Fair Value - Additional Information (Detail) (USD $)	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Fair Value Disclosures [Abstract]
Transfers out of Level 2 to Level 1, Assets	$ 0	$ 23,000,000
Transfers out of Level 1 to Level 2, Assets	$ 0	$ 1,000,000

Fair Value Equity Level One To Level Two Transfer Amount

No definition available.

Name:	l_FairValueEquityLevelOneToLevelTwoTransferAmount
Namespace Prefix:	l_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration