Derivative Instruments (Details 1) (USD $) In Millions, unless otherwise specified	Jun. 30, 2011		Dec. 31, 2010
Net forward notional buy (sell) line items [Abstract]
Nonmonetary notional amounts - Power (MWh)	(40,000,000)		(50,000,000)
Nonmonetary notional amounts - Natural Gas (MMBtu)	170,000,000		31,000,000
Interest rate swaps	$ 5,191	[1]	$ 6,171	[1]

[1] Approximately $4.1 billion and $3.3 billion at June 30, 2011 and December 31, 2010, respectively, related to variable rate debt that was converted to fixed rate debt in 2011 and 2010.