|
Financial Instruments (Schedule Of Investment Securities) (Details) (USD $)
In Millions, unless otherwise specified
|
Sep. 30, 2013
|
Dec. 31, 2012
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Held to maturity Debt securities - Cost |
$ 10 |
$ 9 |
| Held to maturity Debt securities - Unrealized Gains |
|
1 |
| Held to maturity Debt securities - Unrealized Losses |
|
|
| Held to maturity Debt securities - Fair Value |
10 |
10 |
|
CMS Energy Common Stock [Member] | Consumers Energy Company [Member]
|
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available for sale - Cost |
5 |
6 |
| Available for sale - Unrealized Gains |
24 |
26 |
| Available for sale - Unrealized Losses |
|
|
| Available for sale - Fair Value |
29 |
32 |
|
Supplemental Executive Retirement Plan [Member] | Mutual Fund [Member]
|
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available for sale - Cost |
137 |
123 |
| Available for sale - Unrealized Gains |
|
3 |
| Available for sale - Unrealized Losses |
|
|
| Available for sale - Fair Value |
137 |
126 |
|
Supplemental Executive Retirement Plan [Member] | Mutual Fund [Member] | Consumers Energy Company [Member]
|
|
|
| Schedule of Trading Securities and Other Trading Assets [Line Items] |
|
|
| Available for sale - Cost |
96 |
83 |
| Available for sale - Unrealized Gains |
|
2 |
| Available for sale - Unrealized Losses |
|
|
| Available for sale - Fair Value |
$ 96 |
$ 85 |