Retirement Benefits (Target Allocation Of The Plans' Asset Categories) (Details)	Dec. 31, 2020	Dec. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	100.00%	100.00%
Pension Benefits | Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	1.00%	3.00%
Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	59.00%	57.00%
Pension Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	26.00%	27.00%
Pension Benefits | U.S. small and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	9.00%	7.00%
Pension Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	15.00%	14.00%
Pension Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	9.00%	9.00%
Pension Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	36.00%	36.00%
Pension Benefits | Real estate
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	4.00%	4.00%
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	100.00%	100.00%
Postretirement Benefits | Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	3.00%	1.00%
Postretirement Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	64.00%	65.00%
Postretirement Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	31.00%	31.00%
Postretirement Benefits | U.S. small and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	8.00%	9.00%
Postretirement Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	15.00%	14.00%
Postretirement Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	10.00%	11.00%
Postretirement Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Percentage of Plan Assets at December 31,	33.00%	34.00%
Minimum | Pension Benefits | Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum | Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	51.00%
Minimum | Pension Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	21.00%
Minimum | Pension Benefits | U.S. small and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	3.00%
Minimum | Pension Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	9.00%
Minimum | Pension Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	3.00%
Minimum | Pension Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	35.00%
Minimum | Pension Benefits | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum | Pension Benefits | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum | Postretirement Benefits | Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	0.00%
Minimum | Postretirement Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	55.00%
Minimum | Postretirement Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	23.00%
Minimum | Postretirement Benefits | U.S. small and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	3.00%
Minimum | Postretirement Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	9.00%
Minimum | Postretirement Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%
Minimum | Postretirement Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	33.00%
Maximum | Pension Benefits | Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%
Maximum | Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	61.00%
Maximum | Pension Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	31.00%
Maximum | Pension Benefits | U.S. small and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	13.00%
Maximum | Pension Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	19.00%
Maximum | Pension Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	13.00%
Maximum | Pension Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	45.00%
Maximum | Pension Benefits | Real estate
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	9.00%
Maximum | Pension Benefits | Private equity
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%
Maximum | Postretirement Benefits | Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	7.00%
Maximum | Postretirement Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	65.00%
Maximum | Postretirement Benefits | U.S. large-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	33.00%
Maximum | Postretirement Benefits | U.S. small and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	13.00%
Maximum | Postretirement Benefits | International
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	19.00%
Maximum | Postretirement Benefits | Global
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	15.00%
Maximum | Postretirement Benefits | Debt securities
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	43.00%