Pension, OPEB and Savings Plans (Fair Value Measurements And The Levels Of Inputs Used In Determining Fair Values) (Details) - USD ($) $ in Millions		Dec. 31, 2020		Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	$ 6,921		$ 6,449
Net receivables excluded from Fair Value		10		15
Cash and foreign currency excluded from Fair Value		1		5
Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	1		3
Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	85		104
Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	1,763		1,487
Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	1,964		1,707
Government-Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	258		284
US Treasury Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	419		544
Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	823		837
Commingled Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		4		3
Other (Futures Contracts) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets				(3)
Subtotal before Measured at Net Asset Value Practical Expedient [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		5,327		4,985
Commingled Equities at NAV [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[6]	1,283		1,154
Real Estate Investment [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		306	[7]	302
Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	10		19
Private Equity [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[8]	5		8
Quoted Market Prices for Identical Assets (Level 1) [Member] | Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	1		3
Quoted Market Prices for Identical Assets (Level 1) [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	85		103
Quoted Market Prices for Identical Assets (Level 1) [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	1,763		1,487
Quoted Market Prices for Identical Assets (Level 1) [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	1,025		1,042
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] | Commingled Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		4		3
Quoted Market Prices for Identical Assets (Level 1) [Member] | Other (Futures Contracts) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets				(3)
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		2,888		2,654
Quoted Market Prices for Identical Assets (Level 1) [Member] | Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	10		19
Significant Other Observable Inputs (Level 2) [Member] | Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0		0	[2]
Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	0		1
Significant Other Observable Inputs (Level 2) [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	0		0
Significant Other Observable Inputs (Level 2) [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	939		665
Significant Other Observable Inputs (Level 2) [Member] | Government-Other [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	258		284
Significant Other Observable Inputs (Level 2) [Member] | US Treasury Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	419		544
Significant Other Observable Inputs (Level 2) [Member] | Corporate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	823		837
Significant Other Observable Inputs (Level 2) [Member] | Commingled Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0		0
Significant Other Observable Inputs (Level 2) [Member] | Other (Futures Contracts) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets				0
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		2,439		2,331
Significant Other Observable Inputs (Level 2) [Member] | Preferred Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0		0	[2]
Pension And OPEB Plans Level 3 [Member] | Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0		0	[2]
Pension And OPEB Plans Level 3 [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]	0		0
Pension And OPEB Plans Level 3 [Member] | Common Stock [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	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		0		0	[5]
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] | Commingled Debt [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0		0
Pension And OPEB Plans Level 3 [Member] | Other (Futures Contracts) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets				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		0		0	[2]
Long Island Electric Utility Servco LLC Pension and OPEB [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		343		282
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Commingled Equities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[9]	259		202
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	[9]	83		80
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1
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		1		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		0		0	[9]
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		0		0	[9]
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Quoted Market Prices for Identical Assets (Level 1) [Member] | Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1
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		342		282
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		259		202	[9]
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		83		80	[9]
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Significant Other Observable Inputs (Level 2) [Member] | Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0
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		0		0	[9]
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		0		$ 0	[9]
Long Island Electric Utility Servco LLC Pension and OPEB [Member] | Pension And OPEB Plans Level 3 [Member] | Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 0

[1] Excludes net receivables of $10 million and $15 million as of December 31, 2020 and 2019, respectively, which consist of interest, dividends and receivables and payables related to pending securities sales and purchases. In addition, the table excludes cash and foreign currency of $1 million and $5 million as of December 31, 2020 and 2019, respectively.

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

[3] 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).

[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, U.S. 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 quotes for similar securities which are a Level 2 measure.

[6] Certain commingled equity funds are not included in 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 the frequency of publishing NAV (monthly). 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 Morgan Stanley Capital International Index.

[7] The unlisted real estate fund invests in office, apartment, industrial and retail space. The fund is valued using the NAV per unit of funds. The investment value of the real estate properties is determined on a quarterly basis by independent market appraisers engaged by the board of directors of the fund. The ability to redeem funds is subject to the availability of cash arising from net investment income, allocations and the sale of investments in the normal course of business. The fund’s NAV is published quarterly. In addition, redemptions require one quarter advance notice prior to redemption and are fulfilled quarterly. The fund, therefore, does not meet the definition of readily determinable fair value. The purpose of the fund is to acquire, own, hold for investment and ultimately dispose of investments in real estate and real estate-related assets with the intention of achieving current income, capital appreciation or both.

[8] Private equity investments primarily include various limited partnerships that invest in either operating companies through acquisitions or developing a portfolio of non-U.S. distressed investments to maximize total return on capital. These investments are valued at NAV (or its equivalent) on a quarterly 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 are not included in the fair value hierarchy in accordance with the guidance on NAV practical expedient.

[9] 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).