Income Taxes (Narrative) (Details) $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Income Tax Disclosure [Abstract]
Income tax rate	25.50%			25.10%
Decrease in income tax percentage	0.039			0.061
Tax expense for reserves related to the calculation of certain foreign tax credits			$ 114		$ 114
Tax benefit for release of valuation allowance related to deferred income tax assets		$ 232			232
Tax benefits related to effective settlement of IRS audit					152
Tax expense from partial reversal of the tax basis benefit associated with deemed repatriation tax	$ 40			$ 122
Tax expense for valuation allowance on foreign tax credit carryforwards that are not realizable as a result of updates to provisional estimates recorded for the Tax Reform Act	17			51
Tax benefits for the reversal of tax accruals no longer required		$ 36			$ 36
Tax Reform Act, net tax expense (benefit)	(1)			1
Unrecognized tax benefits	(34)			(34)		$ 66
Unrecognized tax benefits that would impact the effective tax rate	58			58		43
Unrecognized tax benefits that would impact deferred taxes	(92)			(92)		$ 23
Possible decrease in unrecognized tax benefits	$ (75)			$ (75)