Derivative and Hedging Activities Derivatives Not Designated as Hedging Instruments (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
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in net income (loss)	$ (50)	$ 7	$ (54)	$ 2
Not designated as hedging instruments
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in net income (loss)	485	994	355	830
Not designated as hedging instruments | Commodity contracts | Natural Gas, Oil and NGL sales
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in net income (loss)	536	988	412	832
Not designated as hedging instruments | Interest rate contract | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in net income (loss)	(51)	5	(57)	(2)
Not designated as hedging instruments | Equity Contracts | Interest Expense
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in net income (loss)	$ 0	$ 1	$ 0	$ 0