Quarterly Results (Unaudited) (Details) - USD ($)	3 Months Ended
	Dec. 31, 2019	Sep. 28, 2019	Jun. 29, 2019	Mar. 30, 2019	Dec. 31, 2018	Sep. 29, 2018	Jun. 30, 2018	Mar. 31, 2018
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 444,600,000	$ 364,800,000	$ 372,400,000	$ 343,600,000	$ 445,000,000.0	$ 362,500,000	$ 379,200,000	$ 351,900,000
Gross profit (loss)	143,500,000	106,200,000	108,200,000	83,200,000	135,200,000	87,700,000	97,700,000	90,100,000
Income from continuing operations	28,500,000	21,200,000	19,400,000	600,000	39,300,000	6,800,000	19,700,000	12,400,000
Income (loss) from discontinued operations, net of tax	(3,100,000)	300,000	(200,000)	(1,400,000)	(100,000)	(200,000)	3,300,000	0
Net income	25,400,000	21,500,000	19,200,000	(800,000)	39,200,000	6,600,000	23,000,000.0	12,400,000
Less: Net loss attributable to noncontrolling interests	0	0	0	0	0	0	0	0
Net income attributable to SPX Corporation common shareholders	25,400,000	21,500,000	19,200,000	(800,000)	39,200,000	6,600,000	23,000,000.0	12,400,000
Preferred Stock Dividends and Other Adjustments	5,600,000	0	0	0	0	0	0	0
Net income attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest	$ 31,000,000.0	$ 21,500,000	$ 19,200,000	$ (800,000)	$ 39,200,000	$ 6,600,000	$ 23,000,000.0	$ 12,400,000
Basic income (loss) per share of common stock:
Continuing operations (in dollars per share)	$ 0.77	$ 0.48	$ 0.44	$ 0.01	$ 0.91	$ 0.16	$ 0.46	$ 0.29
Discontinued operations, net of tax (in dollars per share)	(0.07)	0.01	0	(0.03)	(0.01)	(0.01)	0.08	0
Net income per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)	0.70	0.49	0.44	(0.02)	0.90	0.15	0.54	0.29
Diluted income (loss) per share of common stock:
Continuing operations (in dollars per share)	0.75	0.47	0.43	0.01	0.88	0.15	0.44	0.28
Discontinued operations, net of tax (in dollars per share)	(0.07)	0.01	0	(0.03)	0	0	0.07	0
Net income per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)	$ 0.68	$ 0.48	$ 0.43	$ (0.02)	$ 0.88	$ 0.15	$ 0.51	$ 0.28
Quarterly Financial Information [Line Items]
Reduction of revenue	$ (444,600,000)	$ (364,800,000)	$ (372,400,000)	$ (343,600,000)	$ (445,000,000.0)	$ (362,500,000)	$ (379,200,000)	$ (351,900,000)
Recognized pre-tax actuarial losses	10,000,000.0				6,600,000
Gain on change in fair value of equity security			1,600,000	6,300,000
Recorded charges related to asbestos product liability matters	$ 8,300,000				$ 2,400,000
Balcke Durr
Quarterly Financial Information [Line Items]
Gain (loss) on disposition of discontinued operations, net of tax							$ 3,800,000
South Africa | Large Power Projects | Reportable and other operating segments | All Other | Revisions in estimates for large power projects
Quarterly Financial Information Disclosure [Abstract]
Operating revenues			(6,000,000.0)	(17,500,000)
Quarterly Financial Information [Line Items]
Reduction of revenue			6,000,000.0	$ 17,500,000
Alstom GE | South Africa | Large Power Projects | Reportable and other operating segments | All Other | Revisions in estimates for large power projects
Quarterly Financial Information Disclosure [Abstract]
Operating revenues			(6,000,000.0)
Quarterly Financial Information [Line Items]
Reduction of revenue			$ 6,000,000.0