At September 30, 2023 and December 31, 2022, our long-term debt and interest rates on that debt were as follows (dollars in millions):


	September 30,		December 31,
	2023		2022
Revolving Credit Facility	$	—	$	—
3.65% Senior Notes, net of discount of $0.1 million and $0.2 million as of September 30, 2023 and December 31, 2022, respectively, due September 2024		399.9		399.8
3.40% Senior Notes, net of discount of $0.8 million and $0.9 million as of September 30, 2023 and December 31, 2022, respectively, due December 2027		499.2		499.1
3.00% Senior Notes, net of discount of $0.4 million and $0.5 million as of September 30, 2023 and December 31, 2022, respectively, due December 2029		499.6		499.5
4.05% Senior Notes, net of discount of $3.3 million as of both September 30, 2023 and December 31, 2022, due December 2049		396.7		396.7
3.05% Senior Notes, net of discount of $3.5 million and $3.6 million as of September 30, 2023 and December 31, 2022, respectively, due October 2051		696.5		696.4
Total		2,491.9		2,491.5
Less current portion (a)		399.5		—
Less unamortized debt issuance costs		16.7		17.9
Total long-term debt	$	2,075.7	$	2,473.6

(a)

The current portion of long-term debt excludes unamortized debt issuance costs of $0.4 million at September 30, 2023.

For the nine months ended September 30, 2023 and 2022, cash payments for interest were $49.9 million and $50.6 million, respectively.

Included in interest expense, net is the amortization of financing costs, which includes the amortization of debt issuance costs and amortization of bond discount. For both the three months ended September 30, 2023 and 2022, amortization of debt issuance costs was $0.4 million, and during the nine months ended September 30, 2023 and 2022, amortization of debt issuance costs was $1.2 million for both periods. For the three and nine month periods ended September 30, 2023 and 2022, the amortization of bond discount was insignificant.

At September 30, 2023, we had $2,491.9 million of fixed-rate senior notes outstanding. The fair value of our fixed-rate debt was estimated to be $1,985.5 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 2022 Annual Report on Form 10-K.

On April 27, 2023, we amended our Senior Unsecured Credit Agreement to formally replace the LIBOR benchmark rate with the Term SOFR rate.

For more information on our long-term debt and interest rates on that debt, see Note 11, Debt, of the Notes to Consolidated Financial Statements in "Part II, Item 8. Financial Statements and Supplementary Data" of our 2022 Annual Report on Form 10-K.