Summary of Significant Accounting Policies (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended							6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue Recognition Non-cancelable Lease Term												five to 15 years
Capitalized Labor Costs												$ 246	$ 212	$ 92
Useful life of site rental contracts and customer relationships (years)												20 years
Revenue Recognition Non-cancelable Term for Non-wireless Contracts Range, Minimum												three to 20 years
Portion of company site rental costs that are ground lease expenses												50.00%
Ground Lease Agreement Initial Term												five years
Percentage of tax position that is likely of being realized upon ultimate settlement												50.00%
Asset write-down charges	$ 2	$ 6	$ 6	$ 8	$ 8	$ 6	$ 3	$ 12	$ 9	$ 13	$ 18	$ 19	26	17
Revenue, Performance Obligation, Description of Payment Terms												45 to 60 days
Revenue, Remaining Performance Obligation, Amount				2,700								$ 2,900	2,700	2,500
Contract with Customer, Liability, Revenue Recognized												$ 510	470
Towers [Member]
Estimated useful life, maximum, in years												20 years
Property, Plant and Equipment [Member]
Asset write-down charges												$ 17	22	$ 14
Other Current Assets [Member]
Straight-Line Site Rental Revenues				92								114	92
Deferred Revenue [Domain]
Straight-Line Site Rental Revenues				$ 1,400								$ 1,400	$ 1,400
Preferred Stock [Member]
Antidilutive securities excluded from computation of earnings per share (in shares)												14	15
Minimum [Member]
Ground Lease Agreement Initial Term												five years
Maximum [Member]
Ground Lease Agreement Initial Term												10 years