Lease Commitments - Schedule of Weighted Average Remaining Lease Terms and Discount Rates (Details)	Mar. 31, 2019
Weighted average remaining lease term (In years):
Operating leases	6 years 11 months 12 days
Financing leases	5 years 8 months 26 days
Weighted average discount rate:
Operating leases	3.88%
Financing leases	4.43%
PNM
Weighted average remaining lease term (In years):
Operating leases	7 years 2 months 5 days
Financing leases	5 years 8 months 19 days
Weighted average discount rate:
Operating leases	3.88%
Financing leases	4.34%
TNMP
Weighted average remaining lease term (In years):
Operating leases	4 years 8 months 1 day
Financing leases	5 years 9 months
Weighted average discount rate:
Operating leases	3.88%
Financing leases	4.55%