Segments (Operating Revenues by Service and Products) (Details) - USD ($) $ in Millions		3 Months Ended
		Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Net operating revenues		$ 8,012	$ 8,027
Segment Reporting Information, Total Net Operating Revenues		8,012	8,027
Services [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		5,943	6,351
Wireless Equipment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		1,496	990
Voice [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		112	151
Data [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		21	29
Internet [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		261	284
Other Products or Services [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		179	222
Wireless [Member]
Segment Reporting Information [Line Items]
Net operating revenues		7,597	7,540
Segment Reporting Information, Total Net Operating Revenues		7,597	7,540
Wireless [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		5,943	6,351
Wireless [Member] | Wireless Equipment [Member]
Segment Reporting Information [Line Items]
Net operating revenues		1,496	990
Wireless [Member] | Voice [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0
Wireless [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0
Wireless [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0
Wireless [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		158	199
Wireline [Member]
Segment Reporting Information [Line Items]
Net operating revenues		545	630
Segment Reporting Information, Total Net Operating Revenues		412	483
Wireline [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0
Wireline [Member] | Wireless Equipment [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0
Wireline [Member] | Voice [Member]
Segment Reporting Information [Line Items]
Net operating revenues		181	233
Wireline [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues		43	49
Wireline [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues		302	328
Wireline [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		19	20
Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	(130)	(143)
Segment Reporting Information, Total Net Operating Revenues		3	4
Corporate, Other And Eliminations [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	0	0
Corporate, Other And Eliminations [Member] | Wireless Equipment [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	0	0
Corporate, Other And Eliminations [Member] | Voice [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	(69)	(82)
Corporate, Other And Eliminations [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	(22)	(20)
Corporate, Other And Eliminations [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	(41)	(44)
Corporate, Other And Eliminations [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	$ 2	$ 3

[1] Revenues eliminated in consolidation consist primarily of wireline services provided to the Wireless segment for resale to or use by wireless subscribers.