Risk Management and Trading Activities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Gross volume of the Corporation's derivative contracts and instruments outstanding
Interest rate (millions of U.S. Dollars)	$ 895	$ 310
Gross Volume of Derivative Instruments Outstanding Relating to Trading Activities [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Foreign exchange (millions of U.S. Dollars)	581	506
Interest rate (millions of U.S. Dollars)	182	205
Gross Volume of the corporate risk management derivative instruments outstanding [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Foreign exchange (millions of U.S. Dollars)	900	1,025
Interest rate (millions of U.S. Dollars)	$ 895	$ 310
Crude oil and refined petroleum products (millions of barrels) [Member] | Gross Volume of Derivative Instruments Outstanding Relating to Trading Activities [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Absolute volume of derivative commodity contracts	2,169	3,328
Crude oil and refined petroleum products (millions of barrels) [Member] | Gross Volume of the Corporation's Energy Marketing Commodity Contracts Outstanding [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Absolute volume of derivative commodity contracts	28	30
Commodity, primarily crude oil (millions of barrels) [Member] | Gross Volume of the corporate risk management derivative instruments outstanding [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Absolute volume of derivative commodity contracts	51	35
Natural Gas Millions of Mcf [Member] | Gross Volume of Derivative Instruments Outstanding Relating to Trading Activities [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Absolute volume of derivative commodity contracts	4,203	4,699
Natural Gas Millions of Mcf [Member] | Gross Volume of the Corporation's Energy Marketing Commodity Contracts Outstanding [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Absolute volume of derivative commodity contracts	2,616	2,210
Electricity Millions of Megawatt Hours [Member] | Gross Volume of Derivative Instruments Outstanding Relating to Trading Activities [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Absolute volume of derivative commodity contracts	304	79
Electricity Millions of Megawatt Hours [Member] | Gross Volume of the Corporation's Energy Marketing Commodity Contracts Outstanding [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Absolute volume of derivative commodity contracts	244	301
Equity securities (millions of shares) [Member] | Gross Volume of Derivative Instruments Outstanding Relating to Trading Activities [Member]
Gross volume of the Corporation's derivative contracts and instruments outstanding
Equity Securities (millions of shares)	16	35