Business Combination - Narrative (Details) - USD ($)			1 Months Ended		3 Months Ended		12 Months Ended
	Apr. 01, 2020	Feb. 20, 2020	Feb. 01, 2021	Nov. 30, 2020	Jun. 30, 2021	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Apr. 09, 2020	Jan. 01, 2019
Business Acquisition [Line Items]
Goodwill							$ 11,117,000,000	$ 1,930,000,000
Payments of consent fees							$ 109,000,000	0	$ 0
Sprint
Business Acquisition [Line Items]
Exchange ratio (in shares)	9.75
Exchange ratio (in shares)	0.10256
Stock issued (in shares)	373,396,310
Value of common stock provided in exchange for acquiree common stock	$ 31,328,000,000
Fully-diluted shares of combined company held by public stockholders (percent)							31.70%
Value of contingent consideration	1,882,000,000
Contingent consideration, high end of range	7,300,000,000
Adjustment, property, plant and equipment							$ 1,200,000,000
Adjustment, other long-term liabilities							1,700,000,000
Deferred tax liabilities, adjustment							690,000,000
Deferred tax liabilities, reclassifications							357,000,000
Goodwill	9,401,000,000
Goodwill expected to be tax deductible	0
Spectrum licenses	45,400,000,000
Transaction costs							201,000,000	$ 106,000,000	$ 71,000,000
Transaction costs assumed to have occurred											$ 559,000,000
Total revenue subsequent to Merger date							20,500,000,000
Operating income subsequent to Merger date							$ 1,300,000,000
Total consideration exchanged	40,827,000,000
Sprint | Senior Notes
Business Acquisition [Line Items]
Payments for requisite consents to third-party note holders	95,000,000
Sprint | DT
Business Acquisition [Line Items]
Payments of consent fees						$ 7,000,000
Payments for requisite consents to DT	13,000,000
Sprint | Secured Term Loan Facility
Business Acquisition [Line Items]
Financing commitment, amount	4,000,000,000.0
Sprint | Secured Bridge Loan Facility
Business Acquisition [Line Items]
Financing commitment, amount	19,000,000,000.0									$ 19,000,000,000.0
Sprint | Secured and Unsecured Debt Financing
Business Acquisition [Line Items]
Payments of consent fees	355,000,000
Sprint | Accounts Receivable
Business Acquisition [Line Items]
Fair value of receivables acquired	1,800,000,000
Gross amounts due	1,800,000,000
Sprint | Equipment installment plan receivables, net of allowance for credit losses and imputed discount
Business Acquisition [Line Items]
Fair value of receivables acquired	1,300,000,000
Gross amounts due	1,600,000,000
Sprint | Customer relationships
Business Acquisition [Line Items]
Finite-lived, Fair Value (in millions)	$ 4,900,000,000
Weighted Average Useful Life (in years)	8 years
Sprint | Favorable lease (asset)
Business Acquisition [Line Items]
Finite-lived, Fair Value (in millions)	$ 790,000,000
Weighted Average Useful Life (in years)	18 years
Sprint | SoftBank
Business Acquisition [Line Items]
Fully-diluted shares expected to be held immediately following merger (percent)							24.70%
Settlement to resolve FCC's investigation				$ 200,000,000
Sprint | DT
Business Acquisition [Line Items]
Fully-diluted shares expected to be held immediately following merger (percent)							43.60%
Sprint | Common Stock
Business Acquisition [Line Items]
Exchange ratio (in shares)		11.00
Sprint | Common Stock | SoftBank
Business Acquisition [Line Items]
Aggregate surrendered (in shares)		48,751,557
Exchange ratio (in shares)		11.31
Volume-weighted average price (in USD per share)		$ 150.00
Number of shares issued if threshold not met (in shares)		0
Shentel | Subsequent Event | Scenario, Forecast
Business Acquisition [Line Items]
Asset value					$ 2,100,000,000
Purchase price, percent of assets					90.00%
Total consideration exchanged			$ 1,900,000,000		$ 1,900,000,000