Contingencies And Commitments (Expected Remediation Cost By Year) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013
Site Contingency [Line Items]
Undiscounted amount due in next fiscal year	$ 12
Undiscounted amount due within two year	4
Undiscounted amount due within third year	4
Undiscounted amount due within fourth year	4
Undiscounted amount due within five year	4
Manufactured Gas Plant [Member] | Consumers Energy Company [Member]
Site Contingency [Line Items]
Undiscounted amount due within one year	9
Undiscounted amount due within two year	9
Undiscounted amount due within third year	16
Undiscounted amount due within fourth year	10
Undiscounted amount due within five year	$ 9