Long-term Commitments (Future Minimum Commitments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
2015	$ 195
2016	113us-gaap_OtherCommitmentDueInSecondYear
2017	64us-gaap_OtherCommitmentDueInThirdYear
Subsequent years	69mmc_OtherCommitmentDueAfterThirdYear
Total	$ 441us-gaap_OtherCommitment

Minimum amount of other commitment maturing in the next fiscal year following the latest fiscal year for commitments not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in this taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

No definition available.

Name:	us-gaap_OtherCommitmentDueInNextTwelveMonths
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant