v3.8.0.1
Investments (Other Trading Account Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost $ 21,364 $ 21,407
Fair Value [1] 22,097 21,840
Fixed maturities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 19,841 19,655
Fair Value 20,209 19,850
Equity securities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 1,278 1,097
Fair Value 1,643 1,335
Other trading account assets    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Fair Value 5,752 5,764
Other trading account assets | Short-term investments and cash equivalents    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 25 26
Fair Value 25 26
Other trading account assets | Fixed maturities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 3,509 3,634
Fair Value 3,507 3,453
Other trading account assets | Equity securities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 1,007 985
Fair Value 1,155 1,056
Other trading account assets | Other Assets    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 6 4
Fair Value 7 5
Other trading account assets | Subtotal other trading account assets excluding derivative    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 4,547 4,649
Fair Value 4,694 4,540
Other trading account assets | Derivative Instruments    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Fair Value $ 1,058 $ 1,224
[1] See Note 5 for details of balances associated with variable interest entities.