Debt Obligations - Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument
Junior Subordinated Notes	$ 54	$ 54
Note payable to related party	113	0
Other Long-term Debt	5	5
Unamortized Net Premiums And Fair Value Adjustments	28	51
Total debt outstanding	818	1,141
Less: Current maturities of long-term debt	407	307
Long-term Debt, Excluding Current Maturities	411	834
6.20% Senior Notes due 2017
Debt Instrument
Senior Notes	$ 0	300
Debt Instrument, Interest Rate, Stated Percentage	6.20%
Senior Notes due 2018 [Member]
Debt Instrument
Senior Notes	$ 400	400
Debt Instrument, Interest Rate, Stated Percentage	7.00%
8.125% Senior Notes due 2019
Debt Instrument
Senior Notes	$ 150	150
Debt Instrument, Interest Rate, Stated Percentage	8.125%
7.60% Senior Notes, due February 1, 2024 [Member]
Debt Instrument
Senior Notes	$ 82	82
Debt Instrument, Interest Rate, Stated Percentage	7.60%
Senior Notes Due 2029 [Member]
Debt Instrument
Senior Notes	$ 66	66
Debt Instrument, Interest Rate, Stated Percentage	7.00%
8.25% Senior Notes, due November 14, 2029 [Member]
Debt Instrument
Senior Notes	$ 33	$ 33
Debt Instrument, Interest Rate, Stated Percentage	8.25%
Panhandle [Member]
Debt Instrument
Junior Subordinated Notes	$ 600

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Contractual interest rate for funds borrowed, under the debt agreement.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of long-term debt (with maturities initially due after one year or beyond the operating cycle if longer) identified as Junior Subordinated Notes, which have a lower priority than senior instruments.

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

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Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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The amount for notes payable (written promise to pay), payable to related parties, which are due after one year (or one business cycle).

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Amount of long-term debt classified as other.

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Carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer), excluding current portion. Senior note holders are paid off in full before any payments are made to junior note holders.

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