Severance and Exit Costs (Schedule of Severance and Exit Costs Liability) (Details) - USD ($) $ in Millions		12 Months Ended
		Mar. 31, 2017		Mar. 31, 2016
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning		$ 525		$ 454
Severance costs, beginning		150		119
Restructuring charges		68		391
Severance costs		20	[1]	216	[2]
Restructuring reserve, settled with cash		(292)		(320)
Payments for postemployment benefits		(158)		(185)
Restructuring reserve, end		301		525
Severance costs, end		12		150
Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning		338		291
Restructuring charges		17	[3]	156	[4]
Restructuring reserved settled with cash and other adjustments		(106)		(109)
Restructuring reserve, end		249		338
Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring reserve, beginning		37		44
Restructuring charges		31	[5]	19	[6]
Restructuring reserved settled with cash and other adjustments		(28)		(26)
Restructuring reserve, end		40		37
Severance and exit costs [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges	[5]	29
Wireline [Member]
Restructuring Reserve [Roll Forward]
Severance costs		1		25
Wireline [Member] | Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges	[3]	3
Wireline [Member] | cost of products [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges		2	[5]	2
Wireline [Member] | Severance and exit costs [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges	[5]	17
Wireless [Member]
Restructuring Reserve [Roll Forward]
Severance costs		19		191
Wireless [Member] | Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges excluding US Cellular gain				176
Restructuring charges	[3]	14
Wireless [Member] | cost of products [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges				$ 17
Wireless [Member] | Severance and exit costs [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring charges	[5]	$ 12

[1] (2)For the year ended March 31, 2017, we recognized costs of $20 million ($19 million Wireless, $1 million Wireline).

[2] (5)For the year ended March 31, 2016, we recognized costs of $216 million ($191 million Wireless, $25 million Wireline).

[3] (1)For the year ended March 31, 2017, we recognized costs of $17 million ($14 million Wireless, $3 million Wireline).

[4] (4)We recognized costs of $176 million (Wireless only) for the year ended March 31, 2016, which were offset by $20 million of income (Wireless only) resulting from a revision to our estimate of a previously recorded reserve.

[5] (3)For the year ended March 31, 2017, we recognized $2 million (solely attributable to Wireline) as "Cost of services" and $29 million ($12 million Wireless, $17 million Wireline) as "Severance and exit costs."

[6] (6)For the year ended March 31, 2016, we recognized $2 million (solely attributable to Wireline) as "Cost of services" and $17 million (solely attributable to Wireless) as "Severance and exit costs".