Severance and Exit Costs (Details) $ in Millions	6 Months Ended
	Sep. 30, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Severance Costs	$ 5
Restructuring Charges	0
Wireless [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	3
Wireline [Member]
Restructuring Cost and Reserve [Line Items]
Severance Costs	2
Access [Member] | Severance and exit costs [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	4
Access [Member] | Severance and exit costs [Member] | Wireless [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	1
Access [Member] | Severance and exit costs [Member] | Wireline [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Charges	$ 3