Employee Benefit Plans Employee Benefit Plans 6 (Details)	Dec. 31, 2017	Dec. 31, 2016
Pension Benefits
Employee benefit plans
Actual asset allocations	100.00%	100.00%
Target asset allocations	100.00%
Pension Benefits \| Equity securities
Employee benefit plans
Actual asset allocations	57.00%	57.00%
Target asset allocations	60.00%
Pension Benefits \| Debt securities
Employee benefit plans
Actual asset allocations	39.00%	38.00%
Target asset allocations	40.00%
Pension Benefits \| Real Estate Funds
Employee benefit plans
Actual asset allocations	4.00%	5.00%
Pension Benefits \| Cash equivalents
Employee benefit plans
Actual asset allocations	0.00%	0.00%
Post-Retirement Medical Benefits
Employee benefit plans
Actual asset allocations	100.00%	100.00%
Target asset allocations	100.00%
Post-Retirement Medical Benefits \| Equity securities
Employee benefit plans
Actual asset allocations	59.00%	58.00%
Target asset allocations	60.00%
Post-Retirement Medical Benefits \| Debt securities
Employee benefit plans
Actual asset allocations	37.00%	39.00%
Target asset allocations	40.00%
Post-Retirement Medical Benefits \| Real Estate Funds
Employee benefit plans
Actual asset allocations	0.00%	0.00%
Post-Retirement Medical Benefits \| Cash equivalents
Employee benefit plans
Actual asset allocations	4.00%	3.00%

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- Definition

Percentage of target investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan.

+ 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)(5)(i)
-URI http://asc.fasb.org/extlink&oid=82843861&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=82843861&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=82843861&loc=d3e1928-114920

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