Parent Company Financial Information - Parent Company Condensed Statements of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows From Operating Activities:
Net income	$ 3,237	$ 3,257	$ 2,415
Adjustments to reconcile net income to net cash from operating activities:
Other, net	32	(578)	(120)
Net Cash Provided by (Used in) Operating Activities	1,520	4,349	4,635
Cash Flows From Investing Activities:
Proceeds from maturities, calls and paydowns of AFS securities	4,797	3,674	4,800
Proceeds from maturities, calls and paydowns of HTM securities	2,499	2,442	2,580
Net cash from acquisitions and divestitures	6,256	(296)	0
Payments for (Proceeds from) Other Investing Activities	(6)	139	132
Net Cash Provided by (Used in) Investing Activities	8,348	(4,963)	(5,410)
Cash Flows From Financing Activities:
Proceeds from (Repayments of) Other Debt	6,293	240	3,532
Payments for Repurchase of Common Stock	0	1,205	1,613
Proceeds from Issuance of Preferred Stock and Preference Stock	1,683	0	0
Payments for Repurchase of Preferred Stock and Preference Stock	1,725	0	0
Other, net	(175)	(229)	123
Net Cash Provided by (Used in) Financing Activities	5,353	1,502	(549)
Cash and Cash Equivalents, at Carrying Value	19,065	3,844	2,956	$ 4,280
Parent Company
Cash Flows From Operating Activities:
Net income	3,237	3,257	2,415
Adjustments to reconcile net income to net cash from operating activities:
Equity in earnings of subsidiaries in excess of dividends from subsidiaries	(1,968)	(508)	(558)
Other, net	84	(28)	0
Net Cash Provided by (Used in) Operating Activities	1,353	2,721	1,857
Cash Flows From Investing Activities:
Proceeds from maturities, calls and paydowns of AFS securities	157	33	29
Purchases of AFS securities	(79)	(28)	(29)
Proceeds from maturities, calls and paydowns of HTM securities	0	0	0
Payments to Acquire Equity Method Investments	1	0	0
Investment in subsidiaries	(1)	0	1,100
Advances to subsidiaries	(5,358)	(4,639)	(6,958)
Proceeds from repayment of advances to subsidiaries	8,304	3,665	4,671
Net cash from acquisitions and divestitures	1,903	0	0
Payments for (Proceeds from) Other Investing Activities	0	4	(1)
Net Cash Provided by (Used in) Investing Activities	4,925	(973)	(1,186)
Cash Flows From Financing Activities:
Proceeds from (Repayments of) Other Debt	53	(5)	(39)
Net change in long-term debt	370	1,746	1,319
Payments for Repurchase of Common Stock	0	1,205	1,613
Proceeds from Issuance of Preferred Stock and Preference Stock	1,683	0	0
Payments for Repurchase of Preferred Stock and Preference Stock	1,725	0	0
Cash dividends paid on common and preferred stock	(1,459)	(1,378)	(1,179)
Other, net	(40)	(52)	104
Net Cash Provided by (Used in) Financing Activities	(1,118)	(894)	(1,408)
Cash and Cash Equivalents, Period Increase (Decrease)	5,160	854	(737)
Cash and Cash Equivalents, at Carrying Value	$ 12,392	$ 7,232	$ 6,378	$ 7,115