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Retirement Benefits (Schedule Of Net Benefit Costs) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
DB Pension Plans and DB SERP |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |
Service cost | $ 48 | $ 45 | $ 42
Interest cost | 95 | 93 | 90
Expected return on plan assets | (149) | (153) | (147)
Amortization of |  |  |
Net loss | 76 | 82 | 71
Prior service cost (credit) | 3 | 5 | 4
Net periodic cost (credit) | 73 | 72 | 60
DB Pension Plans and DB SERP | Consumers Energy Company |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |
Service cost | 47 | 44 | 41
Interest cost | 88 | 90 | 87
Expected return on plan assets | (139) | (149) | (143)
Amortization of |  |  |
Net loss | 73 | 79 | 68
Prior service cost (credit) | 3 | 4 | 4
Net periodic cost (credit) | 72 | 68 | 57
OPEB Plan |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |
Service cost | 17 | 19 | 18
Interest cost | 34 | 51 | 46
Expected return on plan assets | (97) | (90) | (85)
Amortization of |  |  |
Net loss | 15 | 29 | 21
Prior service cost (credit) | (67) | (40) | (41)
Net periodic cost (credit) | (98) | (31) | (41)
OPEB Plan | Consumers Energy Company |  |  |
Defined Benefit Plan, Roll Forwards [Abstract] |  |  |
Service cost | 16 | 19 | 17
Interest cost | 33 | 49 | 45
Expected return on plan assets | (91) | (84) | (80)
Amortization of |  |  |
Net loss | 16 | 29 | 22
Prior service cost (credit) | (65) | (39) | (40)
Net periodic cost (credit) | $ (91) | $ (26) | $ (36)

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- Definition Amount of gain (loss) recognized in net periodic benefit (cost) credit of defined benefit plan. + 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 (h)(4) -URI http://asc.fasb.org/extlink&oid=108410482&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=112275985&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(4) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 + Details
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- Definition Amount of cost for actuarial present value of benefits attributed to service rendered by employee for defined benefit plan. + 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 (h)(1) -URI http://asc.fasb.org/extlink&oid=108410482&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=112275985&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
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