%
OTC | Blending products | Long
Derivative [Line Items]
Notional contracts (contract volumes)	2,480
OTC | Blending products | Short
Derivative [Line Items]
Notional contracts (contract volumes) | gal	2,480

[1] Included in exchange-traded are spread contracts in thousands of barrels: Crude oil - 7,470 long and 6,800 short; Refined products - 450 long and 450 short; Blending products - 2,678 long and 2,767 short