Commitments (Other Commitments) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Other Commitments [Line Items]
Commitments	$ 172,944	$ 172,521
Commitments to extend credit [Member]
Other Commitments [Line Items]
Commitments	160,829	159,641
Commitments to extend credit [Member] | Total commercial lending [Member]
Other Commitments [Line Items]
Commitments	113,268	112,125
Commitments to extend credit [Member] | Home Equity Line of Credit [Member]
Other Commitments [Line Items]
Commitments	16,888	17,852
Commitments to extend credit [Member] | Credit Card [Member]
Other Commitments [Line Items]
Commitments	25,861	24,911
Commitments to extend credit [Member] | Other [Member]
Other Commitments [Line Items]
Commitments	4,812	4,753
Standby letters of credit [Member]
Other Commitments [Line Items]
Commitments	8,350	8,651
Standby letters of credit [Member] | Remarketing Programs [Member]
Other Commitments [Line Items]
Commitments	3,100	3,500
Reinsurance Agreements [Member]
Other Commitments [Line Items]
Commitments	1,622	1,654
Reinsurance Agreements [Member] | Accidental Death and Dismemberment [Member]
Other Commitments [Line Items]
Maximum Exposure	1,400	1,500
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	1,014	843
Other commitments [Member]
Other Commitments [Line Items]
Commitments	1,129	$ 1,732
Other commitments [Member] | Investments in qualified affordable housing projects [Member]
Other Commitments [Line Items]
Commitments	$ 500