Earnings Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income attributable to U.S. Cellular shareholders	$ 71	$ 54
Weighted average number of shares used in basic earnings per share (in shares)	86	86
Effects of dilutive securities (in shares)	2	2
Weighted average number of shares used in diluted earnings per share (in shares)	88	88
Basic earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.82	$ 0.63
Diluted earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.81	$ 0.62