| Amortized | Gross Unrealized | Fair | ||||||||||||||
| December 31, 2013 | Cost | Gains | Losses | Value | ||||||||||||
| (Dollars in millions) | ||||||||||||||||
| HTM securities: | ||||||||||||||||
| U.S. Treasury securities | $ | 392 | $ | 0 | $ | 8 | $ | 384 | ||||||||
| GSE securities | 5,603 | 2 | 397 | 5,208 | ||||||||||||
| Mortgage-backed securities issued by GSE | 11,636 | 38 | 220 | 11,454 | ||||||||||||
| States and political subdivisions | 33 | 2 | — | 35 | ||||||||||||
| Other securities | 437 | 12 | — | 449 | ||||||||||||
| Total HTM securities | $ | 18,101 | $ | 54 | $ | 625 | $ | 17,530 | ||||||||
| Amortized | Gross Unrealized | Fair | ||||||||||||||
| December 31, 2012 | Cost | Gains | Losses | Value | ||||||||||||
| (Dollars in millions) | ||||||||||||||||
| HTM securities: | ||||||||||||||||
| GSE securities | 3,808 | 17 | 1 | 3,824 | ||||||||||||
| Mortgage-backed securities issued by GSE | 9,273 | 238 | 1 | 9,510 | ||||||||||||
| States and political subdivisions | 34 | 1 | 1 | 34 | ||||||||||||
| Other securities | 479 | 4 | 3 | 480 | ||||||||||||
| Total HTM securities | $ | 13,594 | $ | 260 | $ | 6 | $ | 13,848 | ||||||||