Long-Term Debt (Senior Unsecured Debt) (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2015		Dec. 31, 2014
Debt Instrument [Line Items]
Principal Outstanding		$ 16,110		$ 9,781
Senior Unsecured Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 16,078		$ 9,750
Weighted average interest rate		8.72%	[1]	7.45%	[2]
Senior Unsecured Debt [Member] | Senior Note Due 3/15/2019 [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 434		$ 434
Interest Rate		7.125%		7.125%
Debt instrument, maturity date		Mar. 15, 2019
Senior Unsecured Debt [Member] | Senior Note Due 9/15/2022 [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 2,000
Interest Rate		10.50%
Debt instrument, maturity date		Sep. 15, 2022
Senior Unsecured Debt [Member] | Senior Note Due 9/15/2025 [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 3,600
Interest Rate		11.00%
Debt instrument, maturity date		Sep. 15, 2025
Senior Unsecured Debt [Member] | Senior Note Due 9/15/2020 [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 1,000
Interest Rate		8.875%
Debt instrument, maturity date		Sep. 15, 2020
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 15,828		$ 9,500
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member] | Senior Note Due 3/15/2015 [Member]
Debt Instrument [Line Items]
Principal Outstanding				$ 105
Interest Rate				6.625%
Debt instrument, maturity date		Mar. 15, 2015
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member] | Senior Note Due 4/15/2015 [Member]
Debt Instrument [Line Items]
Principal Outstanding				$ 97
Interest Rate				7.875%
Debt instrument, maturity date		Apr. 15, 2015
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member] | Senior Note Due 10/14/2016 [Member]
Debt Instrument [Line Items]
Principal Outstanding	[3]	$ 359		$ 402
Interest Rate	[3]	2.575%		3.045%
Debt instrument, maturity date	[3]	Oct. 14, 2016
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member] | Senior Note Due 4/15/2017 [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 607		$ 607
Interest Rate		8.25%		8.25%
Debt instrument, maturity date		Apr. 15, 2017
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member] | Senior Note Due 10/1/2018 [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 583		$ 583
Interest Rate		8.125%		8.125%
Debt instrument, maturity date		Oct. 01, 2018
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member] | Senior Note Due 10/24/2019 [Member]
Debt Instrument [Line Items]
Principal Outstanding	[4]	$ 323		$ 350
Interest Rate	[4]	3.575%		3.545%
Debt instrument, maturity date	[4]	Oct. 24, 2019
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member] | Senior Note Due 4/15/2020 [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 1,022		$ 1,022
Interest Rate		8.50%		8.50%
Debt instrument, maturity date		Apr. 15, 2020
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member] | Senior Note Due 7/1/2021 [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 500		$ 500
Interest Rate		9.25%		9.25%
Debt instrument, maturity date		Jul. 01, 2021
Senior Notes and Debentures [Member] | Senior Unsecured Debt [Member] | Senior Note Due 9/15/2021 [Member]
Debt Instrument [Line Items]
Principal Outstanding		$ 775		$ 775
Interest Rate		6.25%		6.25%
Debt instrument, maturity date		Sep. 15, 2021
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Senior Notes and Debentures [Member] | Senior 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
Subsidiary Senior Notes And Debentures [Member] | Senior Unsecured Debt [Member] | Subsidiary Senior Note 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
Subsidiary Senior Notes And Debentures [Member] | Senior Unsecured Debt [Member] | Subsidiary Senior Note 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

[1] Interest rate represents a weighted average of the stated interest rates of multiple issuances.

[2] Interest rate represents a weighted average of the stated interest rates of multiple issuances.

[3] Represents borrowings under the 2011 CoBank Credit Agreement, as defined below.

[4] Represents borrowings under the 2014 CoBank Credit Agreement, as defined below.