| December 31, | December 31, | |||
| 2013 | 2012 | |||
| (dollars in millions) | ||||
| Commercial Paper: | ||||
| Balance at period-end | $ | 8 | $ | 306 |
| Average balance(1) | $ | 155 | $ | 479 |
| Weighted average interest rate on period-end balance(2) | 10.4% | 10.1% | ||
| Other Short-Term Borrowings(3)(4): | ||||
| Balance at period-end | $ | 2,134 | $ | 1,832 |
| Average balance(1) | $ | 1,872 | $ | 1,461 |
(1) Average balances are calculated based upon weekly balances.
(2) The weighted average interest rates at December 31, 2013 and 2012 were driven primarily by commercial paper issued in a foreign country in which typical funding rates are significantly higher than in the U.S.
(3) These borrowings included bank loans, bank notes and structured notes with original maturities of 12 months or less.
(4) Certain structured short-term borrowings are carried at fair value under the fair value option. See Note 4 for additional information.