Severance and Exit Costs (Schedule of Severance and Exit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2019	Mar. 31, 2019
Restructuring Reserve [Roll Forward]
Restructuring Reserve	$ 47	$ 42
Supplemental Unemployment Benefits, Severance Benefits	3	6
Restructuring Charges	27
Severance Costs	0
Payments for Postemployment Benefits	(3)
Restructuring Reserve, Settled with Cash	(22)
Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	20	131
Restructuring reserved settled with cash and other adjustments	111
Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	44	$ 36
Restructuring reserved settled with cash and other adjustments	19
Wireless [Member] | Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	0
Severance and exit costs [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	$ 27