Quarterly Results (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jul. 01, 2017	Apr. 01, 2017	Dec. 31, 2016	Oct. 01, 2016	Jul. 02, 2016	Apr. 02, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Operating revenues	$ 387.0	$ 348.5	$ 349.7	$ 340.6	$ 395.3	$ 345.0	$ 371.4	$ 360.6	$ 1,425.8	$ 1,472.3	$ 1,559.0
Gross profit (loss)	80.9	85.1	76.1	88.1	114.0	80.8	91.1	89.9
Income (loss) from continuing operations	60.0	22.0	(8.3)	10.3	(3.0)	6.6	6.5	20.2	84.0	30.3	(151.6)
Income (loss) from discontinued operations, net of tax	(1.4)	0.3	(0.7)	7.1	(83.1)	(4.7)	(3.5)	(6.6)	5.3	(97.9)	34.6
Net income (loss)	58.6	22.3	(9.0)	17.4	(86.1)	1.9	3.0	13.6	89.3	(67.6)	(117.0)
Less: Net loss attributable to noncontrolling interests	0.0	0.0	0.0	0.0	0.0	0.0	(1.0)	0.6	0.0	(0.4)	(34.3)
Net income (loss) attributable to SPX Corporation common shareholders	58.6	22.3	(9.0)	17.4	(86.1)	1.9	4.0	13.0	89.3	(67.2)	(82.7)
Adjustment related to redeemable noncontrolling interest	0.0	0.0	0.0	0.0	0.0	0.0	(18.1)	0.0	0.0	(18.1)	0.0
Net income (loss) attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest	$ 58.6	$ 22.3	$ (9.0)	$ 17.4	$ (86.1)	$ 1.9	$ (14.1)	$ 13.0	$ 89.3	$ (85.3)	$ (82.7)
Basic income (loss) per share of common stock:
Continuing operations (in dollars per share)	$ 1.41	$ 0.51	$ (0.19)	$ 0.24	$ (0.07)	$ 0.16	$ (0.25)	$ 0.47	$ 1.98	$ 0.30	$ (2.90)
Discontinued operations, net of tax (in dollars per share)	(0.03)	0.01	(0.02)	0.17	(1.99)	(0.12)	(0.09)	(0.16)	0.13	(2.35)	0.87
Net income (loss) per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)	1.38	0.52	(0.21)	0.41	(2.06)	0.04	(0.34)	0.31	2.11	(2.05)	(2.03)
Diluted income (loss) per share of common stock:
Continuing operations (in dollars per share)	1.35	0.50	(0.19)	0.24	(0.07)	0.16	(0.25)	0.47	1.91	0.30	(2.90)
Discontinued operations, net of tax (in dollars per share)	(0.03)	0.01	(0.02)	0.16	(1.99)	(0.12)	(0.09)	(0.16)	0.12	(2.32)	0.87
Net income (loss) per share attributable to SPX Corporation common shareholders after adjustment related to redeemable noncontrolling interest (in dollars per share)	$ 1.32	$ 0.51	$ (0.21)	$ 0.40	$ (2.06)	$ 0.04	$ (0.34)	$ 0.31	$ 2.03	$ (2.02)	$ (2.03)