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Investments (Evaluation of Available-For-Sale Securities for OTTI and Evaluating Temporarily Impaired AFS Securities - Narrative) (Details)
$ in Millions
12 Months Ended
Dec. 31, 2017
USD ($)
Contracts
Schedule of Available-for-sale Securities [Line Items]  
Fixed securities available-for-sale with gross unrealized loss of equal to or greater than stated percentage 20.00%
Fixed maturity securities  
Schedule of Available-for-sale Securities [Line Items]  
Change in Gross Unrealized Temporary Loss $ 573
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss 349
20% or more | Six months or greater | Fixed maturity securities  
Schedule of Available-for-sale Securities [Line Items]  
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss $ 5
Number of Securities | Contracts 10
20% or more | Six months or greater | Fixed maturity securities | External Credit Rating, Investment Grade  
Schedule of Available-for-sale Securities [Line Items]  
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss $ 2