Investment Securities (Trading) (Details) - USD ($) $ in Millions |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] | |||
| Net proceeds from sales of trading securities | $ 0 | $ 0 | $ 170 |
| U.S. Treasury bonds | |||
| Schedule of Trading Securities and Other Trading Assets [Line Items] | |||
| Net proceeds from sales of trading securities | 170 | ||
| Realized gain (loss) | $ 1 | ||