Income Taxes - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Provisional tax expense estimate as a result of enactment of Tax Cuts and Jobs Act of 2017	$ 395
Tax benefit after finalizing impact of the Tax Cuts and Jobs Act of 2017		$ 26
Change in effective tax rate due to Tax Cuts and Jobs Act of 2017 (percent)	7.20%	(0.50%)	7.20%	0.00%
Foreign earnings on which tax assessed	$ 522		$ 522
Undistributed earnings of foreign subsidiaries		$ 160
AMT credit carryforwards	$ 379	189	$ 379
Operating loss carryforwards		$ 2,200
Operating loss carryforwards, expiration dates		Jan. 01, 2027
Deferred income taxes, pension obligation		$ 688
Pension obligation, time frame for extinguishment		25 years