Commitments and Contingencies - Environmental Matters (Details) - Manufactured Gas Plant Remediation [Member] - Natural Gas Utility - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Manufactured Gas Plant Remediation
Regulatory Asset Recovery of Remediation Expenditures	$ 676.2	$ 45.9
Accrual for Environmental Loss Contingencies	$ 611.3	$ 32.6

Total costs accrued as of the balance sheet date for environmental loss contingencies.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 30

-Section 50

-Paragraph 7

-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13207-110859

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 25

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6395460&loc=d3e13647-108346

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