Earnings Per Share - Reconciliation (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Earnings Per Share [Abstract]
Net income attributable to U.S. Cellular shareholders	$ 54	$ 45
Weighted average number of shares used in basic earnings per share (in shares)	86	85
Effects of dilutive securities (in shares)	2	1
Weighted average number of shares used in diluted earnings per share (in shares)	88	86
Basic earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.63	$ 0.52
Diluted earnings per share attributable to U.S. Cellular shareholders (USD per share)	$ 0.62	$ 0.52