Goodwill and Mortgage Servicing Rights - Changes During Period (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Goodwill [Roll Forward]
Balance at beginning of period	$ 47,488	$ 47,300	$ 47,507	$ 47,288
Changes during the period from:
Other	(5)	9	(24)	21
Balance at end of period	$ 47,483	$ 47,309	$ 47,483	$ 47,309