Consolidated Variable Interest Entities and Investments in Affiliates - Additional Information (Detail) $ in Millions	Sep. 30, 2017 USD ($) Entity	Dec. 31, 2016 USD ($) Entity
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Number of consolidated VIEs | Entity	3	3
Debt of unconsolidated joint ventures | $	$ 862	$ 861