Debt

Long-term debt at December 31, 2016 and 2017 was as follows (in thousands):



	December 31,
	2016			2017
Commercial paper	$	50,000		$	—
6.40% Notes due 2018	250,000			250,000
6.55% Notes due 2019	550,000			550,000
4.25% Notes due 2021	550,000			550,000
3.20% Notes due 2025	250,000			250,000
5.00% Notes due 2026	650,000			650,000
6.40% Notes due 2037	250,000			250,000
4.20% Notes due 2042	250,000			250,000
5.15% Notes due 2043	550,000			550,000
4.20% Notes due 2045	250,000			250,000
4.25% Notes due 2046	500,000			500,000
4.20% Notes due 2047	—			500,000
Face value of long-term debt	4,100,000			4,550,000
Unamortized debt issuance costs⁽¹⁾	(26,948		)	(29,472		)
Net unamortized debt premium⁽¹⁾	6,530			215
Net unamortized amount of gains from historical fair value hedges⁽¹⁾	7,610			3,749
Long-term debt, net, including current portion	4,087,192			4,524,492
Less: current portion of long-term debt, net	—			250,974
Long-term debt, net	$	4,087,192		$	4,273,518


(1)	Debt issuance costs, note discounts and premiums, and realized gains and losses of historical fair value hedges are being amortized or accreted to the applicable notes over the respective lives of those notes.

All of the instruments detailed in the table above are senior indebtedness.

At December 31, 2017, maturities of our debt were as follows: $250.0 million in July 2018; $550.0 million in 2019; $0 in 2020; $550.0 million in 2021; $0 in 2022; and approximately $3.2 billion thereafter.

2017 Debt Offering

On October 3, 2017, we issued $500.0 million of our 4.20% notes due 2047 in an underwritten public offering. The notes were issued at 99.341% of par. Net proceeds from this offering were approximately $491.6 million, after underwriting discounts and offering expenses of $5.1 million. The net proceeds from this offering were used to repay borrowings outstanding under our commercial paper program. The remaining proceeds were used for general partnership purposes, including capital expenditures.

Other Debt

Revolving Credit Facility. At December 31, 2017, the total borrowing capacity under our revolving credit facility maturing October 26, 2022 was $1.0 billion. Any borrowings outstanding under this facility are classified as long-term debt on our consolidated balance sheets. Borrowings under the facility are unsecured and bear interest at LIBOR plus a spread ranging from 1.000% to 1.625% based on our credit ratings. Additionally, an unused commitment fee is assessed at a rate from 0.100% to 0.275% depending on our credit ratings. The unused commitment fee was 0.125% at December 31, 2017. Borrowings under this facility may be used for general purposes, including capital expenditures. As of December 31, 2016 and 2017, respectively, there were no borrowings outstanding under this facility, with $6.3 million obligated for letters of credit. Amounts obligated for letters of credit are not reflected as debt on our consolidated balance sheets, but decrease our borrowing capacity under the facility.

Our revolving credit facility requires us to maintain a specified ratio of consolidated debt to EBITDA (as defined in the credit agreement) of no greater than 5.0 to 1.0. In addition, the revolving credit facility and the indentures under which our senior notes were issued contain covenants that limit our ability to, among other things, incur indebtedness secured by certain liens or encumber our assets, engage in certain sale-leaseback transactions and consolidate, merge or dispose of all or substantially all of our assets. We were in compliance with these covenants as of and during the year ended December 31, 2017.

Commercial Paper Program. We have a commercial paper program under which we may issue commercial paper notes in an amount up to the available capacity under our $1.0 billion revolving credit facility. The maturities of the commercial paper notes vary, but may not exceed 397 days from the date of issuance. Because the commercial paper we can issue is limited to amounts available under our revolving credit facility, amounts outstanding under the program are classified as long-term debt. The commercial paper notes are sold under customary terms in the commercial paper market and are issued at a discount from par, or alternatively, are sold at par and bear varying interest rates on a fixed or floating basis. The weighted-average interest rate for commercial paper borrowings based on the number of days outstanding was 0.8% and 1.3%, respectively, for the year ended December 31, 2016 and 2017.

During the years ending December 31, 2015, 2016 and 2017, total cash payments for interest on all indebtedness, excluding the impact of related interest rate swap agreements, were $156.6 million, $181.7 million and $206.2 million, respectively.