Financings and Capitalization (Major Long-Term Debt Transactions) (Details) (USD $) In Millions, unless otherwise specified		6 Months Ended								6 Months Ended					1 Months Ended	6 Months Ended	1 Months Ended		6 Months Ended
	Jun. 30, 2012 Debt Issuances [Member]	Jun. 30, 2012 Debt Retirements [Member]	Jun. 30, 2012 First Mortgage Bonds 2.85% Due May 2022 [Member] Consumers Energy Company [Member]	Jun. 30, 2012 First Mortgage Bonds 5% Due February 2012 [Member] Consumers Energy Company [Member]	Jun. 30, 2012 First Mortgage Bonds 5.375% Due April 2013 [Member] Consumers Energy Company [Member]	Jul. 25, 2012 Bond Purchase Agreement [Member] First Mortgage Bonds 3.19% Due 2024 [Member] Consumers Energy Company [Member]	Jul. 25, 2012 Bond Purchase Agreement [Member] First Mortgage Bonds 3.39% Due 2027 [Member] Consumers Energy Company [Member]	Jul. 25, 2012 Bond Purchase Agreement [Member] First Mortgage Bonds 4.31% Due 2042 [Member] Consumers Energy Company [Member]	Dec. 31, 2011 Term Loan $180 Million [Member]	Jun. 30, 2012 Senior Notes 5.05% Due March 2022 [Member] Debt Issuances [Member]	Jun. 30, 2012 Term Loan Facility Due December 2016 [Member] Debt Issuances [Member]		Jun. 30, 2012 Senior Notes 2.875% Due December 2024 [Member] Debt Retirements [Member]		Jul. 25, 2012 Senior Notes Variable Rate Due January 2013 [Member] Repayment of Debt [Member]	Jun. 30, 2012 Senior Notes Variable Rate Due January 2013 [Member] Repayment of Debt [Member]	Jun. 30, 2012 Short Term Credit Agreement Due March Two Thousand Thirteen [Member] Consumers Energy Company [Member]	Jul. 25, 2012 Short Term Credit Agreement Due March Two Thousand Thirteen [Member] Debt Drawn [Member] Consumers Energy Company [Member]	Jun. 30, 2012 Trust Preferred Securities [Member] Debt Retirements [Member]
Debt Issuance, Principal	$ 705		$ 375			$ 52	$ 35	$ 263		$ 300	$ 30	[1],[2]
Interest Rate			2.85%	5.00%	5.38%	3.19%	3.39%	4.31%		5.05%			2.88%	[3]					7.75%
Debt Issuance Date			May 01, 2012							Mar. 01, 2012	Feb. 01, 2012	[1],[2]
Maturity Date			May 2022	February 2012	April 2013					March 2022	December 2016	[1],[2]	December 2024	[3]		January 2013	March 2013		July 2027
Debt Retirement, Principal		930		300	375								226	[3]	150				29
Debt Retirement Date				February 2012	May 2012								January 2012and April 2012	[3]					February 2012
Term loan credit agreement									180
LIBOR plus									2.50%
Amount of Facility																	375
Short Term Credit Agreement, Amount Drawn																		$ 350

[1] In December 2011, CMS Energy entered into a $180 million term loan credit agreement that provides for delayed draws through July 20, 2012. Outstanding borrowings bear interest at an annual interest rate of LIBOR plus 2.5 percent.

[2] CMS Energy used these proceeds to retire the 7.75 percent Trust Preferred Securities.

[3] CMS Energy's contingently convertible notes. See the "Contingently Convertible Securities" section in this Note for further discussion of the conversions.