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Segments (Results of Operations and Average Assets by Segment) (Parenthetical) (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Segment Reporting Information
Bank premises impairment	$ 1	$ 41	$ 6
Other Asset Impairment Charges		(1)	(18)
Bank premises and equipment held for sale				$ 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	$ 36	$ 38	$ 36