Commitments (Other Commitments) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Other Commitments [Line Items]
Commitments	$ 184,536	$ 199,618
Liability Related To Investments In Low Income Housing Tax Credits	600	600
Commitments to extend credit [Member]
Other Commitments [Line Items]
Commitments	172,004	185,589
Commitments to extend credit [Member] | Total commercial lending
Other Commitments [Line Items]
Commitments	115,996	131,762
Commitments to extend credit [Member] | Home Equity Line of Credit [Member]
Other Commitments [Line Items]
Commitments	16,843	16,803
Commitments to extend credit [Member] | Credit Card [Member]
Other Commitments [Line Items]
Commitments	32,065	30,862
Commitments to extend credit [Member] | Other [Member]
Other Commitments [Line Items]
Commitments	7,100	6,162
Standby letters of credit [Member]
Other Commitments [Line Items]
Commitments	9,428	9,843
Standby letters of credit [Member] | Remarketing Programs [Member]
Other Commitments [Line Items]
Commitments	4,000	4,100
Reinsurance Agreements [Member]
Other Commitments [Line Items]
Commitments	110	1,393
Reinsurance Agreements [Member] | Accidental Death and Dismemberment [Member]
Other Commitments [Line Items]
Maximum Exposure		1,300
Reinsurance Agreements [Member] | Credit Life Accident and Health [Member]
Other Commitments [Line Items]
Maximum Exposure	100	100
Standby bond purchase agreements [Member]
Other Commitments [Line Items]
Commitments	1,464	1,295
Other commitments [Member]
Other Commitments [Line Items]
Commitments	$ 1,530	$ 1,498