Business Segment Information - Amounts of Consolidated Revenue, Expense, Tax and Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Net interest income (expense)	$ 492			$ 532			$ 1,496	$ 1,140
Provision for credit losses	(85)			227			(245)	502
Noninterest income	247			823			829	1,204
Noninterest expense	526			587			1,567	1,210
Income before income taxes	298			541			1,003	632
Income tax expense (benefit)	63			2			222	20
Net income	235	$ 311	$ 236	539	$ 57	$ 16	781	612
Average assets	88,401			81,683			87,131	57,810
Regional Banking
Disaggregation of Revenue [Line Items]
Net interest income (expense)	444			448			1,314	853
Provision for credit losses	(52)			194			(172)	394
Noninterest income	112			97			320	239
Noninterest expense	301			301			851	639
Income before income taxes	307			50			955	59
Income tax expense (benefit)	72			9			223	7
Net income	235			41			732	52
Average assets	40,722			43,703			41,757	27,962
Specialty Banking
Disaggregation of Revenue [Line Items]
Net interest income (expense)	154			161			464	400
Provision for credit losses	(33)			34			(61)	106
Noninterest income	142			181			476	410
Noninterest expense	141			138			441	359
Income before income taxes	188			170			560	345
Income tax expense (benefit)	45			41			135	84
Net income	143			129			425	261
Average assets	20,460			21,693			20,669	18,885
Corporate
Disaggregation of Revenue [Line Items]
Net interest income (expense)	(106)			(77)			(282)	(113)
Provision for credit losses	0			(1)			(12)	2
Noninterest income	(7)			545			33	555
Noninterest expense	84			148			275	212
Income before income taxes	(197)			321			(512)	228
Income tax expense (benefit)	(54)			(48)			(136)	(71)
Net income	(143)			369			(376)	299
Average assets	$ 27,219			$ 16,287			24,705	$ 10,963
Asset impairment charges							$ 35