Debt (Tables)

3 Months Ended

Mar. 31, 2016

Debt Disclosure [Abstract]

Schedule of Debt

	March 31,   2016			December 31,   2015
	(Millions)
Amended and Restated Credit Agreement
Revolving credit facility, weighted-average variable interest rate of 1.72% and 1.57%, as of March 31, 2016 and December 31, 2015, respectively, due May 1, 2019	$	327		$	375
Debt Securities
Issued November 27, 2012, interest at 2.50% payable semi-annually, due December 1, 2017	500			500
Issued March 13, 2014, interest at 2.70% payable semi-annually, due April 1, 2019	325			325
Issued March 13, 2012, interest at 4.95% payable semi-annually, due April 1, 2022	350			350
Issued March 14, 2013, interest at 3.875% payable semi-annually, due March 15, 2023	500			500
Issued March 13, 2014, interest at 5.60% payable semi-annually, due April 1, 2044	400			400
Unamortized issuance costs	(14		)	(14		)
Unamortized discount	(11		)	(12		)
Total long-term debt	$	2,377		$	2,424

Future Maturities of Long-Term Debt

The future maturities of long-term debt in the year indicated are as follows:

	Debt Maturities
	(Millions)
2017	$	500
2018	—
2019	652
2020	—
2021	—
Thereafter	1,250
	2,402
Unamortized issuance costs	(14		)
Unamortized discount	(11		)
Total	$	2,377