Goodwill and Mortgage Servicing Rights - Changes During Period (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Goodwill [Roll Forward]
Balance at beginning of period	$ 49,248,000,000	$ 47,823,000,000	$ 47,823,000,000
Changes during the period from:
Other	(5,000,000)	(23,000,000)
Balance at end of period	49,243,000,000	$ 47,800,000,000	49,248,000,000
Goodwill impairment	$ 0		$ 0