Derivative Financial Instruments - Counterparty Credit Risk and Credit-Risk Related Contingent Features (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative contracts
Counterparty credit risk adjustments	$ 0.1	$ 0.0	$ 0.2
Credit-risk-related contingent features
Aggregate fair value of derivative instruments in a net liability position	4.5	8.8
Collateral posted for derivatives in a net liability position	4.8	$ 12.1
Interest rate swaps
Derivative contracts
Collateral thresholds for derivative agreements with credit risk related contingent features	$ 0.5

Represents the collateral threshold for derivative instruments with credit-risk-related contingent features.

No definition available.

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- Definition

Amount of net credit risk valuation adjustment during the period to derivative assets and derivative liabilities to properly reflect the credit quality of the counterparties.

+ References

No definition available.

+ Details

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- Definition

The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

+ Details

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Period Type:	instant

- 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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- Definition

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5624258-113959

+ Details

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Balance Type:	credit
Period Type:	instant

- Details

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