Segments (Operating Revenues by Service and Products) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Net operating revenues		$ 8,107	$ 8,973	$ 24,109	$ 26,250
Segment Reporting Information, Total Net Operating Revenues		8,107	8,973	24,109	26,250
Services [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		6,058	6,523	18,631	20,124
Equipment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		1,424	1,701	3,509	3,846
Voice [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		119	195	397	639
Data [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		25	30	79	93
Internet [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		269	291	828	897
Other Products or Services [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		212	233	665	651
Wireless [Member]
Segment Reporting Information [Line Items]
Net operating revenues		7,670	8,433	22,726	24,555
Segment Reporting Information, Total Net Operating Revenues		7,670	8,433	22,726	24,555
Wireless [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		6,058	6,523	18,631	20,124
Wireless [Member] | Equipment [Member]
Segment Reporting Information [Line Items]
Net operating revenues		1,424	1,701	3,509	3,846
Wireless [Member] | Voice [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0	0	0
Wireless [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0	0	0
Wireless [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0	0	0
Wireless [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		188	209	586	585
Wireline [Member]
Segment Reporting Information [Line Items]
Net operating revenues		581	692	1,820	2,146
Segment Reporting Information, Total Net Operating Revenues		434	536	1,372	1,684
Wireline [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0	0	0
Wireline [Member] | Equipment [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0	0	0
Wireline [Member] | Voice [Member]
Segment Reporting Information [Line Items]
Net operating revenues		201	289	646	910
Wireline [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues		42	52	134	161
Wireline [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues		317	333	968	1,018
Wireline [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		21	18	72	57
Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	(144)	(152)	(437)	(451)
Segment Reporting Information, Total Net Operating Revenues		3	4	11	11
Corporate, Other And Eliminations [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	0	0	0	0
Corporate, Other And Eliminations [Member] | Equipment [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	0	0	0	0
Corporate, Other And Eliminations [Member] | Voice [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	(82)	(94)	(249)	(271)
Corporate, Other And Eliminations [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	(17)	(22)	(55)	(68)
Corporate, Other And Eliminations [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	(48)	(42)	(140)	(121)
Corporate, Other And Eliminations [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	$ 3	$ 6	$ 7	$ 9

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