Earnings Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income attributable to U.S. Cellular shareholders	$ 68	$ 31	$ 139	$ 86
Weighted average number of shares used in basic earnings per share (in shares)	86	87	86	87
Effects of dilutive securities (in shares)	1	1	1	1
Weighted average number of shares used in diluted earnings per share (in shares)	87	88	87	88
Basic earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.79	$ 0.36	$ 1.62	$ 0.99
Diluted earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.78	$ 0.35	$ 1.59	$ 0.97