CONDENSED CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	Common Stock	Paid-In Capital	Retained Deficit	Accum. Other Comprehensive Income	Common Stock In Treasury	SPX Corporation Shareholders’ Equity
Equity, beginning of period at Dec. 31, 2017		$ 0.5	$ 1,309.8	$ (742.3)	$ 250.1	$ (503.4)	$ 314.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 42.0			42.0			42.0
Other comprehensive income (loss), net					0.4		0.4
Incentive plan activity			7.8				7.8
Long-term incentive compensation expense			9.4				9.4
Restricted stock and restricted stock unit vesting			(16.8)			13.2	(3.6)
Stranded income tax effects resulting from tax reform - See Note 2				(4.8)			(4.8)
Equity, end of period at Sep. 29, 2018		0.5	1,310.2	(701.3)	250.5	(490.2)	369.7
Equity, beginning of period at Jun. 30, 2018		0.5	1,305.8	(707.9)	251.5	(491.3)	358.6
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6.6			6.6			6.6
Other comprehensive income (loss), net					(1.0)		(1.0)
Incentive plan activity			2.5				2.5
Long-term incentive compensation expense			3.3				3.3
Restricted stock and restricted stock unit vesting			(1.4)			1.1	(0.3)
Equity, end of period at Sep. 29, 2018		0.5	1,310.2	(701.3)	250.5	(490.2)	369.7
Equity, beginning of period at Dec. 31, 2018	414.9	0.5	1,295.4	(650.1)	244.9	(475.8)	414.9
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	39.9			39.9			39.9
Other comprehensive income (loss), net					(5.0)		(5.0)
Incentive plan activity			10.0				10.0
Long-term incentive compensation expense			8.1				8.1
Restricted stock and restricted stock unit vesting			(22.3)			15.7	(6.6)
Equity, end of period at Sep. 28, 2019	461.3	0.5	1,291.2	(610.2)	239.9	(460.1)	461.3
Equity, beginning of period at Jun. 29, 2019		0.5	1,285.3	(631.7)	242.7	(460.1)	436.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	21.5			21.5			21.5
Other comprehensive income (loss), net					(2.8)		(2.8)
Incentive plan activity			3.1				3.1
Long-term incentive compensation expense			2.8				2.8
Restricted stock and restricted stock unit vesting			0.0			0.0	0.0
Equity, end of period at Sep. 28, 2019	$ 461.3	$ 0.5	$ 1,291.2	$ (610.2)	$ 239.9	$ (460.1)	$ 461.3