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Retirement Benefits (Schedule Of Benefit Obligations In Excess Of Fair Value Of Plan Assets) (Details) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended
--- | --- | ---
Jul. 31, 2018 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
DB Pension Plans |  |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |
Benefit obligation at beginning of period |  | $ 2,512 | $ 2,780 |
Service cost |  | 41 | 48 |
Interest cost |  | 98 | 90 |
Plan amendments |  | 0 | 0 |
Actuarial loss (gain) |  | 476 | (258) |
Benefits paid |  | (154) | (148) |
Benefit obligation at end of period |  | 2,973 | 2,512 | $ 2,780
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Plan assets at fair value at beginning of period |  | 2,247 | 2,305 |
Actual return on plan assets |  | 453 | (150) |
Company contribution |  | 0 | 240 |
Actual benefits paid |  | (154) | (148) |
Plan assets at fair value at end of period |  | 2,546 | 2,247 | 2,305
Funded status |  | (427) | (265) |
DB Pension Plans | Consumers Energy Company |  |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Funded status |  | (408) | (246) |
DB SERP |  |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |
Benefit obligation at beginning of period |  | 140 | 154 |
Service cost |  | 0 | 0 |
Interest cost |  | 5 | 5 |
Plan amendments |  | 0 | 0 |
Actuarial loss (gain) |  | 15 | (10) |
Benefits paid |  | (10) | (9) |
Benefit obligation at end of period |  | 150 | 140 | 154
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Plan assets at fair value at beginning of period |  | 0 | 0 |
Actual return on plan assets |  | 0 | 0 |
Company contribution |  | 10 | 9 |
Actual benefits paid |  | (10) | (9) |
Plan assets at fair value at end of period |  | 0 | 0 | 0
Funded status |  | (150) | (140) |
DB SERP | Consumers Energy Company |  |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |
Benefit obligation at beginning of period |  | 101 | 112 |
Service cost |  | 0 | 0 |
Interest cost |  | 4 | 4 |
Plan amendments |  | 0 | 0 |
Actuarial loss (gain) |  | 11 | (8) |
Benefits paid |  | (7) | (7) |
Benefit obligation at end of period |  | 109 | 101 | 112
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Plan assets at fair value at beginning of period |  | 0 | 0 |
Actual return on plan assets |  | 0 | 0 |
Company contribution |  | 7 | 7 |
Actual benefits paid |  | (7) | (7) |
Plan assets at fair value at end of period |  | 0 | 0 | 0
Funded status |  | (109) | (101) |
OPEB Plan |  |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |
Benefit obligation at beginning of period |  | 1,045 | 1,097 |
Service cost |  | 14 | 17 | 19
Interest cost |  | 41 | 34 | 51
Plan amendments | $ 26 | 0 |  |
Actuarial loss (gain) |  | 110 | (74) |
Benefits paid |  | (45) | (55) |
Benefit obligation at end of period |  | 1,165 | 1,045 | 1,097
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Plan assets at fair value at beginning of period |  | 1,280 | 1,420 |
Actual return on plan assets |  | 273 | (86) |
Company contribution |  | 0 | 0 |
Actual benefits paid |  | (44) | (54) |
Plan assets at fair value at end of period |  | 1,509 | 1,280 | 1,420
Funded status |  | 344 | 235 |
OPEB Plan | Consumers Energy Company |  |  |  |
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |  |  |  |
Benefit obligation at beginning of period |  | 1,004 | 1,053 |
Service cost |  | 13 | 16 | 19
Interest cost |  | 40 | 33 | 49
Plan amendments |  | 0 | 25 |
Actuarial loss (gain) |  | 106 | (70) |
Benefits paid |  | (43) | (53) |
Benefit obligation at end of period |  | 1,120 | 1,004 | 1,053
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |  |
Plan assets at fair value at beginning of period |  | 1,197 | 1,329 |
Actual return on plan assets |  | 255 | (80) |
Company contribution |  | 0 | 0 |
Actual benefits paid |  | (42) | (52) |
Plan assets at fair value at end of period |  | 1,410 | 1,197 | $ 1,329
Funded status |  | $ 290 | $ 193 |

X
- Definition Amount of increase (decrease) in plan assets of defined benefit plan from actual return (loss) determined by change in fair value of plan assets adjusted for contributions, benefit payments, and other expenses. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 + Details
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- Definition Amount of gain (loss) from change in actuarial assumptions which (increases) decreases benefit obligation of defined benefit plan. Assumptions include, but are not limited to, interest, mortality, employee turnover, salary, and temporary deviation from substantive plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount of payment to participant of defined benefit plan which decreases benefit obligation. For pension plan, payment includes, but is not limited to, pension benefits and death benefits. For other postretirement plan, payment includes, but is not limited to, prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(6) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -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 + Details
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- Definition Amount of contribution received by defined benefit plan from employer which increases plan assets. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e2709-114920 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(iv)(01) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118257860&loc=d3e4179-114921 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 Reference 6: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(ii) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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