Pension and Other Retirement Plans - Actual Allocations and Target Allocations by Asset Class (Details)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Actual Allocations	100.00%	100.00%
Target Allocations	100.00%	100.00%
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Actual Allocations	52.70%	53.40%
Target Allocations	50.00%	50.00%
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Actual Allocations	40.70%	39.60%
Target Allocations	45.00%	45.00%
Cash and other short-term investments
Defined Benefit Plan Disclosure [Line Items]
Actual Allocations	0.70%	1.00%
Target Allocations	0.00%	0.00%
Other alternative investments
Defined Benefit Plan Disclosure [Line Items]
Actual Allocations	5.90%	6.00%
Target Allocations	5.00%	5.00%

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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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