NW began the year with 15 DC-10 and will finish it with about 8.
The -10 are scheduled to fly 1xDTW-AMS, MEM-AMS, BOM-AMS, MSP-LGW, MSP-HNL, KIX-HNL and 1xNRT-HNL this spring. It's the same this summer, although the -10 on DTW-AMS will be "transferred" to MSP.
Note that unless the fourth DTW-AMS flight is re-upgraded with an additional 333, the aircraft will likely "take-over" a MSP flight: all DC-10 crews are MSP-based, and with the current schedule there's simply no way get the aircraft and crew back to MSP without ferrying it (or operating a domestic DTW-MSP flight, which isn't scheduled and isn't likely to happen).
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A wealth of information on NW's fleet plans is available by doing a search of previous postings.
A quick summary: NW's gotten approval to complete its A330 order; they'll have 12 A332 and 20 A333 within a couple years. They've also placed an order for 18 787, with deliveries beginning in 2008. These aircraft, along with the 16 744 (which NW is currently renegotiating leases on), will make-up NW's widebody fleet well into the future. Don't expect size to be replaced with size (e.g. 787 could replace 747 on LAX-NRT, etc.)