Income Taxes (U.S. Tax Cuts and Jobs Act of 2017) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Change in Accounting Estimate [Line Items]
Deferred tax revaluation from tax law change	$ (1,585)	$ (1,592)
Adoption of modified territorial system	(1,809)	(1,785)
Deemed repatriation	361	497
Total provision for income tax expense (benefit)	(3,033)	$ (2,880)
U.S. Tax Cut and Jobs Act of 2017
Change in Accounting Estimate [Line Items]
Deferred tax revaluation from tax law change	7
Adoption of modified territorial system	(24)
Deemed repatriation	(136)
Total provision for income tax expense (benefit)	$ (153)