Consolidated Statements of Equity - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment		Cumulative Effect, Period of Adoption, Adjusted Balance	Series B Preferred Stock	Series C Preferred Stock	Total	Total Cumulative Effect, Period of Adoption, Adjustment		Total Cumulative Effect, Period of Adoption, Adjusted Balance	Total Series B Preferred Stock	Total Series C Preferred Stock	Preferred Stock	Preferred Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Preferred Stock Series B Preferred Stock	Common Stock	Common Stock Cumulative Effect, Period of Adoption, Adjusted Balance	Additional Paid-in Capital	Additional Paid-in Capital Cumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment		Retained Earnings Cumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings Series B Preferred Stock	Retained Earnings Series C Preferred Stock	Accumulated Other Comprehensive Income (Loss)	Accumulated Other Comprehensive Income (Loss) Cumulative Effect, Period of Adoption, Adjusted Balance	Treasury Stock and Other	Treasury Stock and Other Cumulative Effect, Period of Adoption, Adjusted Balance	Non-controlling Interest	Non-controlling Interest Cumulative Effect, Period of Adoption, Adjustment	[1]	Non-controlling Interest Cumulative Effect, Period of Adoption, Adjusted Balance
Balance (in shares) at Dec. 31, 2017													4,007,000	4,007,000		87,473,708	87,473,708
Balance, beginning of period at Dec. 31, 2017	$ 2,680,584	$ (116)		$ 2,680,468			$ 2,662,757	$ (116)		$ 2,662,641			$ 265,821	$ 265,821		$ 87,474	$ 87,474	$ 791,465	$ 791,465	$ 1,577,311	$ (116)		$ 1,577,195			$ (18,517)	$ (18,517)	$ (40,797)	$ (40,797)	$ 17,827			$ 17,827
Increase (Decrease) in Equity
Net income	315,628						304,358													304,358										11,270
Other comprehensive income (loss), net of tax	(14,621)						(14,621)																			(14,621)
Net investment by (distribution to) non-controlling interest	(10,638)																													(10,638)
Redemption of Series B Preferred Stock (in shares)															(4,000,000)
Redemption of Series B Preferred Stock					$ (100,000)						$ (100,000)				$ (96,519)									$ (3,481)
Repurchases of shares of common stock	$ (212,929)						(212,929)																					(212,929)
Repurchases of shares of common stock (in shares)	4,668,723
Dividends on Preferred Stock					$ (1,613)	$ (9,975)					$ (1,613)	$ (9,975)												$ (1,613)	$ (9,975)
Dividends on common stock	$ (99,490)						(99,490)													(99,490)
Common stock warrants exercised (in shares)																553,279
Common stock warrants exercised																$ 553		(553)
Common shares purchased by TCF employee benefit plans (in shares)																17,594
Common shares purchased by TCF employee benefit plans	715						715									$ 18		697
Stock compensation plans, net of tax (in shares)																153,879
Stock compensation plans, net of tax	8,715						8,715									$ 153		8,184										378
Change in shares held in trust for deferred compensation plans, at cost																		(1,166)										1,166
Balance (in shares) at Dec. 31, 2018													7,000			88,198,460
Balance, end of period at Dec. 31, 2018	2,556,260						2,537,801						$ 169,302			$ 88,198		798,627		1,766,994						(33,138)		(252,182)		18,459
Increase (Decrease) in Equity
Net income	306,926						295,468													295,468										11,458
Other comprehensive income (loss), net of tax	87,415						87,415																			87,415
Reverse merger with Chemical Financial Corporation (in shares)																65,539,678
Reverse merger with Chemical Financial Corporation	3,018,556						3,018,556									$ 65,540		2,687,153										265,863
Net investment by (distribution to) non-controlling interest	(9,691)																													(9,691)
Repurchases of shares of common stock	$ (86,309)						(86,309)									$ (658)		(26,846)										(58,805)
Repurchases of shares of common stock (in shares)	2,111,725															(657,817)
Dividends on Preferred Stock						(9,975)						(9,975)													(9,975)
Dividends on common stock	$ (156,060)						(156,060)													(156,060)
Stock compensation plans, net of tax (in shares)																(114,750)
Stock compensation plans, net of tax	20,119						20,119									$ (114)		4,474										15,759
Change in shares held in trust for deferred compensation plans, at cost																		(1,328)										1,328
Balance (in shares) at Dec. 31, 2019													7,000	7,000		152,965,571	152,965,571
Balance, end of period at Dec. 31, 2019	$ 5,727,241	$ (159,249)	[1]	$ 5,567,992			5,707,015	$ (159,323)	[1]	$ 5,547,692			$ 169,302	$ 169,302		$ 152,966	$ 152,966	3,462,080	$ 3,462,080	1,896,427	$ (159,323)	[1]	$ 1,737,104			54,277	$ 54,277	(28,037)	$ (28,037)	20,226	$ 74		$ 20,300
Increase (Decrease) in Equity
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Net income	$ 230,041						222,759													222,759										7,282
Other comprehensive income (loss), net of tax	128,396						128,396																			128,396
Net investment by (distribution to) non-controlling interest	(9,098)																													(9,098)
Repurchases of shares of common stock	$ (33,098)						(33,098)									$ (873)		(32,225)										0
Repurchases of shares of common stock (in shares)	873,376															873,376
Dividends on Preferred Stock						$ (9,975)						$ (9,975)													$ (9,975)
Dividends on common stock	$ (214,687)						(214,687)													(214,687)
Stock compensation plans, net of tax (in shares)																473,309
Stock compensation plans, net of tax	29,726						29,726									$ 473		29,253										0
Change in shares held in trust for deferred compensation plans, at cost																		(1,306)										1,306
Balance (in shares) at Dec. 31, 2020													7,000			152,565,504
Balance, end of period at Dec. 31, 2020	$ 5,689,297						$ 5,670,813						$ 169,302			$ 152,566		$ 3,457,802		$ 1,735,201						$ 182,673		$ (26,731)		$ 18,484

[1] See "Note 2. Summary of Significant Accounting Policies" for further information