Commitments (Other Commitments) (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Other Commitments [Line Items]
Commitments	$ 220,368,000,000	$ 199,618,000,000
Liability related to investments in low income housing tax credits	1,100,000,000	600,000,000
Commitments to extend credit
Other Commitments [Line Items]
Commitments	207,821,000,000	185,589,000,000
Commitments to extend credit | Total commercial lending
Other Commitments [Line Items]
Commitments	153,089,000,000	131,762,000,000
Commitments to extend credit | Home equity lines of credit
Other Commitments [Line Items]
Commitments	16,626,000,000	16,803,000,000
Commitments to extend credit | Credit card
Other Commitments [Line Items]
Commitments	31,019,000,000	30,862,000,000
Commitments to extend credit | Other
Other Commitments [Line Items]
Commitments	7,087,000,000	6,162,000,000
Standby letters of credit
Other Commitments [Line Items]
Commitments	9,053,000,000	9,843,000,000
Standby letters of credit | Remarketing Programs
Other Commitments [Line Items]
Commitments	3,800,000,000	4,100,000,000
Reinsurance Agreements
Other Commitments [Line Items]
Commitments	0	1,393,000,000
Standby bond purchase agreements
Other Commitments [Line Items]
Commitments	1,448,000,000	1,295,000,000
Other commitments
Other Commitments [Line Items]
Commitments	$ 2,046,000,000	$ 1,498,000,000