Recurring Fair Value Measures (Details) - USD ($)		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Derivatives, Fair Value [Line Items]
Obligation to Return Cash		$ 0		$ 0
Right to Reclaim Cash		5,600,000		3,000,000.0
Commodity Trading
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings		1,000,000.0	$ 700,000
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Transfers into Level 3		0
Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		20,100,000		17,300,000
Netting	[1]	(15,100,000)		(10,100,000)
Derivative Asset		5,000,000.0		7,200,000
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		4,700,000		1,900,000
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		14,800,000		14,500,000
Fair Value Measured on a Recurring Basis | Other Current Assets | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		600,000		900,000
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		7,500,000		9,600,000
Netting	[1]	(7,500,000)		(9,600,000)
Derivative Asset		0		0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		300,000		400,000
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		6,800,000		8,100,000
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		400,000		1,100,000
Fair Value Measured on a Recurring Basis | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		24,300,000		21,800,000
Netting	[1]	(15,600,000)		(13,100,000)
Derivative Liability		8,700,000		8,700,000
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		4,100,000		1,700,000
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		20,200,000		20,100,000
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0		0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		60,800,000		62,100,000
Netting	[1]	(12,600,000)		(9,600,000)
Derivative Liability		48,200,000		52,500,000
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		300,000		400,000
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		44,900,000		47,000,000.0
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		15,600,000		14,700,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Assets | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		20,100,000		13,900,000
Netting	[1]	(15,100,000)		(10,100,000)
Derivative Asset		5,000,000.0		3,800,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Assets | Commodity Trading | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		4,700,000		1,900,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Assets | Commodity Trading | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		14,800,000		11,100,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Assets | Commodity Trading | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		600,000		900,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Assets | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0		3,400,000
Netting	[1]	0		0
Derivative Asset		0		3,400,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Assets | Natural Gas Commodity | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Assets | Natural Gas Commodity | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0		3,400,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Assets | Natural Gas Commodity | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Noncurrent Assets | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		7,500,000		9,600,000
Netting	[1]	(7,500,000)		(9,600,000)
Derivative Asset		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Noncurrent Assets | Commodity Trading | Level 1
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		300,000		400,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Noncurrent Assets | Commodity Trading | Level 2
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		6,800,000		8,100,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Noncurrent Assets | Commodity Trading | Level 3
Derivatives, Fair Value [Line Items]
Derivative Asset, Gross		400,000		1,100,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Liabilities | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		24,300,000		18,400,000
Netting	[1]	(15,600,000)		(13,100,000)
Derivative Liability		8,700,000		5,300,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Liabilities | Commodity Trading | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		4,100,000		1,700,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Liabilities | Commodity Trading | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		20,200,000		16,700,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Liabilities | Commodity Trading | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Liabilities | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0		3,400,000
Netting	[1]	0		0
Derivative Liability		0		3,400,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Liabilities | Natural Gas Commodity | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Liabilities | Natural Gas Commodity | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0		3,400,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Current Liabilities | Natural Gas Commodity | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		0		0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Noncurrent Liabilities | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		60,800,000		62,100,000
Netting	[1]	(12,600,000)		(9,600,000)
Derivative Liability		48,200,000		52,500,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Noncurrent Liabilities | Commodity Trading | Level 1
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		300,000		400,000
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Noncurrent Liabilities | Commodity Trading | Level 2
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		44,900,000		47,000,000.0
Fair Value Measured on a Recurring Basis | Other Derivative Instruments | Other Noncurrent Liabilities | Commodity Trading | Level 3
Derivatives, Fair Value [Line Items]
Derivative Liability, Gross		$ 15,600,000		$ 14,700,000

[1] PSCo 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 liabilities include no obligations to return cash collateral and the right to reclaim cash collateral of $5.6 million and $3.0 million, respectively. The counterparty netting amounts presented exclude settlement receivables and payables and non-derivative amounts that may be subject to the same master netting agreements.