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Retirement Benefits (Schedule Of Benefit Obligations In Excess Of Fair Value Of Plan Assets) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
DB Pension Plan [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of period |  | $ 2,403 | $ 2,547 |
Service cost |  | 42 | 49 |
Interest cost |  | 85 | 102 |
Plan amendments |  |  | 13 |
Actuarial (gain) loss | [1] | 196 | (153) |
Benefits paid |  | (164) | (155) |
Benefit obligation at end of period |  | 2,562 | 2,403 | $ 2,547
Plan assets at fair value at beginning of period |  | 2,013 | 1,979 |
Actual return on plan assets |  | 152 | (36) |
Company contributions |  | 100 | 225 |
Actual benefits paid |  | (164) | (155) |
Plan assets at fair value at end of period |  | 2,101 | 2,013 | 1,979
Funded status | [1],[2] | (461) | (390) |
DB Pension Plan [Member] | Consumers Energy Company [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Funded status |  | (441) | (368) |
DB SERP [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of period |  | 150 | 156 |
Service cost |  |  | 1 |
Interest cost |  | 5 | 6 |
Actuarial (gain) loss |  | 4 | (5) |
Benefits paid |  | (8) | (8) |
Benefit obligation at end of period |  | 151 | 150 | 156
Company contributions |  | 8 | 8 |
Actual benefits paid |  | (8) | (8) |
Funded status |  | (151) | (150) |
DB SERP [Member] | Consumers Energy Company [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of period |  | 106 | 111 |
Service cost |  |  | 1 |
Interest cost |  | 4 | 4 |
Actuarial (gain) loss | [1] | 4 | (5) |
Benefits paid |  | (5) | (5) |
Benefit obligation at end of period |  | 109 | 106 | 111
Company contributions |  | 5 | 5 |
Actual benefits paid |  | (5) | (5) |
Funded status |  | (109) | (106) |
OPEB [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of period |  | 1,227 | 1,378 |
Service cost |  | 18 | 25 | 20
Interest cost |  | 46 | 58 | 56
Plan amendments |  |  | (25) |
Actuarial (gain) loss | [1] | 171 | (152) |
Benefits paid |  | (54) | (57) |
Benefit obligation at end of period |  | 1,408 | 1,227 | 1,378
Plan assets at fair value at beginning of period |  | 1,208 | 1,265 |
Actual return on plan assets |  | 109 | (29) |
Company contributions |  |  | 29 |
Actual benefits paid |  | (53) | (57) |
Plan assets at fair value at end of period |  | 1,264 | 1,208 | 1,265
Funded status |  | (144) | (19) |
OPEB [Member] | Consumers Energy Company [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation at beginning of period |  | 1,188 | 1,336 |
Service cost |  | 17 | 25 | 20
Interest cost |  | 45 | 56 | 54
Plan amendments |  |  | (24) |
Actuarial (gain) loss | [1] | 167 | (150) |
Benefits paid |  | (52) | (55) |
Benefit obligation at end of period |  | 1,365 | 1,188 | 1,336
Plan assets at fair value at beginning of period |  | 1,133 | 1,186 |
Actual return on plan assets |  | 103 | (27) |
Company contributions |  |  | 29 |
Actual benefits paid |  | (52) | (55) |
Plan assets at fair value at end of period |  | 1,184 | 1,133 | $ 1,186
Funded status |  | $ (181) | $ (55) |
[1] | The actuarial loss for 2016 was primarily the result of claims, experience, and lowering the discount rates used in calculating the plans' obligations. The actuarial gain for 2015 was primarily the result of increasing the discount rates used in calculating the plans' obligations.
[2] | At December 31, 2016, $441 million of the total funded status of the DB Pension Plan was attributable to Consumers, based on an allocation of expenses. At December 31, 2015, $368 million of the total funded status of the DB Pension Plan was attributable to Consumers, based on an allocation of expenses.

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- Definition Defined Benfefit Plan Benefits Paid Plus Cash Payments + References No definition available. + Details
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- Definition The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Actual Return on Plan Assets (Component of Net Periodic Postretirement Benefit Cost) -URI http://asc.fasb.org/extlink&oid=6504192 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Actual Return on Plan Assets (Component of Net Periodic Pension Cost) -URI http://asc.fasb.org/extlink&oid=6504226 + Details
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- Definition Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Gain or Loss -URI http://asc.fasb.org/extlink&oid=49168827 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition 1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Projected Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6522206 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Accumulated Postretirement Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6503904 + Details
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- Definition The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 60 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=6414203&loc=d3e39716-114964 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Benefits -URI http://asc.fasb.org/extlink&oid=49170737 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(6) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Postretirement Benefits -URI http://asc.fasb.org/extlink&oid=6521376 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(5) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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- Definition The funded status is measured as the difference between the fair value of plan assets and the benefit obligation. Will normally be the same as the net Defined Benefit Plan, Amounts Recognized in Balance Sheet, Total. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64852052&loc=d3e1703-114919 + Details
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- Definition The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(2) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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