Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Ending balance	$ 247,573	$ 231,727	$ 210,857
Dividends declared:
Common stock, dividends declared (in dollars per share)	$ 1.72	$ 1.58	$ 1.44
Common stock
Ending balance	$ 4,105	$ 4,105	$ 4,105