Financial Instruments (Summary Of Sales Activity For Investment Securities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Financial Instruments [Line Items]
Proceeds from DB SERP investments	$ 146	$ 0	$ 0
Consumers Energy Company
Financial Instruments [Line Items]
Proceeds from DB SERP investments	106	0	0
DB SERP
Financial Instruments [Line Items]
Proceeds from DB SERP investments	142	145	6
DB SERP | Consumers Energy Company
Financial Instruments [Line Items]
Proceeds from DB SERP investments	$ 103	$ 105	$ 4