Regulatory Matters (Regulatory Assets And Liabilities) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Regulatory Assets [Line Items]
Regulatory assets - long-term	$ 9,078	$ 9,337
Regulatory assets - current	127	164
Regulatory liabilities - long-term	1,029	977
Total Regulatory Assets	9,205	9,501
Regulatory liabilities - current	233	118
Total Regulatory Liabilities	1,262	1,095
Unrecognized Pension And Other Postretirement Costs
Regulatory Assets [Line Items]
Regulatory assets - long-term	5,407	5,852
Future Income Tax
Regulatory Assets [Line Items]
Regulatory assets - long-term	1,874	1,798
Environmental Restoration Costs
Regulatory Assets [Line Items]
Regulatory assets - long-term	730	681
Pension And Other Post Retirement Benefits Deferrals
Regulatory Assets [Line Items]
Regulatory assets - long-term	214	198
Revenue Taxes
Regulatory Assets [Line Items]
Regulatory assets - long-term	169	163
Deferred Storm Costs
Regulatory Assets [Line Items]
Regulatory assets - long-term	121	128
Net Electric Deferrals
Regulatory Assets [Line Items]
Regulatory assets - long-term	111	121
Surcharge For New York State Assessment
Regulatory Assets [Line Items]
Regulatory assets - long-term	87	90
Deferred Derivative Losses - Long-Term
Regulatory Assets [Line Items]
Regulatory assets - long-term	70	60
Regulatory assets - current	126	164
O&R Transition Bond Charges
Regulatory Assets [Line Items]
Regulatory assets - long-term	42	44
Preferred Stock Redemption
Regulatory Assets [Line Items]
Regulatory assets - long-term	30
Workers' Compensation
Regulatory Assets [Line Items]
Regulatory assets - long-term	21	23
Property Tax Reconciliation [Member]
Regulatory Assets [Line Items]
Regulatory assets - long-term	13	13
Regulatory liabilities - long-term	97	35
Recoverable Energy Costs
Regulatory Assets [Line Items]
Regulatory assets - long-term		14
Regulatory assets - current	1
Other
Regulatory Assets [Line Items]
Regulatory assets - long-term	189	152
Allowance For Cost Of Removal Less Salvage
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	468	448
Net Unbilled Revenue Deferrals
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	140	104
World Trade Center Settlement Proceeds
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	72	62
Long-Term Interest Rate Reconciliation
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	46	30
Carrying Charges On Transmission And Distribution Net Plant
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	41	38
Gas Line Losses
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	17	21
Expenditure Prudence Proceeding
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	15	11
Energy Efficiency Programs [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	8	22
Other Liabilities
Regulatory Assets [Line Items]
Regulatory liabilities - long-term	125	206
Electric Surcharge Offset
Regulatory Assets [Line Items]
Regulatory liabilities - current	104
Refundable Energy Costs - Current
Regulatory Assets [Line Items]
Regulatory liabilities - current	69	51
Revenue Decoupling Mechanism
Regulatory Assets [Line Items]
Regulatory liabilities - current	59	66
Deferred Derivative Gains - Current [Member]
Regulatory Assets [Line Items]
Regulatory liabilities - current	$ 1	$ 1