Annual report pursuant to Section 13 and 15(d)

BENEFIT PLANS - Narrative (Details)

v3.6.0.2
BENEFIT PLANS - Narrative (Details)
 12 Months Ended
Dec. 31, 2016
USD ($)
age
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Aug. 16, 2016
USD ($)
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Fair Value of Plan Assets $ 745,725,000 $ 594,217,000    
Employer Contributions 150,000,000      
Amount to be Amortized from Accumulated Other Comprehensive Income (Loss) Next Fiscal Year:        
Future amortization of transition obligation (asset) 0      
Future amortization of prior service cost (credit) 2,000,000      
Future amortization gain (loss) $ 7,000,000      
Defined Contribution Plan:        
Employer matching contribution, percent of match 4.00%      
Discretionary profit-share contribution, percent of annual base pay 1.00% 1.00%    
Pension Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Fair Value of Plan Assets $ 745,725,000 $ 594,217,000 $ 653,013,000  
Employer Contributions 150,000,000 0    
Accumulated benefit obligation 736,000,000 755,000,000    
Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets:        
Accumulated benefit obligations in excess of plan assets, aggregate projected benefit obligation 9,000,000      
Defined benefit plan expenses 2,000,000 4,000,000 2,000,000  
Estimated net periodic pension cost in next fiscal year $ 14,000,000      
Defined Benefit Plan, Information about Plan Assets:        
Average duration of plan assets investment in bonds, years 14 years 2 months 3 days      
Estimated life of benefit obligations 12 years 8 months      
Pension Benefits | Equity securities        
Defined Benefit Plan, Information about Plan Assets:        
Actual plan asset allocations 44.00%      
Target plan asset allocations range minimum 20.00%      
Target plan asset allocations range maximum 50.00%      
Pension Benefits | Bonds        
Defined Benefit Plan, Information about Plan Assets:        
Actual plan asset allocations 54.00%      
Target plan asset allocations range minimum 50.00%      
Target plan asset allocations range maximum 80.00%      
Pension Benefits | Cash and cash equivalents        
Defined Benefit Plan, Information about Plan Assets:        
Actual plan asset allocations 2.00%      
Post-Retirement Benefits        
Defined Benefit Plan Disclosure [Line Items]        
Healthcare and life insurance benefits, employee retirement age | age 55      
Healthcare and life insurance benefits, requisite service period 10 years      
Life insurance coverage, maximum $ 50,000      
Reduction in liability due to plan amendment 5,000,000      
Defined Benefit Plan, Information about Plan Assets:        
Estimated future employer contributions in next fiscal year $ 0      
Defined Benefit Plan, Assumed Health Care Cost Trend Rates:        
Health care cost trend rate assumed for next fiscal year 6.80%      
Ultimate health care cost trend rate 4.50%      
Year that rate reaches ultimate trend rate 2028      
Supplemental Executive Retirement Plan        
Pension Plans with Accumulated Benefit Obligations in Excess of Plan Assets:        
Defined benefit plan expenses $ 1,000,000 1,000,000 $ 1,000,000  
Defined Benefit Plan, Assumed Health Care Cost Trend Rates:        
Accrued pension liability $ 33,000,000 $ 34,000,000    
FirstMerit Bank        
Defined Benefit Plan Disclosure [Line Items]        
Defined Benefit Plan, Fair Value of Plan Assets       $ 280,000,000