Disclosures About Fair Value - Notional Amounts of Derivatives (Details)	Mar. 31, 2015 T		Dec. 31, 2014 T
Exchange Traded | Agricultural Commodities | 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)	(104,590,000)	[1]	(99,268,000)	[1]
Exchange Traded | Agricultural Commodities | 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)	(79,533,000)	[1]	(85,602,000)	[1]
Exchange Traded | Natural Gas | 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)	(600,000,000)	[1],[2]	(690,000,000)	[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)	(129,362,000)	[1]	(126,615,000)	[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)	(59,820,000)	[1]	(29,666,000)	[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.