11. Debt and lines of credit

Short-term borrowings

We maintain a line of credit to support commercial paper borrowings, if any, and to provide additional liquidity through bank loans. As of December 31, 2015, we had a variable-rate revolving credit facility from a consortium of investment-grade banks that allows us to borrow up to $2 billion until March 2020. The interest rate on borrowings under this credit facility, if drawn, is indexed to the applicable London Interbank Offered Rate (LIBOR). As of December 31, 2015, our credit facility was undrawn and we had no commercial paper outstanding.

Long-term debt

We retired $250 million of maturing debt in April 2015 and another $750 million in August 2015.

In May 2015, we issued a principal amount of $500 million of fixed-rate long-term debt due in 2020. We incurred $3 million of issuance and other related costs, which are amortized to Interest and debt expense over the term of the debt. The proceeds of the offering were $498 million, net of the original issuance discount, and were used toward the repayment of a portion of the debt that matured in August 2015.

In March 2014, we issued an aggregate principal amount of $500 million of fixed-rate long-term debt, with $250 million due in 2017 and $250 million due in 2021. We incurred $3 million of issuance and other related costs, which are amortized to Interest and debt expense over the term of the debt. The proceeds of the offering were $498 million, net of the original issuance discount and were used toward the repayment of the $1.0 billion of debt that matured in May 2014.

In May 2013, we issued an aggregate principal amount of $1.0 billion of fixed-rate long-term debt, with $500 million due in 2018 and $500 million due in 2023. We incurred $6 million of issuance and other related costs, which are amortized to Interest and debt expense over the term of the debt. The proceeds of the offering were $986 million, net of the original issuance discount and were used toward the repayment of $1.5 billion of maturing debt, including floating-rate notes. In connection with this repayment, we settled a floating-to-fixed interest rate swap associated with the maturing debt.

Long-term debt outstanding as of December 31, 2015 and 2014 is as follows:

	December 31,
	2015			2014
Notes due 2015 at 3.95% (assumed with National acquisition)	$	—		$	250
Notes due 2015 at 0.45%		—			750
Notes due 2016 at 2.375%		1,000			1,000
Notes due 2017 at 6.60% (assumed with National acquisition)		375			375
Notes due 2017 at 0.875%		250			250
Notes due 2018 at 1.00%		500			500
Notes due 2019 at 1.65%		750			750
Notes due 2020 at 1.75%		500			—
Notes due 2021 at 2.75%		250			250
Notes due 2023 at 2.25%		500			500
Total debt		4,125			4,625
Net unamortized (discount) premium and debt issuance costs		(5	)		6
Total debt, including net unamortized (discount) premium and debt issuance costs		4,120			4,631
Current portion of long-term debt		(1,000	)		(1,001	)
Long-term debt	$	3,120		$	3,630

As of December 31, 2015, we retrospectively applied the provisions of ASU 2015-03 and ASU 2015-15 regarding the classification of debt issuance costs. See Note 2 for additional information. As a result, we reclassified $11 million of applicable debt issuance costs as of December 31, 2014, from Other assets to Long-term debt, as comprehended in Net unamortized (discount) premium and debt issuance costs, in the table above.

Interest and debt expense was $90 million in 2015, $94 million in 2014 and $95 million in 2013. This was net of the amortization of the debt (discount) premium and other debt issuance costs. Cash payments for interest on long-term debt were $99 million in 2015 and $102 million in both 2014 and 2013. Capitalized interest was not material.