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Significant Accounting Policies and Responsibility for Financial Statements (Details) | Mar. 31, 2017 USD ($)
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Accounting Policies [Abstract] |
Payment defaults under agreements | $ 0
Unrealized gains, net of income taxes, recorded in AOCI | $ 6,800,000

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Period Type: | instant

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- Definition Collaborative Arrangement, Owner Obligations, Default, Amount + References No definition available. + Details
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Namespace Prefix: | pnm_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration