Retirement Benefits - Schedule of Assumptions Used to Determine Benefit Obligations (Details)	1 Months Ended	12 Months Ended
Dec. 31, 2015	Dec. 31, 2017	Dec. 31, 2016	Nov. 30, 2015
Medical and Life Insurance Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate		3.37%	3.68%
Ultimate healthcare trend rate	5.00%	5.00%	5.00%	5.00%
Initial healthcare trend rate (pre 65/post 65)		6.50%	7.00%
Year ultimate rate attained (pre 65/post 65)	2021	2021	2021	2021
Qualified Plan \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate		3.59%	4.02%
Nonqualified Plan \| Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate		3.62%	4.07%

Defined Benefit Plan, Benefit Obligation, Health Care Cost Trend Rate Assumed, Next Fiscal Year

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit 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 (k)(1)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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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.

+ References

No definition available.

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- Definition

Ultimate trend rate for health care cost for defined benefit postretirement 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 (l)
-URI http://asc.fasb.org/extlink&oid=82843861&loc=d3e1928-114920

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Year ultimate health care cost trend rate is expected to be reached, in CCYY format.

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

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