Debt

Debt consists of (in millions):


	June 30, 2015		December 31, 2014

Senior Notes, interest at 6.125% payable semiannually, principal due on August 15, 2015	$	151	$	151

Senior Notes, interest at 1.35% payable semiannually, principal due on December 1, 2017		500		500

Senior Notes, interest at 2.6% payable semiannually, principal due on December 1, 2022		1,396		1,396

Senior Notes, interest at 3.95% payable semiannually, principal due on December 1, 2042		1,096		1,096

Commercial paper		1,140		—

Other		22		23

Total debt		4,305		3,166
Less current portion		151		152

Long-term debt	$	4,154	$	3,014

During the second quarter of 2015, the Company exercised its accordion option to increase aggregate borrowing capacity under its five-year unsecured revolving credit facility by an additional $1.0 billion, bringing the aggregate borrowing capacity to $4.5 billion. The facility expires September 28, 2018. The Company also has a commercial paper program. Borrowings under the commercial paper program are classified as long-term as the program is supported by the $4.5 billion, five-year revolving credit facility. At June 30, 2015, there were $1,140 million in commercial paper borrowings, and there were $201 million in outstanding letters of credit issued under the credit facility, resulting in $3,159 million of funds available under this revolving credit facility. Interest under this multicurrency facility is based upon LIBOR, NIBOR or EURIBOR plus 0.875% subject to a ratings-based grid, or the U.S. prime rate. The credit facility contains a financial covenant regarding maximum debt to capitalization and the Company was in compliance at June 30, 2015.

The Company also had $3,092 million of additional outstanding letters of credit at June 30, 2015 that are under various bilateral letter of credit facilities. Other letters of credit are issued as bid bonds, advanced payment bonds and performance bonds.

The fair value of the Company’s debt is estimated using Level 2 inputs in the fair value hierarchy and is based on quoted prices for those or similar instruments. At June 30, 2015 and December 31, 2014, the fair value of the Company’s unsecured Senior Notes approximated $2,939 million and $2,974 million, respectively. At both June 30, 2015 and December 31, 2014, the carrying value of the Company’s unsecured Senior Notes approximated $3,143 million. The carrying value of the Company’s variable rate borrowings approximates fair value.