Goodwill and Other Intangible Assets - Rollforward of Goodwill (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 2,262	$ 2,255
Goodwill (deductions) additions	0	7
Goodwill, ending balance	2,262	2,262
Community Banking
Goodwill [Roll Forward]
Goodwill, beginning balance	2,231	2,231
Goodwill (deductions) additions	0	0
Goodwill, ending balance	2,231	2,231
Wealth Management
Goodwill [Roll Forward]
Goodwill, beginning balance	8	8
Goodwill (deductions) additions	0	0
Goodwill, ending balance	8	8
Insurance
Goodwill [Roll Forward]
Goodwill, beginning balance	23	16
Goodwill (deductions) additions	0	7
Goodwill, ending balance	$ 23	$ 23