Segments (Results of Operations and Average Assets by Segment) (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information
Impairment of Branches and Land	$ 28	$ 45	$ 7
Bank premises and equipment held for sale	27	42
Right of use asset, operating lease impairment	15
Commercial Banking
Segment Reporting Information
Other Asset Impairment Charges	3
Commercial Banking | Operating lease equipment
Segment Reporting Information
Other Asset Impairment Charges	3	4	52
General Corporate and Other
Segment Reporting Information
Bank premises and equipment held for sale	$ 27	$ 42	$ 27