Goodwill and Mortgage Servicing Rights - Changes During Period (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Goodwill [Roll Forward]
Balance at beginning of period	$ 47,471	$ 47,507
Changes during the period from:
Other	3	(8)
Balance at end of period	$ 47,474	$ 47,499