Leases (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Line Items]
Option to terminate leases, Lessee	1 year
Increase of accumulated deficit	$ (8,975)	$ (8,573)
Option to terminate leases, Lessor	1 year
Lease revenue	$ 67	70	$ 73
Rental expense			102
Poles [Member]
Leases [Line Items]
Rental expense			$ 55
Accounting Standards Update 2016-02 [Member]
Leases [Line Items]
Deferred gain, Net		11
Increase of accumulated deficit		15
Accounting Standards Update 2018-11 [Member]
Leases [Line Items]
Increase of accumulated deficit		$ 15
Minimum [Member]
Leases [Line Items]
Operating and finance lease terms, Lessee	1 year
Operator lease terms, Lessor	1 year
Maximum [Member]
Leases [Line Items]
Operating and finance lease terms, Lessee	87 years
Operator lease terms, Lessor	65 years