Long-Term Debt (Long-Term Debt) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt, beginning balance	$ 17,516
Payments and Retirements	(5,697)
New Borrowings	4,950
Long-term debt, ending balance	16,769	$ 17,516
Less: Debt Issuance Costs		(168)
Less: Debt Premium/(Discount)	(39)	(46)
Debt, less unamortized debt issuance costs and discounts	16,730	17,302
Less: Current Portion	(5,781)	(994)
Less: Debt subject to compromise	$ (10,949)
Total Long-Term Debt		16,308
Interest Rate	8.065%
Secured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	$ 5,711
Long-term debt, ending balance	4,964	5,711
Secured Debt [Member] | Parent Company [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	5,711
Payments and Retirements	(5,697)
New Borrowings	4,950
Long-term debt, ending balance	$ 4,964	5,711
Interest Rate	5.747%
Secured Debt [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	$ 106
Long-term debt, ending balance	$ 106	106
Interest Rate	8.368%
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	$ 10,949
Long-term debt, ending balance	10,949	10,949
Unsecured Debt [Member] | Parent Company [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	10,949
Long-term debt, ending balance	$ 10,949	10,949
Interest Rate	9.193%
Unsecured Debt [Member] | Subsidiaries [Member]
Debt Instrument [Line Items]
Long-term debt, beginning balance	$ 750
Long-term debt, ending balance	$ 750	$ 750
Interest Rate	6.897%