Deposits - Additional Information (Details) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Deposits [Abstract] | ||
| Certificates of deposits of $250,000 or more, maturities within one year | $ 270 | $ 230 |
| Certificates of deposits of $250,000 or more, maturities after one year | 26 | 58 |
| Certificates of deposits of $250,000 or more, total | 296 | 288 |
| Certificates of deposit of less than $ 250,000, maturities within one year | 699 | 543 |
| Certificates of deposit of less than $ 250,000, maturities after one year | 42 | 70 |
| Certificates of deposit of less than $250,000, total | $ 741 | $ 613 |