Related Party Transactions (Schedule of Base Management Fees and Performance Fees) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
Sep. 30, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Related Party Transactions [Abstract]
Base Management Fee Amount		$ 8	$ 7	$ 8	$ 9	$ 12	$ 11	$ 13
Performance Fee Amount		$ 0	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Shares Issued (in shares)	67,659	201,827	192,103	184,448	220,208	269,286	277,053	265,002

Amount of performance fees incurred by the company for the period to its manager, a related party that was or will be settled in shares of the company and cash.

No definition available.

Name:	mic_PerformanceFeeToManagerRelatedPartySettledInSharesAndOrCash
Namespace Prefix:	mic_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration