Debt Securities (Narrative) (Details) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
|
Dec. 31, 2017
USD ($)
|
Dec. 31, 2019
USD ($)
security
|
Dec. 31, 2018
USD ($)
security
|
|
| Debt Securities, Available-for-sale [Line Items] | |||
| Pledged Assets Separately Reported, Securities Pledged as Collateral, at Fair Value | $ 8,300 | $ 7,900 | |
| Number of individual positions in unrealized loss position | security | 500 | 1,379 | |
| Trading Securities, Realized Gain (Loss) | $ 3 | ||
| US Treasury Securities [Member] | |||
| Debt Securities, Available-for-sale [Line Items] | |||
| Pledged Assets Separately Reported, Securities Pledged as Collateral, at Fair Value | $ 24 | $ 24 |