Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Sep. 30, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Contingency [Line Items]
Deferred income tax provision (benefit), net			$ 16	$ (1,101)	$ 136
Statutory U.S. income tax rate			21.00%	35.00%	35.00%
Tax Cuts and Jobs Act of 2017, Income Tax Expense Benefit, Incomplete Accounting, Provisional Amount		$ (1,220)		$ (1,220)
Tax Cuts and Jobs Act of 2017, Measurement Period Adjustment, Income Tax Expense Benefit			$ (11)
Tax Cuts and Jobs Act of 2017, Change In Tax Rate, Income Tax Expense Benefit, Incomplete Accounting, Provisional Amount				(1,451)
Tax Cuts and Jobs Act of 2017, Increase Decrease in Valuation Allowance for Deferred Tax Assets, Incomplete Accounting, Provisional Amount				(3)
Deferred income tax provision (benefit) for the effect of changes in non-U.S. and U.S. state tax rates			(13)	(1,459)	$ 18
Income tax payments, net of refunds			388	7	$ 90
Deferred tax liabilities, other			1,500
Accrual for the payment of estimated interest and penalties associated with unrecognized tax benefits		$ 17	21	17
Tax positions for which the ultimate benefits are highly certain, but for which there is uncertainty about the timing of such benefits			30
Investment Tax Credit			$ 6	68
Tax Cuts and Jobs Act of 2017, Measurement Period Adjustment, Impact on Effective Tax Rate, Change In Tax Rate, Deferred Tax Asset			(0.60%)
Tax Cuts and Jobs Act of 2017, decrease in deferred tax liabilities			$ (1,462)
Tax Cuts and Jobs Act of 2017, Change In Tax Rate, Income Tax Expense (Benefit), Total			(1,462)
Tax Cuts and Jobs Act of 2017, Measurement Period Adjustment, Income Tax Expense Benefit, Transition Tax			$ (25)
Tax Cuts and Jobs Act of 2017, Measurement Period Adjustment, Impact on Effective Tax Rate, Transition Tax			(1.40%)
Tax Cuts and Jobs Act, Incomplete Accounting, Provisional Amount, Total Income Tax Expense Benefit, Transitional Tax			$ 206
Undistributed Earnings of Foreign Subsidiaries			1,700
Two Thousand And Six Financing Entities [Member]
Income Tax Contingency [Line Items]
Deferred tax liabilities, other			884
Two Thousand Seven Monetized Notes [Member]
Income Tax Contingency [Line Items]
Deferred tax liabilities, other			538
Tax Cuts and Jobs Act [Member]
Income Tax Contingency [Line Items]
Deferred income tax provision (benefit), net				(1,451)
Tax Cuts and Jobs Act of 2017, Incomplete Accounting, Provisional Amount, Income Tax Expense Benefit, Remeasurement of U.S. Deferred Taxes	$ (36)			(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 of 2017, Measurement Period Adjustment, Income Tax Expense Benefit			(36)
State and Local Jurisdiction [Member] | Tax Cuts and Jobs Act [Member]
Income Tax Contingency [Line Items]
Deferred income tax provision (benefit), net				$ (3)
Secretariat of the Federal Revenue Bureau of Brazil [Member]
Income Tax Contingency [Line Items]
Income Tax Examination, Estimate of Possible Loss			150
Income Tax Examination, Penalties and Interest Expense			$ 380