CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (LOSS) (Unaudited) - USD ($) shares in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017	Jun. 30, 2018	Jul. 01, 2017
Income Statement [Abstract]
Revenues	$ 379.2	$ 349.7	$ 731.1	$ 690.3
Costs and expenses:
Cost of products sold	281.5	273.6	543.3	526.1
Selling, general and administrative	72.6	70.3	141.2	138.6
Intangible amortization	0.8	0.1	1.0	0.3
Special charges, net	1.6	0.5	3.6	1.0
Operating income	22.7	5.2	42.0	24.3
Other income (expense), net	2.2	(3.2)	3.2	(5.2)
Interest expense	(5.1)	(4.6)	(9.4)	(8.6)
Interest income	0.3	0.3	0.8	0.7
Income (loss) from continuing operations before income taxes	20.1	(2.3)	36.6	11.2
Income tax provision	(0.4)	(6.0)	(4.5)	(9.2)
Income (loss) from continuing operations	19.7	(8.3)	32.1	2.0
Income (loss) from discontinued operations, net of tax	0.0	0.0	0.0	0.0
Gain (loss) on disposition of discontinued operations, net of tax	3.3	(0.7)	3.3	6.4
Income (loss) from discontinued operations, net of tax	3.3	(0.7)	3.3	6.4
Net income (loss)	$ 23.0	$ (9.0)	$ 35.4	$ 8.4
Basic income (loss) per share of common stock:
Income (loss) from continuing operations attributable to SPX Corporation common shareholders (in dollars per share)	$ 0.46	$ (0.19)	$ 0.75	$ 0.05
Income (loss) from discontinued operations attributable to SPX Corporation common shareholders (in dollars per share)	0.08	(0.02)	0.08	0.15
Net income (loss) per share attributable to SPX Corporation common shareholders (in dollars per share)	$ 0.54	$ (0.21)	$ 0.83	$ 0.20
Weighted-average number of common shares outstanding — basic	42,988	42,388	42,881	42,249
Diluted income (loss) per share of common stock:
Income (loss) from continuing operations attributable to SPX Corporation common shareholders (in dollars per share)	$ 0.44	$ (0.19)	$ 0.72	$ 0.04
Income (loss) from discontinued operations attributable to SPX Corporation common shareholders (in dollars per share)	0.07	(0.02)	0.07	0.15
Net income (loss) per share attributable to SPX Corporation common shareholders (in dollars per share)	$ 0.51	$ (0.21)	$ 0.79	$ 0.19
Weighted-average number of common shares outstanding — diluted	44,723	42,388	44,545	43,622
Comprehensive income (loss)	$ 20.0	$ (8.9)	$ 36.8	$ 7.5