Segments (Operating Revenues by Service and Products) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Restructuring Charges			$ 32
Net operating revenues	$ 8,549	$ 8,107	24,808	$ 24,109
Segment Reporting Information, Total Net Operating Revenues	8,549	8,107	24,808	24,109
Services [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	5,763	6,058	17,555	18,631
Wireless Equipment [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	2,226	1,424	5,556	3,509
Voice [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	92	119	310	397
Data [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	18	25	60	79
Internet [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	243	269	752	828
Other Products or Services [Member]
Segment Reporting Information [Line Items]
Segment Reporting Information, Total Net Operating Revenues	207	212	575	665
Wireless [Member]
Segment Reporting Information [Line Items]
Net operating revenues	8,172	7,670	23,620	22,726
Segment Reporting Information, Total Net Operating Revenues	8,172	7,670	23,620	22,726
Wireless [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues	5,763	6,058	17,555	18,631
Wireless [Member] | Wireless Equipment [Member]
Segment Reporting Information [Line Items]
Net operating revenues	2,226	1,424	5,556	3,509
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	183	188	509	586
Wireline [Member]
Segment Reporting Information [Line Items]
Net operating revenues	497	581	1,563	1,820
Segment Reporting Information, Total Net Operating Revenues	372	434	1,177	1,372
Wireline [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues	0	0	0	0
Wireline [Member] | Wireless 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	153	201	506	646
Wireline [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues	41	42	127	134
Wireline [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues	281	317	871	968
Wireline [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues	22	21	59	72
Corporate, Other And Eliminations [Member]
Segment Reporting Information [Line Items]
Net operating revenues	(120)	(144)	(375)	(437)
Segment Reporting Information, Total Net Operating Revenues	5	3	11	11
Corporate, Other And Eliminations [Member] | Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues	0	0	0	0
Corporate, Other And Eliminations [Member] | Wireless 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	(61)	(82)	(196)	(249)
Corporate, Other And Eliminations [Member] | Data [Member]
Segment Reporting Information [Line Items]
Net operating revenues	(23)	(17)	(67)	(55)
Corporate, Other And Eliminations [Member] | Internet [Member]
Segment Reporting Information [Line Items]
Net operating revenues	(38)	(48)	(119)	(140)
Corporate, Other And Eliminations [Member] | Other Products or Services [Member]
Segment Reporting Information [Line Items]
Net operating revenues	2	$ 3	7	$ 7
Lease [Member]
Segment Reporting Information [Line Items]
Restructuring Charges			(3)
Lease [Member] | Wireless [Member]
Segment Reporting Information [Line Items]
Restructuring Charges	$ 2		(5)
Lease [Member] | Wireline [Member]
Segment Reporting Information [Line Items]
Restructuring Charges			$ 2