Debt Securities (Narrative) (Details) $ in Millions |
Dec. 31, 2020
USD ($)
security
|
Dec. 31, 2019
USD ($)
security
|
|---|---|---|
| Debt Securities, Available-for-sale [Line Items] | ||
| Pledged Assets Separately Reported, Securities Pledged as Collateral, at Fair Value | $ 10,300 | $ 8,300 |
| Number of individual positions in unrealized loss position | security | 129 | 500 |
| US Treasury Securities [Member] | ||
| Debt Securities, Available-for-sale [Line Items] | ||
| Pledged Assets Separately Reported, Securities Pledged as Collateral, at Fair Value | $ 24 | $ 24 |