Severance and Exit Costs (Schedule of Severance and Exit Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Document Period End Date	Jun. 30, 2018
Restructuring Reserve [Roll Forward]
Restructuring Reserve	$ 204	$ 248
Supplemental Unemployment Benefits, Severance Benefits	34	64
Restructuring Charges	8
Severance Costs	2
Payments for Postemployment Benefits	(32)
Restructuring Reserve, Settled with Cash	(52)
Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	148	165
Restructuring reserved settled with cash and other adjustments	17
Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Reserve	22	$ 19
Restructuring reserved settled with cash and other adjustments	3
Wireless [Member]
Restructuring Reserve [Roll Forward]
Severance Costs	2
Wireless [Member] | Lease [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	0
Severance and exit costs [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	6
Severance and exit costs [Member] | Wireless [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	1
Severance and exit costs [Member] | Wireline [Member] | Access [Member]
Restructuring Reserve [Roll Forward]
Restructuring Charges	$ 5