[tadd]

Tobra:
Post office would be in the black if it weren't for having have cash on hand for retirements that are a decade away.

In 2016, the USPS had its fifth straight annual operating loss, in the amount of $5.59 billion, of which $5.8 billion was the accrual of unpaid mandatory retiree health payments.

From here:
"United States Postal Service FY2016 Annual Report to Congress". United States Postal Service. Retrieved 28 January 2017.

I think they will have met that congressionally mandated figure very soon. IIRC it was a 20 year process. ADDED NOTE: it was 10 years and last year was the 10 year mark. So they no longer have to squirrel away >$5B every year now.