Financings and Capitalization (Preferred Stock of Subsidiary) (Details) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Par value of Preferred Stock	$ 0.01
Shares of Preferred Stock authorized	10,000,000
Consumers Energy Company [Member]
Par value of Preferred Stock	$ 100	$ 100
Shares of Preferred Stock authorized	7,500,000	7,500,000
Preferred stock Value	$ 44	$ 44
$4.16 Series [Member] | Consumers Energy Company [Member]
Optional Redemption Price	$ 103.25	$ 103.25
Number of Shares	68,451	68,451
Preferred stock Value	7	7
$4.50 Series [Member] | Consumers Energy Company [Member]
Optional Redemption Price	$ 110.00	$ 110.00
Number of Shares	373,148	373,148
Preferred stock Value	$ 37	$ 37