Commitments (Other Commitments) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Other Commitments [Line Items]
Commitments	$ 181,612	$ 172,521
Commitments to extend credit
Other Commitments [Line Items]
Commitments	169,278	159,641
Commitments to extend credit | Total commercial lending
Other Commitments [Line Items]
Commitments	120,165	112,125
Commitments to extend credit | Home Equity Line of Credit
Other Commitments [Line Items]
Commitments	16,944	17,852
Commitments to extend credit | Credit Card
Other Commitments [Line Items]
Commitments	27,100	24,911
Commitments to extend credit | Other
Other Commitments [Line Items]
Commitments	5,069	4,753
Standby letters of credit
Other Commitments [Line Items]
Commitments	8,655	8,651
Standby letters of credit | Remarketing Programs
Other Commitments [Line Items]
Commitments	3,700	3,500
Reinsurance Agreements
Other Commitments [Line Items]
Commitments	1,549	1,654
Reinsurance Agreements | Accidental Death and Dismemberment
Other Commitments [Line Items]
Maximum Exposure	1,300	1,500
Reinsurance Agreements | Credit Life Accident and Health
Other Commitments [Line Items]
Maximum Exposure	200	200
Standby bond purchase agreements
Other Commitments [Line Items]
Commitments	1,000	843
Other commitments
Other Commitments [Line Items]
Commitments	1,130	1,732
Other commitments | Investments in qualified affordable housing projects
Other Commitments [Line Items]
Commitments	$ 500	$ 500