Guarantor Financial Information (CONDENSED CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME (LOSS)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Condensed Income Statements, Captions [Line Items]
Net operating revenues	$ 8,125	$ 8,157
Sales Revenue, Services, Net	5,740	6,071
Revenue, equipment sales, net	1,173	1,187
Revenue, equipment rentals, net	1,212	899
Cost of Services (exclusive of depreciation and amortization included below)	1,677	1,709
Cost of equipment sales	1,270	1,545
Cost of equipment rentals	124	112
Net operating expenses
Selling, general and administrative	1,867	1,938
Depreciation, network and other	1,023	977
Depreciation, equipment rentals	1,136	854
Amortization	171	223	$ 628
Other, net	42	(364)
Total costs and expenses	7,310	6,994
Operating Income	815	1,163	2,491
Other (expense) income
Interest Income	42	19
Interest Expense	(637)	(613)	(1,789)
(Losses) earnings of Subsidiaries	0	0
Other nonoperating income (expense), excluding interest income	0	(71)
Nonoperating Expense	(595)	(665)
Loss (income) before income taxes	220	498	$ 652
Income tax benefit	(47)	(292)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	173	206
Net Income (Loss) Attributable to Noncontrolling Interest	3	0
Net Income (Loss) Attributable to Parent	176	206
Other Comprehensive Income (Loss), Net of Tax	(4)	(4)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	169
Comprehensive (loss) income	169	202
Consolidation, Eliminations [Member]
Condensed Income Statements, Captions [Line Items]
Net operating revenues	0	0
Sales Revenue, Services, Net	0	0
Revenue, equipment sales, net	0	0
Revenue, equipment rentals, net	0	0
Cost of Services (exclusive of depreciation and amortization included below)	0	0
Cost of equipment sales	0	0
Cost of equipment rentals	0	0
Net operating expenses
Selling, general and administrative	0	0
Depreciation, network and other	0	0
Depreciation, equipment rentals	0	0
Amortization	0	0
Other, net	0	0
Total costs and expenses	0	0
Operating Income	0	0
Other (expense) income
Interest Income	(733)	(228)
Interest Expense	733	228
(Losses) earnings of Subsidiaries	(378)	(730)
Other nonoperating income (expense), excluding interest income	0	0
Nonoperating Expense	(378)	(730)
Loss (income) before income taxes	(378)	(730)
Income tax benefit	0	0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	(378)
Net Income (Loss) Attributable to Noncontrolling Interest	0
Net Income (Loss) Attributable to Parent	(378)	(730)
Other Comprehensive Income (Loss), Net of Tax	17	(1)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	(361)
Comprehensive (loss) income		(731)
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Net operating revenues	0	0
Sales Revenue, Services, Net	0	0
Revenue, equipment sales, net	0	0
Revenue, equipment rentals, net	0	0
Cost of Services (exclusive of depreciation and amortization included below)	0	0
Cost of equipment sales	0	0
Cost of equipment rentals	0	0
Net operating expenses
Selling, general and administrative	0	0
Depreciation, network and other	0	0
Depreciation, equipment rentals	0	0
Amortization	0	0
Other, net	0	0
Total costs and expenses	0	0
Operating Income	0	0
Other (expense) income
Interest Income	226	198
Interest Expense	(226)	(198)
(Losses) earnings of Subsidiaries	176	206
Other nonoperating income (expense), excluding interest income	0	0
Nonoperating Expense	176	206
Loss (income) before income taxes	176	206
Income tax benefit	0	0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	176
Net Income (Loss) Attributable to Noncontrolling Interest	0
Net Income (Loss) Attributable to Parent	176	206
Other Comprehensive Income (Loss), Net of Tax	(4)	(4)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	172
Comprehensive (loss) income		202
Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net operating revenues	0	0
Sales Revenue, Services, Net	0	0
Revenue, equipment sales, net	0	0
Revenue, equipment rentals, net	0	0
Cost of Services (exclusive of depreciation and amortization included below)	0	0
Cost of equipment sales	0	0
Cost of equipment rentals	0	0
Net operating expenses
Selling, general and administrative	0	0
Depreciation, network and other	0	0
Depreciation, equipment rentals	0	0
Amortization	0	0
Other, net	0	(55)
Total costs and expenses	0	(55)
Operating Income	0	55
Other (expense) income
Interest Income	547	45
Interest Expense	(571)	(351)
(Losses) earnings of Subsidiaries	202	524
Other nonoperating income (expense), excluding interest income	(2)	(67)
Nonoperating Expense	176	151
Loss (income) before income taxes	176	206
Income tax benefit	0	0
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	176
Net Income (Loss) Attributable to Noncontrolling Interest	0
Net Income (Loss) Attributable to Parent	176	206
Other Comprehensive Income (Loss), Net of Tax	(4)	(4)
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	172
Comprehensive (loss) income		202
Non-Guarantor Subsidiaries [Member]
Condensed Income Statements, Captions [Line Items]
Net operating revenues	8,125	8,157
Sales Revenue, Services, Net	5,740	6,071
Revenue, equipment sales, net	1,173	1,187
Revenue, equipment rentals, net	1,212	899
Cost of Services (exclusive of depreciation and amortization included below)	1,677	1,709
Cost of equipment sales	1,270	1,545
Cost of equipment rentals	124	112
Net operating expenses
Selling, general and administrative	1,867	1,938
Depreciation, network and other	1,023	977
Depreciation, equipment rentals	1,136	854
Amortization	171	223
Other, net	42	(309)
Total costs and expenses	7,310	7,049
Operating Income	815	1,108
Other (expense) income
Interest Income	2	4
Interest Expense	(573)	(292)
(Losses) earnings of Subsidiaries	0	0
Other nonoperating income (expense), excluding interest income	2	(4)
Nonoperating Expense	(569)	(292)
Loss (income) before income taxes	246	816
Income tax benefit	(47)	(292)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	199
Net Income (Loss) Attributable to Noncontrolling Interest	3
Net Income (Loss) Attributable to Parent	202	524
Other Comprehensive Income (Loss), Net of Tax	(13)	5
Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest	$ 186
Comprehensive (loss) income		$ 529