Long-Term Debt (Long-Term Debt) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term debt, beginning balance		$ 18,178
Payments and Retirements		(38)
Long-term debt, ending balance		18,178	$ 18,140	$ 18,178
Less: Debt Issuance Cost			(206)	(209)
Less: Debt Premium/(Discount)			(45)	(46)
Less: Current Portion			(363)	(363)
Principal Outstanding			$ 17,526	17,560
Weighted average interest rate	[1]		8.62%
Senior And Subsidiary Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		15,900
Long-term debt, ending balance		15,900	$ 15,900	15,900
Weighted average interest rate	[1]		9.18%
Senior Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		2,151
Payments and Retirements		(37)
Long-term debt, ending balance		2,151	$ 2,114	2,151
Weighted average interest rate	[1]		4.49%
Secured Subsidiary Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		100
Long-term debt, ending balance		100	$ 100	100
Weighted average interest rate	[1]		8.50%
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		19
Payments and Retirements		(1)
Long-term debt, ending balance		19	$ 18	19
Weighted average interest rate	[1]		4.73%
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 March 31, 2017 represent a weighted average of multiple issuances.