Debt (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of total debt

Total debt as of December 31 consisted of the following:

(millions)	2017		2016
4.875% senior notes due 2027	$	500	$	—
5.5% senior notes due 2025	350		350
7.75% senior notes due 2018	—		500
Industrial revenue bonds (due 2028 through 2034)	239		239
Total	$	1,089	$	1,089
Less: Unamortized debt issuance costs	11		6
Total	$	1,078	$	1,083

Interest rate	5.5%	4.875%
Principal net of discount (in millions) (a)	$350	$500
Maturity	March 1, 2025	June 1, 2027
Call date (b)	March 1, 2020	June 1, 2022
Mandatory redemption offer	at 101% plus accrued and unpaid interest in the event of a change in control	at 101% plus accrued and unpaid interest in the event of a change in control

(a) Principal amounts exclude unamortized debt issuance costs.

(b) Callable at any time, in whole or in part, prior to the call date at a redemption price equal to 100% of the principal plus a premium (as outlined in the respective indentures), plus any accrued and unpaid interest on the principal amount being called. Callable after the call date at stated redemption prices (as outlined in the applicable indenture), plus any accrued and unpaid interest on the principal amount being called.

Schedule of fair value of debt

(millions)	December 31, 2017		December 31, 2016
Fair value of debt	$	1,134	$	1,129
Accrued interest	12		31

Schedule of amounts of total debt outstanding maturing in each of next five years and beyond

As of December 31, 2017, the amounts of total debt outstanding maturing in each of the next five years and beyond were as follows:

(millions)	2018 through 2022		After 2022
Debt maturities (principal amounts)	$	—	$	1,089