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Commitments and Contingencies - Clean Air Act, Lawsuits (Details) - USD ($) $ in Millions		1 Months Ended
	Aug. 17, 2015	May 31, 2010
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Mercury Control [Member]
Loss Contingencies [Line Items]
Current annual mercury control costs		$ 0.7
Public Service Company of New Mexico [Member] | San Juan Generating Station [Member] | Mercury Control [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Contingent estimated annual mercury control cost		$ 6.6
Public Service Company of New Mexico [Member] | Four Corners Units 4 and 5 (Coal) [Member] | Clean Air Act Lawsuit [Member]
Loss Contingencies [Line Items]
Litigation settlement, amount	$ 1.5
Litigation settlement, expected capital spend, environmental	$ 6.7
Ownership percentage	13.00%
Former Four Corners Co-Owner [Member] | Four Corners Units 4 and 5 (Coal) [Member] | Clean Air Act Lawsuit [Member]
Loss Contingencies [Line Items]
Litigation settlement, expected capital spend, environmental	$ 3.2
Current Four Corners Co-Owners [Member] | Four Corners Units 4 and 5 (Coal) [Member] | Clean Air Act Lawsuit [Member]
Loss Contingencies [Line Items]
Litigation settlement, expected capital spend, environmental	$ 3.5

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Current Annual Mercury Control Costs

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