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Investments (Fixed Maturity Securities Pledged And Received As Collateral) (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2020
Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]    
Document Period End Date Mar. 31, 2020  
Collateral Fixed Maturity Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale Securities, Amortized Cost Basis $ 142 $ 113
Available-for-sale Securities 154 116
Collateral Received Fixed Maturity Securities [Member]    
Debt Securities, Available-for-sale [Line Items]    
Available-for-sale Securities 1,172 727
Reported Value Measurement [Member]    
Debt Securities, Available-for-sale [Line Items]    
Assets Held-in-trust 27,080 27,290
Estimate of Fair Value Measurement [Member]    
Debt Securities, Available-for-sale [Line Items]    
Assets Held-in-trust $ 27,441 $ 29,239