RELATED PARTY TRANSACTIONS RELATED PARTY TRANSACTIONS - OTHER TRANSACTIONS (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
WBS
Related party transactions
Billings from related parties	$ 45.7	$ 36.2	$ 82.4	$ 70.5
Related Party Transaction, Charges To Related Party	3.9	1.9	13.3	4.4
Proceeds received for the transfer of certain software to WBS	0.9		7.3
ATC
Related party transactions
Billings from related parties	27.7	25.4	55.4	50.7
Related Party Transaction, Charges To Related Party	$ 2.0	2.2	$ 4.0	4.6
Equity method investment, ownership interest (as a percent)	34.00%		34.00%
WRPC
Related party transactions
Related Party Transaction, Charges To Related Party	$ 0.2	0.2	$ 0.3	0.5
Related Party Transaction, Purchases from Related Party	0.9	1.1	1.9	2.1
WPS Investments, LLC
Related party transactions
Equity earnings from WPSI	$ 1.8	$ 2.0	$ 4.1	$ 4.3
Equity method investment, ownership interest (as a percent)	10.70%		10.70%

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3602-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.12)
-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 03
-Paragraph 9
-Article 5

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Paragraph 11
-Article 7

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 850
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6457730&loc=d3e39549-107864

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