NOTES PAYABLE AND LONG-TERM DEBT

As of December 31, 2017 and 2016, the Company had short-term and long-term debt outstanding as follows:



	December 31,
(millions of dollars)	2017		2016
Short-term debt
Short-term borrowings	$	68.8	$	156.5

Long-term debt
8.00% Senior notes due 10/01/19 ($134 million par value)	137.4		139.1
4.625% Senior notes due 09/15/20 ($250 million par value)	251.4		251.9
1.80% Senior notes due 11/7/22 (€500 million par value)	595.7		520.7
3.375% Senior notes due 03/15/25 ($500 million par value)	496.1		495.6
7.125% Senior notes due 02/15/29 ($121 million par value)	118.9		118.8
4.375% Senior notes due 03/15/45 ($500 million par value)	493.5		493.3
Term loan facilities and other	26.5		43.6
Total long-term debt	$	2,119.5	$	2,063.0
Less: current portion	15.8		19.4
Long-term debt, net of current portion	$	2,103.7	$	2,043.6

In July 2016, the Company terminated interest rate swaps which had the effect of converting $384 million of fixed rate notes to variable rates. The gain on the termination is being amortized into interest expense over the remaining terms of the notes. The value related to these swap terminations as of December 31, 2017 was $2.9 million and $0.8 million on the 4.625% and 8.00% notes, respectively, as an increase to the notes. The value of these interest rate swaps as of December 31, 2016 was $3.9 million and $1.3 million on the 4.625% and 8.00% notes, respectively, as a decrease to the notes.

The Company terminated fixed to floating interest rate swaps in 2009. The gain on the termination is being amortized into interest expense over the remaining term of the note. The value related to this swap termination at December 31, 2017 was $2.7 million on the 8.00% note as an increase to the note. The value related to these swap terminations at December 31, 2016 was $4.1 million on the 8.00% note as an increase to the note.

The weighted average interest rate on short-term borrowings outstanding as of December 31, 2017 and 2016 was 3.1% and 2.3%, respectively. The weighted average interest rate on all borrowings outstanding, including the effects of outstanding swaps, as of December 31, 2017 and 2016 was 3.8%.

Annual principal payments required as of December 31, 2017 are as follows :



(millions of dollars)
2018	$	84.6
2019	138.7
2020	252.7
2021	2.7
2022	600.4
After 2022	1,121.0
Total payments	$	2,200.1
Less: unamortized discounts	11.8
Total	$	2,188.3

The Company's long-term debt includes various covenants, none of which are expected to restrict future operations.

On June 29, 2017, the Company amended and extended its $1 billion multi-currency revolving credit facility (which included a feature that allowed the Company's borrowings to be increased to $1.25 billion) to a $1.2 billion multi-currency revolving credit facility (which includes a feature that allows the Company's borrowings to be increased to $1.5 billion). The facility provides for borrowings through June 29, 2022. The Company has one key financial covenant as part of the credit agreement which is a debt to EBITDA ("Earnings Before Interest, Taxes, Depreciation and Amortization") ratio. The Company was in compliance with the financial covenant at December 31, 2017 and expects to remain compliant in future periods. At December 31, 2017 and December 31, 2016, the Company had no outstanding borrowings under this facility.

The Company's commercial paper program allows the Company to issue short-term, unsecured commercial paper notes up to a maximum aggregate principal amount outstanding, which increased from $1.0 billion to $1.2 billion effective July 26, 2017. Under this program, the Company may issue notes from time to time and will use the proceeds for general corporate purposes. At December 31, 2017, the Company had no outstanding borrowings under this program. As of December 31, 2016, the Company had outstanding borrowings of $50.8 million under this program, which is classified in the Condensed Consolidated Balance Sheets in Notes payable and other short-term debt.

The total current combined borrowing capacity under the multi-currency revolving credit facility and commercial paper program cannot exceed $1.2 billion.

As of December 31, 2017 and 2016, the estimated fair values of the Company's senior unsecured notes totaled $2,209.1 million and $2,081.4 million, respectively. The estimated fair values were $116.1 million and $62.0 million higher than their carrying value at December 31, 2017 and 2016, respectively. Fair market values of the senior unsecured notes are developed using observable values for similar debt instruments, which are considered Level 2 inputs as defined by ASC Topic 820. The carrying values of the Company's multi-currency revolving credit facility and commercial paper program approximates fair value. The fair value estimates do not necessarily reflect the values the Company could realize in the current markets.

The Company had outstanding letters of credit of $31.4 million and $32.3 million at December 31, 2017 and 2016, respectively. The letters of credit typically act as guarantees of payment to certain third parties in accordance with specified terms and conditions.