Segments (Results of Operations and Average Assets by Segment) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Segment Reporting Information
Impairment of Branches and Land	$ 33	$ 2	$ 41	$ 5
Other Asset Impairment Charges			(2)	(19)
Bank premises and equipment held for sale	37		37		$ 27
Commercial Banking | Operating lease equipment
Segment Reporting Information
Other Asset Impairment Charges			2	31
General Corporate and Other
Segment Reporting Information
Bank premises and equipment held for sale	$ 37	$ 41	$ 37	$ 41