Long-Term Debt (Long-Term Debt) (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Long-term debt, beginning balance		$ 18,178
Payments and Retirements		(1,576)
New Borrowings		1,500
Long-term debt, ending balance		18,178	$ 18,102	$ 18,178
Less: Debt Issuance Cost			199	209
Less: Debt Premium/(Discount)			57	46
Less: Current Portion			(166)	(363)
Long-term Debt, Excluding Current Maturities			$ 17,680	17,560
Weighted average interest rate	[1]		8.35%
Senior And Subsidiary Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		15,900
Payments and Retirements		(1,500)
Long-term debt, ending balance		15,900	$ 14,400	15,900
Weighted average interest rate	[1]		9.22%
Senior Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance		2,151
Payments and Retirements		(74)
New Borrowings		1,500
Long-term debt, ending balance		2,151	$ 3,577	2,151
Weighted average interest rate	[1]		4.86%
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		(2)
Long-term debt, ending balance		19	$ 17	19
Weighted average interest rate	[1]		4.98%
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, 2017 represent a weighted average of multiple issuances.