Long-Term Debt (Long-Term Debt) (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt, beginning balance		$ 16,086
Payments and Retirements		(280)
New Borrowings		1,796
Debt Assumed		600
Long-term debt, ending balance		16,086	$ 18,202	$ 16,086
Less: Debt Issuance Cost			(215)	(196)
Less: Debt Premium/(Discount)			(44)	2
Less: Current Portion			(509)	(384)
Principal Outstanding			$ 17,434	15,508
Weighted average interest rate	[1]		8.55%
Senior And Subsidiary Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		16,055
Payments and Retirements		(189)
New Borrowings		171
Debt Assumed		500
Reclassifications		(637)
Long-term debt, ending balance		16,055	$ 15,900	16,055
Weighted average interest rate	[1]		9.18%
Senior Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		659
Payments and Retirements		(87)
New Borrowings		1,625
Reclassifications		637
Long-term debt, ending balance		659	$ 2,175	659
Weighted average interest rate	[1]		3.97%
Secured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Debt Assumed		100
Long-term debt, ending balance			$ 100
Weighted average interest rate	[1]		8.50%
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		23
Payments and Retirements		(4)
Long-term debt, ending balance		23	$ 19	23
Weighted average interest rate	[1]		4.30%
Rural Utilities Service Loan Contracts [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		8
Long-term debt, ending balance		$ 8	$ 8	$ 8
Weighted average interest rate	[1]		6.15%

[1] Interest rate includes amortization of debt issuance costs and debt premiums or discounts. The interest rates at September 30, 2016 represent a weighted average of multiple issuances.