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, 2016	Sep. 30, 2017	Sep. 30, 2016		Dec. 31, 2016
Segment Reporting Information
Other Asset Impairment Charges			$ (18)	$ (9)	[1]
Bank premises and equipment held for sale	$ 36		36			$ 39
Net tax deficiency reclassified from capital surplus to applicable income tax expense				6
Branch Banking
Segment Reporting Information
Impairment of Branches and Land	1	$ 28	6	31
Commercial Banking | Operating lease equipment
Segment Reporting Information
Other Asset Impairment Charges		4	31	9
General Corporate and Other
Segment Reporting Information
Bank premises and equipment held for sale	$ 36	$ 45	$ 36	45
Net tax deficiency reclassified from capital surplus to applicable income tax expense				$ 6

[1] Net tax deficiencies of $ 6 were reclassified from capital surplus to applicable income tax expense for the nine months ended September 30, 2016, related to the early adoption of ASU 2016-09 during the fourth quarter of 2016, with an effective date of January 1, 2016.