Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Interest payments for financing leases	$ 82
Additional operating leases not yet commenced, payments due	$ 341
Device upgrade period	18 months
Due in 2019		$ 2,700
Due in 2020 and 2021		4,700
Due in 2022 and 2023		3,300
Due thereafter		3,800
Rent expense under operating leases		3,000
Capital leased assets, gross	$ 3,100
Capital leased assets, accumulated amortization		$ 867
Minimum
Lessee, Lease, Description [Line Items]
Lessee leasing arrangements, operating leases, term of contract (years)	5 years	5 years
Option to extend lease term	5 years
Lessee leasing arrangements, finance leases, term of contract	2 years
Maximum
Lessee, Lease, Description [Line Items]
Lessee leasing arrangements, operating leases, term of contract (years)	10 years	10 years
Option to extend lease term	35 years
Lessee leasing arrangements, finance leases, term of contract	5 years