Discontinued Operations and Dispositions (Statement of Operations) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2020	Mar. 31, 2019
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net income from discontinued operations before income taxes	[1]	$ 0	$ 3
Benefit for income taxes	[1]	0	2
Net income from discontinued operations	[1]	0	5
Less: net loss attributable to noncontrolling interests		0	(1)
Net income from discontinued operations attributable to MIC		$ 0	6
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			16
Cost of product sales			(3)
Selling, general & administrative expenses			(4)
Interest expense, net			(5)
Other expense, net			(1)
Net income from discontinued operations before income taxes			3
Benefit for income taxes			2
Net income from discontinued operations			5
Less: net loss attributable to noncontrolling interests			(1)
Net income from discontinued operations attributable to MIC			$ 6

[1] See Note 4, “Discontinued Operations and Dispositions”, for discussions on businesses classified as held for sale.