Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended						3 Months Ended		6 Months Ended		12 Months Ended
	Mar. 31, 2017	Feb. 28, 2017	Jan. 31, 2017	Sep. 30, 2016	Aug. 31, 2016	Mar. 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016	May 31, 2017
Public Utilities, General Disclosures [Line Items]
Regulatory liability current							$ 85		$ 85		$ 95
Accrued rate refunds							77		77		21
Revenue							1,449	$ 1,371	3,278	$ 3,172
Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current							85		85		95
Accrued rate refunds							77		77		21
Revenue							1,362	$ 1,293	3,099	$ 3,016
2016 Electric Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested						$ 225
Rate of return on equity requested						10.70%
Annual rate increase self-implemented				$ 170
Annual rate increase authorized		$ 113
Rate of return on equity authorized		10.10%
2016 Electric Rate Case [Member] | Revenue Subject To Refund [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory liability current							$ 17		$ 17
Gas Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase requested					$ 90
Amended Annual Rate Increase Request	$ 80
Rate of return on equity requested					10.60%
Investment recovery, 2018					$ 35
Investment recovery, 2019					$ 35
Annual rate increase self-implemented			$ 20
Gas Rate Case [Member] | Consumers Energy Company [Member] | Maximum [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase self-implemented			$ 20
Energy Optimization [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Requested recovery/collection												$ 18
Revenue											$ 18
Depreciation Rate Case [Member] | Consumers Energy Company [Member]
Public Utilities, General Disclosures [Line Items]
Annual rate increase authorized	$ (3)
FERC Transmission Order [Member] | Consumers Energy Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Rate of return on equity authorized				10.32%	12.38%
Power Supply Cost Recover (PSCR) [Member] | Consumers Energy Company [Member] | Electric Transmission [Member]
Public Utilities, General Disclosures [Line Items]
Accrued rate refunds		$ 28