Severance and Exit Costs (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Severance Costs	$ 17	$ 22
Restructuring Charges		13
Wireless [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs		19
Wireline [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	1	3
Access [Member] | Severance and exit costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	(1)	3
Access [Member] | Severance and exit costs [Member] | Wireless [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	(9)	(8)
Access [Member] | Severance and exit costs [Member] | Wireline [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 8	$ 11