Industry Segments and Geographic Area Information - Industry Segments Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Net Sales:
Net sales	$ 1,144.1	$ 1,179.7	$ 1,166.7	$ 991.2	$ 917.7	$ 950.5	$ 948.3	$ 852.3	$ 4,481.7	$ 3,668.8	$ 3,505.2
Operating Income:
Operating Income									556.9	518.8	489.8
Interest expense									(72.4)	(44.9)	(43.4)
Loss on extinguishment of debt									0.0	10.1	0.0
Investment income and other expense, net									(17.5)	(20.7)	(16.0)
Income before income taxes									467.0	443.1	430.4
Assets:
Assets	4,872.1				3,720.6				4,872.1	3,720.6	3,525.0
Capital Expenditures:
Capital expenditures									96.2	79.7	67.2
Depreciation and Amortization:
Depreciation and amortization									148.4	98.2	90.9
Electrical
Net Sales:
Net sales									2,660.6	2,532.8	2,460.2
Operating Income:
Operating Income									320.8	294.0	276.4
Depreciation and Amortization:
Depreciation and amortization									61.4	64.7	60.2
Power
Net Sales:
Net sales									1,821.1	1,136.0	1,045.0
Operating Income:
Operating Income									236.1	224.8	213.4
Depreciation and Amortization:
Depreciation and amortization									87.0	33.5	30.7
Operating Segments | Electrical
Assets:
Assets	2,228.5				2,344.7				2,228.5	2,344.7	2,246.0
Capital Expenditures:
Capital expenditures									53.0	48.0	43.4
Operating Segments | Power
Assets:
Assets	2,395.8				1,102.2				2,395.8	1,102.2	911.5
Capital Expenditures:
Capital expenditures									36.8	29.0	22.7
General Corporate
Assets:
Assets	$ 247.8				$ 273.7				247.8	273.7	367.5
Capital Expenditures:
Capital expenditures									$ 6.4	$ 2.7	$ 1.1