DEBT

The carrying value of long-term debt outstanding, net of unamortized debt issuance costs as required by newly adopted guidance disclosed in Note 2, was as follows at March 31, 2016 and December 31, 2015:



	March 31, 2016		December 31, 2015
	(in millions)
Senior notes:
$500 million, 7.20% due June 15, 2018	$	501	$	502
$300 million, 6.30% due August 1, 2018	307		307
$400 million, 2.625% due October 1, 2019	398		398
$600 million, 3.15% due December 1, 2022	595		595
$600 million, 3.85% due October 1, 2024	595		595
$250 million, 8.15% due June 15, 2038	263		263
$400 million, 4.625% due December 1, 2042	396		396
$750 million, 4.95% due October 1, 2044	738		738
Total long-term debt	$	3,793	$	3,794

Senior Notes

Our senior notes, which are unsecured, may be redeemed at our option at any time at 100% of the principal amount plus accrued interest and a specified make-whole amount. The 7.20% and 8.15% senior notes are subject to an interest rate adjustment if the debt ratings assigned to the notes are downgraded (or subsequently upgraded). In addition, each series of our senior notes (other than the 6.30% senior notes) contain a change of control provision that may require us to purchase the notes under certain circumstances. On July 2, 2015 we entered into a Merger Agreement with Aetna that, when closed, may require redemption of the notes if the notes are downgraded below investment grade by both Standard & Poor’s Rating Services, or S&P and Moody’s Investors Services, Inc., or Moody’s.

Prior to 2009, we were parties to interest-rate swap agreements that exchanged the fixed interest rate under our senior notes for a variable interest rate based on LIBOR. As a result, the carrying value of the senior notes was adjusted to reflect changes in value caused by an increase or decrease in interest rates. During 2008, we terminated all of our swap agreements. The cumulative adjustment to the carrying value of our senior notes was $103 million as of the termination date which is being amortized as a reduction to interest expense over the remaining term of the senior notes. In October 2014, the redemption of our 6.45% senior notes reduced the unamortized carrying value adjustment by $12 million. The unamortized carrying value adjustment was $27 million as of March 31, 2016 and $28 million as of December 31, 2015.

Credit Agreement

Our 5-year $1.0 billion unsecured revolving credit agreement expires July 2018. Under the credit agreement, at our option, we can borrow on either a competitive advance basis or a revolving credit basis. The revolving credit portion bears interest at either LIBOR plus a spread or the base rate plus a spread. The LIBOR spread, currently 110 basis points, varies depending on our credit ratings ranging from 90.0 to 150.0 basis points. We also pay an annual facility fee regardless of utilization. This facility fee, currently 15 basis points, may fluctuate between 10.0 and 25.0 basis points, depending upon our credit ratings. The competitive advance portion of any borrowings will bear interest at market rates prevailing at the time of borrowing on either a fixed rate or a floating rate based on LIBOR, at our option.

The terms of the credit agreement include standard provisions related to conditions of borrowing, including a customary material adverse effect clause which could limit our ability to borrow additional funds. In addition, the credit agreement contains customary restrictive and financial covenants as well as customary events of default, including financial covenants regarding the maintenance of a minimum level of net worth of $8.6 billion at March 31, 2016 and a maximum leverage ratio of 3.0:1. We are in compliance with the financial covenants, with actual net worth of $10.5 billion and an actual leverage ratio of 1.5:1, as measured in accordance with the credit agreement as of March 31, 2016. In addition, the credit agreement includes an uncommitted $250 million incremental loan facility.

At March 31, 2016, we had no borrowings outstanding under the credit agreement and we had outstanding letters of credit of $1 million secured under the credit agreement. No amounts have been drawn on these letters of credit. Accordingly, as of March 31, 2016, we had $999 million of remaining borrowing capacity under the credit agreement, none of which would be restricted by our financial covenant compliance requirement. We have other customary, arms-length relationships, including financial advisory and banking, with some parties to the credit agreement.

Commercial Paper

We previously entered into a commercial paper program pursuant to which we may issue short-term, unsecured commercial paper notes privately placed on a discount basis through certain broker dealers. Amounts available under the program may be borrowed, repaid and re-borrowed from time to time, with the aggregate face or principal amount outstanding under the program at any time not to exceed $1 billion. The net proceeds of issuances have been and are expected to be used for general corporate purposes. The maximum principal amount outstanding at any one time during the three months ended March 31, 2016 was $475 million. There were outstanding borrowings of $300 million at March 31, 2016 and $299 million at December 31, 2015.