Borrowings and Other Financing Instruments, Dividend and Other Capital-Related Restrictions (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Dividend and Other Capital-Related Restrictions [Abstract]
Additional Cash Dividends On Common Stock Which Could Have Been Paid Per First Mortgage Indenture	$ 1,700.0	$ 1,700.0
PSCo
Dividend and Other Capital-Related Restrictions [Abstract]
Maximum additional long term debt authorized for issuance	2,200.0
Maximum additional short term debt authorized for issuance	$ 800.0
NSP-Minnesota
Dividend and Other Capital-Related Restrictions [Abstract]
Equity to total capitalization ratio, low end of range (in hundredths)	46.90%
Equity to total capitalization ratio, high end of range (in hundredths)	57.30%
Equity to total capitalization ratio	52.10%
Unrestricted Retained Earnings Per State Regulatory Commissions Dividend Restrictions	$ 1,000.0
Capitalization, Short term debt, long term debt and equity	10,300.0
Maximum total capitalization	$ 10,750.0
Maximum percentage of short term debt to total capitalization (in hundredths)	15.00%
NSP-Wisconsin
Dividend and Other Capital-Related Restrictions [Abstract]
Equity to total capitalization ratio, low end of range (in hundredths)	52.50%
Equity to total capitalization ratio	53.60%
Unrestricted Retained Earnings Per State Regulatory Commissions Dividend Restrictions	$ 33.6
Maximum annual dividends that can be paid if equity capitalization ratio condition is not met	53.1
Maximum additional short term debt authorized for issuance	150.0
SPS
Dividend and Other Capital-Related Restrictions [Abstract]
Unrestricted Retained Earnings Per State Regulatory Commissions Dividend Restrictions	$ 487.0
Equity to total capitalization ratio (excluding short-term debt), low end of range (in hundredths)	45.00%
Equity to total capitalization ratio (excluding short-term debt), high end of range (in hundredths)	55.00%
Equity to total capitalization ratio (excluding short-term debt) (in hundredths)	54.10%
Maximum additional short term debt authorized for issuance	$ 500.0

No definition available.

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- Definition

Additional cash dividends on common stock which the entity's subsidiary could have paid to the entity based on certain restrictions contained in the subsidiary's first mortgage indenture.

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No definition available.

+ Details

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- Definition

Total consolidated (as applicable) capitalization of the entity which is comprised of its short-term debt, long-term debt and equity instruments.

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No definition available.

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- Definition

Equity-to-total capitalization ratio is equal to (i) common stock plus surplus divided by (ii) the sum of common stock plus surplus plus long-term debt.

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No definition available.

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- Definition

The actual ratio of equity to total capitalization, excluding short-term debt.

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No definition available.

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- Definition

The high end of the range of the ratio of equity to total capitalization, excluding short-term debt, required to be maintained by the entity in order to pay dividends.

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No definition available.

+ Details

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- Definition

The low end of the range of the ratio of equity to total capitalization, excluding short-term debt, required to be maintained by the entity in order to pay dividends.

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No definition available.

+ Details

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- Definition

The high end of the range of the ratio of equity to net capital required to be maintained by the entity to engage in issuance of long-term debt securities.

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No definition available.

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- Definition

The low end of the range of the ratio of equity to net capital required to be maintained by the entity to engage in issuance of long-term debt securities.

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No definition available.

+ Details

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- Definition

Maximum additional amount of long-term debt the entity is authorized to issue, subject to the jurisdiction of the applicable state regulatory commissions and/or the Federal Energy Regulatory Commission under the Federal Power Act.

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No definition available.

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- Definition

Maximum additional amount of short-term debt the entity is authorized to issue, subject to the jurisdiction of they applicable state regulatory commissions and/or the Federal Energy Regulatory Commission under the Federal Power Act.

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No definition available.

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- Definition

Maximum annual dividends which can be paid by the entity if its calendar year average equity-to-total capitalization ratio is or falls below the state commission authorized level.

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No definition available.

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- Definition

The maximum percentage of short-term debt to capitalization which the entity cannot exceed in order to issue additional short-term debt.

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No definition available.

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- Definition

The maximum total capitalization allowed for the entity.

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No definition available.

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- Definition

Unrestricted Retained Earnings Per State Regulatory Commissions Dividend Restrictions

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No definition available.

+ Details

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