Supplemental Guarantor Information - Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ in Millions	1 Months Ended	9 Months Ended		12 Months Ended
	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Operating activities
Net cash provided by (used for) operating activities		$ 284.6	$ 361.8
Investing activities
Capital expenditures		(33.8)	(25.4)
Proceeds from sale of property and equipment		(0.4)	3.2
(Payments due to) proceeds from the sale of businesses, net		(12.8)	2,764.0
Acquisitions, net of cash acquired		(0.9)	(45.9)
Net intercompany loan activity		0.0	0.0
Net cash provided by (used for) investing activities of continuing operations		(47.9)	2,695.9
Net cash provided by (used for) investing activities of discontinued operations		(7.1)	(41.3)
Net cash provided by (used for) investing activities		(55.0)	2,654.6
Financing activities
Net receipts of short-term borrowings		0.0	(0.8)
Net receipts (repayments) of commercial paper and revolving long-term debt		46.0	(842.3)
Repayments of long-term debt		(675.1)	(2,009.3)
Debt issuance costs		(2.0)	0.0
Premium paid on early extinguishment of debt		(16.0)	(94.9)
Transfer of cash to nVent		(74.2)	0.0
Distribution of cash from nVent	$ 993.6	993.6	0.0
Net change in advances to subsidiaries		0.0	0.0
Shares issued to employees, net of shares withheld		16.0	34.3
Repurchases of ordinary shares		(400.0)	(100.0)
Dividends paid		(156.7)	(188.9)
Net cash provided by (used for) financing activities of continuing operations		(268.4)	(3,201.9)
Change in cash held for sale		27.0	(5.6)
Effect of exchange rate changes on cash and cash equivalents		(9.8)	55.5
Change in cash and cash equivalents		(21.6)	(135.6)
Cash and cash equivalents, beginning of period		86.3	216.9	$ 216.9
Cash and cash equivalents, end of period		64.7		86.3
Parent Company Guarantor
Operating activities
Net cash provided by (used for) operating activities		180.9	356.3
Investing activities
Capital expenditures		0.0	0.0
Proceeds from sale of property and equipment		0.0	0.0
(Payments due to) proceeds from the sale of businesses, net		0.0	0.0
Acquisitions, net of cash acquired		0.0	0.0
Net intercompany loan activity		0.0	0.0
Net cash provided by (used for) investing activities of continuing operations		0.0	0.0
Net cash provided by (used for) investing activities of discontinued operations		0.0	0.0
Net cash provided by (used for) investing activities		0.0	0.0
Financing activities
Net receipts of short-term borrowings			0.0
Net receipts (repayments) of commercial paper and revolving long-term debt		0.0	0.0
Repayments of long-term debt		0.0	0.0
Debt issuance costs		0.0
Premium paid on early extinguishment of debt		0.0	0.0
Transfer of cash to nVent		0.0
Distribution of cash from nVent		0.0
Net change in advances to subsidiaries		359.9	(101.6)
Shares issued to employees, net of shares withheld		16.0	34.3
Repurchases of ordinary shares		(400.0)	(100.0)
Dividends paid		(156.7)	(188.9)
Net cash provided by (used for) financing activities of continuing operations		(180.8)	(356.2)
Change in cash held for sale		0.0	0.0
Effect of exchange rate changes on cash and cash equivalents		0.0	0.0
Change in cash and cash equivalents		0.1	0.1
Cash and cash equivalents, beginning of period		0.0	0.0	0.0
Cash and cash equivalents, end of period		0.1		0.0
Guarantor Subsidiaries
Operating activities
Net cash provided by (used for) operating activities		269.2	481.8
Investing activities
Capital expenditures		0.0	0.0
Proceeds from sale of property and equipment		0.0	0.0
(Payments due to) proceeds from the sale of businesses, net		0.0	0.0
Acquisitions, net of cash acquired		0.0	0.0
Net intercompany loan activity		24.9	0.0
Net cash provided by (used for) investing activities of continuing operations		24.9	0.0
Net cash provided by (used for) investing activities of discontinued operations		0.0	0.0
Net cash provided by (used for) investing activities		24.9	0.0
Financing activities
Net receipts of short-term borrowings			0.0
Net receipts (repayments) of commercial paper and revolving long-term debt		0.0	0.0
Repayments of long-term debt		0.0	0.0
Debt issuance costs		0.0
Premium paid on early extinguishment of debt		0.0	0.0
Transfer of cash to nVent		0.0
Distribution of cash from nVent		0.0
Net change in advances to subsidiaries		(294.1)	(481.8)
Shares issued to employees, net of shares withheld		0.0	0.0
Repurchases of ordinary shares		0.0	0.0
Dividends paid		0.0	0.0
Net cash provided by (used for) financing activities of continuing operations		(294.1)	(481.8)
Change in cash held for sale		0.0	0.0
Effect of exchange rate changes on cash and cash equivalents		0.0	0.0
Change in cash and cash equivalents		0.0	0.0
Cash and cash equivalents, beginning of period		0.0	0.0	0.0
Cash and cash equivalents, end of period		0.0		0.0
Subsidiary Issuer
Operating activities
Net cash provided by (used for) operating activities		274.7	464.4
Investing activities
Capital expenditures		0.0	0.0
Proceeds from sale of property and equipment		0.0	0.0
(Payments due to) proceeds from the sale of businesses, net		0.0	2,765.6
Acquisitions, net of cash acquired		0.0	0.0
Net intercompany loan activity		(62.0)	119.4
Net cash provided by (used for) investing activities of continuing operations		(62.0)	2,885.0
Net cash provided by (used for) investing activities of discontinued operations		0.0	0.0
Net cash provided by (used for) investing activities		(62.0)	2,885.0
Financing activities
Net receipts of short-term borrowings			0.0
Net receipts (repayments) of commercial paper and revolving long-term debt		65.0	(832.7)
Repayments of long-term debt		(675.1)	(1,917.8)
Debt issuance costs		(2.0)
Premium paid on early extinguishment of debt		(16.0)	(86.0)
Transfer of cash to nVent		0.0
Distribution of cash from nVent		993.6
Net change in advances to subsidiaries		(563.9)	(579.3)
Shares issued to employees, net of shares withheld		0.0	0.0
Repurchases of ordinary shares		0.0	0.0
Dividends paid		0.0	0.0
Net cash provided by (used for) financing activities of continuing operations		(198.4)	(3,415.8)
Change in cash held for sale		0.0	0.0
Effect of exchange rate changes on cash and cash equivalents		(14.2)	66.7
Change in cash and cash equivalents		0.1	0.3
Cash and cash equivalents, beginning of period		0.0	0.0	0.0
Cash and cash equivalents, end of period		0.1		0.0
Non-Guarantor Subsidiaries
Operating activities
Net cash provided by (used for) operating activities		480.5	660.3
Investing activities
Capital expenditures		(33.8)	(25.4)
Proceeds from sale of property and equipment		(0.4)	3.2
(Payments due to) proceeds from the sale of businesses, net		(12.8)	(1.6)
Acquisitions, net of cash acquired		(0.9)	(45.9)
Net intercompany loan activity		618.7	136.0
Net cash provided by (used for) investing activities of continuing operations		570.8	66.3
Net cash provided by (used for) investing activities of discontinued operations		(7.1)	(41.3)
Net cash provided by (used for) investing activities		563.7	25.0
Financing activities
Net receipts of short-term borrowings			(0.8)
Net receipts (repayments) of commercial paper and revolving long-term debt		(19.0)	(9.6)
Repayments of long-term debt		0.0	(91.5)
Debt issuance costs		0.0
Premium paid on early extinguishment of debt		0.0	(8.9)
Transfer of cash to nVent		(74.2)
Distribution of cash from nVent		0.0
Net change in advances to subsidiaries		(1,004.2)	(693.7)
Shares issued to employees, net of shares withheld		0.0	0.0
Repurchases of ordinary shares		0.0	0.0
Dividends paid		0.0	0.0
Net cash provided by (used for) financing activities of continuing operations		(1,097.4)	(804.5)
Change in cash held for sale		27.0	(5.6)
Effect of exchange rate changes on cash and cash equivalents		4.4	(11.2)
Change in cash and cash equivalents		(21.8)	(136.0)
Cash and cash equivalents, beginning of period		86.3	216.9	216.9
Cash and cash equivalents, end of period		64.5		86.3
Consolidation, Eliminations
Operating activities
Net cash provided by (used for) operating activities		(920.7)	(1,601.0)
Investing activities
Capital expenditures		0.0	0.0
Proceeds from sale of property and equipment		0.0	0.0
(Payments due to) proceeds from the sale of businesses, net		0.0	0.0
Acquisitions, net of cash acquired		0.0	0.0
Net intercompany loan activity		(581.6)	(255.4)
Net cash provided by (used for) investing activities of continuing operations		(581.6)	(255.4)
Net cash provided by (used for) investing activities of discontinued operations		0.0	0.0
Net cash provided by (used for) investing activities		(581.6)	(255.4)
Financing activities
Net receipts of short-term borrowings			0.0
Net receipts (repayments) of commercial paper and revolving long-term debt		0.0	0.0
Repayments of long-term debt		0.0	0.0
Debt issuance costs		0.0
Premium paid on early extinguishment of debt		0.0	0.0
Transfer of cash to nVent		0.0
Distribution of cash from nVent		0.0
Net change in advances to subsidiaries		1,502.3	1,856.4
Shares issued to employees, net of shares withheld		0.0	0.0
Repurchases of ordinary shares		0.0	0.0
Dividends paid		0.0	0.0
Net cash provided by (used for) financing activities of continuing operations		1,502.3	1,856.4
Change in cash held for sale		0.0	0.0
Effect of exchange rate changes on cash and cash equivalents		0.0	0.0
Change in cash and cash equivalents		0.0	0.0
Cash and cash equivalents, beginning of period		0.0	$ 0.0	0.0
Cash and cash equivalents, end of period		$ 0.0		$ 0.0