Retirement Benefits (Fair Values Of Pension Benefit Assets And Other Benefit Assets By Asset Category And Level Inputs) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	$ 521	$ 604	$ 663	$ 525
Alternative Investments | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	52	189	221	114
Insurance Company Contracts [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	175	166	173	173
Life Insurance Contracts [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	294	249	269	$ 238
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	2,026	1,818	2,012
Pension Benefits [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	861	671
Pension Benefits [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	890	748
Pension Benefits [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	227	353
Pension Benefits [Member] | U.S. Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	626	488
Pension Benefits [Member] | U.S. Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	626	488
Pension Benefits [Member] | U.S. Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | U.S. Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Foreign Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	197	147
Pension Benefits [Member] | Foreign Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	197	147
Pension Benefits [Member] | Foreign Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Foreign Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	38	36
Pension Benefits [Member] | Mutual Funds [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	38	36
Pension Benefits [Member] | Mutual Funds [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Mutual Funds [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	252	248
Pension Benefits [Member] | Government Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Government Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	252	248
Pension Benefits [Member] | Government Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Corporate Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	339	347
Pension Benefits [Member] | Corporate Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Corporate Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	339	347
Pension Benefits [Member] | Corporate Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Asset-Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	163	153
Pension Benefits [Member] | Asset-Backed Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Asset-Backed Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	163	153
Pension Benefits [Member] | Asset-Backed Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Alternative Investments
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	188	187
Pension Benefits [Member] | Alternative Investments | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Alternative Investments | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	136	0
Pension Benefits [Member] | Alternative Investments | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	52	187
Pension Benefits [Member] | Insurance Company Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	175	166
Pension Benefits [Member] | Insurance Company Contracts [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Insurance Company Contracts [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Pension Benefits [Member] | Insurance Company Contracts [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	175	166
Pension Benefits [Member] | Total Plan Assets Excluding Cash, Investment Income Receivable And Amounts Due (To) From Brokers [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1,978	1,772
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	367	336	$ 356
Other Benefits [Member] | U.S. Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	8	9
Other Benefits [Member] | U.S. Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	8	9
Other Benefits [Member] | U.S. Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | U.S. Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Foreign Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	2	3
Other Benefits [Member] | Foreign Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	2	3
Other Benefits [Member] | Foreign Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Foreign Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Mutual Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	25	27
Other Benefits [Member] | Mutual Funds [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	25	27
Other Benefits [Member] | Mutual Funds [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Mutual Funds [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Government Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	2	3
Other Benefits [Member] | Government Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Government Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	2	3
Other Benefits [Member] | Government Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Corporate Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	4	5
Other Benefits [Member] | Corporate Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Corporate Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	4	5
Other Benefits [Member] | Corporate Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Asset-Backed Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	3	5
Other Benefits [Member] | Asset-Backed Securities [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Asset-Backed Securities [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	3	5
Other Benefits [Member] | Asset-Backed Securities [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Alternative Investments
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1	2
Other Benefits [Member] | Alternative Investments | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Alternative Investments | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	1	0
Other Benefits [Member] | Alternative Investments | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	2
Other Benefits [Member] | Life Insurance Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	294	249
Other Benefits [Member] | Life Insurance Contracts [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Life Insurance Contracts [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Life Insurance Contracts [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	294	249
Other Benefits [Member] | Investment In DOL 103-12 Trust [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	12	10
Other Benefits [Member] | Investment In DOL 103-12 Trust [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Investment In DOL 103-12 Trust [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	12	10
Other Benefits [Member] | Investment In DOL 103-12 Trust [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	0	0
Other Benefits [Member] | Total Plan Assets Excluding Cash, Investment Income Receivable And Amounts Due (To) From Brokers [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	351	313
Other Benefits [Member] | Total Plan Assets Excluding Cash, Investment Income Receivable And Amounts Due (To) From Brokers [Member] | Level I [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	35	39
Other Benefits [Member] | Total Plan Assets Excluding Cash, Investment Income Receivable And Amounts Due (To) From Brokers [Member] | Level II [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	22	23
Other Benefits [Member] | Total Plan Assets Excluding Cash, Investment Income Receivable And Amounts Due (To) From Brokers [Member] | Level III [Member]
Defined Benefit Plan Disclosure [Line Items]
Total pension benefit assets	$ 294	$ 251