Severance and Exit Costs (Schedule of Severance and Exit Costs) (Details) - USD ($) $ in Millions	9 Months Ended
	Dec. 31, 2019	Mar. 31, 2019
Restructuring Reserve [Roll Forward]
Restructuring Reserve	$ 38	$ 67
Supplemental Unemployment Benefits, Severance Benefits	6	6
Restructuring Charges	66
Severance Costs	6
Payments for Postemployment Benefits	(6)
Restructuring Reserve, Settled with Cash	(95)
Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	32	$ 61
Restructuring reserved settled with cash and other adjustments	89
Wireless [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	5
Corporate Segment [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	1
Severance and exit costs [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	60
Severance and exit costs [Member] | Wireless [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	63
Severance and exit costs [Member] | Wireline [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	(2)
Severance and exit costs [Member] | Corporate Segment [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	$ (1)