Regulatory Capital and Reserve Requirements (Tables)

12 Months Ended

Dec. 31, 2017

Banking and Thrift [Abstract]

Corporation's and Chemical Bank's actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy

The summary below compares the actual capital amounts and ratios with the quantitative measures established by regulation to ensure capital adequacy:

	Actual				Minimum Required for Capital Adequacy Purposes				Minimum Required for Capital Adequacy Purposes Plus Capital Conservation Buffer				Required to be Well Capitalized Under Prompt Corrective  Action Regulations
(Dollars in thousands)	Capital Amount		Ratio		Capital Amount		Ratio		Capital Amount		Ratio		Capital Amount		Ratio
December 31, 2017
Total Capital to Risk-Weighted Assets
Corporation	$	1,614,046	11.0	%	$	1,179,076	8.0	%	$	1,363,307	9.3	%	N/A		N/A
Chemical Bank	1,613,087		11.0		1,176,361		8.0		1,360,167		9.3		$	1,470,451	10.0	%
Tier 1 Capital to Risk-Weighted Assets
Corporation	1,498,463		10.2		884,307		6.0		1,068,538		7.3		N/A		N/A
Chemical Bank	1,513,219		10.3		882,271		6.0		1,066,077		7.3		1,176,361		8.0
Common Equity Tier 1 Capital to Risk-Weighted Assets
Corporation	1,498,463		10.2		663,230		4.5		847,461		5.8		N/A		N/A
Chemical Bank	1,513,219		10.3		661,703		4.5		845,509		5.8		955,793		6.5
Leverage Ratio
Corporation	1,498,463		8.3		720,890		4.0		720,890		4.0		N/A		N/A
Chemical Bank	1,513,219		8.4		720,043		4.0		720,043		4.0		900,053		5.0
December 31, 2016
Total Capital to Risk-Weighted Assets
Corporation	$	1,543,018	11.5	%	$	1,073,431	8.0	%	$	1,157,293	8.6	%	N/A		N/A
Chemical Bank	1,608,980		12.0		1,068,560		8.0		$	1,152,041	8.6		$	1,335,700	10.0	%
Tier 1 Capital to Risk-Weighted Assets
Corporation	1,441,209		10.7		805,073		6.0		888,935		6.6		N/A		N/A
Chemical Bank	1,522,711		11.4		801,420		6.0		884,901		6.6		1,068,560		8.0
Common Equity Tier 1 Capital to Risk-Weighted Assets
Corporation	1,441,209		10.7		603,805		4.5		687,667		5.1		N/A		N/A
Chemical Bank	1,522,711		11.4		601,065		4.5		684,546		5.1		868,205		6.5
Leverage Ratio
Corporation	1,441,209		9.0		643,603		4.0		643,603		4.0		N/A		N/A
Chemical Bank	1,522,711		9.5		641,457		4.0		641,457		4.0		801,822		5.0