Derivatives and Hedging Activities Natural Gas and Oil Sales Table (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Disclosure Components Of Natural Gas And Oil Sales [Abstract]
Natural gas, oil and NGL sales	$ 5,359	$ 5,259	$ 4,248
Gains (losses) on natural gas, oil and NGL derivatives	919	772	1,422
Gains (losses) on ineffectiveness of cash flow hedges	0	(7)	(23)
Natural gas, oil and NGL	$ 6,278	$ 6,024	$ 5,647