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Investments - Additional Information (Detail) - USD ($)
3 Months Ended 9 Months Ended 12 Months Ended
Mar. 31, 2014
Dec. 31, 2014
Dec. 31, 2015
Dec. 31, 2013
Schedule of Investments [Line Items]        
Commercial Mortgage Loan   $ 1,139,000,000 $ 1,509,000,000  
Other-than-temporary impairment losses included in accumulated other comprehensive income   0    
Taxable exchanges   3,000,000 72,400,000  
Commercial Mortgage Loans        
Schedule of Investments [Line Items]        
Allowance for credit losses   0 0  
Impaired loans   0 0  
Commitments to fund borrowers troubled debt restructuring   0 0  
Residential mortgage-backed securities ("RMBS")        
Schedule of Investments [Line Items]        
Other-than-temporary impairment losses   $ 0 $ 0  
Predecessor | Residential mortgage-backed securities ("RMBS")        
Schedule of Investments [Line Items]        
Other-than-temporary impairment losses $ 0     $ 2,000