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Investments - Other Investments - Additional Information (Detail)
Dec. 31, 2020
USD ($)
Venture
Investment
Dec. 31, 2019
USD ($)
Schedule of Equity Method Investments [Line Items]    
Assets $ 22,400,000 $ 40,000,000.0
Non controlling interest certified low-income housing developments | Investment 8  
Liabilities $ 16,098,700,000 14,419,300,000
Other Investments [Member]    
Schedule of Equity Method Investments [Line Items]    
Assets 3,900,000 $ 4,500,000
Other Investments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]    
Schedule of Equity Method Investments [Line Items]    
Assets 4,800,000  
Liabilities $ 500,000  
Other Investments [Member] | Four Venture Capital Funds [Member]    
Schedule of Equity Method Investments [Line Items]    
Non controlling interest in venture capital funds number | Venture 4  
Assets $ 3,900,000  
Other Investments [Member] | Eight Certified Low Income Housing Developments [Member] | Variable Interest Entity, Not Primary Beneficiary [Member]    
Schedule of Equity Method Investments [Line Items]    
Carrying value of investments $ 0