Income Taxes - Earnings Before Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Domestic	$ (2,678)	$ (1,651)	$ (1,038)
Foreign	10,405	9,535	7,683
Total earnings before income tax expense	$ 7,727	$ 7,884	$ 6,645