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Investments (Evaluation of Available-For-Sale Securities for OTTI and Evaluating Temporarily Impaired AFS Securities - Narrative) (Details)
$ in Millions
3 Months Ended
Mar. 31, 2018
USD ($)
Contracts
Dec. 31, 2017
USD ($)
Schedule of Available-for-sale Securities [Line Items]    
Equity 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 $ (1,500)  
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 3,400  
Gross Unrealized Temporary Loss 1,847 $ 1,468
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, Less than 12 Months, Accumulated Loss $ 85  
Number of Securities | Contracts 28  
External Credit Rating, Non Investment Grade | 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, Less than 12 Months, Accumulated Loss $ 45  
Number of Securities | Contracts 17  
Percentage of gross unrealized loss 53.00%  
External Credit Rating, Investment Grade | 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, Less than 12 Months, Accumulated Loss $ 40  
Number of Securities | Contracts 11  
Percentage of gross unrealized loss 47.00%