- Industry Segments Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net Sales:
Net sales	$ 917.7	$ 950.5	$ 948.3	$ 852.3	$ 854.2	$ 907.4	$ 908.8	$ 834.8	$ 3,668.8	$ 3,505.2	$ 3,390.4
Operating Income:
Operating Income									503.7	477.8	474.6
Interest expense									(44.9)	(43.4)	(31.0)
Loss on extinguishment of debt									(10.1)	0.0	0.0
Income before income taxes									443.1	430.4	418.6
Assets:
Assets	3,720.6				3,525.0				3,720.6	3,525.0	3,208.7
Capital Expenditures:
Capital expenditures									79.7	67.2	77.1
Depreciation and Amortization:
Depreciation and amortization									99.8	92.3	85.2
Electrical
Net Sales:
Net sales									2,532.8	2,460.2	2,388.3
Operating Income:
Operating Income									282.5	267.4	279.0
Power
Net Sales:
Net sales									1,136.0	1,045.0	1,002.1
Operating Income:
Operating Income									221.2	210.4	195.6
Operating Segments | Electrical
Assets:
Assets	2,344.7				2,246.0				2,344.7	2,246.0	2,120.9
Capital Expenditures:
Capital expenditures									48.0	43.4	47.9
Depreciation and Amortization:
Depreciation and amortization									65.7	61.2	56.2
Operating Segments | Power
Assets:
Assets	1,102.2				911.5				1,102.2	911.5	839.7
Capital Expenditures:
Capital expenditures									29.0	22.7	28.4
Depreciation and Amortization:
Depreciation and amortization									34.1	31.1	29.0
Segment Reconciling Items
Operating Income:
Interest expense									(44.9)	(43.4)	(31.0)
Investment income and other expense, net									(5.6)	(4.0)	(25.0)
General Corporate
Assets:
Assets	$ 273.7				$ 367.5				273.7	367.5	248.1
Capital Expenditures:
Capital expenditures									$ 2.7	$ 1.1	$ 0.8