Pension, OPEB and Savings Plans (Fair Value Measurements And The Levels Of Inputs Used In Determining Fair Values) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	$ 6,310	$ 5,599
Interest and dividend receivables		13	14
Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	133	107
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	1,275	944
Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	1,401	1,387
Government-Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	272	263
US Treasury Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	571	441
Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	963	836
Subtotal before Measured at Net Asset Value Practical Expedient [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		4,621	3,979
Commingled Equities at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[6]	1,675	1,604
Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	6	1
Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[7]	14	16
Quoted Market Prices for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Quoted Market Prices for Identical Assets (Level 1) [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	117	105
Quoted Market Prices for Identical Assets (Level 1) [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	1,275	944
Quoted Market Prices for Identical Assets (Level 1) [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	1,218	1,247
Quoted Market Prices for Identical Assets (Level 1) [Member] | Government-Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	0	0
Quoted Market Prices for Identical Assets (Level 1) [Member] | US Treasury Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	0	0
Quoted Market Prices for Identical Assets (Level 1) [Member] | Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	0	0
Quoted Market Prices for Identical Assets (Level 1) [Member] | Subtotal before Measured at Net Asset Value Practical Expedient [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,616	2,297
Quoted Market Prices for Identical Assets (Level 1) [Member] | Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	6	1
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	16	2
Significant Other Observable Inputs (Level 2) [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	0	0
Significant Other Observable Inputs (Level 2) [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	183	140
Significant Other Observable Inputs (Level 2) [Member] | Government-Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	272	263
Significant Other Observable Inputs (Level 2) [Member] | US Treasury Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	571	441
Significant Other Observable Inputs (Level 2) [Member] | Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	963	836
Significant Other Observable Inputs (Level 2) [Member] | Subtotal before Measured at Net Asset Value Practical Expedient [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2,005	1,682
Significant Other Observable Inputs (Level 2) [Member] | Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	0	0
Pension And OPEB Plans Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Pension And OPEB Plans Level 3 [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	0	0
Pension And OPEB Plans Level 3 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	0	0
Pension And OPEB Plans Level 3 [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	0	0
Pension And OPEB Plans Level 3 [Member] | Government-Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	0	0
Pension And OPEB Plans Level 3 [Member] | US Treasury Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	0	0
Pension And OPEB Plans Level 3 [Member] | Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	0	0
Pension And OPEB Plans Level 3 [Member] | Subtotal before Measured at Net Asset Value Practical Expedient [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Pension And OPEB Plans Level 3 [Member] | Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	0	0
Long Island Electric Utility Servco LLC Pension and OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		191	134
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[8]	137	96
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[8]	54	38
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Quoted Market Prices for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Quoted Market Prices for Identical Assets (Level 1) [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[8]	0	0
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Quoted Market Prices for Identical Assets (Level 1) [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[8]	0	0
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		191	134
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Significant Other Observable Inputs (Level 2) [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[8]	137	96
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Significant Other Observable Inputs (Level 2) [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[8]	54	38
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension And OPEB Plans Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension And OPEB Plans Level 3 [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[8]	0	0
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension And OPEB Plans Level 3 [Member] | Fixed Income Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[8]	$ 0	$ 0

[1] Excludes net receivable of $13 million and $14 million at December 31, 2017 and 2016, respectively, which consists of interest, dividends and receivables and payables related to pending securities sales and purchases.

[2] The Collective Investment Fund publishes a daily net asset value (NAV) which participants may use for daily redemptions without restrictions (Level 1). Certain temporary investments are valued using inputs such as time-to-maturity, coupon rate, quality rating and current yield (Level 2).

[3] Common stocks and preferred stocks are measured using observable data in active markets and considered Level 1.

[4] Commingled Funds that allow daily redemption at their daily published NAV without restrictions are classified as Level 1. Commingled Funds that publish daily NAV but with certain near term redemption restrictions which prevent redemption at the published daily NAV are classified as Level 2.

[5] Debt securities include mainly investment grade corporate and municipal bonds, US Treasury obligations and Federal Agency asset-backed securities with a wide range of maturities. These investments are valued using an evaluated pricing approach that varies by asset class and reflects observable market information such as the most recent exchange price or quoted bid for similar securities. Market-based standard inputs typically include benchmark yields, reported trades, broker/dealer quotes and issuer spreads or the most recent quoted for similar securities which are a Level 2 measure.

[6] In 2016, as part of the implementation of the accounting guidance on investments measured at fair value using NAV as a practical expedient, certain commingled equity funds have been removed from the fair value hierarchy as they are measured at fair value using the NAV per share (or its equivalent) practical expedient. These funds do not meet the definition of readily determinable fair value due to limitations in published NAV (last business day of the month) and include certain redemption restrictions ranging from five to fifteen days advance notice prior to redemption days and limitations on withdrawals over 25% of the total fund. The objectives of these funds are mainly tracking the S&P Index or achieving long-term growth through investment in foreign equity securities and the MSCI Emerging Markets Index.

[7] Private equity investments primarily include various limited partnerships that invest in either operating companies through acquisitions or developing a portfolio of non-US distressed investments to maximize total return on capital. These investments are valued at NAV (or its equivalent) on an annual basis and have significant redemption restrictions preventing redemption until fund liquidation and limited ability to sell these investments. Fund liquidation is not expected to occur for several more years. These investments have been removed from the fair value hierarchy in accordance with the guidance on NAV practical expedient.

[8] Investments in commingled equity and bond funds have a readily determinable fair value as they publish a daily NAV available to investors which is the basis for current transactions and contain certain redemption restrictions requiring advance notice of one to two days for withdrawals (Level 2).