Retirement Benefits (Target Allocation Of The Plans' Asset Categories) (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	100.00%	100.00%
Pension Benefits \| Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	0.00%
Maximum Target Allocation	5.00%
Defined Benefit Plan, Actual Plan Asset Allocations	1.00%	1.00%
Pension Benefits \| Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	51.00%
Maximum Target Allocation	61.00%
Defined Benefit Plan, Actual Plan Asset Allocations	57.00%	57.00%
Pension Benefits \| U.S. large capitalization
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	29.00%
Maximum Target Allocation	39.00%
Defined Benefit Plan, Actual Plan Asset Allocations	34.00%	34.00%
Pension Benefits \| U.S. small and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	3.00%
Maximum Target Allocation	13.00%
Defined Benefit Plan, Actual Plan Asset Allocations	9.00%	9.00%
Pension Benefits \| International and emerging markets
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	9.00%
Maximum Target Allocation	19.00%
Defined Benefit Plan, Actual Plan Asset Allocations	14.00%	14.00%
Pension Benefits \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	35.00%
Maximum Target Allocation	45.00%
Defined Benefit Plan, Actual Plan Asset Allocations	37.00%	37.00%
Pension Benefits \| Real estate
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	0.00%
Maximum Target Allocation	9.00%
Defined Benefit Plan, Actual Plan Asset Allocations	5.00%	5.00%
Pension Benefits \| Private equity
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	0.00%
Maximum Target Allocation	5.00%
Defined Benefit Plan, Actual Plan Asset Allocations	1.00%	1.00%
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Plan Asset Allocations	100.00%	100.00%
Postretirement Benefits \| Cash And Cash Equivalents
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	0.00%
Maximum Target Allocation	7.00%
Defined Benefit Plan, Actual Plan Asset Allocations	2.00%	3.00%
Postretirement Benefits \| Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	55.00%
Maximum Target Allocation	65.00%
Defined Benefit Plan, Actual Plan Asset Allocations	63.00%	61.00%
Postretirement Benefits \| U.S. large capitalization
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	34.00%
Maximum Target Allocation	44.00%
Defined Benefit Plan, Actual Plan Asset Allocations	41.00%	40.00%
Postretirement Benefits \| U.S. small and mid-capitalization
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	2.00%
Maximum Target Allocation	12.00%
Defined Benefit Plan, Actual Plan Asset Allocations	8.00%	7.00%
Postretirement Benefits \| International and emerging markets
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	9.00%
Maximum Target Allocation	19.00%
Defined Benefit Plan, Actual Plan Asset Allocations	14.00%	14.00%
Postretirement Benefits \| Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Minimum Target Allocation	33.00%
Maximum Target Allocation	43.00%
Defined Benefit Plan, Actual Plan Asset Allocations	35.00%	36.00%

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Target allocation maximum percentage of investments of this type to total plan assets presented on a weighted average basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
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Target allocation minimum percentage of investments of this type to total plan assets presented on a weighted average basis.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(i)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920

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Percentage of fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of plan assets held.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e2446-114920

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