6. Debt

Consolidated debt at December 31, 2011 and March 31, 2012 was as follows (in thousands):

					Weighted-
					Average Interest
					Rate at
		December 31,			March 31, 2012
		2011		March 31, 2012	(a)
Revolving credit facility	$	—	$	—	—	%
$250.0 million of 6.45% Notes due 2014		249,844		249,859	6.3	%
$250.0 million of 5.65% Notes due 2016		252,037		251,930	5.6	%
$250.0 million of 6.40% Notes due 2018		263,477		262,962	5.3	%
$550.0 million of 6.55% Notes due 2019		578,521		577,665	5.6	%
$550.0 million of 4.25% Notes due 2021		558,932		558,723	4.0	%
$250.0 million of 6.40% Notes due 2037		248,964		248,968	6.4	%
Total debt	$	2,151,775	$	2,150,107	5.3	%

(a) Weighted-average interest rate includes the impact of interest rate swaps, the amortization/accretion of discounts and premiums and the amortization/accretion of gains and losses realized on historical cash flow and fair value hedges (see Note 7—Derivative Financial Instruments for detailed information regarding fair value hedges and interest rate swaps).

The revolving credit facility and notes detailed in the table above are senior indebtedness.

The face value of our debt at December 31, 2011 and March 31, 2012 was $2.1 billion. The difference between the face value and carrying value of the debt outstanding is the unamortized portion of various fair value hedges and the unamortized discounts and premiums on debt issuances. Note discounts and premiums are being amortized or accreted to the applicable notes over the respective lives of the associated note.

Revolving Credit Facility. The total borrowing capacity under our revolving credit facility, which matures in October 2016, is $800.0 million. Borrowings under the facility are unsecured and bear interest at LIBOR plus a spread ranging from 0.875% to 1.75% based on our credit ratings and amounts outstanding under the facility. Additionally, an unused commitment fee is assessed at a rate from 0.125% to 0.3%, depending on our credit ratings, which was 0.2% at March 31, 2012. Borrowings under this facility may be used for general purposes, including capital expenditures. As of March 31, 2012, there were no borrowings outstanding under this facility and $5.0 million was 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 the facility.