Guarantor Financial Information - Condensed Consolidating Balance Sheet Information (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Current assets
Cash and cash equivalents	$ 1,439		$ 1,203
Accounts receivable, net	1,749		1,769
Equipment installment plan receivables, net	2,466		2,538
Accounts receivable from affiliates	16		11
Inventory	1,261		1,084
Other current assets	1,814	$ 1,598	1,676
Total current assets	8,745		8,281
Property and equipment, net	21,464	21,020	23,359
Operating lease right-of-use assets	9,509	9,251	0
Financing lease right-of-use assets	2,339	2,271	0
Goodwill	1,901		1,901
Spectrum licenses	35,618		35,559
Other intangible assets, net	174	186	198
Investments in subsidiaries, net	0		0
Intercompany receivables and note receivables	0		0
Equipment installment plan receivables due after one year, net	1,662		1,547
Other assets	1,661	1,552	1,623
Total assets	83,073		72,468
Current liabilities
Accounts payable and accrued liabilities	7,330	7,676	7,741
Payables to affiliates	242		200
Short-term debt	250		841
Short-term debt to affiliates	598		0
Deferred revenue	665		698
Short-term operating lease liabilities	2,202		0
Short-term financing lease liabilities	911		0
Other current liabilities	1,129	815	787
Total current liabilities	13,327		10,267
Long-term debt	10,952		12,124
Long-term debt to affiliates	13,985		14,582
Tower obligations	2,244	2,212	2,557
Deferred tax liabilities	4,925	4,703	4,472
Operating lease liabilities	9,339		0
Financing lease liabilities	1,224		0
Deferred rent expense		0	2,781
Negative carrying value of subsidiaries, net	0		0
Intercompany payables and debt	0		0
Other long-term liabilities	896	$ 903	967
Total long-term liabilities	43,565		37,483
Total stockholders' equity (deficit)	26,181		24,718	$ 22,876	$ 22,559
Total liabilities and stockholders' equity	83,073		72,468
Consolidating and Eliminating Adjustments
Current assets
Cash and cash equivalents	0		0
Accounts receivable, net	0		0
Equipment installment plan receivables, net	0		0
Accounts receivable from affiliates	(5)		0
Inventory	0		0
Other current assets	0		0
Total current assets	(5)		0
Property and equipment, net	0		0
Operating lease right-of-use assets	0
Financing lease right-of-use assets	0
Goodwill	0		0
Spectrum licenses	0		0
Other intangible assets, net	0		0
Investments in subsidiaries, net	(74,907)		(71,830)
Intercompany receivables and note receivables	(5,275)		(5,174)
Equipment installment plan receivables due after one year, net	0		0
Other assets	(153)		(145)
Total assets	(80,340)		(77,149)
Current liabilities
Accounts payable and accrued liabilities	0		0
Payables to affiliates	(5)		0
Short-term debt	0		0
Short-term debt to affiliates	0
Deferred revenue	0		0
Short-term operating lease liabilities	0
Short-term financing lease liabilities	0
Other current liabilities	0		0
Total current liabilities	(5)		0
Long-term debt	0		0
Long-term debt to affiliates	0		0
Tower obligations	0		0
Deferred tax liabilities	(153)		(145)
Operating lease liabilities	0
Financing lease liabilities	0
Deferred rent expense			0
Negative carrying value of subsidiaries, net	(761)		(676)
Intercompany payables and debt	(5,275)		(5,174)
Other long-term liabilities	0		0
Total long-term liabilities	(6,189)		(5,995)
Total stockholders' equity (deficit)	(74,146)		(71,154)
Total liabilities and stockholders' equity	(80,340)		(77,149)
Parent | Reportable Legal Entities
Current assets
Cash and cash equivalents	3		2
Accounts receivable, net	0		0
Equipment installment plan receivables, net	0		0
Accounts receivable from affiliates	0		0
Inventory	0		0
Other current assets	0		0
Total current assets	3		2
Property and equipment, net	0		0
Operating lease right-of-use assets	0
Financing lease right-of-use assets	0
Goodwill	0		0
Spectrum licenses	0		0
Other intangible assets, net	0		0
Investments in subsidiaries, net	26,686		25,314
Intercompany receivables and note receivables	0		0
Equipment installment plan receivables due after one year, net	0		0
Other assets	0		0
Total assets	26,689		25,316
Current liabilities
Accounts payable and accrued liabilities	0		0
Payables to affiliates	0		0
Short-term debt	0		0
Short-term debt to affiliates	0
Deferred revenue	0		0
Short-term operating lease liabilities	0
Short-term financing lease liabilities	0
Other current liabilities	0		0
Total current liabilities	0		0
Long-term debt	0		0
Long-term debt to affiliates	0		0
Tower obligations	0		0
Deferred tax liabilities	0		0
Operating lease liabilities	0
Financing lease liabilities	0
Deferred rent expense			0
Negative carrying value of subsidiaries, net	0		0
Intercompany payables and debt	508		598
Other long-term liabilities	0		0
Total long-term liabilities	508		598
Total stockholders' equity (deficit)	26,181		24,718
Total liabilities and stockholders' equity	26,689		25,316
Issuer | Reportable Legal Entities
Current assets
Cash and cash equivalents	2		1
Accounts receivable, net	0		0
Equipment installment plan receivables, net	0		0
Accounts receivable from affiliates	5		0
Inventory	0		0
Other current assets	0		0
Total current assets	7		1
Property and equipment, net	0		0
Operating lease right-of-use assets	0
Financing lease right-of-use assets	0
Goodwill	0		0
Spectrum licenses	0		0
Other intangible assets, net	0		0
Investments in subsidiaries, net	48,221		46,516
Intercompany receivables and note receivables	5,275		5,174
Equipment installment plan receivables due after one year, net	0		0
Other assets	7		7
Total assets	53,510		51,698
Current liabilities
Accounts payable and accrued liabilities	136		228
Payables to affiliates	189		157
Short-term debt	250		0
Short-term debt to affiliates	598
Deferred revenue	0		0
Short-term operating lease liabilities	0
Short-term financing lease liabilities	0
Other current liabilities	714		447
Total current liabilities	1,887		832
Long-term debt	10,952		10,950
Long-term debt to affiliates	13,985		14,582
Tower obligations	0		0
Deferred tax liabilities	0		0
Operating lease liabilities	0
Financing lease liabilities	0
Deferred rent expense			0
Negative carrying value of subsidiaries, net	0		0
Intercompany payables and debt	0		0
Other long-term liabilities	0		20
Total long-term liabilities	24,937		25,552
Total stockholders' equity (deficit)	26,686		25,314
Total liabilities and stockholders' equity	53,510		51,698
Guarantor Subsidiaries | Reportable Legal Entities
Current assets
Cash and cash equivalents	1,314		1,079
Accounts receivable, net	1,465		1,510
Equipment installment plan receivables, net	2,466		2,538
Accounts receivable from affiliates	16		11
Inventory	1,260		1,084
Other current assets	1,155		1,031
Total current assets	7,676		7,253
Property and equipment, net	21,155		23,062
Operating lease right-of-use assets	9,505
Financing lease right-of-use assets	2,338
Goodwill	1,683		1,683
Spectrum licenses	35,618		35,559
Other intangible assets, net	97		116
Investments in subsidiaries, net	0		0
Intercompany receivables and note receivables	0		0
Equipment installment plan receivables due after one year, net	1,662		1,547
Other assets	1,596		1,540
Total assets	81,330		70,760
Current liabilities
Accounts payable and accrued liabilities	6,883		7,240
Payables to affiliates	58		43
Short-term debt	0		841
Short-term debt to affiliates	0
Deferred revenue	665		698
Short-term operating lease liabilities	2,199
Short-term financing lease liabilities	911
Other current liabilities	157		164
Total current liabilities	10,873		8,986
Long-term debt	0		1,174
Long-term debt to affiliates	0		0
Tower obligations	76		384
Deferred tax liabilities	5,078		4,617
Operating lease liabilities	9,337
Financing lease liabilities	1,224
Deferred rent expense			2,781
Negative carrying value of subsidiaries, net	761		676
Intercompany payables and debt	4,412		4,234
Other long-term liabilities	876		926
Total long-term liabilities	21,764		14,792
Total stockholders' equity (deficit)	48,693		46,982
Total liabilities and stockholders' equity	81,330		70,760
Non-Guarantor Subsidiaries | Reportable Legal Entities
Current assets
Cash and cash equivalents	120		121
Accounts receivable, net	284		259
Equipment installment plan receivables, net	0		0
Accounts receivable from affiliates	0		0
Inventory	1		0
Other current assets	659		645
Total current assets	1,064		1,025
Property and equipment, net	309		297
Operating lease right-of-use assets	4
Financing lease right-of-use assets	1
Goodwill	218		218
Spectrum licenses	0		0
Other intangible assets, net	77		82
Investments in subsidiaries, net	0		0
Intercompany receivables and note receivables	0		0
Equipment installment plan receivables due after one year, net	0		0
Other assets	211		221
Total assets	1,884		1,843
Current liabilities
Accounts payable and accrued liabilities	311		273
Payables to affiliates	0		0
Short-term debt	0		0
Short-term debt to affiliates	0
Deferred revenue	0		0
Short-term operating lease liabilities	3
Short-term financing lease liabilities	0
Other current liabilities	258		176
Total current liabilities	572		449
Long-term debt	0		0
Long-term debt to affiliates	0		0
Tower obligations	2,168		2,173
Deferred tax liabilities	0		0
Operating lease liabilities	2
Financing lease liabilities	0
Deferred rent expense			0
Negative carrying value of subsidiaries, net	0		0
Intercompany payables and debt	355		342
Other long-term liabilities	20		21
Total long-term liabilities	2,545		2,536
Total stockholders' equity (deficit)	(1,233)		(1,142)
Total liabilities and stockholders' equity	$ 1,884		$ 1,843