Employee Benefits, Estimated Future Benefit Payments (Details) $ in Millions	Dec. 31, 2017 USD ($)
Retirement Plans
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2018	$ 20.2
2019	14.4
2020	13.8
2021	13.0
2022	14.0
2023-2027	61.1
PBOP
Defined Benefit Plan, Expected Future Benefit Payment [Abstract]
2018	2.7
2019	2.7
2020	2.7
2021	2.8
2022	2.6
2023-2027	$ 12.2

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- Definition

Amount of benefits for defined benefit plan expected to be paid in five fiscal years after fifth fiscal year following latest fiscal year.

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

+ Details

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- Definition

Amount of benefits for defined benefit plan expected to be paid in next fiscal year following latest fiscal year.

+ References

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- Definition

Amount of benefits for defined benefit plan expected to be paid in fifth fiscal year following latest fiscal year.

+ References

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- Definition

Amount of benefits for defined benefit plan expected to be paid in fourth fiscal year following latest fiscal year.

+ References

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Amount of benefits for defined benefit plan expected to be paid in third fiscal year following latest fiscal year.

+ References

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Amount of benefits for defined benefit plan expected to be paid in second fiscal year following latest fiscal year.

+ References

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