NEW YORK -- Citigroup (C.N) lost US$18.3 billion in the fourth quarter as the bank had to take more than US$20 billion in accounting write-downs related to the new tax law.

The bank had a loss of US$7.15 a share, compared with a profit of US$3.57 billion, or US$1.14 a share, in the same period a year ago.

Citigroup wrote off US$19 billion in deferred tax assets, which are credits Citi could have used toward future years. Because the new tax law lowered corporate tax rates, those credits aren't worth as much and Citi, like other major U.S. banks, had to write down their value.

The bank also took a US$3 billion charge for foreign earnings it will bring back to the U.S.

Excluding those charges, Citi earned US$3.7 billion, or US$1.28 a share.