Revenue Recognition - Summary of RPOs Expected Revenue Recognition (Detail) $ in Millions	Sep. 30, 2018 USD ($)
Revenue Performance Obligation [Abstract]
Total RPOs, 2018	$ 2,288
Total RPOs, 2019	6,158
Total RPOs, Thereafter	$ 3,066

Revenue remaining performance obligation remainder of fiscal year.

No definition available.

Name:	mdr_RevenueRemainingPerformanceObligationRemainderOfFiscalYear
Namespace Prefix:	mdr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant