Source: Federal Reserve Bank of Philadelphia  

Release: FR Y-14M Large Bank Credit Card and Mortgage Data  

Units:  Billions of U.S. Dollars, Not Seasonally Adjusted

Frequency:  Quarterly, End of Quarter

The total outstanding balance for first-lien closed-end loans secured by 1-4 family residential real estate in which the borrower does not occupy the property but instead holds it as an investment. Includes both first-lien mortgage and first-lien home equity loan balances held in portfolio as of quarter end.

For more detail see the methodology.