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Retirement Benefits (Schedule Of Net Periodic Benefit Cost Not yet Recognized) (Details) - USD ($) $ in Millions | Dec. 31, 2015 | Dec. 31, 2014
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Pension And DB SERP [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets (liabilities), Net loss | $ 944 | $ 1,012
Regulatory assets (liabilities), Prior service cost (credit) | 19 | 7
Regulatory assets (liabilities) | 963 | 1,019
AOCI, Net loss (gain) | 86 | 99
AOCI, Prior service cost (credit) | 1 | 1
Total amounts not yet recognized as component of net periodic benefit cost | 1,050 | 1,119
Pension And DB SERP [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets (liabilities), Net loss | 944 | 1,012
Regulatory assets (liabilities), Prior service cost (credit) | 19 | 7
Regulatory assets (liabilities) | 963 | 1,019
AOCI, Net loss (gain) | 29 | 39
Total amounts not yet recognized as component of net periodic benefit cost | 992 | 1,058
OPEB [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets (liabilities), Net loss | 360 | 419
Regulatory assets (liabilities), Prior service cost (credit) | (227) | (243)
Regulatory assets (liabilities) | 133 | 176
AOCI, Net loss (gain) | (11) | (18)
AOCI, Prior service cost (credit) | (8) | (8)
Total amounts not yet recognized as component of net periodic benefit cost | 114 | 150
OPEB [Member] | Consumers Energy Company [Member] |  |
Defined Benefit Plan Disclosure [Line Items] |  |
Regulatory assets (liabilities), Net loss | 360 | 419
Regulatory assets (liabilities), Prior service cost (credit) | (227) | (243)
Regulatory assets (liabilities) | 133 | 176
Total amounts not yet recognized as component of net periodic benefit cost | $ 133 | $ 176

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- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in regulatory assets as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References No definition available. + Details
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- Definition Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. + References No definition available. + Details
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- Definition Total amount of regulatory assets and AOCI that have not been recognized as a component of net periodic cost. + References No definition available. + Details
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- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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- Definition Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Prior Service Cost -URI http://asc.fasb.org/extlink&oid=49177896 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The net amount of all regulatory assets less all regulatory liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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