Earnings Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income attributable to U.S. Cellular shareholders	$ 23	$ 36	$ 109	$ 129
Weighted average number of shares used in basic earnings per share (in shares)	86	86	87	85
Effects of dilutive securities (in shares)	2	1	1	1
Weighted average number of shares used in diluted earnings per share (in shares)	88	87	88	86
Basic earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.27	$ 0.42	$ 1.26	$ 1.51
Diluted earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.27	$ 0.41	$ 1.24	$ 1.49