Derivatives and Hedge Accounting Activities (Volume of Derivative Activity) (Details) (USD $)	Mar. 31, 2012
Current Derivative Contract
Interest rate	$ 2,000,000,000
Current Derivative Contract | Natural Gas | Fixed Price
Volume of natural gas (cf)/ liquids (gallons)	315,000,000,000	[1]
Current Derivative Contract | Natural Gas | Basis
Volume of natural gas (cf)/ liquids (gallons)	861,000,000,000	[1]
Current Derivative Contract | Electricity | Fixed Price
Volume of electricity (MWh)	21,953,642	[1]
Current Derivative Contract | Electricity | Financial Transmission Rights
Volume of electricity (MWh)	21,805,241
Current Derivative Contract | Capacity
Capacity (MW)	63,825
Current Derivative Contract | Liquids
Volume of natural gas (cf)/ liquids (gallons)	137,508,000	[2]
Noncurrent Derivative Contract
Interest rate	$ 1,940,000,000
Noncurrent Derivative Contract | Natural Gas | Fixed Price
Volume of natural gas (cf)/ liquids (gallons)	74,000,000,000	[1]
Noncurrent Derivative Contract | Natural Gas | Basis
Volume of natural gas (cf)/ liquids (gallons)	484,000,000,000	[1]
Noncurrent Derivative Contract | Electricity | Fixed Price
Volume of electricity (MWh)	21,718,420	[1]
Noncurrent Derivative Contract | Electricity | Financial Transmission Rights
Volume of electricity (MWh)	810,816
Noncurrent Derivative Contract | Capacity
Capacity (MW)	272,968
Noncurrent Derivative Contract | Liquids
Volume of natural gas (cf)/ liquids (gallons)	221,214,000	[2]

[1] Includes options.

[2] Includes NGLs and oil.