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Significant Subsequent Events - Additional information (Detail) - Subsequent Events [member] - USD ($)
$ in Millions
1 Months Ended
Mar. 31, 2019
Jan. 31, 2019
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]    
Investment in common stock   $ 4,500
Prepaid establishment charges $ 838  
Top of Range [Member]    
Disclosure Of Nonadjusting Events After Reporting Period [Line Items]    
Ownership interest in associates   45.00%