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Consolidated Statements of Changes in Equity (Parenthetical) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009
Net gain (loss) arising during the period, tax | $ (7) | $ (6) | $ (3)
Amortization of net actuarial loss, tax | 1 | 0 | 0
Tax on prior service credit adjustment | 0 | 1 | 0
Unrealized gain (loss) on investments, tax expense (tax benefit) | 0 | 0 | 3
Reclassification adjustments included in net income, tax | 0 | 0 | (3)
Consumers Energy Company [Member] |  |  |
Net gain (loss) arising during the period, tax | (3) | (3) | (2)
Amortization of net actuarial loss, tax | 1 | 0 | 0
Unrealized gain (loss) on investments, tax expense (tax benefit) | 0 | 2 | 6
Reclassification adjustments included in net income, tax | $ 0 | $ 0 | $ (2)

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- Definition Tax effect on the cost of benefit improvement resulting from a plan amendment that occurred during the period. The expense has not been recognized in net periodic benefit cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e640-108580 + Details
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- Definition Tax effect on the reclassification adjustment for gains or losses realized upon the sale of securities during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 130 -Paragraph 25 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6920043&loc=d3e640-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher AICPA -Name Accounting Research Bulletin (ARB) -Number 51 -Paragraph 38 -Subparagraph c(3) -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. + Details
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