Income Taxes - Income Tax Expense (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Current taxes
Total taxes, current	$ 282	$ 289	$ 965	$ 928
Deferred taxes (benefits)
Total taxes, deferred	52	(2)	44	12
Total taxes	$ 334	$ 287	$ 1,009	$ 940