Restructuring Costs - By Segment (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	$ 20.3	$ 35.0	$ 23.6
Cost of goods sold
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	13.7	27.5	15.3
Selling & administrative expense
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	6.6	7.5	8.3
Electrical
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	16.9	33.9	21.7
Electrical | Cost of goods sold
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	11.5	27.3	14.5
Electrical | Selling & administrative expense
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	5.4	6.6	7.2
Power
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	3.4	1.1	1.9
Power | Cost of goods sold
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	2.2	0.2	0.8
Power | Selling & administrative expense
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	$ 1.2	$ 0.9	$ 1.1