Commitments (Other Commitments) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Other Commitments [Line Items]
Commitments	$ 197,868	$ 181,612
Commitments to extend credit [Member]
Other Commitments [Line Items]
Commitments	183,081	169,278
Commitments to extend credit [Member] | Total commercial lending [Member]
Other Commitments [Line Items]
Commitments	129,787	120,165
Commitments to extend credit [Member] | Home Equity Line of Credit [Member]
Other Commitments [Line Items]
Commitments	16,881	16,944
Commitments to extend credit [Member] | Credit Card [Member]
Other Commitments [Line Items]
Commitments	29,886	27,100
Commitments to extend credit [Member] | Other [Member]
Other Commitments [Line Items]
Commitments	6,527	5,069
Standby letters of credit [Member]
Other Commitments [Line Items]
Commitments	9,763	8,655
Standby letters of credit [Member] | Remarketing Programs [Member]
Other Commitments [Line Items]
Commitments	4,100	3,700
Reinsurance Agreements [Member]
Other Commitments [Line Items]
Commitments	1,431	1,549
Reinsurance Agreements [Member] | Accidental Death and Dismemberment [Member]
Other Commitments [Line Items]
Maximum Exposure	1,300	1,300
Reinsurance Agreements [Member] | Credit Life Accident and Health [Member]
Other Commitments [Line Items]
Maximum Exposure	100	200
Standby bond purchase agreements [Member]
Other Commitments [Line Items]
Commitments	1,302	1,000
Other commitments [Member]
Other Commitments [Line Items]
Commitments	2,291	1,130
Other commitments [Member] | Investments in qualified affordable housing projects [Member]
Other Commitments [Line Items]
Commitments	$ 500	$ 500