Recurring Fair Value Measurements (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Obligation to return cash		$ 31.5		$ 31.5
Right to reclaim cash		0.0		7.9
Commodity Trading
Changes in Level 3 Commodity Derivatives [Roll Forward]
Balance at beginning of period		5.3	$ 14.2
Purchases		0.0	0.0
Settlements		(11.7)	(3.4)
Gains (losses) recognized in earnings	[1]	6.2	(18.5)
Net gains (losses) recognized as regulatory assets and liabilities		3.0	(2.4)
Balance at end of period		2.8	(10.1)
Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative asset		25.3		9.2
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative liability		26.4		25.0
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative liability		122.9		110.2
Fair Value Measured on a Recurring Basis | Level 3
Changes in Level 3 Commodity Derivatives [Roll Forward]
Transfers level 3, net		0.0	$ 0.0
Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative asset, gross		70.2		75.5
Netting, asset	[2]	(47.9)		(43.0)
Derivative asset		22.3		32.5
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 1
Derivatives, Fair Value [Line Items]
Derivative asset, gross		3.0		1.6
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 2
Derivatives, Fair Value [Line Items]
Derivative asset, gross		48.0		41.6
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 3
Derivatives, Fair Value [Line Items]
Derivative asset, gross		19.2		32.3
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative asset, gross		66.8		64.7
Netting, asset	[2]	(47.6)		(42.1)
Derivative asset		19.2		22.6
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative asset, gross		3.4		8.7
Netting, asset	[2]	(0.3)		(0.9)
Derivative asset		3.1		7.8
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative asset, gross		0.0		2.1
Netting, asset	[2]	0.0		0.0
Derivative asset		0.0		2.1
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Level 1 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative asset, gross		3.0		1.6
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Level 1 | Electric Commodity
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 | Level 1 | Natural Gas Commodity
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 | Level 2 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative asset, gross		48.0		39.5
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Level 2 | Electric Commodity
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 | Level 2 | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative asset, gross		0.0		2.1
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Level 3 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative asset, gross		15.8		23.6
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Level 3 | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative asset, gross		3.4		8.7
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Level 3 | Natural Gas Commodity
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		62.5		43.9
Netting, asset	[2]	(37.3)		(34.8)
Derivative asset		25.2		9.1
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 1
Derivatives, Fair Value [Line Items]
Derivative asset, gross		9.9		8.5
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 2
Derivatives, Fair Value [Line Items]
Derivative asset, gross		31.2		29.4
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 3
Derivatives, Fair Value [Line Items]
Derivative asset, gross		21.4		6.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative asset, gross		62.5		43.9
Netting, asset	[2]	(37.3)		(34.8)
Derivative asset		25.2		9.1
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Level 1 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative asset, gross		9.9		8.5
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Level 2 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative asset, gross		31.2		29.4
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Level 3 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative asset, gross		21.4		6.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative liability, gross		60.5		62.0
Netting, liability	[2]	(47.9)		(50.8)
Derivative liability		12.6		11.2
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Level 1
Derivatives, Fair Value [Line Items]
Derivative liability, gross		3.8		2.2
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Level 2
Derivatives, Fair Value [Line Items]
Derivative liability, gross		42.3		43.8
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Level 3
Derivatives, Fair Value [Line Items]
Derivative liability, gross		14.4		16.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative liability, gross		60.0		59.3
Netting, liability	[2]	(47.6)		(49.8)
Derivative liability		12.4		9.5
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative liability, gross		0.3		1.0
Netting, liability	[2]	(0.3)		(1.0)
Derivative liability		0.0		0.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative liability, gross		0.2		1.7
Netting, liability	[2]	0.0		0.0
Derivative liability		0.2		1.7
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Level 1 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative liability, gross		3.8		2.2
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Level 1 | Electric Commodity
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 | Level 1 | Natural Gas Commodity
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 | Level 2 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative liability, gross		42.1		42.1
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Level 2 | Electric Commodity
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 | Level 2 | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative liability, gross		0.2		1.7
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Level 3 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative liability, gross		14.1		15.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Level 3 | Electric Commodity
Derivatives, Fair Value [Line Items]
Derivative liability, gross		0.3		1.0
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Level 3 | Natural Gas Commodity
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		69.9		51.3
Netting, liability	[2]	(5.7)		(3.3)
Derivative liability		64.2		48.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Level 1
Derivatives, Fair Value [Line Items]
Derivative liability, gross		2.4		2.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Level 2
Derivatives, Fair Value [Line Items]
Derivative liability, gross		44.1		32.3
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Level 3
Derivatives, Fair Value [Line Items]
Derivative liability, gross		23.4		17.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative liability, gross		69.9		51.3
Netting, liability	[2]	(5.7)		(3.3)
Derivative liability		64.2		48.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Level 1 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative liability, gross		2.4		2.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Level 2 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative liability, gross		44.1		32.3
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Level 3 | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative liability, gross		23.4		17.0
Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets | PPAs
Derivatives, Fair Value [Line Items]
Derivative asset	[3]	0.1		0.1
Fair Value, Measurements, Nonrecurring | Other Current Liabilities | PPAs
Derivatives, Fair Value [Line Items]
Derivative liability	[3]	13.8		13.8
Fair Value, Measurements, Nonrecurring | Other Noncurrent Liabilities | PPAs
Derivatives, Fair Value [Line Items]
Derivative liability	[3]	$ 58.7		$ 62.2

[1] These 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 March 31, 2020 and Dec. 31, 2019. At both March 31, 2020 and Dec. 31, 2019, derivative assets and liabilities include $31.5 million of obligations to return cash collateral. At March 31, 2020, no derivative assets and liabilities include the rights to reclaim cash collateral and $7.9 million at Dec. 31, 2019. 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.