Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Summary of Short-term and Long-term Debt Outstanding

A summary of short-term and long-term debt outstanding is as follows:

(in millions)	December 31,
	2017		2016
2.5% Senior Notes, due 2018 1	$	399	$	398
3.3% Senior Notes, due 2020 2	697		696
4.0% Senior Notes, due 2025 3	692		691
4.4% Senior Notes, due 2026 4	892		891
2.95% Senior Notes, due 2027 5	493		492
6.55% Senior Notes, due 2037 6	396		396
Total debt	3,569		3,564
Less: short-term debt including current maturities	399		—
Long-term debt	$	3,170	$	3,564

¹  Interest payments are due semiannually on February 15 and August 15, and as of December 31, 2017, the unamortized debt discount and issuance costs total $1 million.

²  Interest payments are due semiannually on February 14 and August 14, and as of December 31, 2017, the unamortized debt discount and issuance costs total $3 million.

³  Interest payments are due semiannually on June 15 and December 15, and as of December 31, 2017, the unamortized debt discount and issuance costs total $8 million.

⁴  Interest payments are due semiannually on February 15 and August 15, and as of December 31, 2017, the unamortized debt discount and issuance costs total $8 million.

⁵  Interest payments are due semiannually on January 22 and July 22, and as of December 31, 2017, the unamortized debt discount and issuance costs total $7 million.

⁶  Interest payments are due semiannually on May 15 and November 15, and as of December 31, 2017, the unamortized debt discount and issuance costs total $4 million.