NOTES PAYABLE AND LONG-TERM DEBT

As of December 31, 2015 and 2014, the Company had short-term and long-term debt outstanding as follows:



	December 31,
(millions of dollars)	2015		2014
Short-term debt
Short-term borrowings	$	280.7	$	601.2

Long-term debt
5.75% Senior notes due 11/01/16 ($150 million par value)	$	149.9	$	149.8
8.00% Senior notes due 10/01/19 ($134 million par value)	134.0		134.0
4.625% Senior notes due 09/15/20 ($250 million par value)	248.6		248.4
1.80% Senior notes due 11/7/22 (€500 million par value)	540.9		—
3.375% Senior notes due 03/15/25 ($500 million par value)	499.1		—
7.125% Senior notes due 02/15/29 ($121 million par value)	119.5		119.4
4.375% Senior notes due 03/15/45 ($500 million par value)	498.4		—
Term loan facilities and other	89.7		75.1
Impact of derivatives on debt	5.3		12.1
Total long-term debt	$	2,285.4	$	738.8
Less: current portion	160.8		22.5
Long-term debt, net of current portion	$	2,124.6	$	716.3

The Company entered into interest rate swaps which have the effect of converting $384.0 million of fixed rate notes to variable rates as of December 31, 2015. The weighted average interest rate on short-term borrowings outstanding as of December 31, 2015 and 2014 was 1.3% and 0.8%, respectively. The weighted average interest rate on all borrowings outstanding, including the effects of outstanding swaps, as of December 31, 2015 and 2014 was 3.6% and 2.9%, respectively.

Annual principal payments required as of December 31, 2015 are as follows :



(millions of dollars)
2016	$	441.5
2017	49.9
2018	13.9
2019	134.1
2020	259.9
After 2020	1,674.0
Total payments	$	2,573.3
Less: unamortized discounts	7.2
Total	$	2,566.1

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

On November 6, 2015, BorgWarner Inc. issued €500 million in 1.80% senior notes due November 2022. Interest is payable annually in arrears on November 7 of each year, beginning on November 7, 2016. These senior notes are not guaranteed by any of BorgWarner Inc.'s subsidiaries. These notes were designated as a net investment hedge of the Company's investment in a European subsidiary when issued.

On March 16, 2015, BorgWarner Inc. issued $500 million in 3.375% senior notes due March 2025 and $500 million in 4.375% senior notes due March 2045. Interest is payable semi-annually in arrears on March 15 and September 15 of each year. These senior notes are not guaranteed by any of BorgWarner Inc.'s subsidiaries.

The Company has a $1 billion multi-currency revolving credit facility which includes a feature that allows the Company's borrowings to be increased to $1.25 billion. The facility provides for borrowings through June 30, 2019. 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, 2015 and expects to remain compliant in future periods. At December 31, 2015 and December 31, 2014, 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 of $1 billion. Under this program, the Company may issue notes from time to time and will use the proceeds for general corporate purposes. At December 31, 2015 and 2014, the Company had outstanding borrowings of $215.0 million and $460.9 million, respectively, under this program, which is classified in the 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 billion.

As of December 31, 2015 and 2014, the estimated fair values of the Company's senior unsecured notes totaled $2,197.6 million and $750.3 million, respectively. The estimated fair values were $7.2 million and $98.7 million higher than their carrying value at December 31, 2015 and 2014, 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 $29.3 million and $28.3 million at December 31, 2015 and 2014, respectively. The letters of credit typically act as guarantees of payment to certain third parties in accordance with specified terms and conditions.