Revenue Recognition - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of revenue
Revenue from contracts with customers	$ 1,292	$ 1,235
Operating lease income	26	26
Total operating revenues	1,318	1,261
Transferred over time
Disaggregation of revenue
Revenue from contracts with customers	1,016	1,000
Transferred over time | Retail service
Disaggregation of revenue
Revenue from contracts with customers	685	671
Transferred over time | Inbound roaming
Disaggregation of revenue
Revenue from contracts with customers	28	37
Transferred over time | Residential
Disaggregation of revenue
Revenue from contracts with customers	157	144
Transferred over time | Commercial
Disaggregation of revenue
Revenue from contracts with customers	47	50
Transferred over time | Wholesale
Disaggregation of revenue
Revenue from contracts with customers	45	45
Transferred over time | Other service
Disaggregation of revenue
Revenue from contracts with customers	54	53
Transferred at point in time | Equipment and product sales
Disaggregation of revenue
Revenue from contracts with customers	276	235
UScellular
Disaggregation of revenue
Revenue from contracts with customers	1,003	944
Operating lease income	20	19
Total operating revenues	1,023	963
UScellular | Transferred over time
Disaggregation of revenue
Revenue from contracts with customers	751	743
UScellular | Transferred over time | Retail service
Disaggregation of revenue
Revenue from contracts with customers	685	671
UScellular | Transferred over time | Inbound roaming
Disaggregation of revenue
Revenue from contracts with customers	28	37
UScellular | Transferred over time | Residential
Disaggregation of revenue
Revenue from contracts with customers	0	0
UScellular | Transferred over time | Commercial
Disaggregation of revenue
Revenue from contracts with customers	0	0
UScellular | Transferred over time | Wholesale
Disaggregation of revenue
Revenue from contracts with customers	0	0
UScellular | Transferred over time | Other service
Disaggregation of revenue
Revenue from contracts with customers	38	35
UScellular | Transferred at point in time | Equipment and product sales
Disaggregation of revenue
Revenue from contracts with customers	252	201
TDS Telecom
Disaggregation of revenue
Revenue from contracts with customers	248	240
Operating lease income	1	1
Total operating revenues	249	240
TDS Telecom | Transferred over time
Disaggregation of revenue
Revenue from contracts with customers	248	239
TDS Telecom | Transferred over time | Retail service
Disaggregation of revenue
Revenue from contracts with customers	0	0
TDS Telecom | Transferred over time | Inbound roaming
Disaggregation of revenue
Revenue from contracts with customers	0	0
TDS Telecom | Transferred over time | Residential
Disaggregation of revenue
Revenue from contracts with customers	157	144
TDS Telecom | Transferred over time | Commercial
Disaggregation of revenue
Revenue from contracts with customers	47	50
TDS Telecom | Transferred over time | Wholesale
Disaggregation of revenue
Revenue from contracts with customers	45	45
TDS Telecom | Transferred over time | Other service
Disaggregation of revenue
Revenue from contracts with customers	0	0
TDS Telecom | Transferred at point in time | Equipment and product sales
Disaggregation of revenue
Revenue from contracts with customers	0	0
Corporate, Eliminations and Other
Disaggregation of revenue
Revenue from contracts with customers	40	52
Operating lease income	5	6
Total operating revenues	46	58
Corporate, Eliminations and Other | Transferred over time
Disaggregation of revenue
Revenue from contracts with customers	16	18
Corporate, Eliminations and Other | Transferred over time | Retail service
Disaggregation of revenue
Revenue from contracts with customers	0	0
Corporate, Eliminations and Other | Transferred over time | Inbound roaming
Disaggregation of revenue
Revenue from contracts with customers	0	0
Corporate, Eliminations and Other | Transferred over time | Residential
Disaggregation of revenue
Revenue from contracts with customers	0	0
Corporate, Eliminations and Other | Transferred over time | Commercial
Disaggregation of revenue
Revenue from contracts with customers	0	0
Corporate, Eliminations and Other | Transferred over time | Wholesale
Disaggregation of revenue
Revenue from contracts with customers	0	0
Corporate, Eliminations and Other | Transferred over time | Other service
Disaggregation of revenue
Revenue from contracts with customers	16	18
Corporate, Eliminations and Other | Transferred at point in time | Equipment and product sales
Disaggregation of revenue
Revenue from contracts with customers	$ 24	$ 34