SHAREHOLDERS' EQUITY AND STOCK-BASED COMPENSATION (Details 6) - USD ($) $ in Millions	3 Months Ended					9 Months Ended		12 Months Ended
	Sep. 26, 2015	Jun. 27, 2015	Sep. 27, 2014	Jun. 28, 2014	Mar. 29, 2014	Sep. 26, 2015	Sep. 27, 2014	Dec. 31, 2014
Changes in Equity
Equity, beginning of period	$ 1,749.9		$ 2,249.0		$ 2,167.3	$ 1,811.9	$ 2,167.3	$ 2,167.3
Net income (loss)	(130.6)		63.6			(104.3)	428.7
Net unrealized gains (losses) on qualifying cash flow hedges, net of tax provision of $0.1 and $0.3 for the three months ended June 27, 2015 and June 28, 2014, respectively and $0.7 and $0.1 for the six months June 27, 2015 and June 28, 2014, respectively	0.3		(0.3)			0.2	(0.4)
Net unrealized gains (losses) on qualifying cash flow hedges, tax provision	0.4		0.1			0.3	0.0
Net unrealized gains (losses) on available-for-sale securities							3.7
Pension and postretirement liability adjustment, net of tax benefit (provision) of $0.1 for the three months ended June 27, 2015 and $0.1 and $(2.3) for the six months ended June 27, 2015 and June 28, 2014, respectively	0.4		(0.1)			0.1	5.0
Pension and postretirement liability adjustment, tax benefit (provision)	0.3					0.2	2.3
Foreign currency translation adjustments	(40.6)		(115.5)			(129.7)	(126.4)
Total comprehensive income (loss), net	(170.5)		(52.3)			(233.7)	310.6
Dividends declared	0.0		(15.9)	$ (16.1)	(16.3)	(30.9)	(48.3)
Incentive plan activity	3.8		3.8			12.8	21.9
Stock-based compensation expense	6.8		4.7			35.9	34.0
Restricted stock and restricted stock unit vesting, net of tax withholdings, and related tax (provision) benefit of $(0.1) and $0.4 for the three months ended June 27, 2015 and June 28, 2014, respectively and $0.3 and $9.2 for the six months ended June 27, 2015 and June 28, 2014, respectively	(0.4)		(1.0)			(6.2)	(22.4)
Restricted stock and restricted stock unit vesting, net of tax withholdings, tax (provision) benefit	0.0		0.3			0.3	9.5
Common stock repurchases			(139.9)				(414.3)
Dividends attributable to noncontrolling interests						(0.2)
Other changes in noncontrolling interests			(0.8)				(1.2)
Spin-Off of FLOW Business	(1,270.5)		0.0
Equity, end of period	319.1	$ 1,749.9	2,047.6	2,249.0		319.1	2,047.6	1,811.9
Discontinued operations
Changes in Equity
Stock-based compensation expense		1.3		1.1		5.4	4.2
Restatement Adjustment
Changes in Equity
Equity, beginning of period	9.2		7.4		4.7	9.2	4.7	4.7
Net income (loss)			(0.2)				(2.9)
Equity, end of period		9.2		7.4				9.2
SPX Corporation Shareholders' Equity
Changes in Equity
Equity, beginning of period	1,752.1		2,236.4		2,153.3	1,808.7	2,153.3	2,153.3
Net income (loss)	(105.0)		63.3			(73.2)	430.0
Net unrealized gains (losses) on qualifying cash flow hedges, net of tax provision of $0.1 and $0.3 for the three months ended June 27, 2015 and June 28, 2014, respectively and $0.7 and $0.1 for the six months June 27, 2015 and June 28, 2014, respectively	0.3		(0.3)			0.2	(0.4)
Net unrealized gains (losses) on available-for-sale securities							3.7
Pension and postretirement liability adjustment, net of tax benefit (provision) of $0.1 for the three months ended June 27, 2015 and $0.1 and $(2.3) for the six months ended June 27, 2015 and June 28, 2014, respectively	0.4		(0.1)			0.1	5.0
Foreign currency translation adjustments	(41.5)		(115.3)			(130.9)	(126.8)
Total comprehensive income (loss), net	(145.8)		(52.4)			(203.8)	311.5
Dividends declared	0.0		(15.9)			(30.9)	(48.3)
Incentive plan activity	3.8		3.8			12.8	21.9
Stock-based compensation expense	6.8		4.7			35.9	34.0
Restricted stock and restricted stock unit vesting, net of tax withholdings, and related tax (provision) benefit of $(0.1) and $0.4 for the three months ended June 27, 2015 and June 28, 2014, respectively and $0.3 and $9.2 for the six months ended June 27, 2015 and June 28, 2014, respectively	(0.4)		(1.0)			(6.2)	(22.4)
Common stock repurchases			(139.9)				(414.3)
Spin-Off of FLOW Business	(1,259.8)
Equity, end of period	356.7	1,752.1	2,035.7	2,236.4		356.7	2,035.7	1,808.7
SPX Corporation Shareholders' Equity | Restatement Adjustment
Changes in Equity
Equity, beginning of period	9.2		7.4		4.7	9.2	4.7	4.7
Equity, end of period		9.2		7.4				9.2
Noncontrolling Interests
Changes in Equity
Equity, beginning of period	(2.2)		12.6		$ 14.0	3.2	14.0	14.0
Net income (loss)	(25.6)		0.3			(31.1)	(1.3)
Foreign currency translation adjustments	0.9		(0.2)			1.2	0.4
Total comprehensive income (loss), net	(24.7)		0.1			(29.9)	(0.9)
Dividends attributable to noncontrolling interests						(0.2)
Other changes in noncontrolling interests			(0.8)				(1.2)
Spin-Off of FLOW Business	(10.7)
Equity, end of period	$ (37.6)	$ (2.2)	$ 11.9	$ 12.6		$ (37.6)	$ 11.9	$ 3.2