Commitments, Contingencies and Guarantees (Narrative) (Details) - USD ($) $ in Millions |
Dec. 31, 2020 |
Dec. 31, 2019 |
|---|---|---|
| Commitments and Contingencies Disclosure [Abstract] | ||
| Loss Contingency, Range of Possible Loss, Portion Not Accrued | $ 20 | |
| Long-term Purchase Commitment [Line Items] | ||
| Fannie Mae DUS Servicing Portfolio, Amount | 4,500 | $ 3,900 |
| Maximum Quantifiable Fannie Mae DUS Loss Share Guarantee | 1,500 | 1,300 |
| Estimated Fair Value of the Fannie Mae DUS Loss Share Guarantee | 5 | $ 4 |
| Loss Contingency, Range of Possible Loss, Portion Not Accrued | $ 20 |