Income Taxes (Net Deferred Tax Assets and Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016
Components of Deferred Tax Assets and Liabilities [Abstract]
Deferred tax assets		$ 8,459	$ 13,591
Deferred tax liabilities		(9,888)	(14,502)
Valuation allowance		(69)	(95)
Deferred Tax Liabilities, Net	[1]	$ 1,498	$ 1,006

[1] Included in the net deferred tax (liabilities)/assets as of December 31, 2017 and 2016 are deferred tax assets in the amounts of $4,636 and $7,701 related to Accumulated other comprehensive loss.