Commitments (Other Commitments) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Other Commitments [Line Items]
Commitments	$ 186,484	$ 181,612
Commitments to extend credit [Member]
Other Commitments [Line Items]
Commitments	173,139	169,278
Commitments to extend credit [Member] | Total commercial lending [Member]
Other Commitments [Line Items]
Commitments	122,014	120,165
Commitments to extend credit [Member] | Home Equity Line of Credit [Member]
Other Commitments [Line Items]
Commitments	17,094	16,944
Commitments to extend credit [Member] | Credit Card [Member]
Other Commitments [Line Items]
Commitments	28,187	27,100
Commitments to extend credit [Member] | Other [Member]
Other Commitments [Line Items]
Commitments	5,844	5,069
Standby letters of credit [Member]
Other Commitments [Line Items]
Commitments	9,236	8,655
Standby letters of credit [Member] | Remarketing Programs [Member]
Other Commitments [Line Items]
Commitments	3,700	3,700
Reinsurance Agreements [Member]
Other Commitments [Line Items]
Commitments	1,492	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	200	200
Standby bond purchase agreements [Member]
Other Commitments [Line Items]
Commitments	1,145	1,000
Other commitments [Member]
Other Commitments [Line Items]
Commitments	1,472	1,130
Other commitments [Member] | Investments in qualified affordable housing projects [Member]
Other Commitments [Line Items]
Commitments	$ 500	$ 500