Commitments and Contingencies, Capital Commitments (Details) - Capital Commitments	12 Months Ended
Dec. 31, 2015 kV
TUCO to Yoakum to Hobbs Plant Transmission Line
Capital Commitments [Abstract]
Voltage capacity for transmission line (in kV)	345
Hobbs Plant to China Draw Transmission Line [Member]
Capital Commitments [Abstract]
Voltage capacity for transmission line (in kV)	345

Capacity for the transmission line under construction.

No definition available.

Name:	sps_VoltagecapacityfortransmissionlineinkV
Namespace Prefix:	sps_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration