Quarterly report pursuant to Section 13 or 15(d)

Summary of Significant Accounting Policies - Investments in Affiliates and Other Entities (Detail)

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Summary of Significant Accounting Policies - Investments in Affiliates and Other Entities (Detail)
$ in Millions
3 Months Ended
Sep. 30, 2018
USD ($)
Water and Gas Pipeline Infrastructure Contractor  
Summary Of Significant Accounting Policies [Line Items]  
Equity interest acquired 30.00%
Cash subscription price $ 22.2
Capital for Infrastructure Projects  
Summary Of Significant Accounting Policies [Line Items]  
Capital provided to investors 80.0
Infrastructure Investors Partnership | Capital for Infrastructure Projects  
Summary Of Significant Accounting Policies [Line Items]  
Capital provided to investors $ 1,000.0