Long-Term Debt (Senior Unsecured Debt) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Mar. 19, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Principal Outstanding	$ 17,643		$ 17,863
Secured Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 5,002		3,511
Secured Debt [Member] | Term Loan Due 10/24/2019 [Member]
Debt Instrument [Line Items]
Principal Outstanding			$ 245
Interest Rate	6.625%		5.445%
Debt instrument, maturity date	Oct. 24, 2019
Secured Debt [Member] | Term Loan Due 3/31/2021 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 1,421		$ 1,483
Interest Rate	5.00%		4.32%
Debt instrument, maturity date	Mar. 31, 2021
Secured Debt [Member] | Term Loan Due 10/12/2021 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 246		$ 276
Interest Rate	6.625%		5.445%
Debt instrument, maturity date	Oct. 12, 2021
Secured Debt [Member] | Term Loan Due 6/15/2024 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 1,721		$ 1,492
Interest Rate	6.00%		5.32%
Debt instrument, maturity date	Jun. 15, 2024
Secured Debt [Member] | Second Lien Notes Due 4/1/2026 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 1,600
Interest Rate	8.50%	8.50%
Debt instrument, maturity date	Apr. 01, 2026
Secured Debt [Member] | IDRB Due 5/1/2030 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 13		$ 13
Interest Rate	6.20%		6.20%
Debt instrument, maturity date	May 01, 2030
Secured Debt [Member] | Equipment Financings [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 1		$ 2
Interest Rate	0.00%		0.00%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 11,784		$ 13,495
Unsecured Debt [Member] | Senior Note Due 10/1/2018 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 431		$ 491
Interest Rate	8.125%		8.125%
Debt instrument, maturity date	Oct. 01, 2018
Unsecured Debt [Member] | Senior Note Due 3/15/2019 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 404		$ 404
Interest Rate	7.125%		7.125%
Debt instrument, maturity date	Mar. 15, 2019
Unsecured Debt [Member] | Senior Note Due 4/15/2020 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 172		$ 619
Interest Rate	8.50%		8.50%
Debt instrument, maturity date	Apr. 15, 2020
Unsecured Debt [Member] | Senior Note Due 9/15/2020 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 55		$ 303
Interest Rate	8.875%		8.875%
Debt instrument, maturity date	Sep. 15, 2020
Unsecured Debt [Member] | Senior Note Due 7/1/2021 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 89		$ 490
Interest Rate	9.25%		9.25%
Debt instrument, maturity date	Jul. 01, 2021
Unsecured Debt [Member] | Senior Note Due 9/15/2021 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 220		$ 775
Interest Rate	6.25%		6.25%
Debt instrument, maturity date	Sep. 15, 2021
Unsecured Debt [Member] | Senior Note Due 4/15/2022 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 500		$ 500
Interest Rate	8.75%		8.75%
Debt instrument, maturity date	Apr. 15, 2022
Unsecured Debt [Member] | Senior Note Due 9/15/2022 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 2,188		$ 2,188
Interest Rate	10.50%		10.50%
Debt instrument, maturity date	Sep. 15, 2022
Unsecured Debt [Member] | Senior Note Due 1/15/2023 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 850		$ 850
Interest Rate	7.125%		7.125%
Debt instrument, maturity date	Jan. 15, 2023
Unsecured Debt [Member] | Senior Note Due 4/15/2024 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 750		$ 750
Interest Rate	7.625%		7.625%
Debt instrument, maturity date	Apr. 15, 2024
Unsecured Debt [Member] | Senior Note Due 1/15/2025 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 775		$ 775
Interest Rate	6.875%		6.875%
Debt instrument, maturity date	Jan. 15, 2025
Unsecured Debt [Member] | Senior Note Due 9/15/2025 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 3,600		$ 3,600
Interest Rate	11.00%		11.00%
Debt instrument, maturity date	Sep. 15, 2025
Unsecured Debt [Member] | Debenture Due 11/1/2025 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 138		$ 138
Interest Rate	7.00%		7.00%
Debt instrument, maturity date	Nov. 01, 2025
Unsecured Debt [Member] | Debenture Due 8/15/2026 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 2		$ 2
Interest Rate	6.80%		6.80%
Debt instrument, maturity date	Aug. 15, 2026
Unsecured Debt [Member] | Senior Note Due 1/15/2027 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 346		$ 346
Interest Rate	7.875%		7.875%
Debt instrument, maturity date	Jan. 15, 2027
Unsecured Debt [Member] | Senior Note Due 8/15/2031 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 945		$ 945
Interest Rate	9.00%		9.00%
Debt instrument, maturity date	Aug. 15, 2031
Unsecured Debt [Member] | Debenture Due 10/1/2034 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 1		$ 1
Interest Rate	7.68%		7.68%
Debt instrument, maturity date	Oct. 01, 2034
Unsecured Debt [Member] | Debenture Due 7/1/2035 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 125		$ 125
Interest Rate	7.45%		7.45%
Debt instrument, maturity date	Jul. 01, 2035
Unsecured Debt [Member] | Debenture Due 10/1/2046 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 193		$ 193
Interest Rate	7.05%		7.05%
Debt instrument, maturity date	Oct. 01, 2046
Secured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 107		$ 107
Secured Subsidiary Debt [Member] | Debenture Due 11/15/2031 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 100		$ 100
Interest Rate	8.50%		8.50%
Debt instrument, maturity date	Nov. 15, 2031
Secured Subsidiary Debt [Member] | RUS Loan Contracts Due 1/3/2028 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 7		$ 7
Interest Rate	6.152%		6.152%
Debt instrument, maturity date	Jan. 03, 2028
Unsecured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 750		$ 750
Unsecured Subsidiary Debt [Member] | Debenture Due 5/15/2027 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 200		$ 200
Interest Rate	6.75%		6.75%
Debt instrument, maturity date	May 15, 2027
Unsecured Subsidiary Debt [Member] | Debenture Due 2/1/2028 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 300		$ 300
Interest Rate	6.86%		6.86%
Debt instrument, maturity date	Feb. 01, 2028
Unsecured Subsidiary Debt [Member] | Debenture Due 2/15/2028 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 200		$ 200
Interest Rate	6.73%		6.73%
Debt instrument, maturity date	Feb. 15, 2028
Unsecured Subsidiary Debt [Member] | Debenture Due 10/15/2029 [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 50		$ 50
Interest Rate	8.40%		8.40%
Debt instrument, maturity date	Oct. 15, 2029
Secured Debt, Unsecured Debt, Secured Subsidiary Debt, And Unsecured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding	$ 17,643		$ 17,863
Weighted average interest rate	8.70%		8.10%