Inventories, Net - Reported under LIFO and FIFO (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
Consolidated Statement of Operations
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
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
Adjustment related to redeemable noncontrolling interest									0.0	0.0	5.6
Net income attributable to SPX Corporation common stockholders after adjustment related to redeemable noncontrolling interest									$ 425.4	$ 99.0	$ 70.9
Basic income (loss) 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
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
Gain (loss) from discontinued operations, net of tax (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
Total comprehensive income									$ 440.8	$ 103.2	$ 64.7
Inventories, net	$ 189.8				$ 155.0				189.8	155.0
Assets of discontinued operations	0.0				124.4				0.0	124.4
Deferred and other income taxes	31.3				26.6				31.3	26.6
Non-current liabilities of discontinued operations	0.0				31.4				0.0	31.4
Retained deficit	(51.8)				(477.2)				(51.8)	(477.2)
As Computed under LIFO
Consolidated Statement of Operations
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
Loss from discontinued operations, net of tax									368.5	25.1	(11.0)
Net income									$ 418.8	$ 97.2	65.3
Adjustment related to redeemable noncontrolling interest											5.6
Net income attributable to SPX Corporation common stockholders after adjustment related to redeemable noncontrolling interest											$ 70.9
Basic income (loss) 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
Diluted income per share of common stock:
Income from continuing operations, net of tax (in dollars per share)									1.08	1.57	1.70
Gain (loss) from discontinued operations, net of tax (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
Total comprehensive income									$ 434.3	$ 101.4	$ 64.7
Inventories, net	166.3				143.1				166.3	143.1
Assets of discontinued operations					121.6					121.6
Deferred and other income taxes	25.3				23.5				25.3	23.5
Non-current liabilities of discontinued operations					30.7					30.7
Retained deficit	(69.3)				(488.1)				(69.3)	(488.1)
Effect of Change
Consolidated Statement of Operations
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
Loss from discontinued operations, net of tax									(2.1)	0.1	0.0
Net income									$ 6.6	$ 1.8	0.0
Adjustment related to redeemable noncontrolling interest											0.0
Net income attributable to SPX Corporation common stockholders after adjustment related to redeemable noncontrolling interest											$ 0.0
Basic income (loss) 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
Diluted 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
Inventories, net	23.5				11.9				23.5	11.9
Assets of discontinued operations					2.8					2.8
Deferred and other income taxes	6.0				3.1				6.0	3.1
Non-current liabilities of discontinued operations					0.7					0.7
Retained deficit	$ 17.5				$ 10.9				$ 17.5	$ 10.9