Inventories, Net - Consolidated Statement of Operations and Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Oct. 02, 2021	Jul. 03, 2021	Apr. 03, 2021	Dec. 31, 2020	Sep. 26, 2020	Jun. 27, 2020	Mar. 28, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income from continuing operations before income taxes									$ 69.9	$ 78.6	$ 88.8
Income tax provision									(10.9)	(4.8)	(12.5)
Income from continuing operations	$ 4.4	$ 13.9	$ 17.7	$ 23.0	$ 20.5	$ 19.5	$ 19.3	$ 14.5	59.0	73.8	76.3
Less: Gain (loss) from discontinued operations, net of tax	2.0	316.4	44.2	3.8	5.3	3.1	8.2	8.6	366.4	25.2	(11.0)
Net income	$ 6.4	$ 330.3	$ 61.9	$ 26.8	$ 25.8	$ 22.6	$ 27.5	$ 23.1	$ 425.4	$ 99.0	$ 65.3
Basic income per share of common stock:
Income from continuing operations, net of tax (in dollars per share)	$ 0.10	$ 0.31	$ 0.39	$ 0.51	$ 0.46	$ 0.44	$ 0.43	$ 0.33	$ 1.30	$ 1.65	$ 1.74
Gain (loss) from discontinued operations, net of tax (in dollars per share)	0.04	6.98	0.98	0.08	0.11	0.07	0.19	0.19	8.09	0.57	(0.13)
Net income per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)	0.14	7.29	1.37	0.59	0.57	0.51	0.62	0.52	$ 9.39	$ 2.22	$ 1.61
Total comprehensive income									$ 440.8	$ 103.2	$ 64.7
Diluted income per share of common stock:
Income from continuing operations, net of tax (in dollars per share)	0.10	0.30	0.38	0.50	0.44	0.42	0.42	0.32	$ 1.27	$ 1.61	$ 1.70
Income from discontinued operations (in dollars per share)	0.04	6.78	0.95	0.08	0.12	0.07	0.18	0.19	7.88	0.55	(0.12)
Net income per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)	$ 0.14	$ 7.08	$ 1.33	$ 0.58	$ 0.56	$ 0.49	$ 0.60	$ 0.51	$ 9.15	$ 2.16	$ 1.58
Inventories, net	$ 189.8				$ 155.0				$ 189.8	$ 155.0
Deferred and other income taxes	31.3				26.6				31.3	26.6
Retained deficit	(51.8)				(477.2)				(51.8)	(477.2)
As Computed under LIFO
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income from continuing operations before income taxes									58.3	76.3	$ 88.7
Income tax provision									(8.0)	(4.2)	(12.4)
Income from continuing operations									50.3	72.1	76.3
Less: Gain (loss) from discontinued operations, net of tax									368.5	25.1	(11.0)
Net income									$ 418.8	$ 97.2	$ 65.3
Basic income per share of common stock:
Income from continuing operations, net of tax (in dollars per share)									$ 1.11	$ 1.61	$ 1.74
Gain (loss) from discontinued operations, net of tax (in dollars per share)									8.14	0.57	(0.13)
Net income per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)									$ 9.25	$ 2.18	$ 1.61
Total comprehensive income									$ 434.3	$ 101.4	$ 64.7
Diluted income per share of common stock:
Income from continuing operations, net of tax (in dollars per share)									$ 1.08	$ 1.57	$ 1.70
Income from discontinued operations (in dollars per share)									7.93	0.55	(0.12)
Net income per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)									$ 9.01	$ 2.12	$ 1.58
Inventories, net	166.3				143.1				$ 166.3	$ 143.1
Deferred and other income taxes	25.3				23.5				25.3	23.5
Retained deficit	(69.3)				(488.1)				(69.3)	(488.1)
Effect of Change
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Income from continuing operations before income taxes									11.6	2.3	$ 0.1
Income tax provision									(2.9)	(0.6)	(0.1)
Income from continuing operations									8.7	1.7	0.0
Less: Gain (loss) from discontinued operations, net of tax									(2.1)	0.1	0.0
Net income									$ 6.6	$ 1.8	$ 0.0
Basic income per share of common stock:
Income from continuing operations, net of tax (in dollars per share)									$ 0.19	$ 0.04	$ 0
Gain (loss) from discontinued operations, net of tax (in dollars per share)									(0.05)	0	0
Net income per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)									$ 0.14	$ 0.04	$ 0
Total comprehensive income									$ 6.5	$ 1.8	$ 0.0
Diluted income per share of common stock:
Income from continuing operations, net of tax (in dollars per share)									$ 0.19	$ 0.04	$ 0
Income from discontinued operations (in dollars per share)									(0.05)	0	0
Net income per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)									$ 0.14	$ 0.04	$ 0
Inventories, net	23.5				11.9				$ 23.5	$ 11.9
Deferred and other income taxes	6.0				3.1				6.0	3.1
Retained deficit	$ 17.5				$ 10.9				$ 17.5	$ 10.9