Loans and ACL - Collectively Evaluated for Impairment (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Recorded Investment	$ 141,090	$ 141,395
Related ALLL	1,309	1,297
Commercial | Commercial and industrial
Recorded Investment	51,594	51,253
Related ALLL	451	463
Commercial | CRE-income producing properties
Recorded Investment	14,831	14,455
Related ALLL	134	112
Commercial | CRE-construction and development
Recorded Investment	4,479	3,787
Related ALLL	20	21
Commercial | Dealer floor plan
Recorded Investment	1,607	1,413
Related ALLL	13	11
Commercial | Other lending subsidiaries
Recorded Investment	8,295	7,678
Related ALLL	38	28
Retail | Direct retail lending
Recorded Investment	11,864	12,011
Related ALLL	93	93
Retail | Revolving credit
Recorded Investment	2,668	2,626
Related ALLL	89	95
Retail | Residential mortgage-nonguaranteed
Recorded Investment	27,316	28,488
Related ALLL	137	136
Retail | Residential mortgage-government guaranteed
Recorded Investment	515	466
Related ALLL	7	8
Retail | Sales finance
Recorded Investment	9,443	11,251
Related ALLL	36	37
Retail | Other lending subsidiaries
Recorded Investment	7,767	7,057
Related ALLL	264	249
PCI
Recorded Investment	711	910
Related ALLL	$ 27	$ 44