Risk Management and Trading Activities (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Accounts Receivable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts designated as hedging instruments	$ 357	$ 242
Derivative contracts not designated as hedging instruments	9,469	9,368
Gross fair value of derivative contracts	9,826	9,610
Master netting arrangements	(8,453)	(7,962)
Cash collateral (received) posted	(171)	(121)
Net fair value of derivative contracts	1,202	1,527
Accounts Payable [Member]
Gross and net fair values of the Corporation's risk management and trading derivative instruments
Derivative contracts designated as hedging instruments	(114)	(219)
Derivative contracts not designated as hedging instruments	(9,886)	(9,868)
Gross fair value of derivative contracts	(10,000)	(10,087)
Master netting arrangements	8,453	7,962
Cash collateral (received) posted	65	117
Net fair value of derivative contracts	(1,482)	(2,008)
Commodity contracts [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	287	181
Derivative contracts not designated as hedging instruments	9,430	9,350
Commodity contracts [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	(112)	(216)
Derivative contracts not designated as hedging instruments	(9,848)	(9,823)
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	12	6
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	(19)	(21)
Other contracts [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	27	12
Other contracts [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	(19)	(24)
Interest Rate and 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	70	61
Interest Rate and 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	$ (2)	$ (3)