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Property, Plant, and Equipment (Narrative) (Details) - USD ($)
$ in Millions
1 Months Ended
Jan. 31, 2019
Sep. 30, 2020
Dec. 31, 2019
Property, Plant and Equipment [Line Items]      
Impact of adoption of ASU 2018-02   $ (8,925) $ (8,573)
Deferred gain, Net   11  
Towers [Member]      
Property, Plant and Equipment [Line Items]      
Proceeds from sale of property $ 76    
Aggregate carrying value 1    
Gain on sale of property $ 75    
Accounting Standards Update 2016-02 [Member] | Cumulative Effect, Period of Adoption, Adjustment [Member]      
Property, Plant and Equipment [Line Items]      
Impact of adoption of ASU 2018-02   $ 15