Retirement Benefits (Schedule Of Allocation Of Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 3,402	$ 2,546	$ 2,247
DB Pension Plans | Plan Assets Excluding Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,828	1,293
DB Pension Plans | Plan Assets Excluding Pooled Funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,086	684
DB Pension Plans | Plan Assets Excluding Pooled Funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	742	609
DB Pension Plans | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	115	44
DB Pension Plans | Cash and short-term investments | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	115	44
DB Pension Plans | U.S. government and agencies securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	150	66
DB Pension Plans | U.S. government and agencies securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	150	66
DB Pension Plans | Corporate debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	540	493
DB Pension Plans | Corporate debt | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	540	493
DB Pension Plans | State and municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	17
DB Pension Plans | State and municipal bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	17
DB Pension Plans | Foreign corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41	33
DB Pension Plans | Foreign corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	41	33
DB Pension Plans | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	971	640
DB Pension Plans | Mutual funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	971	640
DB Pension Plans | Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,574	1,253
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,645	1,509	$ 1,280
OPEB Plan | Plan Assets Excluding Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	995	865
OPEB Plan | Plan Assets Excluding Pooled Funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	906	777
OPEB Plan | Plan Assets Excluding Pooled Funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	89	88
OPEB Plan | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33	9
OPEB Plan | Cash and short-term investments | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33	9
OPEB Plan | U.S. government and agencies securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18	10
OPEB Plan | U.S. government and agencies securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18	10
OPEB Plan | Corporate debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64	71
OPEB Plan | Corporate debt | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64	71
OPEB Plan | State and municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	2
OPEB Plan | State and municipal bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	2
OPEB Plan | Foreign corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	5
OPEB Plan | Foreign corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5	5
OPEB Plan | Common stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	66	55
OPEB Plan | Common stocks | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	66	55
OPEB Plan | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	807	713
OPEB Plan | Mutual funds | Fair Value, Inputs, Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	807	713
OPEB Plan | Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 650	$ 644