Widebody; Low Wing; 2 Turbojet Eng
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Flight Crew Last 90 Days 0; Flight Crew Total 9188; Flight Crew Type 1636
ATC Issue All Types; Conflict Airborne Conflict
Air Traffic Control Issued New Clearance; Air Traffic Control Separated Traffic; Flight Crew Overrode Automation
Airspace Structure; Procedure; Software and Automation
I was Pilot Flying (PF). Autopilot (AP) on. Approaching top of descent for DRLLR arrival near TORNN level FL330; Fort Worth Center gave us descent to FL310; then changed it to FL320. I initiated cruise descent. ATC gave us right turn to heading 270; then further descent to FL310; I continued cruise descent. We were then given speed of 250 knots. About the time we rolled out on 270 heading we were given left turn direct TORNN. I initiated turn using LNAV. About this time ATC requested a 'good turn' to TORNN; at which point we were already abeam and the airplane was in 30 degree bank. Traffic was noticed slightly below and to our right on TCAS. I believe I saw it within a couple hundred feet and within 5 miles. Navigation display was on smallest scale. Unsure if airplane could continue turn to TORNN in LNAV due to our position relative to fix; I used Heading (HDG) select to keep turn going. ATC never mentioned the traffic to us; I never saw traffic visually; and no TCAS TA or RA. We were handed off to Houston Center while in the turn. They approved direct to a subsequent fix and flight continued without incident.
First Officer reported noticing traffic within 5miles and a couple hundred feet while complying with vectors on the DRLLR FIVE STAR into IAH: ATC never pointed out the traffic to the flight crew.