v3.8.0.1
Investments (Trading Account Assets Supporting Insurance Liabilities) (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
Short-term investments and cash equivalents    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 245 655
Fair Value 245 655
Corporate securities | Fixed maturities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 13,816 13,903
Fair Value 14,073 13,997
Commercial mortgage-backed securities | Fixed maturities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 2,294 2,032
Fair Value 2,311 2,052
Residential mortgage-backed securities | Fixed maturities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 961 1,142
Fair Value 966 1,150
Asset-backed securities | Fixed maturities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 1,363 1,333
Fair Value 1,392 1,349
Foreign government bonds | Fixed maturities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 1,050 915
Fair Value 1,057 926
U.S. government authorities and agencies and obligations of U.S. states | Fixed maturities    
Schedule of Trading Securities and Other Trading Assets [Line Items]    
Amortized Cost or Cost 357 330
Fair Value $ 410 $ 376
[1] See Note 5 for details of balances associated with variable interest entities.