CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	3 Months Ended				9 Months Ended		12 Months Ended
	Sep. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Operating Activities
Net income	$ 235	$ 236	$ 539	$ 16	$ 781	$ 612
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Provision for credit losses					(245)	502
Deferred income tax expense (benefit)					(28)	(82)
Depreciation and amortization of premises and equipment					46	37
Amortization of intangible assets	14		15		42	25
Net other amortization and accretion					(50)	(18)
Net (increase) decrease in derivatives					309	(325)
Purchase accounting gain	0		(532)		1	(532)
Stock-based compensation expense					31	23
Securities (gains) losses, net					(12)	2
Gain (loss) on extinguishment of debt	23		0		23	0
Net (gains) losses on sale/disposal of fixed assets					32	7
(Gain) loss on BOLI					(5)	(4)
Loans held for sale:
Purchases and originations					(4,682)	(2,780)
Gross proceeds from settlements and sales					3,288	1,578
(Gain) loss due to fair value adjustments and other					(142)	(43)
Other operating activities, net					1,179	725
Total adjustments					(213)	(885)
Net cash provided by (used in) operating activities					568	(273)
Investing Activities
Proceeds from sales of securities available for sale	35		240		68	249
Proceeds from maturities of securities available for sale					1,680	2,993
Purchases of securities available for sale					(2,343)	(3,166)
Purchases of securities held to maturity					(304)	0
Proceeds from prepayments of securities held to maturity					10	0
Proceeds from sales of premises and equipment					22	9
Purchases of premises and equipment					(46)	(35)
Proceeds from BOLI					12	8
Net (increase) decrease in loans and leases					2,891	(2,310)
Net increase in interest-bearing deposits with banks					(6,478)	(3,013)
Cash received for acquisitions, net					0	1,806
Other investing activities, net					15	10
Net cash used in investing activities					(4,473)	(3,449)
Common stock:
Stock options exercised					25	4
Cash dividends paid					(252)	(139)
Repurchase of shares					(272)	(4)
Cancellation of common shares					0	(8)
Preferred stock:
Preferred stock issuance					145	145
Cash dividends paid - preferred stock - noncontrolling interest					(9)	(9)
Cash dividends paid - preferred stock					(24)	(8)
Net increase in deposits					4,287	5,561
Net increase (decrease) in short-term borrowings					27	(1,585)
Proceeds from issuance of term borrowings					0	1,241
Increases (decreases) in term borrowings					(112)	(1,075)
Net cash provided by financing activities					3,815	4,123
Net increase (decrease) in cash and cash equivalents					(90)	401
Cash and cash equivalents at beginning of period		$ 1,648		$ 1,267	1,648	1,267	$ 1,267
Cash and cash equivalents at end of period	$ 1,558		$ 1,668		1,558	1,668	$ 1,648
Supplemental Disclosures
Total interest paid					128	181
Total taxes paid					254	90
Total taxes refunded					28	1
Transfer from loans to OREO					3	2
Transfer from loans HFS to trading securities					1,490	1,083
Transfer from loans to loans HFS					$ (31)	$ 4