Recurring Fair Value Measurements (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Return Cash Collateral		$ 31.5	$ 31.5
Reclaim Cash Collateral		7.9	8.7
Commodity Contract [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at beginning of period		14.3	22.6	$ 15.3
Purchases		16.7	26.4	40.6
Settlements		(27.5)	(17.2)	(41.7)
Gains (losses) recognized in earnings	[1]	3.2	(1.5)	5.5
Net gains (losses) recognized as regulatory assets and liabilities		(1.4)	(16.0)	2.9
Balance at end of period		5.3	14.3	22.6
Transfers Between Levels, Net		0.0	0.0	$ 0.0
Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Net		32.5	25.8
Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Net		9.2	17.0
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Net		25.0	16.5
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Net		110.2	112.2
Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		75.5	41.9
Netting	[2]	(43.0)	(16.1)
Derivative Asset, Net		32.5	25.8
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		1.6	1.1
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		41.6	28.1
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		32.3	12.7
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		64.7	30.4
Netting	[2]	(42.1)	(16.0)
Derivative Asset, Net		22.6	14.4
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Contract [Member] | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		1.6	1.1
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Contract [Member] | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		39.5	27.1
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Contract [Member] | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		23.6	2.2
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		8.7	10.5
Netting	[2]	(0.9)	(0.1)
Derivative Asset, Net		7.8	10.4
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0.0	0.0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0.0	0.0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		8.7	10.5
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		2.1	1.0
Netting	[2]	0.0	0.0
Derivative Asset, Net		2.1	1.0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0.0	0.0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		2.1	1.0
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0.0	0.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		43.9	30.3
Netting	[2]	(34.8)	(13.4)
Derivative Asset, Net		9.1	16.9
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		8.5	0.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		29.4	25.3
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		6.0	5.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		43.9	30.3
Netting	[2]	(34.8)	(13.4)
Derivative Asset, Net		9.1	16.9
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Contract [Member] | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		8.5	0.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Contract [Member] | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		29.4	25.3
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Contract [Member] | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		6.0	5.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		62.0	27.1
Netting	[2]	50.8	24.6
Derivative Liability, Net		11.2	2.5
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		2.2	1.4
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		43.8	23.9
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		16.0	1.8
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		59.3	27.0
Netting	[2]	49.8	24.5
Derivative Liability, Net		9.5	2.5
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Contract [Member] | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		2.2	1.4
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Contract [Member] | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		42.1	23.9
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Contract [Member] | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		15.0	1.7
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		1.0	0.1
Netting	[2]	1.0	0.1
Derivative Liability, Net		0.0	0.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Electric Commodity | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0.0	0.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Electric Commodity | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0.0	0.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Electric Commodity | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		1.0	0.1
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		1.7	0.0
Netting	[2]	0.0	0.0
Derivative Liability, Net		1.7	0.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0.0	0.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		1.7	0.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0.0	0.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		51.3	17.7
Netting	[2]	3.3	17.9
Derivative Liability, Net		48.0	35.6
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		2.0	0.1
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		32.3	16.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		17.0	1.6
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		51.3	17.7
Netting	[2]	3.3	17.9
Derivative Liability, Net		48.0	35.6
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Contract [Member] | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		2.0	0.1
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Contract [Member] | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		32.3	16.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Contract [Member] | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		17.0	1.6
Fair Value, Measurements, Nonrecurring | Other Current Assets | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Asset, Net	[3]	0.0	0.0
Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Asset, Net	[3]	0.1	0.1
Fair Value, Measurements, Nonrecurring | Other Current Liabilities | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Liability, Net	[3]	13.8	14.0
Fair Value, Measurements, Nonrecurring | Other Noncurrent Liabilities | Purchased Power Agreements
Derivatives, Fair Value [Line Items]
Derivative Liability, Net	[3]	$ 62.2	$ 76.6

[1] Amounts relate to commodity derivatives held at the end of the period.

[2] NSP-Minnesota nets derivative instruments and related collateral in its consolidated balance sheet when supported by a legally enforceable master netting agreement, and all derivative instruments and related collateral amounts were subject to master netting agreements at Dec. 31, 2019 and 2018. At both Dec. 31, 2019 and 2018, derivative assets and liabilities include $31.5 million of obligations to return cash collateral, respectively. At Dec. 31, 2019 and 2018, derivative assets and liabilities include the rights to reclaim cash collateral of $7.9 million and $8.7 million, respectively. The counterparty netting excludes settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.

[3] During 2006, Xcel Energy qualified these contracts under the normal purchase exception. Based on this qualification, the contracts are no longer adjusted to fair value and the previous carrying value of these contracts will be amortized over the remaining contract lives along with the offsetting regulatory assets and liabilities.