SHORT-TERM DEBT

Short-term debt consisted of the following (in thousands of dollars):



	As of December 31,
	2017			2016
Lines of Credit
Outstanding at December 31	$	55,603		$	16,392
Maximum month-end balance during the year	$	55,621		$	24,722
Weighted average interest rate during the year	2.41		%	4.04		%
Weighted average interest rate at December 31	2.01		%	5.13		%

Commercial Paper
Outstanding at December 31	$	—		$	369,748
Maximum month-end balance during the year	$	454,696		$	629,712
Weighted average interest rate during the year	0.83		%	0.50		%
Weighted average interest rate at December 31	—		%	0.69		%

Lines of Credit

In October 2017, the Company replaced its U.S. $900 million unsecured revolving line of credit with a new five-year $750 million unsecured revolving line of credit, with the option to extend the line to up to $1.1 billion. The terms of the new line of credit are customary for transactions of this type and do not contain any financial performance covenants. The primary purpose of this credit facility is to provide support to the Company's commercial paper program and for general corporate purposes. There were no borrowings outstanding under these lines of credit as of December 31, 2017 and 2016. The Company paid a commitment fee of 0.06% and 0.07% in 2017 and 2016, respectively.

Foreign subsidiaries utilize lines of credit for working capital purposes and other operating needs, primarily British Pound (£) and Euro (€) revolving credit facilities with £20 million and €12.5 million outstanding at December 31, 2017, respectively, and no outstanding balance at December 31, 2016. The British Pound revolving credit facility bears interest at London Interbank Offered Rate (LIBOR) plus a margin of 75 basis points (1.22% at December 31, 2017) and a commitment fee of 0.26% as of December 31, 2017. The Euro revolving credit facility bears interest at Euro Interbank Offered Rate (EURIBOR) plus a margin of 35 basis points (0.35% at December 31, 2017) and a commitment fee of 0.12% as of December 31, 2017.

Uncommitted Lines of Credit

The Company had $71 million and $88 million of uncommitted lines of credit at December 31, 2017 and 2016, respectively.

Commercial Paper

The Company issued commercial paper for general working capital needs. A portion of the proceeds from the May 2017 bond issuance (see Note 8 to the Consolidated Financial Statements) was used to pay outstanding commercial paper. At December 31, 2017, there was none outstanding.

Letters of Credit

The Company's U.S. business had $33 million and $30 million of letters of credit at December 31, 2017 and 2016, respectively, primarily related to the Company's insurance program. Letters of credit were also issued to facilitate purchases of products. These issued amounts were $1 million and $5 million at December 31, 2017 and 2016, respectively. Letters of credit issued by the Company's international businesses were immaterial.