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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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Debt - Total Debt (Details) - USD ($) $ in Millions	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt, gross	$ 1,089			$ 1,089
Less: Unamortized debt issuance costs	11			6
Total	1,078			1,083
4.875% senior notes due 2027
Debt Instrument [Line Items]
Long-term debt, gross	$ 500			0
Less: Unamortized debt issuance costs			$ 7
Stated interest rate	4.875%	4.875%
5.5% senior notes due 2025
Debt Instrument [Line Items]
Long-term debt, gross	$ 350			350
Less: Unamortized debt issuance costs					$ 6
Stated interest rate	5.50%				5.50%
7.75% senior notes due 2018
Debt Instrument [Line Items]
Long-term debt, gross	$ 0			$ 500
Stated interest rate	7.75%			7.75%
Industrial revenue bonds (due 2028 through 2034)
Debt Instrument [Line Items]
Long-term debt, gross	$ 239			$ 239