8. Debt

Our debt consisted of the following (in millions):

	March 31,			December 31,
	2018			2017
Current portion of long-term debt
2.000% Senior Notes due 2018	$	1,150.0		$	1,150.0
U.S. Term Loan B		75.0			75.0
Multicurrency Revolving Facility		400.0			-
Total current portion of long-term debt	$	1,625.0		$	1,225.0
Long-term debt
4.625% Senior Notes due 2019	$	500.0		$	500.0
2.700% Senior Notes due 2020		1,500.0			1,500.0
Floating Rate Notes due 2021		450.0		-
3.375% Senior Notes due 2021		300.0			300.0
3.150% Senior Notes due 2022		750.0			750.0
3.700% Senior Notes due 2023		300.0		-
3.550% Senior Notes due 2025		2,000.0			2,000.0
4.250% Senior Notes due 2035		253.4			253.4
5.750% Senior Notes due 2039		317.8			317.8
4.450% Senior Notes due 2045		395.4			395.4
1.414% Euro Notes due 2022		614.9			600.4
2.425% Euro Notes due 2026		614.9			600.4
U.S. Term Loan A		610.0			835.0
U.S. Term Loan B		600.0			600.0
Japan Term Loan A		110.2			103.2
Japan Term Loan B		200.5			187.9
Other long-term debt		4.1			4.1
Debt discount and issuance costs		(55.3	)		(53.2	)
Adjustment related to interest rate swaps		21.0			23.1
Total long-term debt	$	9,486.9		$	8,917.5

At March 31, 2018, our total debt balance consisted of $9.1 billion aggregate principal amount of our senior notes, which included $1.2 billion of Euro-denominated senior notes (“Euro Notes”), $610.0 million outstanding under a U.S. term loan (“U.S. Term Loan A”) that will mature on June 24, 2020, $675.0 million outstanding under a U.S. term loan (“U.S. Term Loan B”) that will mature on September 30, 2019, an 11.7 billion Japanese Yen term loan agreement (“Japan Term Loan A”) and a 21.3 billion Japanese Yen term loan agreement (“Japan Term Loan B”) that will each mature on September 27, 2022, and other debt and fair value adjustments totaling $25.1 million, partially offset by debt discount and issuance costs of $55.3 million.

On March 19, 2018, we completed the offering of $450.0 million aggregate principal amount of our floating rate senior notes due March 19, 2021 and $300.0 million aggregate principal amount of our 3.700% senior notes due March 19, 2023. Interest on the floating rate senior notes is equal to three-month LIBOR plus 0.750% and is payable quarterly, commencing on June 19, 2018, until maturity. Interest is payable on the 3.700% senior notes semi-annually, commencing on September 19, 2018, until maturity. We received net proceeds of $749.5 million from this offering. On April 2, 2018, these proceeds, together with borrowings under the Multicurrency Revolving Facility (as defined below) and cash on hand, were used to repay the 2.000% Senior Notes due 2018.

On September 22, 2017, we entered into a term loan agreement for the Japan Term Loan B, and an amended and restated term loan agreement, which amended and restated the Japan Term Loan A loan agreement dated as of May 24, 2012, as amended as of October 31, 2014. As described above, the term loans under both of these agreements will mature on September 27, 2022. Each of these term loans bears interest at a fixed rate of 0.635% per annum.

We have a revolving credit and term loan agreement (the “2016 Credit Agreement”) and a first amendment to our credit agreement executed in 2014 (the “2014 Credit Agreement”). The 2016 Credit Agreement contains the U.S. Term Loan B and a five-year unsecured multicurrency revolving facility of $1.5 billion (the “Multicurrency Revolving Facility”). The Multicurrency Revolving Facility replaced the previous multicurrency revolving facility under the 2014 Credit Agreement and will mature on September 30, 2021, with two available one-year extensions at our discretion. The 2014 Credit Agreement also provided for the U.S. Term Loan A, which remains in effect.

Borrowings under the 2014 and 2016 Credit Agreements generally bear interest at floating rates. We pay a facility fee on the aggregate amount of the Multicurrency Revolving Facility. If our credit rating falls below investment grade, additional restrictions would result, including restrictions on investments and payment of dividends. We were in compliance with all financial covenants under the 2014 and 2016 Credit Agreements as of March 31, 2018. As of March 31, 2018, we had $400.0 million of borrowings outstanding under the Multicurrency Revolving Facility.

Under the terms of U.S. Term Loan A, starting September 30, 2015, principal payments are due as follows: $75.0 million on a quarterly basis during the first three years, $112.5 million on a quarterly basis during the fourth year, and $412.5 million on a quarterly basis during the fifth year. We have paid $2.39 billion in principal under U.S. Term Loan A, resulting in $610.0 million in outstanding borrowings as of March 31, 2018.

Under the terms of U.S. Term Loan B, future principal payments are due as follows: $75.0 million on September 30, 2018, with the remaining balance due on the maturity date of September 30, 2019. We have paid $75.0 million in principal under U.S. Term Loan B, resulting in $675.0 million outstanding on the U.S. Term Loan B as of March 31, 2018.

The estimated fair value of our senior notes as of March 31, 2018, based on quoted prices for the specific securities from transactions in over-the-counter markets (Level 2), was $9,133.7 million. The estimated fair value of Japan Term Loan A and Japan Term Loan B, in the aggregate, as of March 31, 2018, based upon publicly available market yield curves and the terms of the debt (Level 2), was $309.4 million. The carrying values of U.S. Term Loan A, U.S. Term Loan B and the Multicurrency Revolving Facility approximate their fair values as they bear interest at short-term variable market rates.