Restructuring Costs - Summary of Costs (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs		$ 12.0	$ 20.3	$ 35.0
Expected Costs		75.2
Cost incurred to date		12.0	20.3	35.0
Remaining costs		7.9
Withdrawal from Multiemployer Defined Benefit Plan
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	$ 12.5
Remaining costs		23.0
2018 Restructuring Actions
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs		12.7
Expected Costs		20.5
Cost incurred to date		12.7	0.0	0.0
Remaining costs		7.8
2017 Restructuring Actions
Restructuring Cost and Reserve [Line Items]
Expected Costs		13.4
Cost incurred to date		(0.7)	14.0	0.0
Remaining costs		0.1
2016 Restructuring Actions
Restructuring Cost and Reserve [Line Items]
Expected Costs		41.3
Cost incurred to date		0.0	6.3	35.0
Remaining costs		0.0
2016 Restructuring Actions | Withdrawal from Multiemployer Defined Benefit Plan
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs	$ 12.5
Electrical
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs		8.3	16.9	33.9
Electrical | 2018 Restructuring Actions
Restructuring Cost and Reserve [Line Items]
Expected Costs		14.6
Cost incurred to date		8.6	0.0	0.0
Remaining costs		6.0
Electrical | 2017 Restructuring Actions
Restructuring Cost and Reserve [Line Items]
Expected Costs		10.3
Cost incurred to date		(0.3)	10.6	0.0
Remaining costs		0.0
Electrical | 2016 Restructuring Actions
Restructuring Cost and Reserve [Line Items]
Expected Costs		40.2
Cost incurred to date		0.0	6.3	33.9
Remaining costs		0.0
Electrical | 2016 Restructuring Actions | Withdrawal from Multiemployer Defined Benefit Plan
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs				12.5
Power
Restructuring Cost and Reserve [Line Items]
Pre-tax restructuring costs		3.7	3.4	1.1
Power | 2018 Restructuring Actions
Restructuring Cost and Reserve [Line Items]
Expected Costs		5.9
Cost incurred to date		4.1	0.0	0.0
Remaining costs		1.8
Power | 2017 Restructuring Actions
Restructuring Cost and Reserve [Line Items]
Expected Costs		3.1
Cost incurred to date		(0.4)	3.4	0.0
Remaining costs		0.1
Power | 2016 Restructuring Actions
Restructuring Cost and Reserve [Line Items]
Expected Costs		1.1
Cost incurred to date		0.0	$ 0.0	$ 1.1
Remaining costs		$ 0.0