Business Acquisitions - Pro-forma Nonrecurring Adjustments (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	$ 100.3	$ 79.1	$ 158.6	$ 141.9
Diluted (USD per share)	$ 1.82	$ 1.43	$ 2.87	$ 2.56
Aclara | Acquisition-related costs, current period
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	$ 0.3	$ (0.3)	$ 10.6	$ (10.6)
Diluted (USD per share)	$ 0.00	$ 0.00	$ 0.16	$ (0.15)
Aclara | Acquisition-related costs, prior period
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	$ 0.0	$ 0.0	$ 0.0	$ (7.1)
Diluted (USD per share)	$ 0.00	$ 0.00	$ 0.00	$ (0.10)
Aclara | Intangible amortization and inventory step up amortization
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	$ (1.0)	$ (9.9)	$ 0.6	$ (26.8)
Diluted (USD per share)	$ (0.01)	$ (0.11)	$ 0.01	$ (0.30)
Aclara | Interest expense
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income (loss)	$ 0.6	$ (7.1)	$ (1.5)	$ (14.3)
Diluted (USD per share)	$ 0.01	$ (0.08)	$ (0.02)	$ (0.16)