

	December 31, 2019			June 30, 2020
Commercial paper	$	—		$	141,000
4.25% Notes due 2021	550,000			—
3.20% Notes due 2025	250,000			250,000
5.00% Notes due 2026	650,000			650,000
3.25% Notes due 2030	—			500,000
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			500,000
4.85% Notes due 2049	500,000			500,000
3.95% Notes due 2050	500,000			500,000
Face value of long-term debt	4,750,000			4,841,000
Unamortized debt issuance costs⁽¹⁾	(35,263		)	(37,986		)
Net unamortized debt discount⁽¹⁾	(8,662		)	(10,365		)
Long-term debt, net	$	4,706,075		$	4,792,649

In May 2020, we issued $500.0 million of 3.25% senior notes due 2030 in an underwritten public offering. The notes were issued at 99.88% of par. Net proceeds from this offering were approximately $495.2 million after underwriting discounts and offering expenses. The net proceeds from this offering, along with commercial paper borrowings and cash on hand, were used to redeem our $550 million senior notes due in 2021. We recognized $12.9 million of debt prepayment costs as interest expense in our consolidated statements of income related to this early redemption, partially offset by the recognition of a $0.7 million unamortized debt premium, for the three and six month periods ended June 30, 2020.

Revolving Credit Facility. At June 30, 2020, the total borrowing capacity under our revolving credit facility maturing in May 2024 was $1.0 billion. Any borrowings outstanding under this facility are classified as long-term debt on our consolidated balance sheets. Borrowings under this facility are unsecured and bear interest at LIBOR plus a spread ranging from 0.875% to 1.500% based on our credit ratings. Additionally, an unused commitment fee is assessed at a rate between 0.075% and 0.200% depending on our credit ratings. The unused commitment fee was 0.125% at June 30, 2020. Borrowings under this facility may be used for general partnership purposes, including capital expenditures. As of December 31, 2019 and June 30, 2020, there were no borrowings outstanding under this facility and $3.5 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 this facility.

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. Commercial paper borrowings outstanding at June 30, 2020 were $141.0 million. The weighted-average interest rate for commercial paper borrowings based on the number of days outstanding was 1.2% for the six months ended June 30, 2020.