Lease Commitments - Schedule of Weighted Average Remaining Lease Terms and Discount Rates (Details)	Mar. 31, 2020
Weighted average remaining lease term (years):
Operating leases	6 years 4 months 6 days
Financing leases	5 years 6 months 25 days
Weighted average discount rate:
Operating leases	3.92%
Financing leases	3.52%
PNM
Weighted average remaining lease term (years):
Operating leases	6 years 6 months 18 days
Financing leases	5 years 6 months 10 days
Weighted average discount rate:
Operating leases	3.92%
Financing leases	3.57%
TNMP
Weighted average remaining lease term (years):
Operating leases	3 years 11 months 23 days
Financing leases	5 years 8 months 4 days
Weighted average discount rate:
Operating leases	3.97%
Financing leases	3.52%