Investment in Joint Venture (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended						3 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 EGS Electrical Group, LLC and subsidiaries ("EGS") M	Dec. 31, 2010 EGS Electrical Group, LLC and subsidiaries ("EGS")	Dec. 31, 2009 EGS Electrical Group, LLC and subsidiaries ("EGS")	Jul. 03, 2010 EGS Electrical Group, LLC and subsidiaries ("EGS") Nutsteel Industria Metalurgica Ltda
Investment in joint venture under equity method investment
Percentage of interest held in joint venture				44.50%
Lag in including results in consolidated statements (in months)				3
Net sales				$ 495.3	$ 445.4	$ 429.4
Gross profit				201.5	189.2	182.3
Net income				63.7	62.7	62.5
Capital expenditures				16.7	11.9	11.8
Depreciation and amortization	87.8	81.9	75.3	10.3	9.6	8.8
Dividends received				29.4	30.3	30.7
Undistributed earnings attributable to SPX Corporation				4.6	5.5	6.8
SPX's equity earnings in EGS	28.4	30.2	29.4	28.7	28.8	28.0
Carrying value of investment				68.9	69.3
Difference between investment in joint venture and proportionate share of joint venture's net assets				85.1
Business acquisitions, net of cash paid	747.5	114.8	131.4				35.4
Contribution made by the entity to the joint venture to acquire new business							15.8
Condensed balance sheet information of EGS
Current assets				179.7	170.2
Non-current assets				342.5	337.5
Current liabilities				128.0	114.2
Non-current liabilities				$ 30.1	$ 29.0