Operating Segments (Details) - USD ($) $ in Millions		3 Months Ended				6 Months Ended
		Jun. 30, 2020		Jun. 30, 2019		Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		$ 3,448		$ 1,690		$ 7,098	$ 3,386
Allocated provision for credit losses		844		172		1,737	327
Segment net interest income after provision		2,604		1,518		5,361	3,059
Noninterest income		2,423		1,352		4,384	2,554
Total noninterest expense		3,878		1,751		7,309	3,519
Income before income taxes		1,149		1,119		2,436	2,094
Provision for income taxes		191		234		415	411
Net income		958		885		2,021	1,683
Identifiable assets (period end)		504,336				504,336		$ 473,078
CB&W
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		1,843		835		3,703	1,663
C&CB
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		1,351		751		2,885	1,491
IH
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		33		35		69	69
OT&C
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		221	[1]	69	[1]	441	163
Operating Segments
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		3,448		1,690		7,098	3,386
Allocated provision for credit losses		844		172		1,737	327
Segment net interest income after provision		2,604		1,518		5,361	3,059
Noninterest income		2,423		1,352		4,384	2,554
Total noninterest expense		3,878		1,751		7,309	3,519
Income before income taxes		1,149		1,119		2,436	2,094
Provision for income taxes		191		234		415	411
Net income		958		885		2,021	1,683
Identifiable assets (period end)		504,336		230,872		504,336	230,872
Operating Segments | CB&W
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		2,156		1,045		4,406	2,066
Allocated provision for credit losses		270		123		707	254
Segment net interest income after provision		1,886		922		3,699	1,812
Noninterest income		1,006		580		2,073	1,086
Total noninterest expense		1,969		898		3,957	1,778
Income before income taxes		923		604		1,815	1,120
Provision for income taxes		218		146		428	272
Net income		705		458		1,387	848
Identifiable assets (period end)		167,665		78,608		167,665	78,608
Operating Segments | C&CB
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		1,296		642		2,631	1,278
Allocated provision for credit losses		533		51		932	71
Segment net interest income after provision		763		591		1,699	1,207
Noninterest income		624		251		1,084	494
Total noninterest expense		884		326		1,771	641
Income before income taxes		503		516		1,012	1,060
Provision for income taxes		94		107		185	220
Net income		409		409		827	840
Identifiable assets (period end)		198,843		86,501		198,843	86,501
Operating Segments | IH
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		23		25		48	47
Allocated provision for credit losses		6		2		7	4
Segment net interest income after provision		17		23		41	43
Noninterest income		598		570		1,155	1,085
Total noninterest expense		449		444		889	861
Income before income taxes		166		149		307	267
Provision for income taxes		41		38		77	68
Net income		125		111		230	199
Identifiable assets (period end)		7,360		7,162		7,360	7,162
Operating Segments | OT&C
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income	[1]	(27)		(22)		13	(5)
Allocated provision for credit losses		35	[1]	(4)	[1]	91	(2)
Segment net interest income after provision	[1]	(62)		(18)		(78)	(3)
Noninterest income		195	[1]	(49)	[1]	72	(111)
Total noninterest expense		576	[1]	83	[1]	692	239
Income before income taxes	[1]	(443)		(150)		(698)	(353)
Provision for income taxes		(162)	[1]	(57)	[1]	(275)	(149)
Net income	[1]	(281)		(93)		(423)	(204)
Identifiable assets (period end)		130,468		58,601		130,468	58,601
Intersegment Eliminations
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		0		0		0	0
Intersegment Eliminations | CB&W
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		313		210		703	403
Intersegment Eliminations | C&CB
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		(55)		(109)		(254)	(213)
Intersegment Eliminations | IH
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		(10)		(10)		(21)	(22)
Intersegment Eliminations | OT&C
Segment Reporting, Revenue Reconciling Item [Line Items]
Net Interest Income		$ (248)	[1]	$ (91)	[1]	$ (428)	$ (168)

[1] Includes financial data from business units below the quantitative and qualitative thresholds requiring disclosure.