Summary of Significant Accounting Policies (Policies)	6 Months Ended
Jun. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements include Zillow Group, Inc. and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. These condensed consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and note disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the audited financial statements and accompanying notes included in Zillow Group, Inc.’s Annual Report on Form 10-K for the year ended December 31, 2020, which was filed with the SEC on February 12, 2021. The condensed consolidated balance sheet as of December 31, 2020, included herein, was derived from the audited financial statements of Zillow Group, Inc. as of that date. The unaudited condensed consolidated interim financial statements, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, necessary to present fairly our financial position as of June 30, 2021 and our results of operations, comprehensive income (loss) and shareholders’ equity for the three and six month periods ended June 30, 2021 and 2020, and our cash flows for the six month periods ended June 30, 2021 and 2020. The results for the three and six months ended June 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any interim period or for any other future year.
Reclassifications	Reclassifications Certain reclassifications have been made in the condensed consolidated statements of operations to conform data for prior periods to the current format. Beginning with the three and six month periods ended June 30, 2021, we present a gross profit subtotal in our condensed consolidated statements of operations, which requires certain depreciation expense and amortization expense to be included within cost of revenue. We believe the presentation of gross profit is preferable as it facilitates investors’ ability to model across our segments and enhances comparability with our public company peers. To effect the presentation of gross profit, we present the amortization expense for certain intangible assets and data acquisition costs within cost of revenue and have reclassified certain amounts in prior periods in the condensed consolidated statements of operations from technology and development expenses to cost of revenue. Additionally, we reclassified the amortization expense for trade names and trademarks and customer relationship intangible assets from technology and development expenses to sales and marketing expenses. This change has no impact on income (loss) from operations or net income (loss).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and the related disclosures at the date of the financial statements, as well as the reported amounts of revenue and expenses during the periods presented. On an ongoing basis, we evaluate our estimates, including those related to the accounting for certain revenue offerings, the net realizable value of inventory, amortization period and recoverability of contract cost assets, website and software development costs, recoverability of long-lived assets and intangible assets, share-based compensation, income taxes, business combinations and the recoverability of goodwill, among others. To the extent there are material differences between these estimates, judgments or assumptions and actual results, our financial statements will be affected. The COVID-19 pandemic has introduced additional uncertainty with respect to estimates, judgments and assumptions, which may materially impact the estimates previously listed, among others.
Recently Issued Accounting Standards Not Yet Adopted	Recently Issued Accounting Standards Not Yet Adopted In August 2020, the Financial Accounting Standards Board (“FASB”) issued guidance which simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts in an entity’s own equity. Among other changes, the guidance removes the liability and equity separation models for convertible instruments. Instead, entities will account for convertible debt instruments wholly as debt unless convertible instruments contain features that require bifurcation as a derivative or that result in substantial premiums accounted for as paid-in capital. The guidance also requires the application of the if-converted method to calculate the impact of convertible instruments on diluted earnings per share. The guidance is effective for fiscal years beginning after December 15, 2021, with early adoption permitted for fiscal years beginning after December 15, 2020, and can be adopted on either a retrospective or modified retrospective basis. We expect to adopt this guidance on January 1, 2022. Although we continue to evaluate the method of adoption and impact of this guidance on our financial position and results of operations, upon adoption we expect this guidance to result in a reclassification of conversion feature balances from additional paid-in capital to debt and to decrease reported interest expense for our convertible senior notes. In March 2020, the FASB issued guidance which provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference the London Inter-Bank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform. This guidance is optional for a limited period of time to ease the potential burden in accounting for, or recognizing the effects of, reference rate reform on financial reporting. This guidance is effective from March 12, 2020 through December 31, 2022. Entities may elect to adopt the amendments for contract modifications as of any date from the beginning of an interim period that includes or is subsequent to March 12, 2020, or prospectively from a date within an interim period that includes or is subsequent to March 12, 2020, up to the date that the financial statements are available to be issued. We expect to apply some of the expedients and exceptions provided in this guidance to our credit facilities, warehouse line of credit and master repurchase agreements, all of which reference the one-month LIBOR in the applicable interest rate, as publication of the one-month LIBOR is expected to cease after June 30, 2023. We expect to amend our facility agreements prior to that date. As the goal of the reference rate reform transition is for it to be economically neutral to entities, we do not believe the adoption of this guidance will have a material impact on our financial position, results of operations or cash flows.
Fair Value Measurements	We apply the following methods and assumptions in estimating our fair value measurements: Cash equivalents — The fair value measurement of money market funds is based on quoted market prices in active markets (Level 1). The fair value measurement of other cash equivalents is based on observable market-based inputs principally derived from or corroborated by observable market data (Level 2). Short-term investments — The fair value measurement of our short-term investments is based on observable market-based inputs or inputs that are derived principally from or corroborated by observable market data by correlation or other means (Level 2). Restricted cash — The carrying value of restricted cash approximates fair value due to the short period of time amounts are borrowed on our credit facilities, home sales proceeds are held in restricted accounts for repayment of our credit facilities and amounts are held in escrow (Level 1). Mortgage loans held for sale — The fair value of mortgage loans held for sale is generally calculated by reference to quoted prices in secondary markets for commitments to sell mortgage loans with similar characteristics (Level 2). Interest rate lock commitments — The fair value of interest rate lock commitments (“IRLCs”) is calculated by reference to quoted prices in secondary markets for commitments to sell mortgage loans with similar characteristics. Expired commitments are excluded from the fair value measurement. Since not all IRLCs will become closed loans, we adjust our fair value measurements for the estimated amount of IRLCs that will not close. This adjustment is effected through the pull-through rate, which represents the probability that an interest rate lock commitment will ultimately result in a closed loan (Level 3).Forward contracts — The fair value of mandatory loan sales commitments and derivative instruments such as forward sales of mortgage-backed securities that are utilized as economic hedging instruments is calculated by reference to quoted prices for similar assets (Level 2).
Segment Reporting	We have three operating and reportable segments, which have been identified based on the way in which our chief operating decision-maker manages our business, makes operating decisions and evaluates operating performance. The chief executive officer acts as the chief operating decision-maker and reviews financial and operational information for the Homes, Internet, Media & Technology (“IMT”) and Mortgages segments. The Homes segment includes the financial results from Zillow Group’s purchase and sale of homes directly through Zillow Offers and the financial results from title and escrow services through Zillow Closing Services. The IMT segment includes the financial results for the Premier Agent, rentals and new construction marketplaces, dotloop and display, as well as revenue from the sale of various other marketing and business products and services to real estate professionals. The Mortgages segment primarily includes financial results for mortgage originations and the sale of mortgages on the secondary market through Zillow Home Loans and advertising sold to mortgage lenders and other mortgage professionals. Revenue and costs are directly attributed to our segments when possible. However, due to the integrated structure of our business, certain costs incurred by one segment may benefit the other segments. These costs primarily include headcount-related expenses, general and administrative expenses including executive, finance, accounting, legal, human resources, recruiting and facilities costs, product development and data acquisition costs, costs related to operating our mobile applications and websites, and marketing and advertising costs. These costs are allocated to each segment based on the estimated benefit each segment receives from such expenditures. The chief executive officer reviews information about our revenue categories as well as statement of operations data inclusive of income (loss) before income taxes by segment.

Summary of Significant Accounting Policies (Policies)

6 Months Ended

Jun. 30, 2021

The accompanying condensed consolidated financial statements include Zillow Group, Inc. and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. These condensed consolidated financial statements have been prepared in conformity with U.S. generally accepted accounting principles (“GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. Certain information and note disclosures normally included in the financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these interim condensed consolidated financial statements should be read in conjunction with the audited financial statements and accompanying notes included in Zillow Group, Inc.’s Annual Report on Form 10-K for the year ended December 31, 2020, which was filed with the SEC on February 12, 2021. The condensed consolidated balance sheet as of December 31, 2020, included herein, was derived from the audited financial statements of Zillow Group, Inc. as of that date.

The unaudited condensed consolidated interim financial statements, in the opinion of management, reflect all adjustments, consisting only of normal recurring adjustments, necessary to present fairly our financial position as of June 30, 2021 and our results of operations, comprehensive income (loss) and shareholders’ equity for the three and six month periods ended June 30, 2021 and 2020, and our cash flows for the six month periods ended June 30, 2021 and 2020. The results for the three and six months ended June 30, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 or for any interim period or for any other future year.

Reclassifications

Certain reclassifications have been made in the condensed consolidated statements of operations to conform data for prior periods to the current format. Beginning with the three and six month periods ended June 30, 2021, we present a gross profit subtotal in our condensed consolidated statements of operations, which requires certain depreciation expense and amortization expense to be included within cost of revenue. We believe the presentation of gross profit is preferable as it facilitates investors’ ability to model across our segments and enhances comparability with our public company peers. To effect the presentation of gross profit, we present the amortization expense for certain intangible assets and data acquisition costs within cost of revenue and have reclassified certain amounts in prior periods in the condensed consolidated statements of operations from technology and development expenses to cost of revenue. Additionally, we reclassified the amortization expense for trade names and trademarks and customer relationship intangible assets from technology and development expenses to sales and marketing expenses. This change has no impact on income (loss) from operations or net income (loss).

Use of Estimates

The preparation of financial statements in conformity with GAAP requires management to make certain estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and the related disclosures at the date of the financial statements, as well as the reported amounts of revenue and expenses during the periods presented. On an ongoing basis, we evaluate our estimates, including those related to the accounting for certain revenue offerings, the net realizable value of inventory, amortization period and recoverability of contract cost assets, website and software development costs, recoverability of long-lived assets and intangible assets, share-based compensation, income taxes, business combinations and the recoverability of goodwill, among others. To the extent there are material differences between these estimates, judgments or assumptions and actual results, our financial statements will be affected. The COVID-19 pandemic has introduced additional uncertainty with respect to estimates, judgments and assumptions, which may materially impact the estimates previously listed, among others.

Recently Issued Accounting Standards Not Yet Adopted

In August 2020, the Financial Accounting Standards Board (“FASB”) issued guidance which simplifies the accounting for certain financial instruments with characteristics of liabilities and equity, including convertible instruments and contracts in an entity’s own equity. Among other changes, the guidance removes the liability and equity separation models for convertible instruments. Instead, entities will account for convertible debt instruments wholly as debt unless convertible instruments contain features that require bifurcation as a derivative or that result in substantial premiums accounted for as paid-in capital. The guidance also requires the application of the if-converted method to calculate the impact of convertible instruments on diluted earnings per share. The guidance is effective for fiscal years beginning after December 15, 2021, with early adoption permitted for fiscal years beginning after December 15, 2020, and can be adopted on either a retrospective or modified retrospective basis. We expect to adopt this guidance on January 1, 2022. Although we continue to evaluate the method of adoption and impact of this guidance on our financial position and results of operations, upon adoption we expect this guidance to result in a reclassification of conversion feature balances from additional paid-in capital to debt and to decrease reported interest expense for our convertible senior notes.

In March 2020, the FASB issued guidance which provides optional expedients and exceptions for applying GAAP to contracts, hedging relationships and other transactions that reference the London Inter-Bank Offered Rate (“LIBOR”) or another reference rate expected to be discontinued because of reference rate reform. This guidance is optional for a limited period of time to ease the potential burden in accounting for, or recognizing the effects of, reference rate reform on financial reporting. This guidance is effective from March 12, 2020 through December 31, 2022. Entities may elect to adopt the amendments for contract modifications as of any date from the beginning of an interim period that includes or is subsequent to March 12, 2020, or prospectively from a date within an interim period that includes or is subsequent to March 12, 2020, up to the date that the financial statements are available to be issued. We expect to apply some of the expedients and exceptions provided in this guidance to our credit facilities, warehouse line of credit and master repurchase agreements, all of which reference the one-month LIBOR in the applicable interest rate, as publication of the one-month LIBOR is expected to cease after June 30, 2023. We expect to amend our facility agreements prior to that date. As the goal of the reference rate reform transition is for it to be economically neutral to entities, we do not believe the adoption of this guidance will have a material impact on our financial position, results of operations or cash flows.

Fair Value Measurements

We apply the following methods and assumptions in estimating our fair value measurements:

Cash equivalents — The fair value measurement of money market funds is based on quoted market prices in active markets (Level 1). The fair value measurement of other cash equivalents is based on observable market-based inputs principally derived from or corroborated by observable market data (Level 2).

Short-term investments — The fair value measurement of our short-term investments is based on observable market-based inputs or inputs that are derived principally from or corroborated by observable market data by correlation or other means (Level 2).

Restricted cash — The carrying value of restricted cash approximates fair value due to the short period of time amounts are borrowed on our credit facilities, home sales proceeds are held in restricted accounts for repayment of our credit facilities and amounts are held in escrow (Level 1).

Mortgage loans held for sale — The fair value of mortgage loans held for sale is generally calculated by reference to quoted prices in secondary markets for commitments to sell mortgage loans with similar characteristics (Level 2).

Interest rate lock commitments — The fair value of interest rate lock commitments (“IRLCs”) is calculated by reference to quoted prices in secondary markets for commitments to sell mortgage loans with similar characteristics. Expired commitments are excluded from the fair value measurement. Since not all IRLCs will become closed loans, we adjust our fair value measurements for the estimated amount of IRLCs that will not close. This adjustment is effected through the pull-through rate, which represents the probability that an interest rate lock commitment will ultimately result in a closed loan (Level 3).Forward contracts — The fair value of mandatory loan sales commitments and derivative instruments such as forward sales of mortgage-backed securities that are utilized as economic hedging instruments is calculated by reference to quoted prices for similar assets (Level 2).

Segment Reporting

We have three operating and reportable segments, which have been identified based on the way in which our chief operating decision-maker manages our business, makes operating decisions and evaluates operating performance. The chief executive officer acts as the chief operating decision-maker and reviews financial and operational information for the Homes, Internet, Media & Technology (“IMT”) and Mortgages segments.

The Homes segment includes the financial results from Zillow Group’s purchase and sale of homes directly through Zillow Offers and the financial results from title and escrow services through Zillow Closing Services. The IMT segment includes the financial results for the Premier Agent, rentals and new construction marketplaces, dotloop and display, as well as revenue from the sale of various other marketing and business products and services to real estate professionals. The Mortgages segment primarily includes financial results for mortgage originations and the sale of mortgages on the secondary market through Zillow Home Loans and advertising sold to mortgage lenders and other mortgage professionals.

Revenue and costs are directly attributed to our segments when possible. However, due to the integrated structure of our business, certain costs incurred by one segment may benefit the other segments. These costs primarily include headcount-related expenses, general and administrative expenses including executive, finance, accounting, legal, human resources, recruiting and facilities costs, product development and data acquisition costs, costs related to operating our mobile applications and websites, and marketing and advertising costs. These costs are allocated to each segment based on the estimated benefit each segment receives from such expenditures.

The chief executive officer reviews information about our revenue categories as well as statement of operations data inclusive of income (loss) before income taxes by segment.