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Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Level 3 Inputs) (Details) (Fair Value, Inputs, Level 3 [Member], USD $)
In Millions, unless otherwise specified |
3 Months Ended | 9 Months Ended | ||||||||
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Sep. 30, 2012
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Sep. 30, 2011
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Sep. 30, 2012
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Sep. 30, 2011
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| Balance at beginning of period | $ 3 | $ (2) | $ (3) | |||||||
| Total gains (losses) included in earnings | (1) | [1] | (1) | [1] | 1 | [1] | (1) | [1] | ||
| Total gains (losses) offset through regulatory accounting | 1 | (1) | 8 | 1 | ||||||
| Purchases | 1 | |||||||||
| Settlements | (2) | 1 | (6) | 1 | ||||||
| Balance at end of period | 1 | (1) | 1 | (1) | ||||||
| Unrealized gains (losses) included in earnings relating to assets and liabilities still held at end of period | (1) | [1] | (1) | [1] | 1 | [1] | ||||
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Consumers Energy Company [Member]
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| Balance at beginning of period | 5 | 3 | 2 | 1 | ||||||
| Total gains (losses) offset through regulatory accounting | 1 | (1) | 8 | 1 | ||||||
| Purchases | 1 | |||||||||
| Settlements | (2) | (6) | (1) | |||||||
| Balance at end of period | $ 4 | $ 2 | $ 4 | $ 2 | ||||||
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