New Accounting Pronouncements - Cumulative Effects of Accounting Standards Updates on Balance Sheet (Details) - USD ($) $ in Millions	Jun. 30, 2019	Apr. 01, 2019	Mar. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounts and notes receivable, net	$ 3,558		$ 3,554
Device and accessory inventory	726		999
Prepaid expenses and other current assets	1,436	$ 1,178	1,289
Property, Plant and Equipment		41,709
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	(20,420)	(20,512)	(20,539)
Property, plant and equipment, net	20,556	21,197	21,201
Operating Lease, Right-of-Use Asset	7,054	7,358
Property, plant and equipment	1,525	1,650	1,769
Other assets	1,119	1,117	1,118
Accrued expenses and other current liabilities	3,048	3,419	3,597
Current portion of long-term debt, financing and capital lease obligations	2,889	4,514	4,557
Long-term debt, financing and capital lease obligations	35,073	35,299	35,366
Operating Lease, Liability, Noncurrent	5,913	6,263
Operating Lease, Liability, Current	1,680	1,813
Deferred tax liabilities	7,563	7,602	7,556
Other liabilities	2,540	2,564	3,437
(Accumulated deficit) retained earnings	(1,832)	(1,721)	(1,883)
Accumulated other comprehensive loss	$ (414)		(392)
Scenario, Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other current assets			1,289
Property, Plant and Equipment			41,740
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment			(20,539)
Property, plant and equipment, net			21,201
Operating Lease, Right-of-Use Asset			0
Property, plant and equipment			1,769
Other assets			1,118
Accrued expenses and other current liabilities			3,597
Current portion of long-term debt, financing and capital lease obligations			4,557
Long-term debt, financing and capital lease obligations			35,366
Operating Lease, Liability, Noncurrent			0
Operating Lease, Liability, Current			0
Deferred tax liabilities			7,556
Other liabilities			3,437
(Accumulated deficit) retained earnings			$ (1,883)
Accounting Standards Update 2014-09 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other current assets		(111)
Property, Plant and Equipment		(31)
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment		(27)
Property, plant and equipment, net		(4)
Operating Lease, Right-of-Use Asset		7,358
Property, plant and equipment		(119)
Other assets		(1)
Accrued expenses and other current liabilities		(178)
Current portion of long-term debt, financing and capital lease obligations		(43)
Long-term debt, financing and capital lease obligations		(67)
Operating Lease, Liability, Noncurrent		6,263
Operating Lease, Liability, Current		1,813
Deferred tax liabilities		46
Other liabilities		(873)
(Accumulated deficit) retained earnings		$ 162