Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Oct. 01, 2018	Jan. 01, 2018	[1]
Income Taxes [Line Items]
Tax Cuts and Jobs Act of 2017, incomplete accounting, change in tax rate, provisional income tax expense (benefit)	$ (3,367)			$ 188
Unrecognized tax benefits if recognized would impact effective tax rate	43			59	$ 43
Unrecognized tax benefits if recognized would affect deferred taxes	23			26	23
Interest (income) expense associated with uncertain tax position				5	$ (13)	$ 9
Potential decrease in liability for uncertain tax positions				45
Effective income tax rate reconciliation, Tax Cuts and Jobs Act, transition tax on accumulated foreign earnings, amount				140
Effective income tax rate reconciliation, Tax Cuts and Jobs Act, tax credit, foreign				34
Tax Cuts and Jobs Act of 2017, transition tax for accumulated foreign earnings, income tax expense	413			14
Effective income tax rate reconciliation, change in enacted tax rate, amount	3,017
Tax Cuts and Jobs Act of 2017, measurement period adjustment, income tax benefit	$ 763
Tax (benefit) provision recorded		$ (232)
Foreign tax credits and other tax benefits, tax expense						$ 4,900
Foreign tax credits and other tax benefits, tax expense percentage						35.00%
Adoption of ASU No. 2018-02				(397)			$ 408	$ 0
Tax Year 2010 Through Tax Year 2013 [Member]
Income Taxes [Line Items]
Tax (benefit) provision recorded			$ (152)
Accruals no longer required [Member]
Income Taxes [Line Items]
Tax (benefit) provision recorded		$ 114
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Net operating losses carry forward				$ 658

[1] For further discussion, see Note 15. Income Taxes.