Retirement Benefits (Schedule Of Allocation Of Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
DB Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,546	$ 2,247	$ 2,305
DB Pension Plans | Plan Assets Excluding Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,293	1,246
DB Pension Plans | Plan Assets Excluding Pooled Funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	684	794
DB Pension Plans | Plan Assets Excluding Pooled Funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	609	452
DB Pension Plans | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	44	242
DB Pension Plans | Cash and short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	44	242
DB Pension Plans | U.S. government and agencies securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	66	11
DB Pension Plans | U.S. government and agencies securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	66	11
DB Pension Plans | Corporate debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	493	400
DB Pension Plans | Corporate debt | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	493	400
DB Pension Plans | State and municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17	6
DB Pension Plans | State and municipal bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	17	6
DB Pension Plans | Foreign corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33	35
DB Pension Plans | Foreign corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33	35
DB Pension Plans | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	640	552
DB Pension Plans | Mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	640	552
DB Pension Plans | Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,253	1,001
OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,509	1,280	$ 1,420
OPEB Plan | Plan Assets Excluding Pooled Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	865	734
OPEB Plan | Plan Assets Excluding Pooled Funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	777	671
OPEB Plan | Plan Assets Excluding Pooled Funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	88	63
OPEB Plan | Cash and short-term investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	36
OPEB Plan | Cash and short-term investments | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	36
OPEB Plan | U.S. government and agencies securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	2
OPEB Plan | U.S. government and agencies securities | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	10	2
OPEB Plan | Corporate debt
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	71	55
OPEB Plan | Corporate debt | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	71	55
OPEB Plan | State and municipal bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	1
OPEB Plan | State and municipal bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	1
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	55	41
OPEB Plan | Common stocks | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55	41
OPEB Plan | Mutual funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	713	594
OPEB Plan | Mutual funds | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	713	594
OPEB Plan | Pooled funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 644	$ 546