Leases (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Leases [Line Items]
Option to terminate leases, Lessee	1 year
Option to terminate leases, Lessor	1 year
Lease revenue	$ 70
Rental expense		$ 102	$ 106
Poles [Member]
Leases [Line Items]
Rental expense		$ 55	$ 56
Accounting Standards Update 2016-02 [Member]
Leases [Line Items]
Cumulative-effect adjustment	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	99 years
Operator lease terms, Lessor	99 years