Why Bank Balance Sheets Are Different

Look at a bank drawn to scale and the first thing you notice is that the equity block is almost too thin to label.

That is not a rendering bug. A large US bank runs on roughly ten cents of equity per dollar of assets, where a software company might run on sixty. Draw both at true proportion and they look like different kinds of object, which is most of the argument for drawing them at all.

The thin block is the business, not a warning

A bank borrows short and lends long. It takes money that can be withdrawn on demand and turns it into loans and securities that cannot be called back on demand, and it keeps the difference between what it pays for the first and earns on the second. That spread is thin, so it only produces a meaningful return on equity if the equity is small relative to the assets it supports. Leverage is not a risk a bank has taken on top of its business. Leverage is the business.

Which is why the sliver is regulated rather than left to management. Capital requirements are written as ratios, and the ones that bind are risk-weighted: a book of government bonds and a book of unsecured consumer loans do not consume the same capital at the same dollar size. So the equity block you see drawn against total assets is not the ratio a supervisor is looking at. It is the plain arithmetic one — the things, the claims, and what is left over — and it is the one that tells you how much has to go wrong before the claims exceed the things.

The two big lines run backwards

Deposits are a liability. The money in your current account is owed back to you, so it sits on the claims side. Loans are an asset — a promise of repayment the bank owns. A reader who expects "deposits = money the bank has" reads the whole picture backwards, and it is an easy expectation to hold: in almost every other kind of company, a deposit is something the business received and got to keep.

Once that flips, the rest of the shape follows. Deposits are usually the largest single block on the claims side. Loans are usually the largest on the things side. And the difference between how fast each of those can move is most of what makes a bank a bank.

What else is in there

Loans are not the whole asset side. A bank also carries a securities portfolio, and how it is measured depends on what the bank says it intends to do with it. Securities classified available for sale are carried at fair value, so a fall in market price shows up in the carrying amount. Securities classified held to maturity are carried at amortised cost, on the reasoning that a bond held to the end pays par whatever it traded at in between.

That distinction is invisible in the totals and occasionally enormous. A held-to-maturity book bought at low yields and carried at cost can sit on an unrealised loss the balance sheet does not show, and the loss stays theoretical exactly as long as the bank is never forced to sell. When deposits leave faster than expected, it stops being theoretical. That was the mechanism behind the 2023 US regional bank failures, and none of it was concealed — it was in the notes, in a table, beside a total that did not reflect it.

The lesson is not that the totals lie. It is that a balance sheet is a statement of amounts, and the measurement basis behind an amount is a separate question the totals cannot answer.

Why this breaks most XBRL extractors

A bank files Assets for the consolidated group and again for each segment, and the segment figures for a large institution are themselves larger than most companies' entire balance sheets. Picking the biggest number, or the first one, produces something plausible and wrong. The accounting identity is what settles it: only the consolidated set satisfies A = L + E, so that is the set that gets served. The long version of that argument is its own note.

What to look at

• Deposits as a share of liabilities. A deposit-funded bank and a wholesale-funded one behave very differently under stress. Retail deposits are stickier and cheaper; wholesale funding reprices, and it leaves.
• Loans as a share of assets. The rest is securities, cash and trading positions, and a bank that is mostly securities is running a different business from one that is mostly loans.
• The equity sliver. Ten percent is ordinary. Two percent is a different conversation.

All three are ratios between blocks sitting on the same drawing, which is the point of drawing it. Put JPM next to MSFT and the difference is not a number you have to hold in your head — it is the shape of the picture.