Public Service Co Of Colorado 10-Q 1 Aug 19 2019 Q2 Quarterly report Financial data

Cover Page

Cover Page - shares	6 Months Ended
	Jun. 30, 2019	Aug. 01, 2019
Cover page.
Entity Registrant Name	PUBLIC SERVICE CO OF COLORADO
Entity Central Index Key	0000081018
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2
Amendment Flag	false
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2019
Document Transition Report	false
Entity File Number	001-03280
Entity Tax Identification Number	84-0296600
Entity Incorporation, State or Country Code	CO
Entity Address, Address Line One	1800 Larimer, Suite 1100
Entity Address, City or Town	Denver
Entity Address, State or Province	CO
Entity Address, Postal Zip Code	80202
City Area Code	303
Local Phone Number	571-7511
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		100

CONSOLIDATED STATEMENTS OF COMM

CONSOLIDATED STATEMENTS OF COMMON STOCKHOLDER'S EQUITY - USD ($) $ in Millions	Total	Common stock	Additional Paid In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning Balance at Dec. 31, 2017	$ 5,828.3	$ 0	$ 4,032.8	$ 1,822.2	$ (26.7)
Balance (in shares) at Dec. 31, 2017		100
Increase (Decrease) in Stockholder's Equity
Net income	256			256
Other comprehensive income	0.6				0.6
Dividends declared to parent	(195.6)			(195.6)
Contribution of capital by parent	240.3		240.3
Ending Balance at Jun. 30, 2018	6,129.6	$ 0	4,273.1	1,882.6	(26.1)
Balance (in shares) at Jun. 30, 2018		100
Beginning Balance at Mar. 31, 2018	5,867	$ 0	4,032.8	1,860.6	(26.4)
Balance (in shares) at Mar. 31, 2018		100
Increase (Decrease) in Stockholder's Equity
Net income	122.3			122.3
Other comprehensive income	0.3				0.3
Dividends declared to parent	(100.3)			(100.3)
Contribution of capital by parent	240.3		240.3
Ending Balance at Jun. 30, 2018	6,129.6	$ 0	4,273.1	1,882.6	(26.1)
Balance (in shares) at Jun. 30, 2018		100
Beginning Balance at Dec. 31, 2018	$ 6,298.2	$ 0	4,340.5	1,983.2	(25.5)
Balance (in shares) at Dec. 31, 2018	100	100
Increase (Decrease) in Stockholder's Equity
Net income	$ 240.3			240.3
Other comprehensive income	0.6				0.6
Dividends declared to parent	(203.8)			(203.8)
Contribution of capital by parent	277.8		277.8
Ending Balance at Jun. 30, 2019	$ 6,613.1	$ 0	4,618.3	2,019.7	(24.9)
Balance (in shares) at Jun. 30, 2019	100	100
Beginning Balance at Mar. 31, 2019	$ 6,388.4	$ 0	4,390.5	2,023.1	(25.2)
Balance (in shares) at Mar. 31, 2019		100
Increase (Decrease) in Stockholder's Equity
Net income	101.5			101.5
Other comprehensive income	0.3				0.3
Dividends declared to parent	(104.9)			(104.9)
Contribution of capital by parent	227.8		227.8
Ending Balance at Jun. 30, 2019	$ 6,613.1	$ 0	$ 4,618.3	$ 2,019.7	$ (24.9)
Balance (in shares) at Jun. 30, 2019	100	100

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues
Total operating revenues	$ 910	$ 911.9	$ 2,133	$ 1,985.2
Operating expenses
Cost of sales — steam and other	3.9	3.7	8.4	7.5
Operating and maintenance expenses	200.3	189	399.5	372.1
Demand side management expenses	32.2	33.2	64.4	65.9
Depreciation and amortization	148.1	116.5	295	238.2
Taxes (other than income taxes)	52.2	49.7	105.9	102.4
Total operating expenses	747.3	722.6	1,760.5	1,589
Operating income	162.7	189.3	372.5	396.2
Other (expense) income, net	(0.3)	0.8	0.6	1
Interest charges and financing costs
Interest charges — includes other financing costs of $1.6, $1.6, $3.2 and $3.2, respectively	57.7	51.2	117.1	101.2
Allowance for funds used during construction — debt	(2.4)	(5.2)	(4.9)	(9.8)
Total interest charges and financing costs	55.3	46	112.2	91.4
Allowance for funds used during construction — equity	5	13.5	9.1	24.5
Income before income taxes	112.1	157.6	270	330.3
Income taxes	10.6	35.3	29.7	74.3
Net income	101.5	122.3	240.3	256
Electric
Revenues
Total operating revenues	692.7	716.2	1,434.2	1,414.5
Operating expenses
Cost of Goods Sold	240.7	271.9	544.9	553.1
Natural gas
Revenues
Total operating revenues	207.6	186.7	676.7	550.6
Operating expenses
Cost of Goods Sold	69.9	58.6	342.4	249.8
Steam and other
Revenues
Total operating revenues	$ 9.7	$ 9	$ 22.1	$ 20.1

CONSOLIDATED STATEMENTS OF IN_2

CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Interest charges and financing costs
Other financing costs	$ 1.6	$ 1.6	$ 3.2	$ 3.2

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Comprehensive income:
Net income	$ 101.5	$ 122.3	$ 240.3	$ 256
Derivative instruments:
Reclassification of losses to net income, net of tax of $0.1, $0.1, $0.2 and $0.2, respectively	0.3	0.3	0.6	0.6
Other comprehensive income	0.3	0.3	0.6	0.6
Comprehensive income	$ 101.8	$ 122.6	$ 240.9	$ 256.6

CONSOLIDATED STATEMENTS OF CO_2

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Derivative instruments:
Reclassification of losses (gains) to net income, tax	$ 0.1	$ 0.1	$ 0.2	$ 0.2

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Operating activities
Net income	$ 240.3	$ 256
Adjustments to reconcile net income to cash provided by operating activities:
Depreciation and amortization	297.4	240.6
Deferred income taxes	2.8	25.6
Amortization of investment tax credits	(1.3)	(1.4)
Allowance for equity funds used during construction	(9.1)	(24.5)
Net realized and unrealized hedging and derivative transactions	(2.2)	(1.9)
Changes in operating assets and liabilities:
Accounts receivable	63.2	22
Accrued unbilled revenues	77.2	66.5
Inventories	16.5	44.8
Prepayments and other	0.5	1.5
Accounts payable	(111.8)	(22.1)
Net regulatory assets and liabilities	80	30.4
Other current liabilities	(94.6)	(119.1)
Pension and other employee benefit obligations	(43.5)	(27.5)
Other Operating Activities, Cash Flow Statement	0.5	(10.7)
Net cash provided by operating activities	515.9	480.2
Investing activities
Utility capital/construction expenditures	(632.5)	(801)
Investments in utility money pool arrangement	(131)	(198)
Repayments from utility money pool arrangement	131	56
Net cash used in investing activities	(632.5)	(943)
Financing activities
Repayments of short-term borrowings, net	(86)	0
Borrowings under utility money pool arrangement	58	526
Repayments under utility money pool arrangement	(8)	(526)
Proceeds from Issuance of Long-term Debt	391.6	692.7
Repayments of Long-term Debt	400	0
Capital contributions from parent	332.2	216.5
Dividends paid to parent	(190.4)	(171.5)
Other, net	0	(0.1)
Net cash provided by financing activities	97.4	737.6
Net change in cash and cash equivalents	(19.2)	274.8
Cash and cash equivalents at beginning of period	33.4	7.5
Cash and cash equivalents at end of period	14.2	282.3
Supplemental disclosure of cash flow information:
Cash paid for interest (net of amounts capitalized)	(107.4)	(88.9)
Cash paid for income taxes, net	(28.7)	(96.4)
Supplemental disclosure of non-cash investing and financing transactions:
Accrued property, plant and equipment additions	113.1	131.8
Inventory transfers to property, plant and equipment	15.4	9.3
Operating lease right-of-use assets	653.4	0
Allowance for equity funds used during construction	$ 9.1	$ 24.5

CONSOLIDATED BALANCE SHEETS (UN

CONSOLIDATED BALANCE SHEETS (UNAUDITED) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 14.2	$ 33.4
Accounts receivable, net	252.6	310.3
Accounts receivable from affiliates	21.2	80.8
Accrued unbilled revenues	236.3	313.5
Inventory, Net	165.5	197.4
Regulatory assets	68.4	120.6
Derivative instruments	18.4	42.6
Prepayments and other	26.4	23.8
Total current assets	803	1,122.4
Property, plant and equipment, net	15,335.7	15,120
Other assets
Regulatory assets	1,052.3	1,010.7
Derivative instruments	2.5	1.2
Operating Lease, Right-of-Use Asset	613.7	0
Other	175.1	37.2
Total other assets	1,843.6	1,049.1
Total assets	17,982.3	17,291.5
Current liabilities
Current portion of long-term debt	0	406.2
Short-term Debt	221	307
Borrowings Payable Under Utility Money Pool Arrangement	50	0
Accounts payable	383.5	503.4
Accounts payable to affiliates	43.6	46
Regulatory liabilities	116.9	67.3
Taxes accrued	118.5	202
Accrued interest	46.4	43.2
Dividends payable to parent	104.9	91.5
Derivative instruments	9.7	34.6
Other	182.5	101.5
Total current liabilities	1,277	1,802.7
Deferred credits and other liabilities
Deferred income taxes	1,738.6	1,719.3
Deferred investment tax credits	24.1	25.3
Regulatory liabilities	2,023.4	2,021.5
Asset retirement obligations	346.2	338.7
Derivative instruments	0.6	0.6
Customer Advances for Construction	169.1	168.1
Pension and employee benefit obligations	231.3	275.3
Operating Lease, Liability, Noncurrent	560.3	0
Other	152.5	50.4
Total deferred credits and other liabilities	5,246.1	4,599.2
Capitalization
Long-term debt	4,846.1	4,591.4
Common stock — 100 shares authorized at $0.01 par value; 100 shares outstanding at June 30, 2019 and Dec. 31, 2018, respectively	0	0
Additional paid in capital	4,618.3	4,340.5
Retained earnings	2,019.7	1,983.2
Accumulated other comprehensive loss	(24.9)	(25.5)
Total common stockholder’s equity	6,613.1	6,298.2
Total liabilities and equity	$ 17,982.3	$ 17,291.5

CONSOLIDATED BALANCE SHEETS (_2

CONSOLIDATED BALANCE SHEETS (UNAUDITED) (Parenthetical) - $ / shares	Jun. 30, 2019	Dec. 31, 2018
Capitalization, Long-term Debt and Equity [Abstract]
Common stock, shares authorized (in shares)	100	100
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares outstanding (in shares)	100	100

Management's Opinion

Management's Opinion	6 Months Ended
	Jun. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Management's Opinion	In the opinion of management, the accompanying unaudited consolidated financial statements contain all adjustments necessary to present fairly, in accordance with GAAP, the financial position of PSCo and its subsidiaries as of June 30, 2019 and Dec. 31, 2018 ; the results of its operations, including the components of net income and comprehensive income, and changes in stockholders’ equity for the three and six months ended June 30, 2019 and 2018 ; and its cash flows for the six months ended June 30, 2019 and 2018 . All adjustments are of a normal, recurring nature, except as otherwise disclosed. Management has also evaluated the impact of events occurring after June 30, 2019 up to the date of issuance of these consolidated financial statements. These statements contain all necessary adjustments and disclosures resulting from that evaluation. The Dec. 31, 2018 balance sheet information has been derived from the audited 2018 consolidated financial statements included in the PSCo Annual Report on Form 10-K for the year ended Dec. 31, 2018 . These notes to the consolidated financial statements have been prepared pursuant to the rules and regulations of the SEC for Quarterly Reports on Form 10-Q. Certain information and note disclosures normally included in financial statements prepared in accordance with GAAP on an annual basis have been condensed or omitted pursuant to such rules and regulations. For further information, refer to the consolidated financial statements and notes thereto, included in the PSCo Annual Report on Form 10-K for the year ended Dec. 31, 2018 , filed with the SEC on Feb. 22, 2019. Due to the seasonality of PSCo’s electric and natural gas sales, interim results are not necessarily an appropriate base from which to project annual results.

Selected Balance Sheet Data

Selected Balance Sheet Data	6 Months Ended
	Jun. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Selected Balance Sheet Data	Selected Balance Sheet Data (Millions of Dollars) June 30, 2019 Dec. 31, 2018 Accounts receivable, net Accounts receivable $ 272.3 $ 330.8 Less allowance for bad debts (19.7 ) (20.5 ) $ 252.6 $ 310.3 (Millions of Dollars) June 30, 2019 Dec. 31, 2018 Inventories Materials and supplies $ 61.8 $ 61.9 Fuel 71.7 69.5 Natural gas 32.0 66.0 $ 165.5 $ 197.4 (Millions of Dollars) June 30, 2019 Dec. 31, 2018 Property, plant and equipment, net Electric plant $ 13,922.3 $ 13,604.5 Natural gas plant 4,443.0 4,387.6 Common and other property 1,052.3 1,023.7 Plant to be retired (a) 290.2 321.9 Construction work in progress 638.9 573.3 Total property, plant and equipment 20,346.7 19,911.0 Less accumulated depreciation (5,011.0 ) (4,791.0 ) $ 15,335.7 $ 15,120.0 (a) In 2018, the CPUC approved early retirement of PSCo’s Comanche Units 1 and 2 in approximately 2022 and 2025, respectively. PSCo also expects Craig Unit 1 to be retired early in 2025. Amounts are presented net of accumulated depreciation.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies The significant accounting policies set forth in Note 1 to the consolidated financial statements in the PSCo Annual Report on Form 10-K for the year ended Dec. 31, 2018, appropriately represent, in all material respects, the current status of accounting policies and are incorporated herein by reference.

Accounting Pronouncements

Accounting Pronouncements	6 Months Ended
	Jun. 30, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Accounting Pronouncements	Accounting Pronouncements Recently Issued Credit Losses — In 2016, the FASB issued Financial Instruments - Credit Losses, Topic 326 (ASC Topic 326), which changes how entities account for losses on receivables and certain other assets. The guidance requires use of a current expected credit loss model, which may result in earlier recognition of credit losses than under previous accounting standards. ASC Topic 326 is effective for interim and annual periods beginning on or after Dec. 15, 2019, and will be applied on a modified-retrospective approach through a cumulative-effect adjustment to retained earnings as of Jan. 1, 2020. PSCo is currently evaluating the impact of adoption of the new standard on its consolidated financial statements. Recently Adopted Leases — In 2016, the FASB issued Leases , Topic 842 (ASC Topic 842) , which provides new accounting and disclosure guidance for leasing activities, most significantly requiring that operating leases be recognized on the balance sheet. PSCo adopted the guidance on Jan. 1, 2019 utilizing the package of transition practical expedients provided by the new standard, including carrying forward prior conclusions on whether agreements existing before the adoption date contain leases and whether existing leases are operating or finance leases; ASC Topic 842 refers to capital leases as finance leases. Specifically for land easement contracts, PSCo has elected the practical expedient provided by ASU No. 2018-01 Leases: Land Easement Practical Expedient for Transition to Topic 842 , and as a result, only those easement contracts entered on or after Jan. 1, 2019 will be evaluated to determine if lease treatment is appropriate. PSCo also utilized the transition practical expedient offered by ASU No. 2018-11 Leases: Targeted Improvements to implement the standard on a prospective basis. As a result, reporting periods in the consolidated financial statements beginning Jan. 1, 2019 reflect the implementation of ASC Topic 842, while prior periods continue to be reported in accordance with Leases, Topic 840 (ASC Topic 840) . Other than first-time recognition of operating leases on its consolidated balance sheet, the implementation of ASC Topic 842 did not have a significant impact on PSCo’s consolidated financial statements. Adoption resulted in recognition of approximately $0.7 billion of operating lease ROU assets and current/noncurrent operating lease liabilities. See Note 9 for leasing disclosures.

Borrowings and Other Financing

Borrowings and Other Financing Instruments	6 Months Ended
	Jun. 30, 2019
Debt Disclosure [Abstract]
Borrowings and Other Financing Instruments	Borrowings and Other Financing Instruments Short-Term Borrowings PSCo meets its short-term liquidity requirements primarily through the issuance of commercial paper and borrowings under its credit facility and the money pool. Money Pool — Xcel Energy Inc. and its utility subsidiaries have established a money pool arrangement that allows for short-term investments in and borrowings between the utility subsidiaries. Xcel Energy Inc. may make investments in the utility subsidiaries at market-based interest rates; however, the money pool arrangement does not allow the utility subsidiaries to make investments in Xcel Energy Inc. Money pool borrowings for PSCo were as follows: (Amounts in Millions, Except Interest Rates) Three Months Ended June 30, 2019 Year Ended Dec. 31, 2018 Borrowing limit $ 250 $ 250 Amount outstanding at period end 50 — Average amount outstanding 3 25 Maximum amount outstanding 50 156 Weighted average interest rate, computed on a daily basis 2.41 % 1.93 % Weighted average interest rate at period end 2.41 N/A Commercial Paper — Commercial paper outstanding for PSCo was as follows: (Amounts in Millions, Except Interest Rates) Three Months Ended June 30, 2019 Year Ended Dec. 31, 2018 Borrowing limit $ 700 $ 700 Amount outstanding at period end 221 307 Average amount outstanding 244 55 Maximum amount outstanding 432 309 Weighted average interest rate, computed on a daily basis 2.65 % 2.28 % Weighted average interest rate at period end 2.59 2.95 Letters of Credit — PSCo uses letters of credit, generally with terms of one year , to provide financial guarantees for certain operating obligations. There were $10 million of letters of credit outstanding under the credit facility at June 30, 2019 and Dec. 31, 2018 . The contract amounts of these letters of credit approximate their fair value and are subject to fees. Credit Facility — In order to use its commercial paper program to fulfill short-term funding needs, PSCo must have a revolving credit facility in place at least equal to the amount of its commercial paper borrowing limit and cannot issue commercial paper in an aggregate amount exceeding available capacity under this credit facility. The credit facility provides short-term financing in the form of notes payable to banks, letters of credit and back-up support for commercial paper borrowings. At June 30, 2019 , PSCo had the following committed credit facility available (in millions of dollars): Credit Facility (a) Outstanding (b) Available $ 700 $ 231 $ 469 (a) This credit facility expires in June 2024 . (b) Includes outstanding commercial paper and letters of credit. All credit facility bank borrowings, outstanding letters of credit and outstanding commercial paper reduce the available capacity under the credit facility. PSCo had no direct advances on the credit facility outstanding at June 30, 2019 and Dec. 31, 2018 . Long-Term Borrowings During the six months ended June 30, 2019 , PSCo issued $400 million of 4.05% first mortgage bonds due Sep. 15, 2049.

Revenues

Revenues	6 Months Ended
	Jun. 30, 2019
Revenue from Contract with Customer [Abstract]
Revenues	Revenues Revenue is classified by the type of goods/services rendered and market/customer type. PSCo’s operating revenues consists of the following: Three Months Ended June 30, 2019 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 211.5 $ 130.1 $ 2.8 $ 344.4 C&I 384.4 49.4 5.7 439.5 Other 11.8 — — 11.8 Total retail 607.7 179.5 8.5 795.7 Wholesale 29.1 — — 29.1 Transmission 11.6 — — 11.6 Other 6.5 23.3 — 29.8 Total revenue from contracts with customers 654.9 202.8 8.5 866.2 Alternative revenue and other 37.8 4.8 1.2 43.8 Total revenues $ 692.7 $ 207.6 $ 9.7 $ 910.0 Three Months Ended June 30, 2018 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 222.7 $ 104.0 $ 2.6 $ 329.3 C&I 383.7 38.9 5.3 427.9 Other 11.4 — — 11.4 Total retail 617.8 142.9 7.9 768.6 Wholesale 36.2 — — 36.2 Transmission 13.2 — — 13.2 Other 14.7 18.8 — 33.5 Total revenue from contracts with customers 681.9 161.7 7.9 851.5 Alternative revenue and other 34.3 25.0 1.1 60.4 Total revenues $ 716.2 $ 186.7 $ 9.0 $ 911.9 Six Months Ended June 30, 2019 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 456.6 $ 441.5 $ 5.3 $ 903.4 C&I 752.3 169.7 14.5 936.5 Other 24.3 — — 24.3 Total retail 1,233.2 611.2 19.8 1,864.2 Wholesale 86.4 — — 86.4 Transmission 25.0 — — 25.0 Other 18.1 54.9 — 73.0 Total revenue from contracts with customers 1,362.7 666.1 19.8 2,048.6 Alternative revenue and other 71.5 10.6 2.3 84.4 Total revenues $ 1,434.2 $ 676.7 $ 22.1 $ 2,133.0 Six Months Ended June 30, 2018 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 450.3 $ 331.8 $ 5.2 $ 787.3 C&I 727.0 124.9 12.5 864.4 Other 23.6 — 0.1 23.7 Total retail 1,200.9 456.7 17.8 1,675.4 Wholesale 84.1 — — 84.1 Transmission 25.4 — — 25.4 Other 33.5 43.8 — 77.3 Total revenue from contracts with customers 1,343.9 500.5 17.8 1,862.2 Alternative revenue and other 70.6 50.1 2.3 123.0 Total revenues $ 1,414.5 $ 550.6 $ 20.1 $ 1,985.2

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes Except to the extent noted below, Note 8 to the consolidated financial statements included in PSCo’s Annual Report on Form 10-K for the year ended Dec. 31, 2018 represents, in all material respects, the current status of other income tax matters, and are incorporated herein by reference. The following table reconciles the difference between the statutory rate and the ETR: Six Months Ended June 30 2019 2018 Federal statutory rate 21.0 % 21.0 % State tax (net of federal tax effect) 3.7 3.7 Increases (decreases) in tax from: Wind PTCs (9.4 ) — Plant regulatory differences (a) (3.4 ) (1.5 ) Other tax credits and allowances (net) (1.0 ) (1.0 ) Other (net) 0.1 0.3 Effective income tax rate 11.0 % 22.5 % (a) Regulatory differences for income tax primarily relate to the flow back of excess deferred taxes to customers through the average rate assumption method and the impact of AFUDC - Equity. Year-to-date variations primarily relates to the deferral of the flow back of excess deferred taxes in 2018, as a result of pending regulatory decisions. Treatment of most tax reform items was established prior to the first quarter of 2019, resulting in a reduction in deferred amounts. Income tax benefits associated with the flow back of excess deferred credits are offset by corresponding revenue reductions and additional prepaid pension asset amortization. Federal Audits — PSCO is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. Statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows: Tax Year(s) Expiration 2009 - 2013 June 2020 2014 - 2016 September 2020 2017 September 2021 In 2015, the IRS commenced an examination of tax years 2012 and 2013. In 2017, the IRS concluded the audit of tax years 2012 and 2013 and proposed an adjustment that would impact Xcel Energy’s NOL and ETR. Xcel Energy filed a protest with the IRS. As of June 30, 2019 , the case has been forwarded to Office of Appeals and Xcel Energy has recognized its best estimate of income tax expense that will result from a final resolution of this issue; however, the outcome and timing of a resolution is unknown. In 2018, the IRS began an audit of tax years 2014 - 2016. As of June 30, 2019 no adjustments have been proposed. State Audits — PSCo is a member of the Xcel Energy affiliated group that files consolidated state income tax returns. As of June 30, 2019 , PSCo’s earliest open tax year that is subject to examination by state taxing authorities under applicable statutes of limitations is 2009. There are currently no state income tax audits in progress. Unrecognized Benefits — Unrecognized tax benefit balance includes permanent tax positions, which if recognized would affect the annual ETR. In addition, the unrecognized tax benefit balance includes temporary tax positions for which the ultimate deductibility is highly certain, but for which there is uncertainty about the timing of such deductibility. A change in the period of deductibility would not affect the ETR but would accelerate the payment to the taxing authority to an earlier period. Unrecognized tax benefits - permanent vs temporary: (Millions of Dollars) June 30, 2019 Dec. 31, 2018 Unrecognized tax benefit — Permanent tax positions $ 6.0 $ 5.4 Unrecognized tax benefit — Temporary tax positions 4.7 4.9 Total unrecognized tax benefit $ 10.7 $ 10.3 Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards: (Millions of Dollars) June 30, 2019 Dec. 31, 2018 NOL and tax credit carryforwards $ (6.1 ) $ (5.6 ) Net deferred tax liability associated with the unrecognized tax benefit amounts and related NOLs and tax credits carryforwards were $2.6 million and $2.0 million for June 30, 2019 and Dec. 31, 2018, respectively. As the IRS Appeals and federal audit progress, it is reasonably possible that the amount of unrecognized tax benefit could decrease up to approximately $8.7 million in the next 12 months. Payables for interest related to unrecognized tax benefits were not material and no amounts were accrued for penalties related to unrecognized tax benefits as of June 30, 2019 or Dec. 31, 2018.

Fair Value of Financial Assets

Fair Value of Financial Assets and Liabilities	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets and Liabilities	Fair Value of Financial Assets and Liabilities Fair Value Measurements The accounting guidance for fair value measurements and disclosures provides a single definition of fair value, hierarchical framework for measuring assets and liabilities and requires disclosure about assets and liabilities measured at fair value. Level 1 — Quoted prices are available in active markets for identical assets or liabilities as of the reporting date. The types of assets and liabilities included in Level 1 are highly liquid and actively traded instruments with quoted prices. Level 2 — Pricing inputs are other than quoted prices in active markets, but are either directly or indirectly observable as of the reporting date. The types of assets and liabilities included in Level 2 are typically either comparable to actively traded securities or contracts, or priced with models using highly observable inputs. Level 3 — Significant inputs to pricing have little or no observability as of the reporting date. The types of assets and liabilities included in Level 3 are those valued with models requiring significant management judgment or estimation. Specific valuation methods include: Cash equivalents — The fair values of cash equivalents are generally based on cost plus accrued interest; money market funds are measured using quoted net asset value. Interest rate derivatives — The fair values of interest rate derivatives are based on broker quotes that utilize current market interest rate forecasts. Commodity derivatives — The methods used to measure the fair value of commodity derivative forwards and options generally utilize observable forward prices and volatilities, as well as observable pricing adjustments for specific delivery locations, and are generally assigned a Level 2 classification. When contractual settlements relate to delivery locations for which pricing is relatively unobservable, or extend to periods beyond those readily observable on active exchanges or quoted by brokers, the significance of the use of less observable inputs on a valuation is evaluated, and may result in Level 3 classification. Derivative Instruments Fair Value Measurements PSCo enters into derivative instruments, including forward contracts, futures, swaps and options, for trading purposes and to manage risk in connection with changes in interest rates, utility commodity prices and vehicle fuel prices. Interest Rate Derivatives — PSCo enters into various instruments that effectively fix the yield or price on a specified benchmark interest rate for an anticipated debt issuance for a specific period. These derivative instruments are generally designated as cash flow hedges for accounting purposes. At June 30, 2019 , accumulated other comprehensive loss related to interest rate derivatives included $1.2 million of net losses expected to be reclassified into earnings during the next 12 months as the related hedged interest rate transactions impact earnings, including forecasted amounts for unsettled hedges, as applicable. Wholesale and Commodity Trading Risk — PSCo conducts various wholesale and commodity trading activities, including the purchase and sale of electric capacity, energy, energy-related instruments and natural gas-related instruments, including derivatives. PSCo is allowed to conduct these activities within guidelines and limitations as approved by its risk management committee, comprised of management personnel not directly involved in activities governed by this policy. Commodity Derivatives — PSCo enters into derivative instruments to manage variability of future cash flows from changes in commodity prices in its electric and natural gas operations, as well as for trading purposes. This could include the purchase or sale of energy or energy-related products, natural gas to generate electric energy, natural gas for resale, and vehicle fuel. PSCo may enter into derivative instruments that mitigate commodity price risk on behalf of electric and natural gas customers but may not be designated as qualifying hedging transactions. Changes in the fair value of non-trading commodity derivative instruments are recorded as other comprehensive income or deferred as a regulatory asset or liability. The classification as a regulatory asset or liability is based on commission approved regulatory recovery mechanisms. As of June 30, 2019, PSCo had no commodity contracts designated as cash flow hedges. PSCo also enters into commodity derivative instruments for trading purposes not directly related to commodity price risks associated with serving its electric and natural gas customers. Changes in the fair value of these commodity derivatives are recorded in electric operating revenues, net of amounts credited to customers under margin-sharing mechanisms. Gross notional amounts of commodity forwards and options: (Amounts in Millions) (a)(b) June 30, 2019 Dec. 31, 2018 Megawatt hours of electricity 16.3 24.4 Million British thermal units of natural gas 51.3 48.4 (a) Amounts are not reflective of net positions in the underlying commodities. (b) Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise. Consideration of Credit Risk and Concentrations — PSCo continuously monitors the creditworthiness of the counterparties to its interest rate derivatives and commodity derivative contracts prior to settlement, and assesses each counterparty’s ability to perform on the transactions set forth in the contracts. The impact of credit risk was immaterial to the fair value of unsettled commodity derivatives presented in the consolidated balance sheets. PSCo’s most significant concentrations of credit risk with particular entities or industries are contracts with counterparties to its wholesale, trading and non-trading commodity activities. At June 30, 2019, six of PSCo’s 10 most significant counterparties for these activities, comprising $33.0 million or 49% of this credit exposure, had investment grade credit ratings from S&P Global Ratings, Moody’s Investor Services or Fitch Ratings. Three of the 10 most significant counterparties, comprising $7.7 million or 11% of this credit exposure, were not rated by these external agencies, but based on PSCo’s internal analysis, had credit quality consistent with investment grade. One of these significant counterparties, comprising $8.4 million or 12% of this credit exposure, had credit quality less than investment grade, based on external analysis. Seven of these significant counterparties are municipal or cooperative electric entities, or other utilities. Impact of derivative activity: Pre-Tax Fair Value Gains (Losses) Recognized During the Period in: (Millions of Dollars) Accumulated Other Regulatory(Assets) and Liabilities Three Months Ended June 30, 2019 Other derivative instruments Natural gas commodity $ — $ (1.5 ) Total $ — $ (1.5 ) Six Months Ended June 30, 2019 Other derivative instruments Natural gas commodity $ — $ (1.5 ) Total $ — $ (1.5 ) Three Months Ended June 30, 2018 Other derivative instruments Natural gas commodity $ — $ (0.2 ) Total $ — $ (0.2 ) Six Months Ended June 30, 2018 Other derivative instruments Natural gas commodity $ — $ (0.4 ) Total $ — $ (0.4 ) Pre-Tax (Gains) Losses Pre-Tax Gains (Losses) Recognized (Millions of Dollars) Accumulated Regulatory Three Months Ended June 30, 2019 Derivatives designated as cash flow hedges Interest rate $ 0.4 (a) $ — $ — Total $ 0.4 $ — $ — Other derivative instruments Commodity trading $ — $ — $ 3.3 (b) Total $ — $ — $ 3.3 Six Months Ended June 30, 2019 Derivatives designated as cash flow hedges Interest rate $ 0.8 (a) $ — $ — Total $ 0.8 $ — $ — Other derivative instruments Commodity trading $ — $ — $ 4.7 (b) Natural gas commodity — (1.3 ) (c) (2.0 ) (c) Total $ — $ (1.3 ) $ 2.7 Three Months Ended June 30, 2018 Derivatives designated as cash flow hedges Interest rate $ 0.4 (a) $ — $ — Total $ 0.4 $ — $ — Other derivative instruments Commodity trading $ — $ — $ 0.2 (b) Total $ — $ — $ 0.2 Six Months Ended June 30, 2018 Derivatives designated as cash flow hedges Interest rate $ 0.8 (a) $ — $ — Total $ 0.8 $ — $ — Other derivative instruments Commodity trading $ — $ — $ 0.7 (b) Natural gas commodity — 2.7 (c) (1.6 ) (c) Total $ — $ 2.7 $ (0.9 ) (a) Amounts are recorded to interest charges. (b) Amounts are recorded to interest charges. Amounts are recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue as appropriate. (c) Amounts for both the three and six months ended June 30, 2019 included no settlement gain or losses on derivatives entered to mitigate natural gas price risk for electric generation recorded to electric fuel and purchased power, subject to cost-recovery mechanisms and reclassified to a regulatory asset, as appropriate. Amounts for the three and six months ended June 30, 2018 included no such settlement gains or losses and $1.2 million of such settlement losses, respectively. Remaining derivative settlement losses for the three and six months ended June 30, 2019 and 2018 relate to natural gas operations and are recorded to cost of natural gas sold and transported. These gains and losses are subject to cost-recovery mechanisms and reclassified out of income to a regulatory asset or liability, as appropriate. PSCo had no derivative instruments designated as fair value hedges during the three and six months ended June 30, 2019 and 2018 . Credit Related Contingent Features — Contract provisions for derivative instruments that PSCo enters into, including those accounted for as normal purchase-normal sale contracts and therefore not reflected on the consolidated balance sheets, may require the posting of collateral or settlement of the contracts for various reasons, including if PSCo’s credit ratings are downgraded below its investment grade credit rating by any of the major credit rating agencies, or for cross-default contractual provisions if there was a failure under other financing arrangements related to payment terms or other covenants. At June 30, 2019 and Dec. 31, 2018 , there were no derivative instruments in a liability position with such underlying contract provisions with no offsetting positions or posted collateral. Certain derivative instruments are also subject to contract provisions that contain adequate assurance clauses. These provisions allow counterparties to seek performance assurance, including cash collateral, in the event that PSCo’s ability to fulfill its contractual obligations is reasonably expected to be impaired. PSCo had no collateral posted related to adequate assurance clauses in derivative contracts as of June 30, 2019 and Dec. 31, 2018 . Recurring Fair Value Measurements — PSCo’s assets and liabilities measured at fair value on a recurring basis: June 30, 2019 Dec. 31, 2018 Fair Value Fair Value Netting (a) Fair Value Fair Value Netting (a) (Millions of Dollars) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Current derivative assets Other derivative instruments: Commodity trading $ 5.4 $ 33.3 $ 0.2 $ 38.9 $ (20.9 ) $ 18.0 $ 2.3 $ 65.0 $ 0.1 $ 67.4 $ (28.2 ) $ 39.2 Natural gas commodity — 0.4 — 0.4 — 0.4 — 3.4 — 3.4 — 3.4 Total current derivative assets $ 5.4 $ 33.7 $ 0.2 $ 39.3 $ (20.9 ) 18.4 $ 2.3 $ 68.4 $ 0.1 $ 70.8 $ (28.2 ) 42.6 PPAs (b) — — Current derivative instruments $ 18.4 $ 42.6 Noncurrent derivative assets Other derivative instruments: Commodity trading $ 0.2 $ 4.6 $ — $ 4.8 $ (2.3 ) $ 2.5 $ — $ 1.6 $ — $ 1.6 $ (0.4 ) $ 1.2 Total noncurrent derivative assets $ 0.2 $ 4.6 $ — $ 4.8 $ (2.3 ) 2.5 $ — $ 1.6 $ — $ 1.6 $ (0.4 ) 1.2 PPAs (b) — — Noncurrent derivative instruments $ 2.5 $ 1.2 June 30, 2019 Dec. 31, 2018 Fair Value Fair Value Netting (a) Fair Value Fair Value Netting (a) (Millions of Dollars) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Current derivative liabilities Other derivative instruments: Commodity trading $ 5.5 $ 31.4 $ — $ 36.9 $ (27.3 ) $ 9.6 $ 2.4 $ 64.2 $ — $ 66.6 $ (34.7 ) $ 31.9 Total current derivative liabilities $ 5.5 $ 31.4 $ — $ 36.9 $ (27.3 ) 9.6 $ 2.4 $ 64.2 $ — $ 66.6 $ (34.7 ) 31.9 PPAs (b) 0.1 2.7 Current derivative instruments $ 9.7 $ 34.6 Noncurrent derivative liabilities Other derivative instruments: Commodity trading $ 0.2 $ 2.7 $ — $ 2.9 $ (2.3 ) $ 0.6 $ — $ 1.1 $ — $ 1.1 $ (0.5 ) $ 0.6 Total noncurrent derivative liabilities $ 0.2 $ 2.7 $ — $ 2.9 $ (2.3 ) 0.6 $ — $ 1.1 $ — $ 1.1 $ (0.5 ) 0.6 PPAs (b) — — Noncurrent derivative instruments $ 0.6 $ 0.6 (a) 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 June 30, 2019 and Dec. 31, 2018. At both June 30, 2019 and Dec. 31, 2018, derivative assets and liabilities include no obligations to return cash collateral. At June 30, 2019 and Dec. 31, 2018, derivative assets and liabilities include the rights to reclaim cash collateral of $6.4 million and $6.5 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. (b) During 2006, PSCo 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. There were $0.3 million and $1.0 million of gains recognized in earnings for Level 3 commodity trading derivatives in the three and six months ended June 30, 2019 , respectively. There were $0.1 million of gains recognized in earnings for Level 3 commodity trading derivatives in both the three and six months ended June 30, 2018 . PSCo recognizes transfers between fair value hierarchy levels as of the beginning of each period. There were no transfers of amounts between levels for derivative instruments for the three and six months ended June 30, 2019 and 2018 . Fair Value of Long-Term Debt Other financial instruments for which the carrying amount did not equal fair value: June 30, 2019 Dec. 31, 2018 (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Long-term debt, including current portion $ 4,846.1 $ 5,333.3 $ 4,997.6 $ 5,123.2 Fair value of PSCo’s long-term debt is estimated based on recent trades and observable spreads from benchmark interest rates for similar securities. Fair value estimates are based on information available to management as of June 30, 2019 and Dec. 31, 2018 , and given the observability of the inputs, fair values presented for long-term debt were assigned as Level 2.

Benefit Plans and Other Postret

Benefit Plans and Other Postretirement Benefits	6 Months Ended
	Jun. 30, 2019
Retirement Benefits [Abstract]
Benefit Plans and Other Postretirement Benefits	Benefit Plans and Other Postretirement Benefits Components of Net Periodic Benefit Cost (Credit) Three Months Ended June 30 2019 2018 2019 2018 (Millions of Dollars) Pension Benefits Postretirement Health Service cost $ 6.4 $ 7.3 $ 0.1 $ 0.2 Interest cost (a) 12.9 11.8 3.9 3.8 Expected return on plan assets (a) (17.1 ) (17.1 ) (4.7 ) (5.7 ) Amortization of prior service credit (a) (0.8 ) (0.9 ) (1.3 ) (1.6 ) Amortization of net loss (a) 6.3 7.8 0.7 1.0 Net periodic benefit cost (credit) 7.7 8.9 (1.3 ) (2.3 ) Credits not recognized due to the effects of regulation 1.8 0.9 0.2 — Net benefit cost (credit) recognized for financial reporting $ 9.5 $ 9.8 $ (1.1 ) $ (2.3 ) Six Months Ended June 30 2019 2018 2019 2018 (Millions of Dollars) Pension Benefits Postretirement Health Service cost $ 12.8 $ 14.6 $ 0.2 $ 0.3 Interest cost (a) 25.8 23.6 7.8 7.5 Expected return on plan assets (a) (34.2 ) (34.3 ) (9.4 ) (11.3 ) Amortization of prior service credit (a) (1.7 ) (1.7 ) (2.7 ) (3.1 ) Amortization of net loss (a) 12.7 15.6 1.5 2.0 Net periodic benefit cost (credit) 15.4 17.8 (2.6 ) (4.6 ) Credits not recognized due to the effects of regulation 3.6 2.4 0.5 — Net benefit cost (credit) recognized for financial reporting $ 19.0 $ 20.2 $ (2.1 ) $ (4.6 ) (a) The components of net periodic cost other than the service cost component are included in the line item “other income, net” in the consolidated statement of income or capitalized on the consolidated balance sheet as a regulatory asset. In January 2019, contributions of $150 million were made across four of Xcel Energy’s pension plans, of which $43 million was attributable to PSCo. On July 1, 2019, Xcel Energy made a $4 million contribution to the Xcel Energy Inc. Non-Bargaining Pension Plan (South), of which $3 million

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Contingencies PSCo is involved in various litigation matters in the ordinary course of business. The assessment of whether a loss is probable or is a reasonable possibility, and whether the loss or a range of loss is estimable, often involves a series of complex judgments about future events. Management maintains accruals for losses probable of being incurred and subject to reasonable estimation. Management is sometimes unable to estimate an amount or range of a reasonably possible loss in certain situations, including but not limited to, when (1) the damages sought are indeterminate, (2) the proceedings are in the early stages, or (3) the matters involve novel or unsettled legal theories. In such cases, there is considerable uncertainty regarding the timing or ultimate resolution of such matters, including a possible eventual loss. For current proceedings not specifically reported herein, management does not anticipate that the ultimate liabilities, if any, would have a material effect on PSCo’s financial statements. Unless otherwise required by GAAP, legal fees are expensed as incurred. Gas Trading Litigation — e prime is a wholly owned subsidiary of Xcel Energy. e prime was in the business of natural gas trading and marketing but has not engaged in natural gas trading or marketing activities since 2003. Multiple lawsuits seeking monetary damages were commenced against e prime and its affiliates, including Xcel Energy, between 2003 and 2009 alleging fraud and anticompetitive activities in conspiring to restrain the trade of natural gas and manipulate natural gas prices. Cases were all consolidated in the U.S. District Court in Nevada. Two cases remain active which include an MDL matter consisting of a Colorado purported class (Breckenridge) and a Wisconsin purported class (Arandell Corp.). Breckenridge/Colorado - The MDL panel remanded Breckenridge back to the U.S. District Court in Colorado and assigned to a judge. Arandell Corp. - In February 2019, Xcel Energy filed a no opposition motion to have the case remanded back to the U.S. District Court in Wisconsin. The motion was granted and the case has been remanded back to the District Court. Xcel Energy has concluded that a loss is remote for both remaining lawsuits. Employment, Tort and Commercial Litigation Line Extension Disputes — In December 2015, the DRC filed a lawsuit seeking monetary damages in the Denver District Court, stating PSCo failed to award proper allowances and refunds for line extensions to new developments pursuant to the terms of electric and gas service agreements. The dispute involves claims by over fifty developers. In February 2018, the Colorado Supreme Court denied DRC’s petition to appeal the Denver District Court’s dismissal of the lawsuit, effectively terminating this litigation. However, in January 2018, DRC filed a new lawsuit in Boulder County District Court, asserting a single claim that PSCo was required to file its line extension agreements with the CPUC but failed to do so. This claim is similar to the arguments previously raised by DRC. PSCo filed a motion to dismiss this claim, which was granted in May 2018. DRC subsequently filed an appeal to the Colorado Court of Appeals. Briefs have been filed and it is uncertain when a decision will be rendered. PSCo has concluded that a loss is remote with respect to both of these matters as the service agreements were developed to implement CPUC approved tariffs and PSCo has complied with the tariff provisions. If a loss were sustained, PSCo believes it would be allowed to recover costs through traditional regulatory mechanisms. Amount or range in dispute is presently unknown and no accrual has been recorded for this matter. Environmental MGP, Landfill or Disposal Sites — PSCo is cooperating with the City of Denver on an environmental investigation of the Rice Yards Site in the Central Platte Valley of Denver, Colorado, which had various historic industrial uses by multiple parties, including railroad, maintenance shop, scrap metal yard, and MGP operations. In the 1990’s, environmental remediation activities took place at the site under state oversight to accommodate the development of an amusement park and parking lots. The area is being redeveloped into residential and commercial mixed uses, and PSCo is in discussions with the current property owner regarding legal claims related to the Rice Yards Site. In addition, PSCo is currently investigating or remediating two other MGP, landfill or other disposal sites across its service territories. PSCo has recognized its best estimate of costs/liabilities that will result from final resolution of these issues, however, the outcome and timing is unknown. In addition, there may be insurance recovery and/or recovery from other potentially responsible parties, offsetting a portion of the costs incurred. Environmental Requirements — Water and Waste Coal Ash Regulation — PSCo’s operations are subject to federal and state laws that impose requirements for handling, storage, treatment and disposal of solid waste. Under the CCR Rule, utilities are required to complete groundwater sampling around their CCR landfills and surface impoundments. By the end of 2019, only six of PSCo’s regulated ash units are expected to be in operation. PSCo is conducting groundwater sampling, and where appropriate, initiating the assessment of corrective measures and evaluating whether corrective action is required at any CCR landfills or surface impoundments. Until PSCo completes its assessment, it is uncertain what impact, if any, there will be on the operations, financial condition or cash flows. Leases PSCo evaluates contracts that may contain leases, including PPAs and arrangements for the use of office space and other facilities, vehicles and equipment. Under ASC Topic 842, adopted by PSCo on Jan. 1, 2019, a contract contains a lease if it conveys the exclusive right to control the use of a specific asset. A contract determined to contain a lease is evaluated further to determine if the arrangement is a finance lease. ROU assets represent PSCo's rights to use leased assets. Starting in 2019, the present value of future operating lease payments are recognized in other current liabilities and noncurrent operating lease liabilities. These amounts, adjusted for any prepayments or incentives, are recognized as operating lease ROU assets. Most of PSCo’s leases do not contain a readily determinable discount rate. Therefore, the present value of future lease payments is calculated using the estimated incremental borrowing rate (weighted-average of 4.1% ). PSCo has elected to utilize the practical expedient under which non-lease components, such as asset maintenance costs included in payments, are not deducted from minimum lease payments for the purposes of lease accounting and disclosure. Leases with an initial term of 12 months or less are classified as short-term leases and are not recognized on the consolidated balance sheet. Operating lease ROU assets: (Millions of Dollars) June 30, 2019 PPAs $ 585.1 Other 68.3 Gross operating lease ROU assets 653.4 Accumulated amortization (39.7 ) Net operating lease ROU assets $ 613.7 In 2019, ROU assets for finance leases are included in other noncurrent assets, and the present value of future finance lease payments is included in other current liabilities and other noncurrent liabilities. Prior to 2019, finance leases were included in property, plant and equipment, the current portion of long-term debt and long-term debt. PSCo’s most significant finance lease activities are related to WYCO. WYCO is a joint venture with CIG to develop and lease natural gas pipeline, storage and compression facilities. Xcel Energy Inc. has a 50% ownership interest in WYCO. WYCO leases its facilities to CIG, and CIG operates the facilities, providing natural gas storage and transportation services to PSCo under separate service agreements. PSCo accounts for its Totem natural gas storage service and Front Range pipeline arrangements with CIG and WYCO, respectively, as finance leases. Finance lease ROU assets: (Millions of Dollars) June 30, 2019 Gas storage facilities $ 200.5 Gas pipeline 20.7 Gross finance lease ROU assets 221.2 Accumulated amortization (79.2 ) Net finance lease ROU assets $ 142.0 Components of lease expense: (Millions of Dollars) Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating leases PPA capacity payments $ 24.7 $ 49.0 Other operating leases (a) 3.6 7.2 Total operating lease expense (b) $ 28.3 $ 56.2 Finance leases Amortization of ROU assets $ 1.5 $ 3.0 Interest expense on lease liability 4.7 9.5 Total finance lease expense $ 6.2 $ 12.5 (a) Includes short-term lease expense of $0.3 million for three months ended June 30, 2019 and $0.7 million for six months ended June 30, 2019 . (b) PPA capacity payments are included in electric fuel and purchased power on the consolidated statements of income. Expense for other operating leases is included in O&M expense and electric fuel and purchased power. Future commitments under operating and finance leases as of June 30, 2019: (Millions of Dollars) PPA (a) (b) Operating Leases Other Operating Leases Total Leases Finance Leases 2019 $ 47.8 $ 6.5 $ 54.3 $ 12.4 2020 95.9 13.2 109.1 24.8 2021 96.4 12.1 108.5 23.6 2022 82.6 11.2 93.8 20.5 2023 70.0 10.9 80.9 20.3 Thereafter 288.6 29.2 317.8 420.4 Total minimum obligation 681.3 83.1 764.4 522.0 Interest component of obligation (106.4 ) (13.8 ) (120.2 ) (380.0 ) Present value of minimum obligation $ 574.9 $ 69.3 644.2 142.0 Less current portion (83.9 ) (6.5 ) Noncurrent operating and finance lease liabilities $ 560.3 $ 135.5 Weighted-average remaining lease term in years 8.3 39.0 (a) Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs. (b) PPA operating leases contractually expire at various dates through 2032. Future commitments under operating and finance leases as of Dec. 31, 2018: (Millions of Dollars) PPA (a) (b) Operating Leases Other Operating Leases Total Leases Finance Leases 2019 $ 95.5 $ 10.8 $ 106.3 $ 24.9 2020 95.9 10.7 106.6 24.8 2021 96.4 9.5 105.9 23.6 2022 82.6 8.4 91.0 20.5 2023 70.0 8.1 78.1 20.3 Thereafter 288.6 53.4 342.0 420.4 Total minimum obligation 534.5 Interest component of obligation (389.5 ) Present value of minimum obligation $ 145.0 (a) Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs. (b) PPA operating leases contractually expire at various dates through 2032. Variable Interest Entities Under certain PPAs, PSCo purchases power from IPPs and is required to reimburse the IPPs for fuel costs, or to participate in tolling arrangements under which PSCo procures the natural gas required to produce the energy that it purchases. These specific PPAs create a variable interest in the associated IPP. PSCo had approximately 1,442 MW and 1,571 MW of capacity under long-term PPAs as of June 30, 2019 and Dec. 31, 2018, respectively, with entities that have been determined to be VIEs. PSCo concluded that these entities are not required to be consolidated in its financial statements because it does not have the power to direct the activities that significantly impact the entities’ economic performance. These agreements have various expiration dates through 2032 .

Other Comprehensive Income

Other Comprehensive Income	6 Months Ended
	Jun. 30, 2019
Stockholders' Equity Note [Abstract]
Other Comprehensive Income	Other Comprehensive Income (Loss) Changes in accumulated other comprehensive loss, net of tax, for the three and six months ended June 30, 2019 and 2018 : Three Months Ended June 30, 2019 Three Months Ended June 30, 2018 (Millions of Dollars) Gains and Losses on Cash Flow Hedges Defined Benefit Pension and Postretirement Items Total Gains and Losses on Cash Flow Hedges Defined Benefit Pension and Postretirement Items Total Accumulated other comprehensive loss at April 1 $ (25.0 ) $ (0.2 ) $ (25.2 ) $ (26.1 ) $ (0.3 ) $ (26.4 ) Losses reclassified from net accumulated other comprehensive loss: Interest rate derivatives (net of taxes of $0.1, $0, $0.1 and $0, respectively) (a) 0.3 — 0.3 0.3 — 0.3 Net current period other comprehensive income 0.3 — 0.3 0.3 — 0.3 Accumulated other comprehensive loss at June 30 $ (24.7 ) $ (0.2 ) $ (24.9 ) $ (25.8 ) $ (0.3 ) $ (26.1 ) Six Months Ended June 30, 2019 Six Months Ended June 30, 2018 (Millions of Dollars) Gains and Losses on Cash Flow Hedges Defined Benefit Pension and Postretirement Items Total Gains and Losses on Cash Flow Hedges Defined Benefit Pension and Postretirement Items Total Accumulated other comprehensive loss at Jan. 1 $ (25.3 ) $ (0.2 ) $ (25.5 ) $ (26.4 ) $ (0.3 ) $ (26.7 ) Losses reclassified from net accumulated other comprehensive loss: Interest rate derivatives (net of taxes of $0.1, $0, $0.2 and $0, respectively) (a) 0.6 — 0.6 0.6 — 0.6 Net current period other comprehensive income 0.6 — 0.6 0.6 — 0.6 Accumulated other comprehensive loss at June 30 $ (24.7 ) $ (0.2 ) $ (24.9 ) $ (25.8 ) $ (0.3 ) $ (26.1 ) (a) Included in interest charges.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2019
Segment Reporting [Abstract]
Segment Information	Segment Information Operating results from the regulated electric utility and regulated natural gas utility are each separately and regularly reviewed by PSCo’s chief operating decision maker. PSCo evaluates performance based on profit or loss generated from the product or service provided. These segments are managed separately because the revenue streams are dependent upon regulated rate recovery, which is separately determined for each segment. PSCo has the following reportable segments: regulated electric utility, regulated natural gas utility and all other. • Regulated Electric - The regulated electric utility segment generates electricity which is transmitted and distributed in Colorado. This segment includes sales for resale and provides wholesale transmission service to various entities in the United States. Regulated electric utility also includes PSCo’s wholesale commodity and trading operations. • Regulated Natural Gas - The regulated natural gas utility segment transports, stores and distributes natural gas in portions of Colorado. • All Other - Revenues from operating segments not included above are below the necessary quantitative thresholds are included in the all other category. Those primarily include steam revenue, appliance repair services and nonutility real estate activities. Asset and capital expenditure information is not provided for PSCo’s reportable segments because as an integrated electric and natural gas utility, PSCo operates significant assets that are not dedicated to a specific business segment, and reporting assets and capital expenditures by business segment would require arbitrary and potentially misleading allocations which may not necessarily reflect the assets that would be required for the operation of the business segments on a stand-alone basis. Certain costs, such as common depreciation, common O&M expenses and interest expense are allocated based on cost causation allocators across each segment. In addition, a general allocator is used for certain general and administrative expenses, including office supplies, rent, property insurance and general advertising. PSCo’s segment information for the three and six months ended June 30 : Three Months Ended June 30 (Millions of Dollars) 2019 2018 Regulated Electric Operating revenues $ 692.7 $ 716.2 Intersegment revenues 0.1 0.1 Total revenue 692.8 716.3 Net income 84.8 101.9 Regulated Natural Gas Operating revenues $ 207.6 $ 186.7 Intersegment revenues — 0.1 Total revenue 207.6 186.8 Net income 17.6 21.0 All Other Operating revenues (a) $ 9.7 $ 9.0 Net loss (0.9 ) (0.6 ) Consolidated Total Operating revenues (a) $ 910.1 $ 912.1 Reconciling eliminations (0.1 ) (0.2 ) Total revenue $ 910.0 $ 911.9 Net income 101.5 122.3 (a) Operating revenues include $1.1 million of other affiliate revenue for the three months ended June 30, 2019 and 2018 . Six Months Ended June 30 (Millions of Dollars) 2019 2018 Regulated Electric Operating revenues $ 1,434.2 $ 1,414.5 Intersegment revenues 0.2 0.2 Total revenue 1,434.4 1,414.7 Net income 167.2 181.5 Regulated Natural Gas Operating revenues $ 676.7 $ 550.6 Intersegment revenues 0.1 0.1 Total revenue 676.8 550.7 Net income 76.8 74.7 All Other Operating revenues (a) $ 22.1 $ 20.1 Net loss (3.7 ) (0.2 ) Consolidated Total Operating revenues (a) $ 2,133.3 $ 1,985.5 Reconciling eliminations (0.3 ) (0.3 ) Total revenue $ 2,133.0 $ 1,985.2 Net income 240.3 256.0 (a) Operating revenues include $2.2 million of other affiliate revenue for the six months ended June 30, 2019 and 2018 .

Selected Balance Sheet Data (Ta

Selected Balance Sheet Data (Tables)	6 Months Ended
	Jun. 30, 2019
Balance Sheet Related Disclosures [Abstract]
Accounts Receivable, Net	(Millions of Dollars) June 30, 2019 Dec. 31, 2018 Accounts receivable, net Accounts receivable $ 272.3 $ 330.8 Less allowance for bad debts (19.7 ) (20.5 ) $ 252.6 $ 310.3
Inventories	(Millions of Dollars) June 30, 2019 Dec. 31, 2018 Inventories Materials and supplies $ 61.8 $ 61.9 Fuel 71.7 69.5 Natural gas 32.0 66.0 $ 165.5 $ 197.4
Property, Plant and Equipment, Net	(Millions of Dollars) June 30, 2019 Dec. 31, 2018 Property, plant and equipment, net Electric plant $ 13,922.3 $ 13,604.5 Natural gas plant 4,443.0 4,387.6 Common and other property 1,052.3 1,023.7 Plant to be retired (a) 290.2 321.9 Construction work in progress 638.9 573.3 Total property, plant and equipment 20,346.7 19,911.0 Less accumulated depreciation (5,011.0 ) (4,791.0 ) $ 15,335.7 $ 15,120.0 (a) In 2018, the CPUC approved early retirement of PSCo’s Comanche Units 1 and 2 in approximately 2022 and 2025, respectively. PSCo also expects Craig Unit 1 to be retired early in 2025. Amounts are presented net of accumulated depreciation.

Borrowings and Other Financin_2

Borrowings and Other Financing Instruments (Tables)	6 Months Ended
	Jun. 30, 2019
Borrowings and Other Financing Instruments [Abstract]
Credit Facilities	At June 30, 2019 , PSCo had the following committed credit facility available (in millions of dollars): Credit Facility (a) Outstanding (b) Available $ 700 $ 231 $ 469 (a) This credit facility expires in June 2024 . (b) Includes outstanding commercial paper and letters of credit.
Money Pool
Borrowings and Other Financing Instruments [Abstract]
Short-Term Borrowings	Money pool borrowings for PSCo were as follows: (Amounts in Millions, Except Interest Rates) Three Months Ended June 30, 2019 Year Ended Dec. 31, 2018 Borrowing limit $ 250 $ 250 Amount outstanding at period end 50 — Average amount outstanding 3 25 Maximum amount outstanding 50 156 Weighted average interest rate, computed on a daily basis 2.41 % 1.93 % Weighted average interest rate at period end 2.41 N/A
Commercial Paper
Borrowings and Other Financing Instruments [Abstract]
Short-Term Borrowings	Commercial paper outstanding for PSCo was as follows: (Amounts in Millions, Except Interest Rates) Three Months Ended June 30, 2019 Year Ended Dec. 31, 2018 Borrowing limit $ 700 $ 700 Amount outstanding at period end 221 307 Average amount outstanding 244 55 Maximum amount outstanding 432 309 Weighted average interest rate, computed on a daily basis 2.65 % 2.28 % Weighted average interest rate at period end 2.59 2.95

Revenues (Tables)

Revenues (Tables)	6 Months Ended
	Jun. 30, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	PSCo’s operating revenues consists of the following: Three Months Ended June 30, 2019 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 211.5 $ 130.1 $ 2.8 $ 344.4 C&I 384.4 49.4 5.7 439.5 Other 11.8 — — 11.8 Total retail 607.7 179.5 8.5 795.7 Wholesale 29.1 — — 29.1 Transmission 11.6 — — 11.6 Other 6.5 23.3 — 29.8 Total revenue from contracts with customers 654.9 202.8 8.5 866.2 Alternative revenue and other 37.8 4.8 1.2 43.8 Total revenues $ 692.7 $ 207.6 $ 9.7 $ 910.0 Three Months Ended June 30, 2018 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 222.7 $ 104.0 $ 2.6 $ 329.3 C&I 383.7 38.9 5.3 427.9 Other 11.4 — — 11.4 Total retail 617.8 142.9 7.9 768.6 Wholesale 36.2 — — 36.2 Transmission 13.2 — — 13.2 Other 14.7 18.8 — 33.5 Total revenue from contracts with customers 681.9 161.7 7.9 851.5 Alternative revenue and other 34.3 25.0 1.1 60.4 Total revenues $ 716.2 $ 186.7 $ 9.0 $ 911.9 Six Months Ended June 30, 2019 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 456.6 $ 441.5 $ 5.3 $ 903.4 C&I 752.3 169.7 14.5 936.5 Other 24.3 — — 24.3 Total retail 1,233.2 611.2 19.8 1,864.2 Wholesale 86.4 — — 86.4 Transmission 25.0 — — 25.0 Other 18.1 54.9 — 73.0 Total revenue from contracts with customers 1,362.7 666.1 19.8 2,048.6 Alternative revenue and other 71.5 10.6 2.3 84.4 Total revenues $ 1,434.2 $ 676.7 $ 22.1 $ 2,133.0 Six Months Ended June 30, 2018 (Millions of Dollars) Electric Natural Gas All Other Total Major revenue types Revenue from contracts with customers: Residential $ 450.3 $ 331.8 $ 5.2 $ 787.3 C&I 727.0 124.9 12.5 864.4 Other 23.6 — 0.1 23.7 Total retail 1,200.9 456.7 17.8 1,675.4 Wholesale 84.1 — — 84.1 Transmission 25.4 — — 25.4 Other 33.5 43.8 — 77.3 Total revenue from contracts with customers 1,343.9 500.5 17.8 1,862.2 Alternative revenue and other 70.6 50.1 2.3 123.0 Total revenues $ 1,414.5 $ 550.6 $ 20.1 $ 1,985.2

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jun. 30, 2019
Income Tax Disclosure [Abstract]
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	The following table reconciles the difference between the statutory rate and the ETR: Six Months Ended June 30 2019 2018 Federal statutory rate 21.0 % 21.0 % State tax (net of federal tax effect) 3.7 3.7 Increases (decreases) in tax from: Wind PTCs (9.4 ) — Plant regulatory differences (a) (3.4 ) (1.5 ) Other tax credits and allowances (net) (1.0 ) (1.0 ) Other (net) 0.1 0.3 Effective income tax rate 11.0 % 22.5 % (a) Regulatory differences for income tax primarily relate to the flow back of excess deferred taxes to customers through the average rate assumption method and the impact of AFUDC - Equity. Year-to-date variations primarily relates to the deferral of the flow back of excess deferred taxes in 2018, as a result of pending regulatory decisions. Treatment of most tax reform items was established prior to the first quarter of 2019, resulting in a reduction in deferred amounts. Income tax benefits associated with the flow back of excess deferred credits are offset by corresponding revenue reductions and additional prepaid pension asset amortization.
Summary of Statute of Limitations Applicable to Open Tax Years [Table Text Block]	Federal Audits — PSCO is a member of the Xcel Energy affiliated group that files a consolidated federal income tax return. Statute of limitations applicable to Xcel Energy’s federal income tax returns expire as follows: Tax Year(s) Expiration 2009 - 2013 June 2020 2014 - 2016 September 2020 2017 September 2021
Reconciliation of Unrecognized Tax Benefits	Unrecognized tax benefits - permanent vs temporary: (Millions of Dollars) June 30, 2019 Dec. 31, 2018 Unrecognized tax benefit — Permanent tax positions $ 6.0 $ 5.4 Unrecognized tax benefit — Temporary tax positions 4.7 4.9 Total unrecognized tax benefit $ 10.7 $ 10.3
Tax Benefits Associated with NOL and Tax Credit Carryforwards	Unrecognized tax benefits were reduced by tax benefits associated with NOL and tax credit carryforwards: (Millions of Dollars) June 30, 2019 Dec. 31, 2018 NOL and tax credit carryforwards $ (6.1 ) $ (5.6 )

Fair Value of Financial Asset_2

Fair Value of Financial Assets and Liabilities (Tables)	6 Months Ended
	Jun. 30, 2019
Fair Value Disclosures [Abstract]
Gross Notional Amounts of Commodity Forwards and Options	Gross notional amounts of commodity forwards and options: (Amounts in Millions) (a)(b) June 30, 2019 Dec. 31, 2018 Megawatt hours of electricity 16.3 24.4 Million British thermal units of natural gas 51.3 48.4 (a) Amounts are not reflective of net positions in the underlying commodities. (b) Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income	Impact of derivative activity: Pre-Tax Fair Value Gains (Losses) Recognized During the Period in: (Millions of Dollars) Accumulated Other Regulatory(Assets) and Liabilities Three Months Ended June 30, 2019 Other derivative instruments Natural gas commodity $ — $ (1.5 ) Total $ — $ (1.5 ) Six Months Ended June 30, 2019 Other derivative instruments Natural gas commodity $ — $ (1.5 ) Total $ — $ (1.5 ) Three Months Ended June 30, 2018 Other derivative instruments Natural gas commodity $ — $ (0.2 ) Total $ — $ (0.2 ) Six Months Ended June 30, 2018 Other derivative instruments Natural gas commodity $ — $ (0.4 ) Total $ — $ (0.4 ) Pre-Tax (Gains) Losses Pre-Tax Gains (Losses) Recognized (Millions of Dollars) Accumulated Regulatory Three Months Ended June 30, 2019 Derivatives designated as cash flow hedges Interest rate $ 0.4 (a) $ — $ — Total $ 0.4 $ — $ — Other derivative instruments Commodity trading $ — $ — $ 3.3 (b) Total $ — $ — $ 3.3 Six Months Ended June 30, 2019 Derivatives designated as cash flow hedges Interest rate $ 0.8 (a) $ — $ — Total $ 0.8 $ — $ — Other derivative instruments Commodity trading $ — $ — $ 4.7 (b) Natural gas commodity — (1.3 ) (c) (2.0 ) (c) Total $ — $ (1.3 ) $ 2.7 Three Months Ended June 30, 2018 Derivatives designated as cash flow hedges Interest rate $ 0.4 (a) $ — $ — Total $ 0.4 $ — $ — Other derivative instruments Commodity trading $ — $ — $ 0.2 (b) Total $ — $ — $ 0.2 Six Months Ended June 30, 2018 Derivatives designated as cash flow hedges Interest rate $ 0.8 (a) $ — $ — Total $ 0.8 $ — $ — Other derivative instruments Commodity trading $ — $ — $ 0.7 (b) Natural gas commodity — 2.7 (c) (1.6 ) (c) Total $ — $ 2.7 $ (0.9 ) (a) Amounts are recorded to interest charges. (b) Amounts are recorded to interest charges. Amounts are recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue as appropriate. (c) Amounts for both the three and six months ended June 30, 2019 included no settlement gain or losses on derivatives entered to mitigate natural gas price risk for electric generation recorded to electric fuel and purchased power, subject to cost-recovery mechanisms and reclassified to a regulatory asset, as appropriate. Amounts for the three and six months ended June 30, 2018 included no such settlement gains or losses and $1.2 million of such settlement losses, respectively. Remaining derivative settlement losses for the three and six months ended June 30, 2019 and 2018 relate to natural gas operations and are recorded to cost of natural gas sold and transported. These gains and losses are subject to cost-recovery mechanisms and reclassified out of income to a regulatory asset or liability, as appropriate.
Derivative Assets and Liabilities Measured at Fair Value on a Recurring Basis by Hierarchy Level	Recurring Fair Value Measurements — PSCo’s assets and liabilities measured at fair value on a recurring basis: June 30, 2019 Dec. 31, 2018 Fair Value Fair Value Netting (a) Fair Value Fair Value Netting (a) (Millions of Dollars) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Current derivative assets Other derivative instruments: Commodity trading $ 5.4 $ 33.3 $ 0.2 $ 38.9 $ (20.9 ) $ 18.0 $ 2.3 $ 65.0 $ 0.1 $ 67.4 $ (28.2 ) $ 39.2 Natural gas commodity — 0.4 — 0.4 — 0.4 — 3.4 — 3.4 — 3.4 Total current derivative assets $ 5.4 $ 33.7 $ 0.2 $ 39.3 $ (20.9 ) 18.4 $ 2.3 $ 68.4 $ 0.1 $ 70.8 $ (28.2 ) 42.6 PPAs (b) — — Current derivative instruments $ 18.4 $ 42.6 Noncurrent derivative assets Other derivative instruments: Commodity trading $ 0.2 $ 4.6 $ — $ 4.8 $ (2.3 ) $ 2.5 $ — $ 1.6 $ — $ 1.6 $ (0.4 ) $ 1.2 Total noncurrent derivative assets $ 0.2 $ 4.6 $ — $ 4.8 $ (2.3 ) 2.5 $ — $ 1.6 $ — $ 1.6 $ (0.4 ) 1.2 PPAs (b) — — Noncurrent derivative instruments $ 2.5 $ 1.2 June 30, 2019 Dec. 31, 2018 Fair Value Fair Value Netting (a) Fair Value Fair Value Netting (a) (Millions of Dollars) Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Current derivative liabilities Other derivative instruments: Commodity trading $ 5.5 $ 31.4 $ — $ 36.9 $ (27.3 ) $ 9.6 $ 2.4 $ 64.2 $ — $ 66.6 $ (34.7 ) $ 31.9 Total current derivative liabilities $ 5.5 $ 31.4 $ — $ 36.9 $ (27.3 ) 9.6 $ 2.4 $ 64.2 $ — $ 66.6 $ (34.7 ) 31.9 PPAs (b) 0.1 2.7 Current derivative instruments $ 9.7 $ 34.6 Noncurrent derivative liabilities Other derivative instruments: Commodity trading $ 0.2 $ 2.7 $ — $ 2.9 $ (2.3 ) $ 0.6 $ — $ 1.1 $ — $ 1.1 $ (0.5 ) $ 0.6 Total noncurrent derivative liabilities $ 0.2 $ 2.7 $ — $ 2.9 $ (2.3 ) 0.6 $ — $ 1.1 $ — $ 1.1 $ (0.5 ) 0.6 PPAs (b) — — Noncurrent derivative instruments $ 0.6 $ 0.6 (a) 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 June 30, 2019 and Dec. 31, 2018. At both June 30, 2019 and Dec. 31, 2018, derivative assets and liabilities include no obligations to return cash collateral. At June 30, 2019 and Dec. 31, 2018, derivative assets and liabilities include the rights to reclaim cash collateral of $6.4 million and $6.5 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. (b) During 2006, PSCo 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.
Carrying Amount and Fair Value of Long-term Debt	Other financial instruments for which the carrying amount did not equal fair value: June 30, 2019 Dec. 31, 2018 (Millions of Dollars) Carrying Amount Fair Value Carrying Amount Fair Value Long-term debt, including current portion $ 4,846.1 $ 5,333.3 $ 4,997.6 $ 5,123.2

Benefit Plans and Other Postr_2

Benefit Plans and Other Postretirement Benefits (Tables)	6 Months Ended
	Jun. 30, 2019
Retirement Benefits [Abstract]
Components of Net Periodic Benefit Cost (Credit)	Components of Net Periodic Benefit Cost (Credit) Three Months Ended June 30 2019 2018 2019 2018 (Millions of Dollars) Pension Benefits Postretirement Health Service cost $ 6.4 $ 7.3 $ 0.1 $ 0.2 Interest cost (a) 12.9 11.8 3.9 3.8 Expected return on plan assets (a) (17.1 ) (17.1 ) (4.7 ) (5.7 ) Amortization of prior service credit (a) (0.8 ) (0.9 ) (1.3 ) (1.6 ) Amortization of net loss (a) 6.3 7.8 0.7 1.0 Net periodic benefit cost (credit) 7.7 8.9 (1.3 ) (2.3 ) Credits not recognized due to the effects of regulation 1.8 0.9 0.2 — Net benefit cost (credit) recognized for financial reporting $ 9.5 $ 9.8 $ (1.1 ) $ (2.3 ) Six Months Ended June 30 2019 2018 2019 2018 (Millions of Dollars) Pension Benefits Postretirement Health Service cost $ 12.8 $ 14.6 $ 0.2 $ 0.3 Interest cost (a) 25.8 23.6 7.8 7.5 Expected return on plan assets (a) (34.2 ) (34.3 ) (9.4 ) (11.3 ) Amortization of prior service credit (a) (1.7 ) (1.7 ) (2.7 ) (3.1 ) Amortization of net loss (a) 12.7 15.6 1.5 2.0 Net periodic benefit cost (credit) 15.4 17.8 (2.6 ) (4.6 ) Credits not recognized due to the effects of regulation 3.6 2.4 0.5 — Net benefit cost (credit) recognized for financial reporting $ 19.0 $ 20.2 $ (2.1 ) $ (4.6 ) (a) The components of net periodic cost other than the service cost component are included in the line item “other income, net” in the consolidated statement of income or capitalized on the consolidated balance sheet as a regulatory asset.

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule of Operating and Finance Lease Right-of-Use Assets	Finance lease ROU assets: (Millions of Dollars) June 30, 2019 Gas storage facilities $ 200.5 Gas pipeline 20.7 Gross finance lease ROU assets 221.2 Accumulated amortization (79.2 ) Net finance lease ROU assets $ 142.0 Operating lease ROU assets: (Millions of Dollars) June 30, 2019 PPAs $ 585.1 Other 68.3 Gross operating lease ROU assets 653.4 Accumulated amortization (39.7 ) Net operating lease ROU assets $ 613.7
Schedule of Components of Lease Expense	Components of lease expense: (Millions of Dollars) Three Months Ended June 30, 2019 Six Months Ended June 30, 2019 Operating leases PPA capacity payments $ 24.7 $ 49.0 Other operating leases (a) 3.6 7.2 Total operating lease expense (b) $ 28.3 $ 56.2 Finance leases Amortization of ROU assets $ 1.5 $ 3.0 Interest expense on lease liability 4.7 9.5 Total finance lease expense $ 6.2 $ 12.5 (a) Includes short-term lease expense of $0.3 million for three months ended June 30, 2019 and $0.7 million for six months ended June 30, 2019 . (b) PPA capacity payments are included in electric fuel and purchased power on the consolidated statements of income. Expense for other operating leases is included in O&M expense and electric fuel and purchased power.
Schedule of Future Commitments under Finance Leases	Future commitments under operating and finance leases as of June 30, 2019: (Millions of Dollars) PPA (a) (b) Operating Leases Other Operating Leases Total Leases Finance Leases 2019 $ 47.8 $ 6.5 $ 54.3 $ 12.4 2020 95.9 13.2 109.1 24.8 2021 96.4 12.1 108.5 23.6 2022 82.6 11.2 93.8 20.5 2023 70.0 10.9 80.9 20.3 Thereafter 288.6 29.2 317.8 420.4 Total minimum obligation 681.3 83.1 764.4 522.0 Interest component of obligation (106.4 ) (13.8 ) (120.2 ) (380.0 ) Present value of minimum obligation $ 574.9 $ 69.3 644.2 142.0 Less current portion (83.9 ) (6.5 ) Noncurrent operating and finance lease liabilities $ 560.3 $ 135.5 Weighted-average remaining lease term in years 8.3 39.0 (a) Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs. (b) PPA operating leases contractually expire at various dates through 2032. Future commitments under operating and finance leases as of Dec. 31, 2018: (Millions of Dollars) PPA (a) (b) Operating Leases Other Operating Leases Total Leases Finance Leases 2019 $ 95.5 $ 10.8 $ 106.3 $ 24.9 2020 95.9 10.7 106.6 24.8 2021 96.4 9.5 105.9 23.6 2022 82.6 8.4 91.0 20.5 2023 70.0 8.1 78.1 20.3 Thereafter 288.6 53.4 342.0 420.4 Total minimum obligation 534.5 Interest component of obligation (389.5 ) Present value of minimum obligation $ 145.0 (a) Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs. (b) PPA operating leases contractually expire at various dates through 2032.
Schedule of Future Commitments under Operating Leases	Future commitments under operating and finance leases as of June 30, 2019: (Millions of Dollars) PPA (a) (b) Operating Leases Other Operating Leases Total Leases Finance Leases 2019 $ 47.8 $ 6.5 $ 54.3 $ 12.4 2020 95.9 13.2 109.1 24.8 2021 96.4 12.1 108.5 23.6 2022 82.6 11.2 93.8 20.5 2023 70.0 10.9 80.9 20.3 Thereafter 288.6 29.2 317.8 420.4 Total minimum obligation 681.3 83.1 764.4 522.0 Interest component of obligation (106.4 ) (13.8 ) (120.2 ) (380.0 ) Present value of minimum obligation $ 574.9 $ 69.3 644.2 142.0 Less current portion (83.9 ) (6.5 ) Noncurrent operating and finance lease liabilities $ 560.3 $ 135.5 Weighted-average remaining lease term in years 8.3 39.0 (a) Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs. (b) PPA operating leases contractually expire at various dates through 2032. Future commitments under operating and finance leases as of Dec. 31, 2018: (Millions of Dollars) PPA (a) (b) Operating Leases Other Operating Leases Total Leases Finance Leases 2019 $ 95.5 $ 10.8 $ 106.3 $ 24.9 2020 95.9 10.7 106.6 24.8 2021 96.4 9.5 105.9 23.6 2022 82.6 8.4 91.0 20.5 2023 70.0 8.1 78.1 20.3 Thereafter 288.6 53.4 342.0 420.4 Total minimum obligation 534.5 Interest component of obligation (389.5 ) Present value of minimum obligation $ 145.0 (a) Amounts do not include PPAs accounted for as executory contracts and/or contingent payments, such as energy payments on renewable PPAs. (b) PPA operating leases contractually expire at various dates through 2032.

Other Comprehensive Income (Tab

Other Comprehensive Income (Tables)	6 Months Ended
	Jun. 30, 2019
Stockholders' Equity Note [Abstract]
Changes in Accumulated Other Comprehensive Loss, Net of Tax	Changes in accumulated other comprehensive loss, net of tax, for the three and six months ended June 30, 2019 and 2018 : Three Months Ended June 30, 2019 Three Months Ended June 30, 2018 (Millions of Dollars) Gains and Losses on Cash Flow Hedges Defined Benefit Pension and Postretirement Items Total Gains and Losses on Cash Flow Hedges Defined Benefit Pension and Postretirement Items Total Accumulated other comprehensive loss at April 1 $ (25.0 ) $ (0.2 ) $ (25.2 ) $ (26.1 ) $ (0.3 ) $ (26.4 ) Losses reclassified from net accumulated other comprehensive loss: Interest rate derivatives (net of taxes of $0.1, $0, $0.1 and $0, respectively) (a) 0.3 — 0.3 0.3 — 0.3 Net current period other comprehensive income 0.3 — 0.3 0.3 — 0.3 Accumulated other comprehensive loss at June 30 $ (24.7 ) $ (0.2 ) $ (24.9 ) $ (25.8 ) $ (0.3 ) $ (26.1 ) Six Months Ended June 30, 2019 Six Months Ended June 30, 2018 (Millions of Dollars) Gains and Losses on Cash Flow Hedges Defined Benefit Pension and Postretirement Items Total Gains and Losses on Cash Flow Hedges Defined Benefit Pension and Postretirement Items Total Accumulated other comprehensive loss at Jan. 1 $ (25.3 ) $ (0.2 ) $ (25.5 ) $ (26.4 ) $ (0.3 ) $ (26.7 ) Losses reclassified from net accumulated other comprehensive loss: Interest rate derivatives (net of taxes of $0.1, $0, $0.2 and $0, respectively) (a) 0.6 — 0.6 0.6 — 0.6 Net current period other comprehensive income 0.6 — 0.6 0.6 — 0.6 Accumulated other comprehensive loss at June 30 $ (24.7 ) $ (0.2 ) $ (24.9 ) $ (25.8 ) $ (0.3 ) $ (26.1 )

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2019
Segment Reporting [Abstract]
Results from Operations by Reportable Segment	PSCo’s segment information for the three and six months ended June 30 : Three Months Ended June 30 (Millions of Dollars) 2019 2018 Regulated Electric Operating revenues $ 692.7 $ 716.2 Intersegment revenues 0.1 0.1 Total revenue 692.8 716.3 Net income 84.8 101.9 Regulated Natural Gas Operating revenues $ 207.6 $ 186.7 Intersegment revenues — 0.1 Total revenue 207.6 186.8 Net income 17.6 21.0 All Other Operating revenues (a) $ 9.7 $ 9.0 Net loss (0.9 ) (0.6 ) Consolidated Total Operating revenues (a) $ 910.1 $ 912.1 Reconciling eliminations (0.1 ) (0.2 ) Total revenue $ 910.0 $ 911.9 Net income 101.5 122.3 (a) Operating revenues include $1.1 million of other affiliate revenue for the three months ended June 30, 2019 and 2018 . Six Months Ended June 30 (Millions of Dollars) 2019 2018 Regulated Electric Operating revenues $ 1,434.2 $ 1,414.5 Intersegment revenues 0.2 0.2 Total revenue 1,434.4 1,414.7 Net income 167.2 181.5 Regulated Natural Gas Operating revenues $ 676.7 $ 550.6 Intersegment revenues 0.1 0.1 Total revenue 676.8 550.7 Net income 76.8 74.7 All Other Operating revenues (a) $ 22.1 $ 20.1 Net loss (3.7 ) (0.2 ) Consolidated Total Operating revenues (a) $ 2,133.3 $ 1,985.5 Reconciling eliminations (0.3 ) (0.3 ) Total revenue $ 2,133.0 $ 1,985.2 Net income 240.3 256.0 (a) Operating revenues include $2.2 million of other affiliate revenue for the six months ended June 30, 2019 and 2018 .

Selected Balance Sheet Data (De

Selected Balance Sheet Data (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Accounts receivable, net
Accounts receivable	$ 272.3	$ 330.8
Less allowance for bad debts	(19.7)	(20.5)
Accounts receivable, net	$ 252.6	$ 310.3

Selected Balance Sheet Data Bal

Selected Balance Sheet Data Balance Sheet Related Disclosures, Inventories (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Public Utilities, Inventory [Line Items]
Inventories	$ 165.5	$ 197.4
Materials and supplies
Public Utilities, Inventory [Line Items]
Inventories	61.8	61.9
Fuel
Public Utilities, Inventory [Line Items]
Inventories	71.7	69.5
Natural gas
Public Utilities, Inventory [Line Items]
Inventories	$ 32	$ 66

Selected Balance Sheet Data B_2

Selected Balance Sheet Data Balance Sheet Related Disclosures, Property, Plant and Equipment (Details) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 20,346.7	$ 19,911
Less accumulated depreciation		(5,011)	(4,791)
Property, plant and equipment, net		15,335.7	15,120
Electric plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		13,922.3	13,604.5
Natural gas plant
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		4,443	4,387.6
Common and other property
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		1,052.3	1,023.7
Plant to be retired
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	[1]	290.2	321.9
Construction work in progress
Public Utility, Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross		$ 638.9	$ 573.3
[1]	In 2018, the CPUC approved early retirement of PSCo’s Comanche Units 1 and 2 in approximately 2022 and 2025, respectively. PSCo also expects Craig Unit 1 to be retired early in 2025. Amounts are presented net of accumulated depreciation.

Accounting Pronouncements (Deta

Accounting Pronouncements (Details) - USD ($) $ in Millions	Jun. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset	$ 613.7		$ 0
Operating Lease, Liability	$ 644.2
Accounting Standards Update 2016-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating Lease, Right-of-Use Asset		$ 700
Operating Lease, Liability		$ 700

Borrowings and Other Financin_3

Borrowings and Other Financing Instruments, Short-Term Borrowings (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Short-term Debt [Line Items]
Amount outstanding at period end	$ 221,000,000	$ 307,000,000
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	700,000,000	700,000,000
Amount outstanding at period end	221,000,000	307,000,000
Average amount outstanding	244,000,000	55,000,000
Maximum amount outstanding	$ 432,000,000	$ 309,000,000
Weighted average interest rate, computed on a daily basis	2.65%	2.28%
Weighted average interest rate at period end	2.59%	2.95%
Money Pool
Short-term Debt [Line Items]
Borrowing limit	$ 250,000,000	$ 250,000,000
Amount outstanding at period end	50,000,000	0
Average amount outstanding	3,000,000	25,000,000
Maximum amount outstanding	$ 50,000,000	$ 156,000,000
Weighted average interest rate, computed on a daily basis	2.41%	1.93%
Weighted average interest rate at period end	2.41%

Borrowings and Other Financin_4

Borrowings and Other Financing Instruments, Letters of Credit (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Amount outstanding at period end	$ 221	$ 307
Letter of Credit
Line of Credit Facility [Line Items]
Letters of Credit, Term	1 year
Amount outstanding at period end	$ 10	$ 10

Borrowings and Other Financin_5

Borrowings and Other Financing Instruments, Credit Facility (Details) - Credit Facility - USD ($)		Jun. 30, 2019	Dec. 31, 2018
Line of Credit Facility [Line Items]
Credit Facility	[1]	$ 700,000,000
Outstanding	[2]	231,000,000
Available		469,000,000
Direct advances on the credit facility outstanding		$ 0	$ 0
[1]	This credit facility expires in June 2024 .
[2]	Includes outstanding commercial paper and letters of credit.

Borrowings and Other Financin_6

Borrowings and Other Financing Instruments Long-Term Borrowings (Details) - Bonds [Member] - Series Due September 15, 2049 [Domain] $ in Millions	Jun. 30, 2019USD ($)
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 400
Debt Instrument, Interest Rate, Stated Percentage	4.05%

Revenues (Details)

Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 910	$ 911.9	$ 2,133	$ 1,985.2
Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	866.2	851.5	2,048.6	1,862.2
Retail
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	795.7	768.6	1,864.2	1,675.4
Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	344.4	329.3	903.4	787.3
Retail | Commercial and Industrial Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	439.5	427.9	936.5	864.4
Retail | Other Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	11.8	11.4	24.3	23.7
Wholesale Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	29.1	36.2	86.4	84.1
Transmission Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	11.6	13.2	25	25.4
Other
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	29.8	33.5	73	77.3
Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	43.8	60.4	84.4	123
Regulated Electric
Disaggregation of Revenue [Line Items]
Total operating revenues	692.7	716.2	1,434.2	1,414.5
Regulated Electric | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	654.9	681.9	1,362.7	1,343.9
Regulated Electric | Retail
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	607.7	617.8	1,233.2	1,200.9
Regulated Electric | Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	211.5	222.7	456.6	450.3
Regulated Electric | Retail | Commercial and Industrial Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	384.4	383.7	752.3	727
Regulated Electric | Retail | Other Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	11.8	11.4	24.3	23.6
Regulated Electric | Wholesale Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	29.1	36.2	86.4	84.1
Regulated Electric | Transmission Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	11.6	13.2	25	25.4
Regulated Electric | Other
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	6.5	14.7	18.1	33.5
Regulated Electric | Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	37.8	34.3	71.5	70.6
Regulated Natural Gas
Disaggregation of Revenue [Line Items]
Total operating revenues	207.6	186.7	676.7	550.6
Regulated Natural Gas | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	202.8	161.7	666.1	500.5
Regulated Natural Gas | Retail
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	179.5	142.9	611.2	456.7
Regulated Natural Gas | Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	130.1	104	441.5	331.8
Regulated Natural Gas | Retail | Commercial and Industrial Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	49.4	38.9	169.7	124.9
Regulated Natural Gas | Retail | Other Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
Regulated Natural Gas | Wholesale Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
Regulated Natural Gas | Transmission Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
Regulated Natural Gas | Other
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	23.3	18.8	54.9	43.8
Regulated Natural Gas | Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	4.8	25	10.6	50.1
All Other
Disaggregation of Revenue [Line Items]
Total operating revenues	9.7	9	22.1	20.1
All Other | Total revenue from contracts with customers
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	8.5	7.9	19.8	17.8
All Other | Retail
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	8.5	7.9	19.8	17.8
All Other | Retail | Residential
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	2.8	2.6	5.3	5.2
All Other | Retail | Commercial and Industrial Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	5.7	5.3	14.5	12.5
All Other | Retail | Other Customers [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0.1
All Other | Wholesale Distribution [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
All Other | Transmission Services [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
All Other | Other
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	0	0	0	0
All Other | Alternative and Other [Member]
Disaggregation of Revenue [Line Items]
Total operating revenues	$ 1.2	$ 1.1	$ 2.3	$ 2.3

Income Taxes (Details)

Income Taxes (Details) - USD ($)		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Income Tax Examination [Line Items]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent		3.70%	3.70%
Effective Income Tax Rate Reconciliation, Tax Credit, Percent		(9.40%)	0.00%
Effective Income Tax Rate Reconciliation, Other Regulatory Items, Percent	[1]	(3.40%)	(1.50%)
Regulatory differences - reversal of prior quarters' ARAM deferral (b)		(1.00%)	(1.00%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent		0.10%	0.30%
Effective Income Tax Rate Reconciliation, Percent		11.00%	22.50%
Unrecognized Tax Benefits [Abstract]
Unrecognized tax benefit — Permanent tax positions		$ 6,000,000		$ 5,400,000
Unrecognized tax benefit — Temporary tax positions		4,700,000		4,900,000
Total unrecognized tax benefit		10,700,000		10,300,000
NOL and tax credit carryforwards		(6,100,000)		(5,600,000)
Net Deferred Tax Liability associated with the Unrecognized Tax Benefit Amounts and Related NOLs and Tax Credit Carryforwards		(2,600,000)		(2,000,000)
Upper bound of decrease in unrecognized tax benefit that is reasonably possible		8,700,000
Amounts accrued for penalties related to unrecognized tax benefits		0		$ 0
Internal Revenue Service (IRS) [Member]
Income Tax Examination [Line Items]
Potential Tax Adjustments		$ 0
[1]	Regulatory differences for income tax primarily relate to the flow back of excess deferred taxes to customers through the average rate assumption method and the impact of AFUDC - Equity. Year-to-date variations primarily relates to the deferral of the flow back of excess deferred taxes in 2018, as a result of pending regulatory decisions. Treatment of most tax reform items was established prior to the first quarter of 2019, resulting in a reduction in deferred amounts. Income tax benefits associated with the flow back of excess deferred credits are offset by corresponding revenue reductions and additional prepaid pension asset amortization.

Fair Value of Financial Asset_3

Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) MWh in Millions, MMBTU in Millions, $ in Millions		Jun. 30, 2019USD ($)MMBTUMWhCounterparty	Dec. 31, 2018MMBTUMWh
Credit Concentration Risk
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty		10
Credit Concentration Risk | Municipal or Cooperative Entities or Other Utilities [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty		7
Credit Concentration Risk | External Credit Rating, Investment Grade [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty		6
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $		$ 33
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		49.00%
Credit Concentration Risk | Internal Investment Grade [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty		3
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $		$ 7.7
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		11.00%
Credit Concentration Risk | External Credit Rating, Non Investment Grade [Member]
Consideration of Credit Risk and Concentrations [Abstract]
Number of most significant counterparties for wholesale, trading and non-trading commodity activities with credit exposure | Counterparty		1
Wholesale, trading and non-trading commodity credit exposure for the most significant counterparties | $		$ 8.4
Percentage of wholesale, trading and non-trading commodity credit exposure for the most significant counterparties (in hundredths)		12.00%
Interest Rate Swap
Interest Rate Derivatives [Abstract]
Amount of accumulated other comprehensive gains (losses) related to interest rate derivatives expected to be reclassified into earnings within the next twelve months | $		$ (1.2)
Electric Commodity (in megawatt hours)
Gross Notional Amounts of Commodity Forwards and Options [Abstract]
Derivative, Nonmonetary Notional amount | MWh	[1],[2]	16.3	24.4
Natural Gas Commodity (in million British thermal units)
Gross Notional Amounts of Commodity Forwards and Options [Abstract]
Derivative, Nonmonetary Notional amount | MMBTU	[1],[2]	51.3	48.4
cash flow hedge commodity [Member]
Commodity Derivatives [Abstract]
Commodity contracts designated as cash flow hedges | $		$ 0
[1]	Notional amounts for options are included on a gross basis, but are weighted for the probability of exercise.
[2]	Amounts are not reflective of net positions in the underlying commodities.

Fair Value of Financial Asset_4

Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) - USD ($)		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]
Derivative instruments designated as fair value hedges		$ 0	$ 0	$ 0	$ 0
Designated as Hedging Instrument | Cash Flow Hedges
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		400,000	400,000	800,000	800,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0	0	0
Pre-tax gains (losses) recognized during the period in income		0	0	0	0
Designated as Hedging Instrument | Cash Flow Hedges | Interest Rate
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss	[1]	400,000	400,000	800,000	800,000
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0	0	0
Pre-tax gains (losses) recognized during the period in income		0	0	0	0
Other Derivative Instruments
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss		0	0	0	0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		(1,500,000)	(200,000)	(1,500,000)	(400,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0	0	0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0	(1,300,000)	2,700,000
Pre-tax gains (losses) recognized during the period in income		3,300,000	200,000	2,700,000	(900,000)
Other Derivative Instruments | Commodity Trading
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss		0	0	0	0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)		0	0	0	0
Pre-tax gains (losses) recognized during the period in income	[2]	3,300,000	200,000	4,700,000	700,000
Other Derivative Instruments | Natural Gas Commodity
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in accumulated other comprehensive loss		0	0	0	0
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		(1,500,000)	(200,000)	(1,500,000)	(400,000)
Pre-tax (gains) losses reclassified into income during the period from accumulated other comprehensive loss				0	0
Pre-tax (gains) losses reclassified into income during the period from regulatory assets and (liabilities)	[3]			(1,300,000)	2,700,000
Pre-tax gains (losses) recognized during the period in income	[3]			(2,000,000)	(1,600,000)
Other Derivative Instruments | Natural Gas Commodity for Electric Generation
Impact of Derivative Activity on Accumulated Other Comprehensive Loss, Regulatory Assets and Liabilities, and Income [Abstract]
Pre-tax fair value gains (losses) recognized during the period in regulatory (assets) and liabilities		$ 0	$ 0	$ 0	$ 1,200,000
[1]	Amounts are recorded to interest charges.
[2]	Amounts are recorded to interest charges. Amounts are recorded to electric operating revenues. Portions of these gains and losses are subject to sharing with electric customers through margin-sharing mechanisms and deducted from gross revenue as appropriate.
[3]	Amounts for both the three and six months ended June 30, 2019 included no settlement gain or losses on derivatives entered to mitigate natural gas price risk for electric generation recorded to electric fuel and purchased power, subject to cost-recovery mechanisms and reclassified to a regulatory asset, as appropriate. Amounts for the three and six months ended June 30, 2018 included no such settlement gains or losses and $1.2 million of such settlement losses, respectively. Remaining derivative settlement losses for the three and six months ended June 30, 2019 and 2018

Fair Value of Financial Asset_5

Fair Value of Financial Assets and Liabilities, Credit Related Contingent Features (Details) - USD ($)	Jun. 30, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Derivative instruments in a gross liability position	$ 0	$ 0
Collateral posted on derivative instruments	0	0
Collateral posted related to adequate assurance clauses in derivative contracts	$ 0	$ 0

Fair Value of Financial Asset_6

Fair Value of Financial Assets and Liabilities, Derivative Assets and Liabilities at Fair Value (Details) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative Asset, Collateral, Obligation to Return Cash, Offset		$ 0	$ 0
Derivative Liability, Collateral, Right to Reclaim Cash, Offset		6.4	6.5
Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		18.4	42.6
Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		2.5	1.2
Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		9.7	34.6
Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0.6	0.6
Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		18.4	42.6
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[1]	(20.9)	(28.2)
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		18	39.2
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[1]	(20.9)	(28.2)
Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0.4	3.4
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[1]	0	0
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		2.5	1.2
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[1]	(2.3)	(0.4)
Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		2.5	1.2
Derivative Asset, Fair Value, Gross Liability and Obligation to Return Cash, Offset	[1]	(2.3)	(0.4)
Fair Value Measured on a Recurring Basis | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		9.6	31.9
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	[1]	(27.3)	(34.7)
Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		9.6	31.9
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	[1]	(27.3)	(34.7)
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0.6	0.6
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	[1]	(2.3)	(0.5)
Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0.6	0.6
Derivative Liability, Fair Value, Gross Asset and Right to Reclaim Cash, Offset	[1]	(2.3)	(0.5)
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		5.4	2.3
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		5.4	2.3
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0	0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0.2	0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0.2	0
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		5.5	2.4
Fair Value Measured on a Recurring Basis | Level 1 | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		5.5	2.4
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0.2	0
Fair Value Measured on a Recurring Basis | Level 1 | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0.2	0
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		33.7	68.4
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		33.3	65
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0.4	3.4
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		4.6	1.6
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		4.6	1.6
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		31.4	64.2
Fair Value Measured on a Recurring Basis | Level 2 | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		31.4	64.2
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		2.7	1.1
Fair Value Measured on a Recurring Basis | Level 2 | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		2.7	1.1
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0.2	0.1
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0.2	0.1
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0	0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0	0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0	0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0	0
Fair Value Measured on a Recurring Basis | Level 3 | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0	0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0	0
Fair Value Measured on a Recurring Basis | Level 3 | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		0	0
Fair Value, Measurements, Nonrecurring | Other Current Assets | PPAs
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[2]	0	0
Fair Value, Measurements, Nonrecurring | Other Noncurrent Assets | PPAs
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	[2]	0	0
Fair Value, Measurements, Nonrecurring | Other Current Liabilities | PPAs
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[2]	0.1	2.7
Fair Value, Measurements, Nonrecurring | Other Noncurrent Liabilities | PPAs
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	[2]	0	0
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		39.3	70.8
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		38.9	67.4
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Assets | Other Derivative Instruments | Natural Gas Commodity
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		0.4	3.4
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Assets
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		4.8	1.6
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Assets | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset		4.8	1.6
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		36.9	66.6
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Current Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		36.9	66.6
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		2.9	1.1
Estimate of Fair Value Measurement [Member] | Fair Value Measured on a Recurring Basis | Other Noncurrent Liabilities | Other Derivative Instruments | Commodity Trading
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability		$ 2.9	$ 1.1
[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 June 30, 2019 and Dec. 31, 2018. At both June 30, 2019 and Dec. 31, 2018, derivative assets and liabilities include no obligations to return cash collateral. At June 30, 2019 and Dec. 31, 2018, derivative assets and liabilities include the rights to reclaim cash collateral of $6.4 million and $6.5 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.
[2]	During 2006, PSCo 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.

Fair Value of Financial Asset_7

Fair Value of Financial Assets and Liabilities, Changes in Level 3 Commodity Derivatives (Details) - Commodity Contract - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Inputs Reconciliation, Gain (Loss) Included in Earnings	$ 300,000	$ 100,000	$ 1,000,000	$ 100,000
Transfers into Level 3	0	0	0	0
Transfers out of Level 3	$ 0	$ 0	$ 0	$ 0

Fair Value of Financial Asset_8

Fair Value of Financial Assets and Liabilities, Fair Value of Long-Term Debt (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Carrying Amount
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 4,846.1	$ 4,997.6
Fair Value
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term debt, including current portion	$ 5,333.3	$ 5,123.2

Benefit Plans and Other Postr_3

Benefit Plans and Other Postretirement Benefits (Details) $ in Millions		Jul. 01, 2019USD ($)	Jan. 31, 2019USD ($)Plan	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2018USD ($)
Other Postretirement Benefits Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost				$ 0.1	$ 0.2	$ 0.2	$ 0.3
Interest cost	[1]			3.9	3.8	7.8	7.5
Expected return on plan assets	[1]			(4.7)	(5.7)	(9.4)	(11.3)
Amortization of prior service credit	[1]			(1.3)	(1.6)	(2.7)	(3.1)
Amortization of net loss	[1]			0.7	1	1.5	2
Net periodic benefit cost (credit)				(1.3)	(2.3)	(2.6)	(4.6)
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation				0.2	0	0.5	0
Net benefit cost (credit) recognized for financial reporting				(1.1)	(2.3)	(2.1)	(4.6)
Pension Plan [Member]
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Service cost				6.4	7.3	12.8	14.6
Interest cost	[1]			12.9	11.8	25.8	23.6
Expected return on plan assets	[1]			(17.1)	(17.1)	(34.2)	(34.3)
Amortization of prior service credit	[1]			(0.8)	(0.9)	(1.7)	(1.7)
Amortization of net loss	[1]			6.3	7.8	12.7	15.6
Net periodic benefit cost (credit)				7.7	8.9	15.4	17.8
Defined Benefit Plan Credits Not Recognized Due To Effects of Regulation				1.8	0.9	3.6	2.4
Net benefit cost (credit) recognized for financial reporting				$ 9.5	$ 9.8	$ 19	$ 20.2
Total contributions to the pension plans during the period		$ 3	$ 43
Pension Plan [Member] | Xcel Energy Inc.
Components of Net Periodic Benefit Cost (Credit) [Abstract]
Total contributions to the pension plans during the period		$ 4	$ 150
Number of Xcel Energy's pension plans to which contributions were made | Plan			4
[1]	The components of net periodic cost other than the service cost component are included in the line item “other income, net” in the consolidated statement of income or capitalized on the consolidated balance sheet as a regulatory asset.

Commitments and Contingencies_2

Commitments and Contingencies Commitments and Contingencies, Leases - Narrative (Details)	6 Months Ended
	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Operating Lease, Weighted Average Discount Rate, Percent	4.10%
Maximum lease term for short-term lease classification	12 months
WYCO
Lessee, Lease, Description [Line Items]
Equity Method Investment, Ownership Percentage	50.00%

Commitments and Contingencies_3

Commitments and Contingencies Commitments and Contingencies, Leases - Right-of-Use Assets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross	$ 653.4
Operating Lease, Right-of-Use Asset, Accumulated Depreciation	(39.7)
Operating Lease, Right-of-Use Asset	613.7	$ 0
Finance Lease, Assets and Liabilities, Lessee [Abstract]
Finance Lease, Right-of-Use Asset, Gross	221.2
Finance Lease, Right-of-Use Asset, Accumulated Depreciation	(79.2)
Finance Lease, Right-of-Use Asset	142
PPAs
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross	585.1
Other
Operating Lease, Assets and Liabilities, Lessee [Abstract]
Operating Lease, Right-of-Use Asset, Gross	68.3
Gas storage facilities
Finance Lease, Assets and Liabilities, Lessee [Abstract]
Finance Lease, Right-of-Use Asset, Gross	200.5
Gas pipeline
Finance Lease, Assets and Liabilities, Lessee [Abstract]
Finance Lease, Right-of-Use Asset, Gross	$ 20.7

Commitments and Contingencies_4

Commitments and Contingencies Commitments and Contingencies, Leases - Components of Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Short-term Lease, Cost	$ 0.3	$ 0.7
Operating Lease, Cost	28.3	56.2
Finance Lease, Right-of-Use Asset, Amortization	1.5	3
Finance Lease, Interest Expense	4.7	9.5
Finance Lease, Cost	6.2	12.5
PPAs
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	24.7	49
Other
Lessee, Lease, Description [Line Items]
Operating Lease, Cost	$ 3.6	$ 7.2

Commitments and Contingencies_5

Commitments and Contingencies Commitments and Contingencies, Leases - Future Commitments (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Operating Leases after Adoption of ASC Topic 842
2019	$ 54.3
2020	109.1
2021	108.5
2022	93.8
2023	80.9
Thereafter	317.8
Total minimum obligation	764.4
Interest component of obligation	(120.2)
Present value of minimum obligation	644.2
Less current portion	(83.9)
Operating Lease, Liability, Noncurrent	$ 560.3	$ 0
Weighted-average remaining lease term in years	8 years 3 months 18 days
Finance Leases after Adoption of ASC Topic 842
2019	$ 12.4
2020	24.8
2021	23.6
2022	20.5
2023	20.3
Thereafter	420.4
Total minimum obligation	522
Interest component of obligation	380
Present value of minimum obligation	142
Less current portion	(6.5)
Noncurrent operating and finance lease liabilities	$ 135.5
Weighted-average remaining lease term in years	39 years
Operating Leases before Adoption of ASC Topic 842
2019		106.3
2020		106.6
2021		105.9
2022		91
2023		78.1
Thereafter		342
Finance Leases before Adoption of ASC Topic 842
2019		24.9
2020		24.8
2021		23.6
2022		20.5
2023		20.3
Thereafter		420.4
Total minimum obligation		534.5
Interest component of obligation		(389.5)
Present value of minimum obligation		145
PPAs
Operating Leases after Adoption of ASC Topic 842
2019	$ 47.8
2020	95.9
2021	96.4
2022	82.6
2023	70
Thereafter	288.6
Total minimum obligation	681.3
Interest component of obligation	(106.4)
Present value of minimum obligation	574.9
Operating Leases before Adoption of ASC Topic 842
2019		95.5
2020		95.9
2021		96.4
2022		82.6
2023		70
Thereafter		288.6
Other
Operating Leases after Adoption of ASC Topic 842
2019	6.5
2020	13.2
2021	12.1
2022	11.2
2023	10.9
Thereafter	29.2
Total minimum obligation	83.1
Interest component of obligation	(13.8)
Present value of minimum obligation	$ 69.3
Operating Leases before Adoption of ASC Topic 842
2019		10.8
2020		10.7
2021		9.5
2022		8.4
2023		8.1
Thereafter		$ 53.4

Commitments and Contingencies,

Commitments and Contingencies, Purchased Power Agreements (Details) - MW	Jun. 30, 2019	Dec. 31, 2018
Independent Power Producing Entities
Purchased Power Agreements [Abstract]
Generating capacity under long term purchased power agreements (in MW)	1,442	1,571

Commitments and Contingencies_6

Commitments and Contingencies, Environmental Contingencies (Details)	Jun. 30, 2019
Other MGP, Landfill, or Disposal Sites [Domain]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of identified MGP sites under current investigation and/or remediation	2
Federal Coal Ash Regulation [Domain]
Unrecorded Unconditional Purchase Obligation [Line Items]
Number of regulated ash units that will still be in operation by the end of 2019	6

Commitments and Contingencies_7

Commitments and Contingencies, Legal Contingencies (Details)	1 Months Ended
	Dec. 31, 2015	Mar. 31, 2019USD ($)	Dec. 31, 2018
Gas Trading Litigation [Member]
Loss Contingencies [Line Items]
Loss Contingency, Pending Claims, Number			2
PSCo | Minimum [Member] | Line Extension Disputes
Legal Contingencies [Abstract]
Loss Contingency, Number of Plaintiffs	50
Loss Contingency Accrual		$ 0

Other Comprehensive Income (Det

Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019		Jun. 30, 2018		Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income taxes	$ 10.6		$ 35.3		$ 29.7	$ 74.3
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period					6,298.2
Net current period other comprehensive loss	0.3		0.3		0.6	0.6
Accumulated other comprehensive loss at end of period	6,613.1				6,613.1
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period	(25)		(26.1)		(25.3)	(26.4)
Net current period other comprehensive loss	0.3		0.3		0.6	0.6
Accumulated other comprehensive loss at end of period	(24.7)		(25.8)		(24.7)	(25.8)
Defined Benefit and Postretirement Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period	(0.2)		(0.3)			(0.3)
Net current period other comprehensive loss	0		0		0	0
Accumulated other comprehensive loss at end of period	(0.2)		(0.3)		(0.2)	(0.3)
Total
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Accumulated other comprehensive loss at beginning of period	(25.2)		(26.4)		(25.5)	(26.7)
Accumulated other comprehensive loss at end of period	(24.9)		(26.1)		(24.9)	(26.1)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income taxes	0		0		0	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Income taxes	0.1		0.1		0.1	0.2
Interest Rate Swap
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Losses reclassified from net accumulated other comprehensive loss	(0.3)	[1]	(0.3)	[1]	(0.6)	(0.6)
Interest Rate Swap | Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Losses reclassified from net accumulated other comprehensive loss	(0.3)	[1]	(0.3)	[1]	(0.6)	(0.6)
Interest Rate Swap | Defined Benefit and Postretirement Items
Accumulated Other Comprehensive Income (Loss), Net of Tax [Roll Forward]
Losses reclassified from net accumulated other comprehensive loss	$ 0	[1]	$ 0	[1]	$ 0	$ 0
[1]	(a) Included in interest charges.

Segment Information (Details)

Segment Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Regulated Operating Revenue	$ 910.1	$ 912.1	$ 2,133.3	$ 1,985.5
Revenues	910	911.9	2,133	1,985.2
Net income	101.5	122.3	240.3	256
Affiliate Revenue	1.1	1.1	2.2	2.2
Regulated Electric
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues	692.8	716.3	1,434.4	1,414.7
Revenues	692.7	716.2	1,434.2	1,414.5
Net income	84.8	101.9	167.2	181.5
Regulated Natural Gas
Segment Reporting Information [Line Items]
Revenues Including Intersegment Revenues	207.6	186.8	676.8	550.7
Revenues	207.6	186.7	676.7	550.6
Net income	17.6	21	76.8	74.7
All Other
Segment Reporting Information [Line Items]
Revenues	9.7	9	22.1	20.1
Net income	(0.9)	(0.6)	(3.7)	(0.2)
Total revenues
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	692.7	716.2	1,434.2	1,414.5
Regulated Operating Revenue, Gas	207.6		676.7	550.6
Regulated Operating Revenue, Other	9.7	9	22.1	20.1
Total revenues | Regulated Natural Gas
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Gas		186.7
Intersegment Eliminations
Segment Reporting Information [Line Items]
Regulated Operating Revenue, Electric	0.1	0.1	0.2	0.2
Regulated Operating Revenue, Gas	0	0.1	0.1	0.1
Regulated Operating Revenue	$ (0.1)	$ (0.2)	$ (0.3)	$ (0.3)