Disclosures About Fair Value of Financial Instruments - Notional Amounts of Derivatives (Details)	Sep. 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)	(64,749)	(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)	(51,024)	(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)	(520,000)	(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)	(147,586)	(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)	(55,208)	(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.