12.

Debt

At June 30, 2018 and December 31, 2017, our long-term debt and interest rates on that debt were as follows (dollars in millions):

	June 30, 2018					December 31, 2017
	Amount		Interest Rate			Amount		Interest Rate
6.50% Senior Notes due March 2018	$	—		—	%	$	150.0		6.50	%
2.45% Senior Notes, net of discount of $0.4 million and $0.5 million as of June 30, 2018 and December 31, 2017, respectively, due December 2020		499.6		2.45	%		499.5		2.45	%
3.90% Senior Notes, net of discount of $0.1 million and $0.2 million as of June 30, 2018 and December 31, 2017, respectively, due June 2022		399.9		3.90	%		399.8		3.90	%
4.50% Senior Notes, net of discount of $1.1 million and $1.2 million as of June 30, 2018 and December 31, 2017, respectively, due November 2023		698.9		4.50	%		698.8		4.50	%
3.65% Senior Notes, net of discount of $0.8 million as of June 30, 2018 and December 31, 2017, due September 2024		399.2		3.65	%		399.2		3.65	%
3.40% Senior Notes, net of discount of $1.6 million as of June 30, 2018 and December 31, 2017, due December 2027		498.4		3.40	%		498.4		3.40	%
Total		2,496.0		3.64	%		2,645.7		3.80	%
Less current portion		—		—	%		150.0		6.50	%
Less unamortized debt issuance costs		13.9					15.3
Total long-term debt	$	2,482.1		3.64	%	$	2,480.4		3.64	%

During the six months ended June 30, 2018, we used cash on hand to repay debt outstanding of $150.0 million under the 6.50% Senior Notes due March 2018. For the six months ended June 30, 2018 and 2017, cash payments for interest were $51.1 million and $48.1 million, respectively.

Included in interest expense, net and other, are amortization of treasury lock settlements and amortization of financing costs. For the three months ended June 30, 2018 and 2017, amortization of treasury lock settlements was $1.3 million and $1.4 million, respectively, and for the six months ended June 30, 2018 and 2017, amortization of treasury locks was $2.7 million and $2.8 million, respectively. For the three months ended June 30, 2018 and 2017, amortization of financing costs was $0.7 million and $0.5 million, respectively, and during the six months ended June 30, 2018 and 2017, amortization of financing costs was $1.3 million and $1.0 million, respectively.

At June 30, 2018, we had $2,496.0 million of fixed-rate senior notes outstanding. The fair value of our fixed-rate debt was estimated to be $2,487.1 million. The difference between the book value and fair value is due to the difference between the period-end market interest rate and the stated rate of our fixed-rate debt. We estimated the fair value of our fixed-rate debt using quoted market prices (Level 2 inputs) within the fair value hierarchy, which is further defined in Note 2, Summary of Significant Accounting Policies, of the Notes to Consolidated Financial Statements in "Part II, Item 8. Financial Statements and Supplementary Data" of our 2017 Annual Report on Form 10-K.

For more information on our long-term debt and interest rates on that debt, see Note 9, Debt, of the Notes to Consolidated Financial Statements in "Part II, Item 8. Financial Statements and Supplementary Data" of our 2017 Annual Report on Form 10-K.