Regulatory Matters (Regulatory Assets And Liabilities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Regulatory Assets [Line Items]
Regulatory assets	$ 9,337	$ 7,683
Regulatory assets - current	164	203
Total Regulatory Assets	9,501	7,886
Regulatory liabilities	977	788
Regulatory liabilities - current	118	159
Total Regulatory Liabilities	1,095	947
Unrecognized Pension And Other Postretirement Costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	5,852	4,371
Future Federal Income Tax [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,798	1,592
Environmental Remediation Costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	681	695
Pension And Other Post Retirement Benefits Deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets	198	138
Revenue Taxes [Member]
Regulatory Assets [Line Items]
Regulatory assets	163	145
Surcharge For New York State Assessment [Member]
Regulatory Assets [Line Items]
Regulatory assets	90	121
Net Electric Deferrals [Member]
Regulatory Assets [Line Items]
Regulatory assets	121	156
Deferred Storm Costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	128	57
O & R Transition Bond Charges [Member]
Regulatory Assets [Line Items]
Regulatory assets	44	48
Deferred Derivative Losses - Long-Term [Member]
Regulatory Assets [Line Items]
Regulatory assets	60	74
Workers' Compensation [Member]
Regulatory Assets [Line Items]
Regulatory assets	23	31
Property Tax Reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory assets	13	34
Regulatory liabilities	35
World Trade Center Restoration Costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	5	45
Recoverable Energy Cost [Member]
Regulatory Assets [Line Items]
Regulatory assets	14	42
Long-Term Interest Rate Reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	30	13
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	147	134
Deferred Derivative Losses - Current [Member]
Regulatory Assets [Line Items]
Regulatory assets - current	164	190
Recoverable Energy Costs - Current [Member]
Regulatory Assets [Line Items]
Regulatory assets - current		13
Allowance For Cost Of Removal Less Salvage [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	448	422
Net Unbilled Revenue Deferrals [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	104	136
World Trade Center Settlement Proceeds [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	62
Carrying Charges On Transmission And Distribution Net Plant [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	38	28
Bonus Depreciation [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	35	1
Energy Efficiency Programs [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	22	12
Gas Line Losses [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	21
New York State Tax Refund [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	20	30
Gain On Sale Of Properties [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	14	28
Expenditure Prudence Proceeding [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	11
Other Liabilities [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	137	118
Revenue Decoupling Mechanism [Member]
Regulatory Assets [Line Items]
Regulatory liabilities	66	38
Refundable Energy Cost - Current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	51	117
Deferred Derivative Gains - Current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	$ 1	$ 4