Pension and Other Post-Retirement Benefit Plans (Savings Plans) (Details) - Non-Qualified Plan $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation, non-current	$ 29.4
Employer matching contributions	20.3
Employer contributions	12.5
Defined benefit plan, equity securities, common stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation plan assets	25.1
Asset held in trust
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Deferred compensation plan assets	$ 4.8

Defined Contribution Plan, Employer Matching Contribution, Amount

No definition available.

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- Definition

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements payable beyond one year (or the operating cycle, if longer).

+ References

No definition available.

+ Details

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- Definition

Carrying amount as of the balance sheet date of assets held under deferred compensation agreements.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.17)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

+ Details

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- Definition

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.

+ Details

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