Long-Term Debt (Long-Term Debt) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt, beginning balance		$ 16,086
Payments and Retirements		(849)
New Borrowings		2,341
Debt Assumed		600
Long-term debt, ending balance		(16,086)	$ (18,178)	$ (16,086)
Less: Debt Issuance Cost			(209)	(196)
Less: Debt Discount/Premium			(46)	2
Less: Current Portion			(363)	(384)
Principal Outstanding			$ 17,560	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		(419)
New Borrowings		401
Debt Assumed		500
Relcassifications		(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]
Payments and Retirements		(426)
New Borrowings		1,940
Relcassifications		637
Long-term debt, ending balance			$ (2,151)
Weighted average interest rate	[1]		3.89%
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]		4.50%
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 December 31, 2016 represent a weighted average of multiple issuances.