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 |