Severance and Exit Costs (Schedule of Severance and Exit Costs) (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2019	Mar. 31, 2019
Restructuring Reserve [Roll Forward]
Restructuring Reserve	$ 55	$ 67
Supplemental Unemployment Benefits, Severance Benefits	3	6
Restructuring Charges	46
Severance Costs	1
Payments for Postemployment Benefits	(4)
Restructuring Reserve, Settled with Cash	(58)
Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	52	$ 61
Restructuring reserved settled with cash and other adjustments	54
Wireless [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	1
Wireline [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	1
Corporate Segment [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	(1)
Severance and exit costs [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	45
Severance and exit costs [Member] | Wireless [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	45
Severance and exit costs [Member] | Wireline [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	(1)
Severance and exit costs [Member] | Corporate Segment [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	$ 1