Quarterly Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Revenue from continuing operations	$ 424	$ 405	$ 416	$ 482	$ 437	$ 421	$ 436	$ 467	$ 1,727	$ 1,761	$ 1,669
Operating income from continuing operations	55	56	55	123	47	53	58	76	289	234	282
Net income from continuing operations attributable to MIC	16	15	6	64	(1)	2	27	40	101	68	434
Net income (loss) from discontinued operations attributable to MIC	$ (2)	$ 46	$ 5	$ 6	$ 1	$ 20	$ 11	$ 37	$ 55	$ 69	$ 17
Per share information attributable to MIC:
Basic income (loss) per share from continuing operations attributable to MIC (in dollars per share)	$ 0.18	$ 0.18	$ 0.07	$ 0.75	$ (0.01)	$ 0.02	$ 0.32	$ 0.47	$ 1.17	$ 0.80	$ 5.22
Basic income (loss) per share from discontinued operations attributable to MIC (in dollars per share)	(0.02)	0.53	0.06	0.07	0	0.23	0.13	0.44	0.65	0.80	0.20
Basic income (loss) per share attributable to MIC (in dollars per share)	0.16	0.71	0.13	0.82	(0.01)	0.25	0.45	0.91	1.82	1.60	5.42
Diluted income (loss) per share from continuing operations attributable to MIC (in dollars per share)	0.18	0.18	0.07	0.73	(0.01)	0.02	0.32	0.47	1.17	0.80	4.94
Diluted income (loss) per share from discontinued operations attributable to MIC (in dollars per share)	(0.02)	0.53	0.06	0.06	0	0.23	0.13	0.44	0.65	0.80	0.19
Diluted income (loss) per share attributable to MIC (in dollars per share)	0.16	0.71	0.13	0.79	(0.01)	0.25	0.45	0.91	1.82	1.60	5.13
Cash dividends declared per share (in dollars per share)	$ 1.00	$ 1.00	$ 1.00	$ 1.00	$ 1.00	$ 1.00	$ 1.00	$ 1.00	$ 4.00	$ 4.00	$ 5.56