New Accounting Pronouncements - Cumulative Effects of Accounting Standards Update on Statement of Comprehensive Income and Balance Sheet (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales Revenue, Services, Net	$ 5,740	$ 6,071
Revenue, equipment sales, net	1,173	1,187
Revenue, equipment rentals, net	1,212	899
Revenues	8,125	8,157
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
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)
Costs and Expenses	7,310	6,994
Operating Income	815	1,163	2,491
Total other 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
Basic net (loss) income per common share	$ 0.04	$ 0.05
Diluted net (loss) income per common share	$ 0.04	$ 0.05
Basic weighted average common shares outstanding	4,010	3,993
Diluted weighted average common shares outstanding	4,061	4,076
Change | Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales Revenue, Services, Net	$ (143)
Revenue, equipment sales, net	281
Revenue, equipment rentals, net	(16)
Revenues	122
Cost of Services (exclusive of depreciation and amortization included below)	(11)
Cost of equipment sales	22
Cost of equipment rentals	0
Selling, general and administrative	(81)
Depreciation, network and other	0
Depreciation, equipment rentals	0
Amortization	0
Other, net	0
Costs and Expenses	(70)
Operating Income	192
Total other expense	0
Loss (income) before income taxes	192
Income tax benefit	(40)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	152
Net Income (Loss) Attributable to Noncontrolling Interest	0
Net Income (Loss) Attributable to Parent	$ 152
Basic net (loss) income per common share	$ 30,000
Diluted net (loss) income per common share	$ 30,000
Basic weighted average common shares outstanding	0
Diluted weighted average common shares outstanding	0
Balances without adoption of Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales Revenue, Services, Net	$ 5,883
Revenue, equipment sales, net	892
Revenue, equipment rentals, net	1,228
Revenues	8,003
Cost of Services (exclusive of depreciation and amortization included below)	1,688
Cost of equipment sales	1,248
Cost of equipment rentals	124
Selling, general and administrative	1,948
Depreciation, network and other	1,023
Depreciation, equipment rentals	1,136
Amortization	171
Other, net	42
Costs and Expenses	7,380
Operating Income	623
Total other expense	(595)
Loss (income) before income taxes	28
Income tax benefit	(7)
Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest	21
Net Income (Loss) Attributable to Noncontrolling Interest	3
Net Income (Loss) Attributable to Parent	$ 24
Basic net (loss) income per common share	$ 10,000
Diluted net (loss) income per common share	$ 10,000
Basic weighted average common shares outstanding	4,010
Diluted weighted average common shares outstanding	4,061