Regulatory Matters (Narrative) (Details) $ in Millions		1 Months Ended								3 Months Ended								12 Months Ended
	Mar. 31, 2019 USD ($)	Oct. 31, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Apr. 30, 2019 USD ($)	Jan. 31, 2019 USD ($)	Nov. 30, 2018 USD ($)	Oct. 31, 2018 USD ($)	May 31, 2018 USD ($)	Dec. 31, 2019 USD ($) coal_fueled_electric_generating_unit site	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Mar. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) coal_fueled_electric_generating_unit site	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 site	Dec. 31, 2015 site	Dec. 31, 2013 USD ($)
Public Utilities, General Disclosures [Line Items]
Revenue										$ 1,795	$ 1,546	$ 1,445	$ 2,059	$ 1,829	$ 1,599	$ 1,492	$ 1,953	$ 6,845	$ 6,873	$ 6,583
Regulatory liability, noncurrent										3,742				3,681				3,742	3,681
Regulatory liabilities, current										87				155				87	155
Regulatory assets, noncurrent										2,489				1,743				2,489	1,743
Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Revenue										1,670	1,429	1,334	1,943	1,712	$ 1,502	$ 1,395	$ 1,855	$ 6,376	6,464	6,222
Number of units retired | site																		10
Regulatory liability, noncurrent										3,742				3,681				$ 3,742	3,681
Regulatory liabilities, current										87				155				87	155
Regulatory assets, noncurrent										$ 2,489				1,743				2,489	1,743
Purchased and interchange power																		1,470	1,587	1,491
Cost of gas sold																		$ 754	819	$ 730
Costs of coal-fueled electric generating units to be retired | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Number of units | coal_fueled_electric_generating_unit										2								2
Coal-Fueled Electric Generation | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Number of units retired | site																					7
Gas-Fueled Electric Generation | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Number of units retired | site																						3
Energy Waste Reduction Plan Incentive | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Authorized recovery collection										$ 34								$ 34
Revenue																		34	34
Requested recovery/collection										34								$ 34
Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized						$ (113)
Electric Rate Case Net Of TCJA Impact | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized						89
Electric Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized						$ (24)
Annual rate increase requested									$ 58
Rate of return on equity requested									10.75%
Annual rate increase requested, amended								$ 44
Rate of return on equity authorized						10.00%
Gas Rate Case | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized			$ 144
Annual rate increase requested							$ 229
Rate of return on equity requested							10.75%
Annual rate increase requested, amended					$ 204
Rate of return on equity authorized			9.90%
Gas Rate TCJA Adjustment | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized			$ (13)
PSCR overrecoveries | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Purchased and interchange power	$ 2,000	$ 1,900
Over (under) recovery authorized by the MPSC	$ (31)	$ 32											$ (31)
GCR underrecoveries | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Over (under) recovery authorized by the MPSC			1	$ (18)							1	$ (18)
Cost of gas sold			600	$ 600
Manufactured Gas Plant | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent														133					133
Gas Storage Inventory Adjustments | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory asset collection period																		5 years
Regulatory assets, noncurrent										3				4				$ 3	4
Renewable energy grant | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent										52				54				52	54
Proceeds from government grant																							$ 69
Revenue subject to refund tax reform rate change | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current							$ 31
Revenue subject to refund tax reform rate change | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liabilities, current														70					70
Income Taxes, Net | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent								1,600
Income Taxes, Net | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent								400
Income Taxes, Net | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent								1,200
Approved temporary bill credit			32
Income Taxes Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent								$ 1,700
Income Taxes Subject To Normalization | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability remaining book life								44 years
Income Taxes Subject To Normalization | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability remaining book life								27 years
Income Taxes Not Subject To Normalization | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory assets, noncurrent								$ 300
Income Taxes Not Subject To Normalization | Gas Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory asset collection period								44 years
Income Taxes Not Subject To Normalization | Electric Rate Case Tax Reform Rate Change | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory asset collection period								27 years
Taxes Not Related To Plant Assets | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent								$ 200
Regulatory liability remaining book life								10 years
TCJA reserve for refund | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Regulatory liability, noncurrent			$ 62							0	$ 62			35				0	35
Regulatory liabilities, current										$ 0				$ 98				$ 0	$ 98
Manufactured Gas Plant | Consumers Energy Company
Public Utilities, General Disclosures [Line Items]
Number of former MGPs | site										23								23
Regulatory asset collection period																		10 years
Regulatory assets, noncurrent										$ 130								$ 130