Parent Company Financial Information - Parent Company Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows From Operating Activities:
Net income	$ 3,257	$ 2,415	$ 2,442
Adjustments to reconcile net income to net cash from operating activities:
Other, net	(202)	(120)	(292)
Net cash from operating activities	4,349	4,635	3,115
Cash Flows From Investing Activities:
Proceeds from maturities, calls, paydowns and sales of AFS securities	3,674	4,800	5,888
Proceeds from maturities, calls and paydowns of HTM securities	2,442	2,580	7,022
Net cash from acquisitions and divestitures	(296)	0	(726)
Other, net	(123)	(149)	371
Net cash from investing activities	(4,947)	(5,427)	(976)
Cash Flows From Financing Activities:
Net change in short-term borrowings	240	3,532	(3,581)
Repurchase of common stock	(1,205)	(1,613)	(520)
Net proceeds from preferred stock issued	0	0	450
Other, net	(229)	123	325
Net cash from financing activities	1,502	(549)	(1,882)
Net Change in Cash, Cash Equivalents and Restricted Cash	904	(1,341)	257
Cash and Cash Equivalents at Beginning of Period	3,083	4,424	4,167
Cash, Cash Equivalents and Restricted Cash at End of Period	3,987	3,083	4,424
Parent Company
Cash Flows From Operating Activities:
Net income	3,257	2,415	2,442
Adjustments to reconcile net income to net cash from operating activities:
Equity in earnings of subsidiaries in excess of dividends from subsidiaries	(508)	(558)	(1,188)
Other, net	(28)	0	(14)
Net cash from operating activities	2,721	1,857	1,240
Cash Flows From Investing Activities:
Proceeds from maturities, calls, paydowns and sales of AFS securities	33	29	27
Purchases of AFS securities	(28)	(29)	(31)
Proceeds from maturities, calls and paydowns of HTM securities	0	0	2
Investment in subsidiaries	0	1,100	(85)
Advances to subsidiaries	(4,639)	(6,958)	(7,719)
Proceeds from repayment of advances to subsidiaries	3,665	4,671	6,975
Net cash from acquisitions and divestitures	0	0	(254)
Other, net	(4)	1	0
Net cash from investing activities	(973)	(1,186)	(1,085)
Cash Flows From Financing Activities:
Net change in short-term borrowings	(5)	(39)	(60)
Net change in long-term debt	1,746	1,319	465
Repurchase of common stock	(1,205)	(1,613)	(520)
Net proceeds from preferred stock issued	0	0	450
Cash dividends paid on common and preferred stock	(1,378)	(1,179)	(1,092)
Other, net	(52)	104	225
Net cash from financing activities	(894)	(1,408)	(532)
Net Change in Cash, Cash Equivalents and Restricted Cash	854	(737)	(377)
Cash and Cash Equivalents at Beginning of Period	6,378	7,115	7,492
Cash, Cash Equivalents and Restricted Cash at End of Period	$ 7,232	$ 6,378	$ 7,115