When appropriate, we use derivatives as a risk management tool to mitigate the potential impact of certain market risks. The primary risks managed by using derivative financial instruments are interest rate risks. We do not enter into derivative financial instruments for trading or speculative purposes.

The Company previously used treasury lock derivative instruments to manage interest costs and the risk associated with changes in the ten-year U.S. Treasury Note rate, which served as a reference in determining the interest rates applicable to the Company's debt securities issued in March 2008 and June 2012. Upon settlement of the interest rate protection agreements, the Company recorded the effective portion of the settlements in accumulated OCI. These amounts were then amortized over the terms of the respective notes.

During the fourth quarter of 2019, the Company recorded a charge of $13.1 million in interest expense from the write-off of the remaining treasury lock balance due to the redemption of the 3.90% notes on December 23, 2019. The Company has not entered into any new interest rate protection agreements subsequent to the fourth quarter 2019 write-off of the remaining treasury lock balance.

The impact of derivative instruments on the consolidated statements of income and accumulated OCI was as follows (dollars in millions):


	Loss Reclassified from Accumulated OCI into Income (Effective Portion) Year Ended December 31,
	2021		2020		2019
Amortization of treasury locks (included in interest expense, net)	$	—	$	—	$	(18.2	)

As a result of our November 2019 debt refinancing and redemption of the 3.90% notes due June 15, 2022, the Company accelerated the amortization of the remaining treasury lock balance of $13.1 million ($6.5 million after tax) during the fourth quarter of 2019. The after tax amount includes $3.2 million of income tax benefit from the stranded tax effects in accumulated OCI related to the write-off of the remaining treasury lock balance.