Hospitals are making a fortune on Wall Street

The nation's largest not-for-profit hospital systems reaped more than $21 billion last year from their Wall Street investments, mergers and other investment options, according to an Axios analysis of financial documents.

Why it matters: Hospitals say they're having trouble staying afloat because insurance programs, namely Medicare and Medicaid, aren't paying them enough. But while their margins on patient care are slim, they've more than made up for it on Wall Street.

Data: Axios review of health system financial documents; Chart: Chris Canipe and Andrew Witherspoon / Axios