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Commitments and Contingencies - Additional Information (Details)
$ in Millions
12 Months Ended
Dec. 31, 2018
USD ($)
Lease_Renewal_Option
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Sale Leaseback Transaction [Line Items]      
Net assets of subsidiaries subject to restrictions $ 2,262 $ 1,691  
Aggregate statutory capital and surplus 2,388    
Required minimum statutory capital surplus 1,040    
Rental expense related to leases $ 62 75 $ 64
Minimum      
Sale Leaseback Transaction [Line Items]      
Operating lease terms 5 years    
Operating lease renewal options | Lease_Renewal_Option 1    
Maximum      
Sale Leaseback Transaction [Line Items]      
Operating lease terms 10 years    
Operating lease renewal options | Lease_Renewal_Option 2    
Parent Company      
Sale Leaseback Transaction [Line Items]      
Cash, cash equivalents, and investments $ 170 $ 696