Brief Exercise 17-15 (Algo) Postretirement benefits; changes in the APBO [LO17-11) On January 1, 2021, Medical Transport Company's accumulated postretirement benefit obligation was $120 million. At the end of 2021, retiree benefits paid were $13 million Service cost for 2021 is $10 million Assumptions regarding the trend of future health care costs were revised at the end of 2021, causing the actuary to revise downward the estimate of the APBO by $7 million. The actuary's discount rate is 5% Determine the amount of the accumulated postretirement benefit obligation at December 31, 2021. APBO million