Business Segment Information - Amounts of Consolidated Revenue, Expense, Tax and Assets by Segment (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Net interest income (expense)	$ 508	$ 303
Provision for credit losses	(45)	154
Noninterest income	298	174
Noninterest expense (a)	544	302
Income (loss) before income taxes	307	21
Income tax expense	71	5
Net income	236	16
Average assets	85,401	43,552
Regional Banking
Disaggregation of Revenue [Line Items]
Net interest income (expense)	426	194
Provision for credit losses	(32)	98
Noninterest income	100	73
Noninterest expense (a)	272	173
Income (loss) before income taxes	286	(4)
Income tax expense	66	(2)
Net income	220	(2)
Average assets	42,371	19,044
Specialty Banking
Disaggregation of Revenue [Line Items]
Net interest income (expense)	159	109
Provision for credit losses	(7)	54
Noninterest income	185	104
Noninterest expense (a)	154	111
Income (loss) before income taxes	197	48
Income tax expense	47	11
Net income	150	37
Average assets	21,503	16,890
Corporate
Disaggregation of Revenue [Line Items]
Net interest income (expense)	(77)	0
Provision for credit losses	(6)	2
Noninterest income	13	(3)
Noninterest expense (a)	118	18
Income (loss) before income taxes	(176)	(23)
Income tax expense	(42)	(4)
Net income	(134)	(19)
Average assets	21,527	$ 7,618
Asset impairment charges	$ 33