Income Taxes - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Provisional tax expense estimate as a result of enactment of Tax Cuts and Jobs Act	$ 150
Increase in effective tax rate due to Tax Cuts and Jobs Act (percent)	2.60%	2.60%	0.00%	0.00%
Foreign earnings on which tax assessed	$ 732	$ 732
Undistributed earnings of foreign subsidiaries			$ 379
AMT credit carryforwards	379	379	$ 379
Operating loss carryforwards	$ 5,100	$ 5,100
Operating loss carryforwards, expiration dates		Jan. 01, 2027
Deferred income taxes, pension obligation		$ 700
Pension obligation, time frame for extinguishment		25 years