Summary of Significant Accounting Policies - Investments in Affiliates and Other Entities (Details) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2014 substation kV km
Water and Gas Pipeline Infrastructure Contractor
Summary Of Significant Accounting Policies [Line Items]
Equity interest acquired				30.00%
Cash subscription price				$ 22.2
Cash dividends			$ 1.1	$ 3.9
Equity Method Investment in Electric Power Infrastructure Services Company
Summary Of Significant Accounting Policies [Line Items]
Equity interest				49.00%
Payment to acquire equity method investments and intangible assets				$ 12.3
Infrastructure Investors Partnership
Summary Of Significant Accounting Policies [Line Items]
Contributions to partnership in connection with certain investments	$ 20.0		20.0
EPC Electric Transmission Project
Summary Of Significant Accounting Policies [Line Items]
Length of electrical transmission line to be constructed under contract | km					500
Number of substations | substation					2
Voltage of substations | kV					500
Deferred earnings recognized		$ 60.3
Gain related to the sale of interest in limited partnership	13.0
Capital for Infrastructure Projects
Summary Of Significant Accounting Policies [Line Items]
Capital commitment	80.0		80.0
Infrastructure Investors Partnership | Capital for Infrastructure Projects
Summary Of Significant Accounting Policies [Line Items]
Capital commitment	$ 1,000.0		$ 1,000.0