NOTE 14. LONG-TERM DEBT

At December 31,	2017 Weighted-average Coupon⁽¹⁾			2017			2016
(millions, except percentages)
Unsecured Senior and Medium-Term Notes:
2.98% to 7.20%, due 2017 to 2051		4.60	%	$	720.0		$	634.5
Total principal					720.0			634.5
Securities due within one year		5.72	%		(120.0	)		(14.5	)
Debt issuance costs					(4.1	)		(3.7	)
Total long-term debt				$	595.9		$	616.3

(1)	Represents weighted-average coupon rates for debt outstanding as of December 31, 2017.

Based on stated maturity dates, the scheduled principal payments of long-term debt at December 31, 2017, were as follows:

	2018			2019		2020		2021		2022		Thereafter			Total
(millions, except percentages)
Questar Gas	$	120.0		$	—	$	—	$	—	$	—	$	600.0		$	720.0
Weighted-average Coupon		5.72	%										4.37	%

In October 2017, Questar Gas’ entered into an agreement with certain investors to issue through private placement $50 million of 3.30% 12-year senior notes and $100 million of 3.97% 30-year senior notes in April 2018.

Questar Gas short-term credit facilities and long-term debt agreements contain customary covenants and default provisions. As of December 31, 2017, there were no events of default under these covenants.

Any new long-term debt issuance by Questar Gas is subject to approval by the Wyoming Commission.