Goodwill and Other Intangible Assets - Summary Of Gross Goodwill And Accumulated Impairment Losses And Write-Offs Detailed By Reportable Segments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Goodwill [Roll Forward]
Goodwill, Beginning balance	$ 1,433	$ 1,433	$ 1,387
Additions	78	0	46
Goodwill, Ending balance	1,511	1,433	1,433
Regional Banking
Goodwill [Roll Forward]
Goodwill, Beginning balance	802	802	773
Additions	78	0	29
Goodwill, Ending balance	880	802	802
Specialty Banking
Goodwill [Roll Forward]
Goodwill, Beginning balance	631	631	614
Additions	0	0	17
Goodwill, Ending balance	$ 631	$ 631	$ 631