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Contingencies and Commitments - Narrative (Detail) - USD ($)
3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2016
Jun. 30, 2016
Berkadia Commercial Mortgage (investee) [Member]      
Contingencies and Commitments [Line Items]      
Voting interest in investee 50.00% 50.00%  
Commercial paper outstanding $ 1,470,000,000 $ 1,470,000,000  
Berkadia Commercial Mortgage (investee) [Member] | Commercial Paper [Member]      
Contingencies and Commitments [Line Items]      
Maximum outstanding balance of commercial paper borrowings $ 1,500,000,000 $ 1,500,000,000  
Berkadia Commercial Mortgage (investee) [Member] | Leucadia National Corporation (venture partner) [Member]      
Contingencies and Commitments [Line Items]      
Voting interest in investee 50.00% 50.00%  
Berkshire Hathaway Insurance Group [Member]      
Contingencies and Commitments [Line Items]      
Reimbursement rate from joint venture partner of Company's surety bond claim losses   50.00%  
Purchase Agreement [Member] | National Indemnity Company [Member] | Medical Liability Mutual Insurance Company [Member]      
Contingencies and Commitments [Line Items]      
Statutory assets     $ 5,500,000,000
Statutory policyholders' surplus     $ 1,900,000,000
Acquisition price in addition to tangible book value of acquiree $ 100,000,000