Significant Accounting Policies (Details Textuals) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Significant Accounting Policies [Line Items]
Maturities on Temporary Investments	3 months
Receivables Due Date	21 days
Number of Days in a Year	365 days
Time Period Customer Accounts are Written off After Service Termination	150 days
Specific Review of Probable Future Collections Based on Receivable Balances in Excess of 90 Days	30 days
Unbilled Contracts Receivable	$ 686,000,000	$ 597,000,000
Notes Receivable Considered Delinquent Minimum Due Date	60 days
Notes Receivable Considered Delinquent Maximum Due Date	120 days
LIFO Inventory Amount	37,000,000	52,000,000
Excess of Replacement or Current Costs over Stated LIFO Value	113,000,000	95,000,000
Expense Related to Refueling Outages	12,000,000	23,000,000
Period Expenses Related To Refueling Outages Are Accrued	18 months
Amortization of Intangible Assets	6,000,000	5,000,000	4,000,000
Estimated Amount of Amortization	13,000,000
Excise Sales Tax Net Impact on Statement of Operations	0
Collateral Already Posted, Aggregate Fair Value	20,000,000	71,000,000
Cash Collateral Paid or Received for Derivative Assets or Derivative Liabilities	0
Cash Collateral Paid or Received for Derivative Assets		19,000,000
Cash Collateral Paid or Received for Derivative Liabilities		74,000,000
Cash Collateral Paid	4,000,000	16,000,000
Cash Collateral Received	24,000,000
Charitable Contributions to a Foundation	$ 21,000,000	$ 21,000,000	$ 14,000,000
Restricted Cash Time Period to be Classified as Current	1 year
Minimum [Member]
Significant Accounting Policies [Line Items]
Finite Lived Asset Useful Life	3 years
Maximum [Member]
Significant Accounting Policies [Line Items]
Finite Lived Asset Useful Life	15 years
Finite Lived Intangible Asset, Useful Life 1	28 years