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Derivative Instruments and Risk Management Activities - Notional Value of the Annual Expiration of Swaps in Effect (Details) $ in Millions	Dec. 31, 2018 USD ($)
2019
Derivative [Line Items]
Notional amount of swaps expiring	$ 353.0
2020
Derivative [Line Items]
Notional amount of swaps expiring	253.0
2021
Derivative [Line Items]
Notional amount of swaps expiring	111.3
2022
Derivative [Line Items]
Notional amount of swaps expiring	18.1
2023
Derivative [Line Items]
Notional amount of swaps expiring	13.6
2024
Derivative [Line Items]
Notional amount of swaps expiring	$ 4.2

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- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ 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.

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