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Summary of Significant Accounting Policies - Investments in Affiliates and Other Entities (Detail) $ in Millions | 3 Months Ended
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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

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