Lease Commitments (Details) - PNM $ in Millions	Jan. 15, 2016 USD ($) lease MW	Jun. 30, 2017 USD ($) lease	Jan. 31, 2016 lease	Jan. 15, 2015 lease
Palo Verde Nuclear Generating Station, Unit 1 Leases
Operating Leased Assets [Line Items]
Number of leases, expiring				4
Number of leases under which lease term was extended				4
Palo Verde Nuclear Generating Station, Unit 2 Leases
Operating Leased Assets [Line Items]
Number of leases, expiring	4
Number of leases under which lease term was extended	1
Number of leases under which assets were purchased	3	3	3
Leased capacity to be purchased (in megawatts) | MW	32.8
Palo Verde Nuclear Generating Station, Unit 2 Leases, 31.25 MW
Operating Leased Assets [Line Items]
Number of leases under which assets were purchased	1
Payment to lessors | $	$ 78.1
Palo Verde Nuclear Generating Station, Unit 2 Leases, January 15, 2016
Operating Leased Assets [Line Items]
Leased capacity to be purchased (in megawatts) | MW	31.3
Palo Verde Nuclear Generating Station, Unit 2 Leases, 32.76 MW
Operating Leased Assets [Line Items]
Number of leases under which assets were purchased	2
Payment to lessors | $	$ 85.2
Palo Verde Nuclear Generating Station
Operating Leased Assets [Line Items]
Loss contingency, lease arrangements (up to) | $		$ 173.0