Goodwill and Mortgage Servicing Rights - Changes During Period (Details) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Goodwill [Roll Forward]
Balance at beginning of period	$ 47,800,000,000	$ 47,474,000,000	$ 47,823,000,000	$ 47,471,000,000	$ 47,471,000,000
Changes during the period from:
Other	11,000,000	3,000,000	(12,000,000)	6,000,000
Balance at end of period	$ 47,811,000,000	$ 47,477,000,000	47,811,000,000	$ 47,477,000,000	47,823,000,000
Goodwill impairment			$ 0		$ 0