Regulatory and Rate Matters - Renewable Energy Rider (Details) - Public Service Company of New Mexico [Member] - Renewable Energy Rider [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Public Utilities, General Disclosures [Line Items]
Revenue from renewable energy rider	$ 42.0	$ 41.9	$ 31.9
Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Annual revenue to be collected	42.4
Proposed collection through energy rider	$ 50.0
NMPRC-approved return on equity	0.50%		10.50%
Initial approved return on equity	10.00%