Income Taxes - Income Tax Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current taxes
U.S. income	$ 1,076	$ 1,068	$ 382
Foreign income	93	115	77
State income	60	49	42
Total taxes, current	1,229	1,232	501
Deferred taxes (benefits)
U.S. Income	22	10	152
Foreign income	(6)	(22)	46
State income	5	(10)	(1)
Total taxes, deferred	21	(22)	197
Total taxes	$ 1,250	$ 1,210	$ 698