Financial Instruments (Schedule Of Investment Securities) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Held to maturity
Cost	$ 22	$ 16
Unrealized Gains	0	0
Unrealized Losses	1	0
Fair Value	21	16
Common Stock \| Consumers Energy Company
Debt Securities, Available-for-sale [Abstract]
CMS Energy common stock cost		2
CMS Energy common stock unrealized gains		19
CMS Energy common stock unrealized losses		0
CMS Energy common stock fair value		21
DB SERP
Debt Securities, Available-for-sale [Abstract]
Cost	0	141
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	0	141
DB SERP \| Consumers Energy Company
Debt Securities, Available-for-sale [Abstract]
Cost	0	102
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	$ 0	$ 102

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