Derivatives and Hedge Accounting Activities (Volume of our Derivative Activity) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011
Current Derivative Contract [Member]
Interest rate	$ 2,200
Current Derivative Contract [Member] | Natural Gas [Member] | Fixed Price [Member]
Volume of natural gas (in billion cubic feet and gallons)	279	[1]
Current Derivative Contract [Member] | Natural Gas [Member] | Basis [Member]
Volume of natural gas (in billion cubic feet and gallons)	822	[1]
Current Derivative Contract [Member] | Electricity [Member] | Fixed Price [Member]
Volume of electricity (in Megawatt hours)	19,955,507	[1]
Current Derivative Contract [Member] | Electricity [Member] | Financial Transmission Rights [Member]
Volume of electricity (in Megawatt hours)	50,859,304
Current Derivative Contract [Member] | Capacity [Member]
Capacity of Electricity (in Megawatts)	109,416
Current Derivative Contract [Member] | Liquids [Member]
Volume of natural gas (in billion cubic feet and gallons)	140,658,000	[2]
Noncurrent Derivative Contract [Member]
Interest rate	$ 2,090
Noncurrent Derivative Contract [Member] | Natural Gas [Member] | Fixed Price [Member]
Volume of natural gas (in billion cubic feet and gallons)	79	[1]
Noncurrent Derivative Contract [Member] | Natural Gas [Member] | Basis [Member]
Volume of natural gas (in billion cubic feet and gallons)	400	[1]
Noncurrent Derivative Contract [Member] | Electricity [Member] | Fixed Price [Member]
Volume of electricity (in Megawatt hours)	20,056,109	[1]
Noncurrent Derivative Contract [Member] | Electricity [Member] | Financial Transmission Rights [Member]
Volume of electricity (in Megawatt hours)	1,277,239
Noncurrent Derivative Contract [Member] | Capacity [Member]
Capacity of Electricity (in Megawatts)	281,185
Noncurrent Derivative Contract [Member] | Liquids [Member]
Volume of natural gas (in billion cubic feet and gallons)	248,220,000	[2]

[1] Includes options.

[2] Includes NGLs and oil.