Discontinued Operations and Dispositions (Statement of Operations) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 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	$ 5	$ 0	$ 8
Provision for income taxes	[1]	0	(2)	0	0
Net income from discontinued operations	[1]	0	3	0	8
Less: net loss attributable to noncontrolling interests		0	(2)	0	(3)
Net income from discontinued operations attributable to MIC		$ 0	5	$ 0	11
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			18		34
Cost of product sales			(3)		(6)
Selling, general & administrative expenses			(3)		(7)
Interest expense, net			(7)		(12)
Other expense, net			0		(1)
Net income from discontinued operations before income taxes			5		8
Provision for income taxes			(2)		0
Net income from discontinued operations			3		8
Less: net loss attributable to noncontrolling interests			(2)		(3)
Net income from discontinued operations attributable to MIC			$ 5		$ 11

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