Lease Commitments - Schedule of Weighted Average Remaining Lease Terms and Discount Rates (Details)	Jun. 30, 2020
Weighted average remaining lease term (years):
Operating leases	5 years 11 months 4 days
Financing leases	5 years 2 months 15 days
Weighted average discount rate:
Operating leases	3.91%
Financing leases	3.19%
PNM
Weighted average remaining lease term (years):
Operating leases	6 years 1 month 6 days
Financing leases	4 years 11 months 8 days
Weighted average discount rate:
Operating leases	3.90%
Financing leases	3.12%
TNMP
Weighted average remaining lease term (years):
Operating leases	3 years 10 months 6 days
Financing leases	5 years 5 months 23 days
Weighted average discount rate:
Operating leases	4.00%
Financing leases	3.26%