Segments (Operating Revenues by Service and Products) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting Information [Line Items]
Net operating revenues		$ 7,975	$ 8,488	$ 16,002	$ 17,277
Segment Reporting Information, Total Net Operating Revenues		7,975	8,488	16,002	17,277
Services [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		6,222	6,693	12,573	13,601
Equipment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		1,095	1,039	2,085	2,145
Voice [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		127	208	278	444
Data [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		25	31	54	63
Internet [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		275	299	559	606
Other Products or Services [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues		231	218	453	418
Wireless [Member]
Segment Reporting Information [Line Items]
Net operating revenues		7,516	7,929	15,056	16,122
Segment Reporting Information, Total Net Operating Revenues		7,516	7,929	15,056	16,122
Wireless [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		6,222	6,693	12,573	13,601
Wireless [Member] | Equipment [Member]
Segment Reporting Information [Line Items]
Net operating revenues		1,095	1,039	2,085	2,145
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		199	197	398	376
Wireline [Member]
Segment Reporting Information [Line Items]
Net operating revenues		609	708	1,239	1,454
Segment Reporting Information, Total Net Operating Revenues		455	555	938	1,148
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		212	294	445	621
Wireline [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues		43	53	92	109
Wireline [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues		323	340	651	685
Wireline [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		31	21	51	39
Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Net operating revenues	[1]	(150)	(149)	(293)	(299)
Segment Reporting Information, Total Net Operating Revenues		4	4	8	7
Corporate, Other And Eliminations [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0	0	0
Corporate, Other And Eliminations [Member] | Equipment [Member]
Segment Reporting Information [Line Items]
Net operating revenues		0	0	0	0
Corporate, Other And Eliminations [Member] | Voice [Member]
Segment Reporting Information [Line Items]
Net operating revenues		(85)	(86)	(167)	(177)
Corporate, Other And Eliminations [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues		(18)	(22)	(38)	(46)
Corporate, Other And Eliminations [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues		(48)	(41)	(92)	(79)
Corporate, Other And Eliminations [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues		$ 1	$ 0	$ 4	$ 3

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