Fair Value Disclosures (Fair Value Of Financial Liabilities Measured On A Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	$ 4,569	[1]	$ 4,577
Transition Bonds issued by ACE Funding, Fair Value	370	[2]	380
Long-term Project Funding, Fair Value	15		15
Total Liabilities, Fair Value	4,954
Long-Term Debt, Carrying Amount	3,868		3,867
Transition Bonds issued by ACE Funding, Carrying Amount	323		332
Quoted Prices In Active Markets For Identical Instruments (Level 1) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	408	[1]
Total Liabilities, Fair Value	408
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	3,681	[1]
Transition Bonds issued by ACE Funding, Fair Value	370	[2]
Total Liabilities, Fair Value	4,051
Significant Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, Fair Value	480	[1]
Long-term Project Funding, Fair Value	15
Total Liabilities, Fair Value	$ 495

[1] The carrying amount for Long-term debt is $3,868 million as of March 31, 2012.

[2] The carrying amount for Transition Bonds issued by ACE Funding, including amounts due within one year, is $323 million as of March 31, 2012.