Goodwill (Details) $ in Millions	6 Months Ended
Jun. 30, 2016 USD ($)
Goodwill
Accumulated impairment losses	$ 0.0
Changes to our goodwill balances by segment
Goodwill balance as of January 1, 2016	3,023.5
Adjustment to Integrys purchase price allocation	22.7
Goodwill balance as of June 30, 2016	3,046.2
Wisconsin
Changes to our goodwill balances by segment
Goodwill balance as of January 1, 2016	2,109.5
Adjustment to Integrys purchase price allocation	(5.2)
Goodwill balance as of June 30, 2016	2,104.3
Wisconsin \| Integrys
Changes to our goodwill balances by segment
Goodwill balance as of June 30, 2016	1,662.4
Illinois
Changes to our goodwill balances by segment
Goodwill balance as of January 1, 2016	731.2
Adjustment to Integrys purchase price allocation	27.5
Goodwill balance as of June 30, 2016	758.7
Other States
Changes to our goodwill balances by segment
Goodwill balance as of January 1, 2016	182.8
Adjustment to Integrys purchase price allocation	0.4
Goodwill balance as of June 30, 2016	$ 183.2

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

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Amount of accumulated impairment loss for an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a,h)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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Amount of increase (decrease) from adjustments after acquisition date under purchase accounting of an asset representing the future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 16
-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e961-128460

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

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