Business Acquisitions - Pro-forma Nonrecurring Adjustments (Details) - USD ($) $ / shares in Units, $ 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
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income	$ 88.0	$ 113.6	$ 100.3	$ 58.3	$ 20.4	$ 80.8	$ 79.1	$ 62.8	$ 360.2	$ 243.1	$ 293.0
Diluted (USD per share)	$ 1.60	$ 2.06	$ 1.82	$ 1.05	$ 0.37	$ 1.47	$ 1.43	$ 1.13	$ 6.54	$ 4.39	$ 5.24
Aclara | Aclara transaction costs incurred in 2018
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income									$ 12.8	$ (12.8)
Diluted (USD per share)									$ 0.19	$ (0.16)
Aclara | Intangible amortization and inventory step up
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income									$ 1.3	$ (44.3)
Diluted (USD per share)									$ 0.02	$ (0.50)
Aclara | Interest expense
Business Acquisition, Pro Forma Information, Nonrecurring Adjustment [Line Items]
Net income									$ 3.8	$ (27.6)
Diluted (USD per share)									$ 0.05	$ (0.31)