Fair Value Measurements (Policies)

12 Months Ended

Dec. 31, 2011

Fair Value Measurements, Policies [Abstract]

Offsetting fair value amounts of commodity derivative contracts

We have elected to offset the fair value amounts recognized for multiple similar derivative instruments executed with the same counterparty, including any related cash collateral asset or obligation under the column “Netting Adjustments” below; however, fair value amounts by hierarchy level are presented on a gross basis in the tables below.