Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2007
Income Tax Contingency [Line Items]
Deferred Income Tax Expense (Benefit)			$ (1,101)	$ 136	$ 268
Statutory U.S. income tax rate			35.00%	35.00%	35.00%
Tax Cuts and Jobs Act of 2017, Income Tax Expense Benefit, Incomplete Accounting, Provisional Amount	$ (1,222)		$ 1,220
Change In Tax Rate, Income Tax Expense Benefit, Incomplete Accounting, Provisional Amount			1,451
Tax Cuts and Jobs Act of 2017, Accrued Income Taxes, Current	17		17
Tax Cuts and Jobs Act of 2017, Increase Decrease in Valuation Allowance for Deferred Tax Assets, Incomplete Accounting, Provisional Amount			3
Deferred Tax Liability Not Recognized, Description of Temporary Difference, Undistributed Earnings of Foreign Subsidiaries			5,900
Deferred income tax provision (benefit) for the effect of changes in non-U.S. and U.S. state tax rates			(1,459)	$ 18	$ 3
Income tax payments, net of refunds			7	90	149
Deferred tax liabilities, other	1,500		1,500
Accrual for the payment of estimated interest and penalties associated with unrecognized tax benefits	17		17	$ 22
Tax positions for which the ultimate benefits are highly certain, but for which there is uncertainty about the timing of such benefits	5		5
Investment Tax Credit			68
Two Thousand And Six Financing Entities [Member]
Income Tax Contingency [Line Items]
Deferred tax liabilities, other	884		884		$ 1,400
Two Thousand Seven Monetized Notes [Member]
Income Tax Contingency [Line Items]
Deferred tax liabilities, other	$ 538		538			$ 831
Scenario, Forecast [Member]
Income Tax Contingency [Line Items]
Statutory U.S. income tax rate		21.00%
Tax Cuts and Jobs Act [Member]
Income Tax Contingency [Line Items]
Deferred Income Tax Expense (Benefit)			1,451
Tax Cuts and Jobs Act of 2017, Income Tax Expense Benefit, Incomplete Accounting, Provisional Amount, Remeasurement of U.S. Deferred Taxes			1,454
Tax Cuts and Jobs Act of 2017, Income Tax Expense Benefit, Incomplete Accounting, Provisional Amount, Transition Tax			231
Tax Cuts and Jobs Act [Member] | State and Local Jurisdiction [Member]
Income Tax Contingency [Line Items]
Deferred Income Tax Expense (Benefit)			$ 3