Financing (Details) $ in Millions	6 Months Ended
Jun. 30, 2016 USD ($) item
Unsecured revolving credit facility
Schedule of debt instruments
Unsecured revolving credit facility	$ 200.0
Additional borrowing capacity	$ 75.0
Number of extensions \| item	2
Extension period	1 year
Maximum percentage of total indebtedness to total capitalization under the financial covenants of the credit facility agreement	65.00%
Percentage of total indebtedness to total capitalization under the financial covenants of the credit facility agreement	52.00%
Aggregate amount of default on other indebtedness subject to cross-default under the terms of the credit facility.	$ 25.0
Outstanding borrowings	0.0
Swingline loan
Schedule of debt instruments
Unsecured revolving credit facility	20.0
Letters of credit
Schedule of debt instruments
Unsecured revolving credit facility	20.0
Commercial paper
Schedule of debt instruments
Amount of credit facility used to back up outstanding commercial paper borrowings	$ 30.5

Represents the period of extension to the maturity of debt instrument.

No definition available.

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- Definition

Represents the number of extensions to the maturity of debt instrument.

+ References

No definition available.

+ Details

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- Definition

Represents the amount of additional borrowing capacity under the credit facility.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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- Definition

Represents the amount of the borrowing capacity under the credit facility used to back up outstanding commercial paper borrowings.

+ References

No definition available.

+ Details

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- Definition

Represents the aggregate amount of default by the entity on other indebtedness subject to the cross-default provisions of the credit facility agreement.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents of Line Of Credit Facility Debt To Capital Ratio Covenant Compliance

+ References

No definition available.

+ Details

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- Definition

Represents the maximum debt to capital ratio allowable under the financial covenant.

+ References

No definition available.

+ Details

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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 02
-Paragraph 19, 20, 22
-Article 5

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ 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 210.5-02.19(b),22(b))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Balance Type:	credit
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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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- Details

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