Commitments - Extensions of Credit (Details) - USD ($) $ in Millions |
Mar. 31, 2018 |
Dec. 31, 2017 |
|---|---|---|
| Extended lines of credit | ||
| Commitments, guarantees: | ||
| Unused amounts in lines of credit to third-party entities and commitments for future financing to clients | $ 7,909 | $ 8,111 |
| Financing for client purchase agreements | ||
| Commitments, guarantees: | ||
| Unused amounts in lines of credit to third-party entities and commitments for future financing to clients | $ 3,357 | $ 3,569 |