Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 354			$ 504	$ 842	$ 1,192
Estimated annual effective tax rate					20.00%
Statutory corporate tax rate					21.00%
Additional tax expense							$ 773
Non-U.S. earnings, Increase (decrease) in income tax expense	678		$ 669				714
Remeasurement of deferred tax balance	$ 51	$ 50					$ 59