Repurchases of Common Stock - Narrative (Details) - USD ($)	3 Months Ended		5 Months Ended	6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Apr. 27, 2018	Jun. 30, 2018	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 06, 2017
Affiliated Entity | Deutsche Telekom AG
Equity, Class of Treasury Stock [Line Items]
Additional shares purchased (in shares)	0	3,300,000
Aggregate market value of shares purchased		$ 200,000,000
2017 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount			$ 9,000,000,000					$ 1,500,000,000
Common stock repurchased (in shares)	6,200,000		23,700,000	16,700,000
Common stock repurchased	$ 388,000,000		$ 1,500,000,000	$ 1,100,000,000
Average price paid per share (usd per share)			$ 63.07
2018 Stock Repurchase Program
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, increase in authorized amount			$ 7,500,000,000
2018 Stock Repurchase Program | Scenario, Forecast
Equity, Class of Treasury Stock [Line Items]
Stock repurchase program, authorized amount					$ 4,000,000,000	$ 3,000,000,000	$ 500,000,000