Like the other big banks, Bank of America took a hit from the recently enacted tax law, writing down \$2.9 billion primarily in deferred tax assets that declined in value.
JPMorgan earlier reported a \$2.4 billion fourth-quarter loss because of the new tax law, and Citigroup reported a $22 billion loss.
My simple minded expectation is that when you lower a tax rate companies should have more money.
I tried reading about 'deferred tax assets': https://www.investopedia.com/terms/d/deferredtaxasset.asp
Where I found:
The simplest example of a deferred tax asset is the carry-over of losses. If a business incurs a loss in a financial year, it usually is entitled to use that loss in order to lower its taxable income in following years. In that sense, the loss is an asset.
So perhaps there is a place for clever accounting around expenses and taxes. But what is the exact mechanism? Why some companies are reporting loss due to the new US tax law?