SHORT-TERM INVESTMENTS: (Tables)

6 Months Ended

Jun. 30, 2021

SHORT-TERM INVESTMENTS:

Schedule of short-term investments

Short-term investments were as follows (in millions):

	At June 30,			At December 31,
	2021			2020
Trading securities	$	545.3		$	410.2
Weighted average interest rate		0.3	%		0.4	%
Available-for-sale	$	0.5		$	0.6
Weighted average interest rate		0.7	%		0.7	%
Total	$	545.8		$	410.8

Summary of activity investments

The following table summarizes the activity of these investments by category (in millions):

	Three months ended				Six months ended
	June 30,				June 30,
	2021		2020		2021		2020
Trading:
Interest earned	$	0.2	$	(*)	$	0.7	$	0.4
Unrealized gain (loss) at the end of the period	$	(*)	$	(*)	$	(*)	$	(*)
Available-for-sale:
Interest earned	$	(*)	$	(*)	$	(*)	$	(*)
Investment redeemed	$	—	$	—	$	0.1	$	0.1

(*) Less than $0.1 million.