Retirement Benefits (Plan Target and Actual Asset Allocation) (Details)	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Equity securities \| All Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Target Mix	33.00%	37.00%
Actual Mix	34.00%	37.00%
Equity securities \| Postretirement Health Care Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Target Mix	37.00%	36.00%
Actual Mix	37.00%	37.00%
Fixed income securities \| All Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Target Mix	46.00%	45.00%
Actual Mix	47.00%	44.00%
Fixed income securities \| Postretirement Health Care Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Target Mix	43.00%	42.00%
Actual Mix	43.00%	41.00%
Cash and other investments \| All Pension Benefit Plans
Defined Benefit Plan Disclosure [Line Items]
Target Mix	21.00%	18.00%
Actual Mix	19.00%	19.00%
Cash and other investments \| Postretirement Health Care Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Target Mix	20.00%	22.00%
Actual Mix	20.00%	22.00%

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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- Definition

Target allocation 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

Reference 2: 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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- Definition

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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(1)
-URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920

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