Commitments (Other Commitments) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Other Commitments [Line Items]
Commitments	$ 168,846	$ 163,897
Commitments to extend credit [Member]
Other Commitments [Line Items]
Commitments	156,633	151,981
Commitments to extend credit [Member] | Total commercial lending [Member]
Other Commitments [Line Items]
Commitments	109,687	108,256
Commitments to extend credit [Member] | Home Equity Line of Credit [Member]
Other Commitments [Line Items]
Commitments	17,778	17,438
Commitments to extend credit [Member] | Credit Card [Member]
Other Commitments [Line Items]
Commitments	24,184	22,095
Commitments to extend credit [Member] | Other [Member]
Other Commitments [Line Items]
Commitments	4,984	4,192
Standby letters of credit [Member]
Other Commitments [Line Items]
Commitments	8,609	8,324
Standby letters of credit [Member] | Remarketing Programs [Member]
Other Commitments [Line Items]
Commitments	3,800	3,900
Reinsurance Agreements [Member]
Other Commitments [Line Items]
Commitments	1,690	1,835
Reinsurance Agreements [Member] | Accidental Death and Dismemberment [Member]
Other Commitments [Line Items]
Maximum Exposure	1,500	1,500
Reinsurance Agreements [Member] | Credit Life Accident and Health [Member]
Other Commitments [Line Items]
Maximum Exposure	200	300
Standby bond purchase agreements [Member]
Other Commitments [Line Items]
Commitments	924	790
Other commitments [Member]
Other Commitments [Line Items]
Commitments	990	967
Other commitments [Member] | Investments in qualified affordable housing projects [Member]
Other Commitments [Line Items]
Commitments	$ 500	$ 500