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Investments (Concentrations of Credit Risk & Securities Lending - Narrative) (Details) - USD ($)
3 Months Ended
Mar. 31, 2019
Dec. 31, 2018
Securities Financing Transaction [Line Items]    
Investments in any counterparty that were greater than 10% of equity $ 0 $ 0
Securities holdings exposure in single issuer greater than stated percentage of Company's equity 10.00%  
Securities Investment    
Securities Financing Transaction [Line Items]    
Percentage of Reinvestment Portfolio in Fixed Maturity Securities 53.00%  
Estimated fair value    
Securities Financing Transaction [Line Items]    
Cash collateral on deposit from counterparties $ 1,500,000,000  
Estimated fair value | U.S. government and agency    
Securities Financing Transaction [Line Items]    
Percentage Of US Treasury And Agency Securities At Estimated Fair Value Of Securities On Loan Relating To Cash Collateral On Open 100.00%