Discontinued Operations and Dispositions (Statement of Operations) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net income from discontinued operations before income taxes	[1]	$ 78	$ 26	$ 86	$ 41
Provision for income taxes	[1]	(32)	(6)	(32)	(5)
Net income from discontinued operations	[1]	46	20	54	36
Less: net loss attributable to noncontrolling interests		0	0	(3)	(32)
Net income from discontinued operations attributable to MIC		46	20	57	68
Solar and wind Facilities | Disposal Group, Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on disposition of business		80
Contracted Power Segment | Discontinued Operations, Held-for-sale or Disposed of by Sale
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Product revenue		10	52	44	129
Cost of product sales		(1)	(8)	(7)	(20)
Selling, general & administrative expenses		(11)	(8)	(18)	(22)
Depreciation and amortization		0	(8)	0	(38)
Interest expense, net		(1)	(5)	(13)	(11)
Other income, net		81	3	80	3
Net income from discontinued operations before income taxes		78	26	86	41
Provision for income taxes		(32)	(6)	(32)	(5)
Net income from discontinued operations		46	20	54	36
Less: net loss attributable to noncontrolling interests		0	0	(3)	(32)
Net income from discontinued operations attributable to MIC		$ 46	$ 20	$ 57	$ 68

[1] See Note 3, “Discontinued Operations and Dispositions”, for discussions on businesses classified as held for sale.