XML 156 R109.htm IDEA: XBRL DOCUMENT v3.6.0.2
Retirement Benefits (Schedule Of Plan Contributions) (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]      
Postretirement benefits contributions $ 108 $ 262 $ 32
Consumers Energy Company [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement benefits contributions 98 243 29
OPEB [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement benefits contributions   29 25
OPEB [Member] | Consumers Energy Company [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement benefits contributions   29 $ 25
DB Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement benefits contributions 100 225  
DB Pension Plan [Member] | Consumers Energy Company [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Postretirement benefits contributions $ 93 $ 209  
Equity Securities [Member] | Postretirement Health Trusts [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 50.00%    
Equity Securities [Member] | Postretirement Life Trusts [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 42.00%    
Equity Securities [Member] | DB Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 53.00%    
Fixed Income Funds [Member] | Postretirement Health Trusts [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 30.00%    
Fixed Income Funds [Member] | Postretirement Life Trusts [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 28.00%    
Fixed Income Funds [Member] | DB Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 32.00%    
Alternative Strategy Investments [Member] | Postretirement Health Trusts [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 20.00%    
Alternative Strategy Investments [Member] | Postretirement Life Trusts [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 30.00%    
Alternative Strategy Investments [Member] | DB Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Target Plan Asset Allocations 15.00%