Commitments and Contingencies - Outstanding Capital Commitments Associated with Investments in Unconsolidated Affiliates (Parenthetical) (Detail) $ in Millions	6 Months Ended
Jun. 30, 2016 USD ($)
Other Commitments, Engineering, Procurement and Construction Electric Transmission Project [Member] \| Corporate Joint Venture [Member]
Other Commitments [Line Items]
Return of capital from unconsolidated affiliates anticipated for 2017	$ 43.8

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

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