Note 3 - Acquisitions and Divestitures - Unaudited Pro Forma Results (Details) - USD ($) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Revenue (less agency commissions)	$ 1,751	$ 1,678
Net income	126	153
Net income attributable to common stockholders	$ 87	$ 114
Basic net income attributable to common stockholders, per share (in dollars per share)	$ 0.93	$ 1.18
Diluted net income attributable to common stockholders, per share (in dollars per share)	$ 0.92	$ 1.18