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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