Business Acquisitions - Pro-forma Nonrecurring Adjustments (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)		$ 113.6	$ 80.8	$ 272.2	$ 222.7
Diluted (USD per share)		$ 2.06	$ 1.47	$ 4.93	$ 4.02
Aclara | Acquisition-related costs, current period
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	[1]	$ 1.5	$ (1.5)	$ 12.1	$ (12.1)
Diluted (USD per share)	[1]	$ 0.02	$ (0.02)	$ 0.18	$ (0.16)
Aclara | Acquisition-related costs, prior period
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	[1]			$ 0.0	$ (7.1)
Diluted (USD per share)	[1]			$ 0.00	$ (0.10)
Aclara | Intangible amortization and inventory step up amortization
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	[2]	$ (1.9)	$ (10.0)	$ (1.3)	$ (36.8)
Diluted (USD per share)	[2]	$ (0.03)	$ (0.11)	$ (0.02)	$ (0.41)
Aclara | Interest expense
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	[3]	$ 4.6	$ (8.0)	$ 3.1	$ (22.3)
Diluted (USD per share)	[3]	$ 0.06	$ (0.09)	$ 0.04	$ (0.25)

[1] Aclara transaction costs incurred in the three and nine months ended September 30, 2018 have been reclassified into the comparable pro-forma September 30, 2017 period. The pro-forma nine months ended September 30, 2017 period also includes transaction costs incurred by the Company during the fourth quarter of 2017.

[2] Aclara intangible amortization and inventory step up amortization incurred in three and nine months ended September 30, 2018 has been reclassified into the comparable pro-forma September 30, 2017 period and, in the nine month period, increased to reflect the assumption the transaction was completed on January 1, 2017. The pro-forma September 30, 2018 periods include the intangible amortization that would be incurred assuming the transaction had been completed on January 1, 2017.

[3] Interest expense incurred in the three and nine months ended September 30, 2018, reflecting amounts incurred from the date of the acquisition, has been reclassified into the pro-forma September 30, 2017 period and, in the nine month period, increased to reflect the assumption the transaction was completed on January 1, 2017. The pro-forma September 30, 2018 period includes the interest expense that would have been incurred assuming the transaction had been completed on January 1, 2017.