v3.8.0.1
Certain Long-Duration Contracts With Guarantees (Separate Account Investment Options) (Details) - Annuity Contracts - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Separate Account Investment Options $ 158,510 $ 146,578
Equity funds    
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Separate Account Investment Options 93,798 86,751
Bond funds    
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Separate Account Investment Options 58,939 48,789
Balanced funds    
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Separate Account Investment Options 1,382 914
Money market funds    
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]    
Separate Account Investment Options $ 4,391 $ 10,124