Tower Obligations - Narrative (Details) $ in Millions	3 Months Ended		6 Months Ended	12 Months Ended
	Jun. 30, 2020 USD ($) tower_site	Mar. 31, 2020 USD ($) tower_site	Jun. 30, 2020 USD ($) tower_site	Dec. 31, 2012 USD ($) tower_site	Apr. 01, 2020 USD ($)
Sale Leaseback Transaction [Line Items]
Lease liabilities	$ 19,651		$ 19,651
Crown Castle International Corp.
Sale Leaseback Transaction [Line Items]
Managed sites | tower_site	900		900
Lease liabilities	$ 292		$ 292
Minimum
Sale Leaseback Transaction [Line Items]
Lessee leasing arrangements, operating leases, term of contract (years)	5 years		5 years
Maximum
Sale Leaseback Transaction [Line Items]
Lessee leasing arrangements, operating leases, term of contract (years)	10 years		10 years
Tower Transaction
Sale Leaseback Transaction [Line Items]
Number of wireless communications tower sites sold | tower_site				7,100
Lessee leasing arrangements, operating leases, term of contract (years)				10 years
Sale leaseback transaction, fixed-price purchase options				$ 2,000
Interest rate on tower obligations	6.00%			8.00%
Weighted average remaining term			6 years
Tower Transaction | Crown Castle International Corp.
Sale Leaseback Transaction [Line Items]
Property subject to failed sale leaseback transaction, number of units | tower_site		6,400
Remaining term of lease		17 years
Fixed-price purchase option on leased or subleased sites		$ 2,300
Fixed-price purchase option on lease or subleased sites, exercisable period		1 year
Days prior to expiration of agreement		120 days
Property and equipment at fair value					$ 1,500
Tower obligations					$ 1,100
Tower Transaction | Minimum
Sale Leaseback Transaction [Line Items]
Lessee leasing arrangements, operating leases, term of contract (years)				23 years
Tower Transaction | Maximum
Sale Leaseback Transaction [Line Items]
Lessee leasing arrangements, operating leases, term of contract (years)				37 years