Derivatives and Hedge Accounting Activities (Volume of Derivative Activity) (Details) (USD $)	6 Months Ended
	Jun. 30, 2011 mW
Current Derivative Contract [Member]
Interest rate	600,000,000
Current Derivative Contract [Member] | Natural Gas [Member] | Fixed Price [Member]
Volume of natural gas	245,000,000,000	[1]
Current Derivative Contract [Member] | Natural Gas [Member] | Basis [Member]
Volume of natural gas	1,019,000,000,000
Current Derivative Contract [Member] | Electricity [Member] | Fixed Price [Member]
Volume of electricity	19,363,209	[1]
Current Derivative Contract [Member] | Electricity [Member] | Financial Transmission Rights [Member]
Volume of electricity	108,707,777
Current Derivative Contract [Member] | Capacity [Member]
Capacity (MW)	201,416
Current Derivative Contract [Member] | Liquids [Member]
Volume of natural gas	143,136,000	[2]
Noncurrent Derivative Contract [Member]
Interest rate	3,100,000,000
Noncurrent Derivative Contract [Member] | Natural Gas [Member] | Fixed Price [Member]
Volume of natural gas	60,000,000,000	[1]
Noncurrent Derivative Contract [Member] | Natural Gas [Member] | Basis [Member]
Volume of natural gas	458,000,000,000
Noncurrent Derivative Contract [Member] | Electricity [Member] | Fixed Price [Member]
Volume of electricity	24,512,834	[1]
Noncurrent Derivative Contract [Member] | Electricity [Member] | Financial Transmission Rights [Member]
Volume of electricity	1,074,048
Noncurrent Derivative Contract [Member] | Capacity [Member]
Capacity (MW)	297,985
Noncurrent Derivative Contract [Member] | Liquids [Member]
Volume of natural gas	300,006,000	[2]

[1] Includes options.

[2] Includes NGLs and oil.