Parent Company Financial Statements (Condensed Statement of Cash Flow - Parent Company Only) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Operating Activities
Net income (loss)	$ 2,512	$ 2,193	$ 2,180
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
(Benefit from) provision for deferred income taxes	(246)	30	(252)
Net change in undistributed earnings	2	1	47
Net change in:
Equity securities	29	(132)	442
Other assets	(20)	(303)	22
Accrued expenses and other liabilities	(49)	147	(138)
Net change in:
Other short-term investments	(647)	928	1
Financing Activities
Dividends paid on common shares	(660)	(467)	(430)
Dividends paid on preferred shares	(93)	(98)	(75)
Proceeds from issuance of long-term debt	3,866	2,438	2,490
Repayment of long-term debt	(4,212)	(2,884)	(1,969)
Issuance of preferred stock	242	0	0
Repurchase of treasury stock and related forward contract	(1,763)	(1,453)	(1,605)
Other, net	(58)	(69)	(57)
Cash and Due from Banks at Beginning of Period	2,681	2,514	2,392
Cash and Due from Banks at End of Period	3,278	2,681	2,514
Parent Company Only
Operating Activities
Net income (loss)	2,512	2,193	2,180
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
(Benefit from) provision for deferred income taxes	(11)	3	2
Securities gains, net	(2)	0	0
Net change in undistributed earnings	(594)	(474)	34
Net change in:
Equity securities	(49)	0	0
Other assets	(80)	61	37
Accrued expenses and other liabilities	134	(116)	(15)
Net Cash Provided by (Used in) Operating Activities	1,910	1,667	2,238
Net change in:
Other short-term investments	(1,081)	(149)	(419)
Loans to subsidiaries	127	272	126
Net cash paid on acquisition	(469)	0	0
Net Cash Provided by (Used in) Investing Activities	(1,423)	123	(293)
Financing Activities
Net change in other short-term borrowings	106	(62)	(29)
Dividends paid on common shares	(660)	(467)	(430)
Dividends paid on preferred shares	(93)	(98)	(75)
Proceeds from issuance of long-term debt	2,235	895	697
Repayment of long-term debt	(500)	(500)	(500)
Issuance of preferred stock	242	0	0
Repurchase of treasury stock and related forward contract	(1,763)	(1,453)	(1,605)
Other, net	(56)	(65)	(53)
Net Cash Provided (Used in) Provided by Financing Activities	(489)	(1,750)	(1,995)
Net (Decrease) Increase in Cash	(2)	40	(50)
Cash and Due from Banks at Beginning of Period	120	80	130
Cash and Due from Banks at End of Period	$ 118	$ 120	$ 80