Severance and Exit Costs (Schedule of Severance and Exit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Mar. 31, 2016
Restructuring Cost and Reserve [Line Items]
Document Period End Date			Dec. 31, 2016
Restructuring Reserve [Roll Forward]
Restructuring Reserve	$ 288		$ 288		$ 525
Supplemental Unemployment Benefits, Severance Benefits	20		20		150
Restructuring Charges			32
Payments for Postemployment Benefits			(145)
Restructuring Reserve, Settled with Cash			(269)
Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	235		235		338
Restructuring Charges			(3)
Restructuring reserved settled with cash and other adjustments			(100)
Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	33		33		$ 37
Restructuring reserved settled with cash and other adjustments			(24)
Wireless [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	6		15
Wireless [Member] | Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	$ 2		(5)
Wireless [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges			20
Wireline [Member] | Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges			2
Other Operating Income (Expense) [Member] | Wireless [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Accrual Adjustment		$ 41
Successor [Member] | Cost of Sales [Member] | Wireline [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges			$ 2
Successor [Member] | Other Operating Income (Expense) [Member] | Wireless [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Accrual Adjustment				$ 20