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Debt (Narrative) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Debt Disclosure [Abstract]    
Federal Home Loan Bank stock $ 5  
Federal Home Loan Bank, advances, general debt obligations, maximum amount available 111  
Federal Home Loan Bank, advances, branch of FHLB Bank, amount of advances 0 $ 0
Line of credit, current borrowing capacity 250  
Additional borrowing capacity available 100  
Line of credit, minimum net worth required for compliance 8,700  
Line of credit, amount outstanding $ 0 $ 0