Goodwill and Other Intangible Assets (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2008
Customer Lists [Member]
Schedule of Goodwill and Other Intangible Assets [Line Items]
Finite-Lived Intangible Asset, Useful Life	8 years
Impairment of Intangible Assets, Finite-lived		$ 4.8
Trade Names [Member]
Schedule of Goodwill and Other Intangible Assets [Line Items]
Impairment of Intangible Assets, Indefinite-lived (Excluding Goodwill)		42.6
Public Service Company of New Mexico [Member]
Schedule of Goodwill and Other Intangible Assets [Line Items]
Goodwill, Impairment Loss		51.1
Texas-New Mexico Power Company [Member]
Schedule of Goodwill and Other Intangible Assets [Line Items]
Goodwill, Impairment Loss		34.5
First Choice [Member]
Schedule of Goodwill and Other Intangible Assets [Line Items]
Goodwill, Impairment Loss		$ 88.8