v3.8.0.1
Fair Value of Assets and Liabilities (Quantitative Info for Level 3 Inputs) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Fair Value Quantiative Information [Line Items]    
Future policy benefits $ 257,317 $ 240,908
Fair Value, Measurements, Recurring    
Fair Value Quantiative Information [Line Items]    
Future policy benefits $ 8,720 8,238
Level 3 | Minimum    
Fair Value Quantiative Information [Line Items]    
Fair Value Inputs, Policyholder Age 35 years  
Level 3 | Minimum | Future policy benefits    
Fair Value Quantiative Information [Line Items]    
Mortality rate 0.00%  
Level 3 | Maximum    
Fair Value Quantiative Information [Line Items]    
Fair Value Inputs, Policyholder Age 90 years  
Level 3 | Fair Value, Measurements, Recurring    
Fair Value Quantiative Information [Line Items]    
Future policy benefits $ 8,720 $ 8,238
Level 3 | Internal | Minimum | Discounted cash flow | Future policy benefits    
Fair Value Quantiative Information [Line Items]    
Lapse rate 1.00% 0.00%
Spread over LIBOR 0.12% 0.25%
Utilization rate 52.00% 52.00%
Withdrawal rate (greater than maximum range) 78.00% 78.00%
Mortality rate 0.00% 0.00%
Equity volatility curve 13.00% 16.00%
Level 3 | Internal | Minimum | Discounted cash flow | Corporate securities    
Fair Value Quantiative Information [Line Items]    
Discount rate 0.65% 0.70%
Level 3 | Internal | Minimum | Discounted cash flow | Separate Accounts Commercial Mortgage Loan    
Fair Value Quantiative Information [Line Items]    
Fair value inputs credit risk 1.08% 1.19%
Level 3 | Internal | Minimum | Market comparables | Corporate securities    
Fair Value Quantiative Information [Line Items]    
EBITDA multiples 7.4 4.0
Level 3 | Internal | Minimum | Liquidation | Corporate securities    
Fair Value Quantiative Information [Line Items]    
Liquidation value 13.10% 15.19%
Level 3 | Internal | Maximum | Discounted cash flow | Future policy benefits    
Fair Value Quantiative Information [Line Items]    
Lapse rate 12.00% 13.00%
Spread over LIBOR 1.10% 1.50%
Utilization rate 97.00% 96.00%
Withdrawal rate (greater than maximum range) 100.00% 100.00%
Mortality rate 14.00% 14.00%
Equity volatility curve 24.00% 25.00%
Level 3 | Internal | Maximum | Discounted cash flow | Corporate securities    
Fair Value Quantiative Information [Line Items]    
Discount rate 22.00% 20.00%
Level 3 | Internal | Maximum | Discounted cash flow | Separate Accounts Commercial Mortgage Loan    
Fair Value Quantiative Information [Line Items]    
Fair value inputs credit risk 2.78% 2.90%
Level 3 | Internal | Maximum | Market comparables | Corporate securities    
Fair Value Quantiative Information [Line Items]    
EBITDA multiples 7.4 4.0
Level 3 | Internal | Maximum | Liquidation | Corporate securities    
Fair Value Quantiative Information [Line Items]    
Liquidation value 25.00% 98.68%
Level 3 | Internal | Weighted Average | Discounted cash flow | Corporate securities    
Fair Value Quantiative Information [Line Items]    
Discount rate 7.20% 7.12%
Level 3 | Internal | Weighted Average | Discounted cash flow | Separate Accounts Commercial Mortgage Loan    
Fair Value Quantiative Information [Line Items]    
Fair value inputs credit risk 1.20% 1.37%
Level 3 | Internal | Weighted Average | Market comparables | Corporate securities    
Fair Value Quantiative Information [Line Items]    
EBITDA multiples 7.4 4.0
Level 3 | Internal | Weighted Average | Liquidation | Corporate securities    
Fair Value Quantiative Information [Line Items]    
Liquidation value 14.68% 91.72%
Level 3 | Internal | Fair Value, Measurements, Recurring | Future policy benefits    
Fair Value Quantiative Information [Line Items]    
Future policy benefits $ 8,720 $ 8,238
Level 3 | Internal | Fair Value, Measurements, Recurring | Corporate securities    
Fair Value Quantiative Information [Line Items]    
Corporate securities 1,352 1,848
Level 3 | Internal | Fair Value, Measurements, Recurring | Separate Accounts Commercial Mortgage Loan    
Fair Value Quantiative Information [Line Items]    
Commercial mortgage loans $ 821 $ 971