Derivative and Hedging Activities Natural Gas and Oil Sales (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Disclosure Components Of Natural Gas And Oil Sales [Abstract]
Natural gas, oil and NGL sales	$ 1,869	$ 1,112	$ 3,464	$ 2,334
Gains (losses) on natural gas, oil and NGL derivatives	537	1,005	394	851
Natural gas, oil and NGL	$ 2,406	$ 2,117	$ 3,858	$ 3,185