Earnings Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Earnings Per Share [Abstract]
Net income attributable to U.S. Cellular shareholders	$ 31	$ 49	$ 86	$ 93
Weighted average number of shares used in basic earnings per share (in shares)	87	86	87	85
Effects of dilutive securities (in shares)	1	0	1	1
Weighted average number of shares used in diluted earnings per share (in shares)	88	86	88	86
Basic earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.36	$ 0.57	$ 0.99	$ 1.09
Diluted earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.35	$ 0.56	$ 0.97	$ 1.08