Severance and Exit Costs (Schedule of Severance and Exit Costs) (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2018	Mar. 31, 2018
Restructuring Reserve [Roll Forward]
Restructuring Reserve	$ 181	$ 248
Supplemental Unemployment Benefits, Severance Benefits	12	64
Restructuring Charges	63
Severance Costs	22
Payments for Postemployment Benefits	(74)
Restructuring Reserve, Settled with Cash	(130)
Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	145	165
Restructuring Charges	23
Restructuring reserved settled with cash and other adjustments	43
Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	24	$ 19
Restructuring reserved settled with cash and other adjustments	13
Wireless [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	15
Wireless [Member] | Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	23
Wireline [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	7
Severance and exit costs [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	18
Severance and exit costs [Member] | Wireless [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	7
Severance and exit costs [Member] | Wireline [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	$ 11