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Compensation Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions | 1 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Jan. 31, 2021 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018 | May 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Cash settled for awards |  |  |  | $ 6.9 |
Stock compensation expense |  | $ 66.3 | $ 61.8 | 59.0 |
Unrecognized compensation expense |  | $ 79.0 |  |  |
Remaining weighted average vesting periods of unrecognized compensation expenses |  | 1 year 10 months 24 days |  |  |
Employer matching contribution percent |  | 100.00% |  |  |
Defined Contribution Plan, Plan Name [Extensible List] |  | trgp:FourZeroOneKPlanMember |  |  |
Percentage of employees' gross pay for which employer contributes matching contribution |  | 5.00% |  |  |
Percentage of additional contribution per employee made by employer |  | 3.00% |  |  |
Percentage of contributions made in cash |  | 100.00% |  |  |
Contributions to defined contribution plan |  | $ 16.2 | 23.7 | 19.5 |
Accounting Standard Update 2016-09 [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Tax deficiencies of dividends on share-based compensation recognized as income tax expenses |  | $ 2.0 |  | $ 0.7 |
Accounting Standard Update 2016-09 [Member] | Windfall Tax Benefit [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Tax deficiencies of dividends on share-based compensation recognized as income tax expenses |  |  | $ 7.7 |  |
Director Grants [Member] | Subsequent Event [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Cash-settled awards vested | 29,472 |  |  |  |
Shares withheld to satisfy tax withholding obligations | 0 |  |  |  |
Restricted Stock Units (RSUs) [Member] | Subsequent Event [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Cash-settled awards vested | 517,026 |  |  |  |
Shares withheld to satisfy tax withholding obligations | 180,304 |  |  |  |
PSUs [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Expected volatility, minimum |  | 73.00% | 32.00% | 29.00% |
Expected volatility, maximum |  | 128.00% | 37.00% | 53.00% |
PSUs [Member] | Subsequent Event [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Cash-settled awards vested | 296,121 |  |  |  |
Shares withheld to satisfy tax withholding obligations | 104,357 |  |  |  |
Cash-Settled Performance Units [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Cash-settled awards vested |  |  |  | 112,550 |
2010 TRC Stock Incentive Plan [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Total number of units authorized (in shares) |  |  |  |  | 15,000,000
Total number of units available (in shares) |  |  |  |  | 5,000,000
Total number of additional units available (in shares) |  |  |  |  | 10,000,000
Fair values of share-based awards vested |  | $ 62.7 | $ 55.4 | $ 18.8 |
Cash dividends paid for the vested awards |  | $ 9.4 | $ 15.0 | $ 3.5 |
2010 TRC Stock Incentive Plan [Member] | Director Grants [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  | 31,621 | 25,344 | 16,955 |
Granted (in dollars per shares) |  | $ 39.85 | $ 42.83 | $ 51.21 |
2010 TRC Stock Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  | 1,299,592 | 1,042,344 | 1,393,812 |
Granted (in dollars per shares) |  | $ 24.64 | $ 39.95 | $ 51.71 |
2010 TRC Stock Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | New retention program [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  | 16,134 | 85,547 | 275,076 |
Vesting date of awards |  | 2022-10 |  |  |
2010 TRC Stock Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Third Year [Member] | 2020 Compensation Cycle [Member] | Executive Management | Subsequent Event [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) | 288,983 |  |  |  |
Vesting date of awards | 2024-01 |  |  |  |
2010 TRC Stock Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Minimum [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Vesting period of awards |  | 1 year |  |  |
2010 TRC Stock Incentive Plan [Member] | Restricted Stock Units (RSUs) [Member] | Maximum [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Vesting period of awards |  | 6 years |  |  |
2010 TRC Stock Incentive Plan [Member] | Restricted Stock Units In Lieu Of Bonus [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  | 81,336 | 95,687 | 112,438 |
Granted (in dollars per shares) |  | $ 41.39 | $ 42.83 | $ 51.09 |
Vesting period of awards |  | 3 years |  |  |
2010 TRC Stock Incentive Plan [Member] | PSUs [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  | 291,365 |  |  |
Granted (in dollars per shares) |  | $ 69.70 |  |  |
Vesting period of awards |  | 3 years |  |  |
Expected term of grant date fair value |  | 3 years |  |  |
Outstanding (in shares) |  | 719,054 | 528,719 |  |
Cash-settled awards vested |  | 101,030 |  |  |
2010 TRC Stock Incentive Plan [Member] | PSUs [Member] | 2020 Compensation Cycle [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  | 291,365 |  |  |
Vesting date of awards |  | 2023-01 |  |  |
2010 TRC Stock Incentive Plan [Member] | PSUs [Member] | 2019 Compensation Cycle [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  |  | 261,245 |  |
Vesting date of awards |  |  | 2022-01 |  |
2010 TRC Stock Incentive Plan [Member] | PSUs [Member] | 2018 Compensation Cycle [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  |  |  | 182,849 |
Vesting date of awards |  |  |  | 2021-01 |
2010 TRC Stock Incentive Plan [Member] | PSUs [Member] | 2020 Compensation Cycle [Member] | Executive Management | Subsequent Event [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) | 288,983 |  |  |  |
Vesting date of awards | 2024-01 |  |  |  |
2010 TRC Stock Incentive Plan [Member] | PSUs [Member] | First Year [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Awards vesting percentage |  | 25.00% |  |  |
2010 TRC Stock Incentive Plan [Member] | PSUs [Member] | Second Year [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Awards vesting percentage |  | 25.00% |  |  |
2010 TRC Stock Incentive Plan [Member] | PSUs [Member] | Third Year [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Awards vesting percentage |  | 25.00% |  |  |
2010 TRC Stock Incentive Plan [Member] | PSUs [Member] | Entirety of Performance Period [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Awards vesting percentage |  | 25.00% |  |  |
2010 TRC Stock Incentive Plan [Member] | PSU’s Granted in 2018 and 2019 [Member] | Minimum [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Guideline performance percentage based on total shareholder return |  | 0.00% |  |  |
2010 TRC Stock Incentive Plan [Member] | PSU’s Granted in 2018 and 2019 [Member] | Maximum [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Guideline performance percentage based on total shareholder return |  | 250.00% |  |  |
2010 TRC Stock Incentive Plan [Member] | Cash Settled Restricted Stock Units [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) |  | 7,836 | 69,042 |  |
Vesting period of awards |  | 1 year |  |  |
2010 TRC Stock Incentive Plan [Member] | Restricted Stock [Member] | Outside Directors [Member] | Subsequent Event [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Granted (in shares) | 63,907 |  |  |  |
Vesting date of awards | 2022-01 |  |  |  |
TRC Equity Compensation Plan [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Termination date |  | Feb. 28, 2017 |  |  |
TRC Equity Compensation Plan [Member] | Restricted Stock Units (RSUs) [Member] |  |  |  |  |
Share Based Compensation Arrangement By Share Based Payment Award [Line Items] |  |  |  |  |
Outstanding (in shares) |  | 0 |  |  |

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- Definition Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References No definition available. + Details
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- Definition The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period. + References No definition available. + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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