TW (current market cap of $4.5B) has a large nationwide fiber network (connects 20K+ commercial buildings) that would bolster Level 3's own network, and bills itself of the top 3 U.S. business Ethernet providers. Both companies are based out of Colorado.
BrightWire states Level 3 was also interested in TW back in 2012, when the company (per reports) hired Evercore to explore its options. But Level 3 is in much better shape today to make a bid.
Speculation that Level 3 could bid for TW has been around for a while.