The largest bank in the U.S. hit a milestone during the first quarter, crossing $3 trillion in assets for the first time. JPMorgan Chase & Co.'s assets surged by almost 17% between Dec. 31, 2019, and March 31, 2020, based on GAAP financials.

The other Big Three banks also saw their balance sheets grow larger, with Citigroup Inc. passing $2.0 trillion in assets for the first time since the first quarter of 2010.

Banks were expected to report bigger balance sheets due to interventions by bank regulators as well as commercial borrowers tapping credit lines.

At JPMorgan, loans only accounted for a portion of the growth, increasing by $45.5 billion, or 4.80%, during the period. According to the bank's first-quarter financial supplement, other balance sheet items that saw high growth included JPMorgan's deposits with banks, investment securities and "other assets."

On the liability side, JPMorgan's deposits also jumped by a huge amount, rising by $273.58 billion, or 17.5%. That compares to average growth in prior quarters of just 1.0%.

JPMorgan CFO Jennifer Piepszak attributed some of the increase in deposits to "clients drawing on their credit lines and holding their cash with us as they look to secure liquidity," according to comments made during the company's April 14 call to discuss earnings.

While $3 trillion in assets is high compared to other banks that report under GAAP, U.S. accounting standards understate total assets compared to other standards implemented around the globe. If JPMorgan reported under IFRS accounting instead of GAAP, its assets would have totaled more than $3 trillion for at least the last several years. A large part of the difference is that under GAAP, banks report the net value of derivatives, but under IFRS, they report the gross value of derivatives.

Based on each bank's reporting standards, just four banks in the world had more than US$3 trillion in assets at the end of 2019, and they were all located in China and reporting under IFRS: Industrial & Commercial Bank of China Ltd., China Construction Bank Corp., Agricultural Bank of China Ltd. and Bank of China Ltd.