Goodwill and Mortgage Servicing Rights - Goodwill Changes During Period (Details) - USD ($)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Goodwill [Roll Forward]
Balance at beginning of period	$ 49,256,000,000	$ 47,811,000,000	$ 49,248,000,000	$ 47,823,000,000	$ 47,823,000,000
Changes during the period from:
Business combinations	1,065,000,000	0	1,065,000,000	0
Other	(8,000,000)	8,000,000	0	(4,000,000)
Balance at end of period	$ 50,313,000,000	$ 47,819,000,000	50,313,000,000	$ 47,819,000,000	49,248,000,000
Goodwill impairment			$ 0		$ 0