Guarantor Financial Information - Condensed Consolidating Statement of Cash Flows Information (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating activities
Net cash provided by operating activities		$ 6,824	$ 3,899	$ 3,831
Investing activities
Purchases of property and equipment		(6,391)	(5,541)	(5,237)
Purchases of spectrum licenses and other intangible assets, including deposits		(967)	(127)	(5,828)
Proceeds from sales of tower sites	$ 38	38	0	0
Proceeds related to beneficial interests in securitization transactions		3,876	5,406	4,319
Net cash related to derivative contracts under collateral exchange arrangements	632	(632)	0	0
Acquisition of companies, net of cash acquired		(31)	(338)	0
Equity investment in subsidiary			0	0
Other, net		(18)	21	1
Net cash used in investing activities		(4,125)	(579)	(6,745)
Financing activities
Proceeds from issuance of long-term debt		0	2,494	10,480
Proceeds from borrowing on revolving credit facility		2,340	6,265	2,910
Repayments of revolving credit facility		(2,340)	(6,265)	(2,910)
Repayments of financing lease obligations		(798)	(700)	(486)
Repayments of short-term debt for purchases of inventory, property and equipment, net		(775)	(300)	(300)
Repayments of long-term debt		(600)	(3,349)	(10,230)
Repurchases of common stock		0	(1,071)	(427)
Intercompany advances, net		0	0	0
Equity investment from parent			0	0
Tax withholdings on share-based awards		(156)	(146)	(166)
Dividends on preferred stock				(55)
Cash payments for debt prepayment or debt extinguishment costs		(28)	(212)	(188)
Intercompany dividend paid		0	0	0
Other, net		(17)	(52)	5
Net cash used in financing activities		(2,374)	(3,336)	(1,367)
Change in cash and cash equivalents		325	(16)	(4,281)
Beginning of period		1,203	1,219	5,500
End of period	1,528	1,528	1,203	1,219
Consolidating and Eliminating Adjustments
Operating activities
Net cash provided by operating activities		(555)	(220)	(100)
Investing activities
Purchases of property and equipment		0	0	0
Purchases of spectrum licenses and other intangible assets, including deposits		0	0	0
Proceeds from sales of tower sites		0
Proceeds related to beneficial interests in securitization transactions		0	0	0
Net cash related to derivative contracts under collateral exchange arrangements		0
Acquisition of companies, net of cash acquired		0	0
Equity investment in subsidiary			43	308
Other, net		0	0	0
Net cash used in investing activities		0	43	308
Financing activities
Proceeds from issuance of long-term debt			0	0
Proceeds from borrowing on revolving credit facility		0	0	0
Repayments of revolving credit facility		0	0	0
Repayments of financing lease obligations		0	0	0
Repayments of short-term debt for purchases of inventory, property and equipment, net		0	0
Repayments of long-term debt		0	0	0
Repurchases of common stock			0	0
Intercompany advances, net		0	0	0
Equity investment from parent			(43)	(308)
Tax withholdings on share-based awards		0	0	0
Dividends on preferred stock				0
Cash payments for debt prepayment or debt extinguishment costs		0	0	0
Intercompany dividend paid		555	220	100
Other, net		0	0	0
Net cash used in financing activities		555	177	(208)
Change in cash and cash equivalents		0	0	0
Beginning of period		0	0	0
End of period	0	0	0	0
Parent | Reportable Legal Entities
Operating activities
Net cash provided by operating activities		0	0	1
Investing activities
Purchases of property and equipment		0	0	0
Purchases of spectrum licenses and other intangible assets, including deposits		0	0	0
Proceeds from sales of tower sites		0
Proceeds related to beneficial interests in securitization transactions		0	0	0
Net cash related to derivative contracts under collateral exchange arrangements		0
Acquisition of companies, net of cash acquired		0	0
Equity investment in subsidiary			0	(308)
Other, net		0	0	0
Net cash used in investing activities		0	0	(308)
Financing activities
Proceeds from issuance of long-term debt			0	0
Proceeds from borrowing on revolving credit facility		0	0	0
Repayments of revolving credit facility		0	0	0
Repayments of financing lease obligations		0	0	0
Repayments of short-term debt for purchases of inventory, property and equipment, net		0	0
Repayments of long-term debt		0	0	0
Repurchases of common stock			(1,071)	(427)
Intercompany advances, net		1	995	484
Equity investment from parent			0	0
Tax withholdings on share-based awards		0	0	0
Dividends on preferred stock				(55)
Cash payments for debt prepayment or debt extinguishment costs		0	0	0
Intercompany dividend paid		0	0	0
Other, net		2	4	21
Net cash used in financing activities		3	(72)	23
Change in cash and cash equivalents		3	(72)	(284)
Beginning of period		2	74	358
End of period	5	5	2	74
Issuer | Reportable Legal Entities
Operating activities
Net cash provided by operating activities		(752)	(1,254)	(1,613)
Investing activities
Purchases of property and equipment		0	0	0
Purchases of spectrum licenses and other intangible assets, including deposits		0	0	0
Proceeds from sales of tower sites		0
Proceeds related to beneficial interests in securitization transactions		0	0	0
Net cash related to derivative contracts under collateral exchange arrangements		(632)
Acquisition of companies, net of cash acquired		(32)	0
Equity investment in subsidiary			0	0
Other, net		(12)	(7)	0
Net cash used in investing activities		(676)	(7)	0
Financing activities
Proceeds from issuance of long-term debt			2,494	10,480
Proceeds from borrowing on revolving credit facility		2,340	6,265	2,910
Repayments of revolving credit facility		0	0	0
Repayments of financing lease obligations		0	0	0
Repayments of short-term debt for purchases of inventory, property and equipment, net		0	0
Repayments of long-term debt		0	0	0
Repurchases of common stock			0	0
Intercompany advances, net		(912)	(7,498)	(14,817)
Equity investment from parent			0	308
Tax withholdings on share-based awards		0	0	0
Dividends on preferred stock				0
Cash payments for debt prepayment or debt extinguishment costs		0	0	0
Intercompany dividend paid		0	0	0
Other, net		0	0	0
Net cash used in financing activities		1,428	1,261	(1,119)
Change in cash and cash equivalents		0	0	(2,732)
Beginning of period		1	1	2,733
End of period	1	1	1	1
Guarantor Subsidiaries | Reportable Legal Entities
Operating activities
Net cash provided by operating activities		11,338	10,414	9,761
Investing activities
Purchases of property and equipment		(6,391)	(5,536)	(5,237)
Purchases of spectrum licenses and other intangible assets, including deposits		(967)	(127)	(5,828)
Proceeds from sales of tower sites		38
Proceeds related to beneficial interests in securitization transactions		37	53	43
Net cash related to derivative contracts under collateral exchange arrangements		0
Acquisition of companies, net of cash acquired		1	(338)
Equity investment in subsidiary			(43)	0
Other, net		(6)	28	1
Net cash used in investing activities		(7,288)	(5,963)	(11,021)
Financing activities
Proceeds from issuance of long-term debt			0	0
Proceeds from borrowing on revolving credit facility		0	0	0
Repayments of revolving credit facility		(2,340)	(6,265)	(2,910)
Repayments of financing lease obligations		(798)	(700)	(486)
Repayments of short-term debt for purchases of inventory, property and equipment, net		(775)	(300)
Repayments of long-term debt		(600)	(3,349)	(10,230)
Repurchases of common stock			0	0
Intercompany advances, net		934	6,530	14,300
Equity investment from parent			43	0
Tax withholdings on share-based awards		(156)	(146)	(166)
Dividends on preferred stock				0
Cash payments for debt prepayment or debt extinguishment costs		(28)	(212)	(188)
Intercompany dividend paid		0	0	0
Other, net		(19)	(56)	(16)
Net cash used in financing activities		(3,782)	(4,455)	4
Change in cash and cash equivalents		268	(4)	(1,256)
Beginning of period		1,082	1,086	2,342
End of period	1,350	1,350	1,082	1,086
Non-Guarantor Subsidiaries | Reportable Legal Entities
Operating activities
Net cash provided by operating activities		(3,207)	(5,041)	(4,218)
Investing activities
Purchases of property and equipment		0	(5)	0
Purchases of spectrum licenses and other intangible assets, including deposits		0	0	0
Proceeds from sales of tower sites		0
Proceeds related to beneficial interests in securitization transactions		3,839	5,353	4,276
Net cash related to derivative contracts under collateral exchange arrangements		0
Acquisition of companies, net of cash acquired		0	0
Equity investment in subsidiary			0	0
Other, net		0	0	0
Net cash used in investing activities		3,839	5,348	4,276
Financing activities
Proceeds from issuance of long-term debt			0	0
Proceeds from borrowing on revolving credit facility		0	0	0
Repayments of revolving credit facility		0	0	0
Repayments of financing lease obligations		0	0	0
Repayments of short-term debt for purchases of inventory, property and equipment, net		0	0
Repayments of long-term debt		0	0	0
Repurchases of common stock			0	0
Intercompany advances, net		(23)	(27)	33
Equity investment from parent			0	0
Tax withholdings on share-based awards		0	0	0
Dividends on preferred stock				0
Cash payments for debt prepayment or debt extinguishment costs		0	0	0
Intercompany dividend paid		(555)	(220)	(100)
Other, net		0	0	0
Net cash used in financing activities		(578)	(247)	(67)
Change in cash and cash equivalents		54	60	(9)
Beginning of period		118	58	67
End of period	$ 172	$ 172	$ 118	$ 58