Parent Company Financial Statements (Condensed Statement of Cash Flow - Parent Company Only) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Operating Activities
Net income (loss)	$ 2,194		$ 1,564		$ 1,712
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
(Benefit from) provision for deferred income taxes	(251)		(148)		(71)
Net change in undistributed earnings	47		66		63
Net change in:
Other assets	(23)		351		94
Accrued expenses and other liabilities	(138)		(157)		327
Net Cash Provided by (Used in) Operating Activities	1,494		2,114		2,418
Net change in:
Other short-term investments	1		(83)		5,243
Net Cash Provided by (Used in) Investing Activities	414		(2,887)		(3,931)
Financing Activities
Net change in other short-term borrowings	477		2,028		(49)
Dividends paid on common shares	430		402		422
Dividends paid on preferred shares	75		52		75
Proceeds from issuance of long-term debt	2,490		3,735		3,091
Repayment of long-term debt	1,969		5,119		2,205
Repurchase of treasury stock and related forward contract	1,605		661		850
Other, net	(57)		(31)		(28)
Net Cash Provided (Used in) Provided by Financing Activities	(1,786)		625		962
Net (Decrease) Increase in Cash	122		(148)		(551)
Cash and Due from Banks at Beginning of Period	2,392	[1]	2,540		3,091
Cash and Due from Banks at End of Period	2,514	[1]	2,392	[1]	2,540
Parent Company Only
Operating Activities
Net income (loss)	2,194		1,564		1,712
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
(Benefit from) provision for deferred income taxes	2		0		(4)
Net change in undistributed earnings	20		214		(788)
Net change in:
Other assets	37		14		(18)
Accrued expenses and other liabilities	(15)		(35)		31
Net Cash Provided by (Used in) Operating Activities	2,238		1,757		933
Net change in:
Other short-term investments	(419)		654		(539)
Loans to subsidiaries	126		13		2
Net Cash Provided by (Used in) Investing Activities	(293)		667		(537)
Financing Activities
Net change in other short-term borrowings	(29)		(60)		(22)
Dividends paid on common shares	(430)		(402)		(422)
Dividends paid on preferred shares	(75)		(52)		(75)
Proceeds from issuance of long-term debt	697		0		1,099
Repayment of long-term debt	(500)		(1,250)		0
Repurchase of treasury stock and related forward contract	(1,605)		(661)		(850)
Other, net	(53)		3		2
Net Cash Provided (Used in) Provided by Financing Activities	(1,995)		(2,422)		(268)
Net (Decrease) Increase in Cash	(50)		2		128
Cash and Due from Banks at Beginning of Period	130		128		0
Cash and Due from Banks at End of Period	$ 80		$ 130		$ 128

[1] Includes $ 0 and $ 85 of cash and due from banks, $ 62 and $ 0 of other short-term investments, $ 1,297 and $ 1,216 of portfolio loans and leases, $ (6) and $ (26) of ALLL, $ 7 and $ 9 of other assets, $ 2 and $ 3 of other liabilities and $ 1,190 and $ 1,094 of long-term debt from consolidated VIEs that are included in their respective captions above at December 31, 2017 and 2016 , respectively. For further information, refer to Note 11 .