Property, Plant and Equipment (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Non Utility Plant Net Book Value	$ 247.8
Depreciation	503.4	$ 501.5	$ 475.1
Capitalized Computer Software, Gross	159.5	189.0
Capitalized Computer Software, Amortization	$ 54.1	$ 44.0	$ 41.4

Non Utility Plant Net Book Value

No definition available.

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- Definition

Amount of expense for amortization of capitalized computer software costs.

+ References

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-Publisher FASB
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-Topic 985
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- Definition

Amount before accumulated amortization of capitalized costs for computer software, including but not limited to, acquired and internally developed computer software.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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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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