Contingencies And Commitments (Expected Remediation Cost By Year) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 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 in next fiscal year	11
Undiscounted amount due within two year	11
Undiscounted amount due within third year	20
Undiscounted amount due within fourth year	11
Undiscounted amount due within five year	$ 10