Quarterly Results (Unaudited) - Quarterly Information (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
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 350.0	$ 285.7	$ 296.6	$ 287.2	$ 348.3	$ 267.8	$ 257.3	$ 254.7	$ 1,219.5	$ 1,128.1	$ 1,123.6
Gross profit	129.3	95.8	102.3	104.4	123.5	92.1	89.4	90.5
Income from continuing operations, net of tax	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
Basic income (loss) per share of common stock:
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
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 (loss) per share of common stock:
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
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