Goodwill and Other Intangible Assets - Summary Of Gross Goodwill And Accumulated Impairment Losses And Write-Offs Detailed By Reportable Segments (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 1,511	$ 1,433
Additions and adjustments	0	78
Goodwill, ending balance	1,511	1,511
Regional Banking
Goodwill [Roll Forward]
Goodwill, beginning balance	880	802
Additions and adjustments	0	78
Goodwill, ending balance	880	880
Specialty Banking
Goodwill [Roll Forward]
Goodwill, beginning balance	631	631
Additions and adjustments	0	0
Goodwill, ending balance	$ 631	$ 631