Risk Management and Trading Activities (Details 5) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Accounts Receivable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts designated as hedging instruments	$ 242	$ 235
Derivative contracts not designated as hedging instruments	9,368	11,619
Gross fair value of derivative contracts	9,610	11,854
Master netting arrangements	(7,962)	(10,178)
Cash collateral (received) posted	(121)	(213)
Net fair value of derivative contracts	1,527	1,463
Accounts Payable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts designated as hedging instruments	(219)	(485)
Derivative contracts not designated as hedging instruments	(9,868)	(12,434)
Gross fair value of derivative contracts	(10,087)	(12,919)
Master netting arrangements	7,962	10,178
Cash collateral (received) posted	117	34
Net fair value of derivative contracts	(2,008)	(2,707)
Commodity [Member] | Accounts Receivable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts designated as hedging instruments	181	225
Derivative contracts not designated as hedging instruments	9,350	11,581
Commodity [Member] | Accounts Payable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts designated as hedging instruments	(216)	(483)
Derivative contracts not designated as hedging instruments	(9,823)	(12,383)
Foreign Exchange [Member] | Accounts Receivable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts not designated as hedging instruments	6	7
Foreign Exchange [Member] | Accounts Payable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts not designated as hedging instruments	(21)	(19)
Other [Member] | Accounts Receivable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts designated as hedging instruments	61	10
Derivative contracts not designated as hedging instruments	12	31
Other [Member] | Accounts Payable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts designated as hedging instruments	(3)	(2)
Derivative contracts not designated as hedging instruments	$ (24)	$ (32)