The following table summarizes the major components of debt as of each balance sheet date (in millions) and provides the maturities and interest rate ranges of each major category as of March 31, 2019:


	March 31,		December 31,
	2019		2018
$2.75 billion revolving credit facility (weighted average interest rate of 3.1% as of December 31, 2018)	$	—	$	11
Commercial paper program (weighted average interest rate of 2.8% as of March 31, 2019 and 2.9% as of December 31, 2018)		1,354		990
Senior notes, maturing through 2045, interest rates ranging from 2.4% to 7.75% (weighted average interest rate of 4.3% as of March 31, 2019 and December 31, 2018)		6,222		6,222
Tax-exempt bonds, maturing through 2048, fixed and variable interest rates ranging from 1.35% to 4.3% (weighted average interest rate of 2.4% as of March 31, 2019 and 2.35% as of December 31, 2018)		2,354		2,388
Financing leases and other, maturing through 2040, interest rates up to 9%		486		467
Debt issuance costs, discounts and other		(50)		(52)
		10,366		10,026
Current portion of long-term debt		1,043		432
	$	9,323	$	9,594