Long-Term Debt (Long-Term Debt) (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt, beginning balance		$ 16,086
Payments and Retirements		(69)
New Borrowings		1,625
Debt Assumed		600
Long-term debt, ending balance		16,086	$ 18,242	$ 16,086
Less: Debt Issuance Cost			(223)	(196)
Less: Debt (Discount)/Premium			(53)	2
Less: Current Portion			(1,043)	(384)
Principal Outstanding			$ 16,923	15,508
Weighted average interest rate	[1]		8.47%
Senior And Subsidiary Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		16,055
Payments and Retirements		(22)
Debt Assumed		500
Reclassifications		(637)
Long-term debt, ending balance		16,055	$ 15,896	16,055
Weighted average interest rate	[1]		9.15%
Senior Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		659
Payments and Retirements		(45)
New Borrowings		1,625
Reclassifications		637
Long-term debt, ending balance		659	$ 2,217	659
Weighted average interest rate	[1]		3.63%
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		(2)
Long-term debt, ending balance		23	$ 21	23
Weighted average interest rate	[1]		4.11%
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 June 30, 2016 represent a weighted average of multiple issuances.