Income Taxes, Income Statement Components of Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
U.S. operations	$ 2,283	$ 1,733	$ 5,327
International operations	924	1,449	644
Income before income tax expense (benefit)	$ 3,207	$ 3,182	$ 5,971