Disclosures About Fair Value of Financial Instruments - Notional Amounts of Derivatives (Details)	Jun. 30, 2014 T	Dec. 31, 2013 T
Exchange Traded | Agricultural Commodities Futures | Short
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative (agricultural commodities in tons, natural gas in millions of British thermal units, and forwards in tons)	(96,350)	(23,038)	[1]
Exchange Traded | Agricultural Commodities Futures | Long
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative (agricultural commodities in tons, natural gas in millions of British thermal units, and forwards in tons)	75,062	34,380	[1]
Exchange Traded | Natural Gas Futures | Long
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative (agricultural commodities in tons, natural gas in millions of British thermal units, and forwards in tons)	340,000	460,000	[1],[2]
Non-Exchange Traded | Forwards | Short
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative (agricultural commodities in tons, natural gas in millions of British thermal units, and forwards in tons)	(119,962)	(132,428)	[1]
Non-Exchange Traded | Forwards | Long
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative (agricultural commodities in tons, natural gas in millions of British thermal units, and forwards in tons)	61,741	30,367	[1]
Non-Exchange Traded | Swaps | Long
Derivatives, Fair Value [Line Items]
Notional amount of nonmonetary derivative (agricultural commodities in tons, natural gas in millions of British thermal units, and forwards in tons)		75,000	[1]

[1] Exchange and non-exchange traded futures, forwards, and swaps are presented on a gross (short) and long position basis.

[2] Million Metric British Thermal Units.