Financial Instruments (Schedule Of Investment Securities) (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Available for sale
Held-to-maturity Securities		$ 19	$ 16
Held to maturity
Unrealized Gains		0	0
Unrealized Losses		0	0
Securities held to maturity		19	16
Consumers Energy Company
Held to maturity
Investments		1	21
Common Stock | Consumers Energy Company
Available for sale
CMS Energy common stock cost	[1]		2
CMS Energy common stock - unrealized gains	[1]		19
CMS Energy Common Stock - unrealized losses	[1]		0
CMS Energy common stock - Fair Value	[1]		21
DB SERP
Available for sale
Cost		135	141
Unrealized Gains		0	0
Unrealized Losses		(2)	0
Fair Value	[2]	133	141
DB SERP | Consumers Energy Company
Available for sale
Cost		98	102
Unrealized Gains		0	0
Unrealized Losses		(1)	0
Fair Value	[2]	$ 97	102
Accounting Standards Update 2016-01 | Consumers Energy Company
Held to maturity
Cumulative effect of change in accounting principle			$ 19

[1] In January 2018, Consumers implemented ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities. In accordance with the standard, as of January 1, 2018, Consumers removed a $19 million unrealized gain on its investment in CMS Energy common stock from AOCI and recorded the gain in retained earnings. For further details on CMS Energy’s and Consumers’ accounting for this new standard, see Note 1, New Accounting Standards.In January 2018, Consumers transferred substantially all of its shares in CMS Energy common stock to a related charitable foundation. Consumers’ remaining equity investment in CMS Energy common stock was $1 million at June 30, 2018. There were no material changes in the fair value of Consumers’ investment in CMS Energy common stock during the six months ended June 30, 2018.

[2] 1 All assets and liabilities were classified as Level 1 with the exception of some commodity contracts, which were classified as Level 3.