It is the third transaction of the company for the past eight days to strengthen its financial positions.
A unit of Williams' gas pipelines business held a 14.6 percent ownership interest in the 1,900-mile Alliance Pipeline that transports natural gas from western Canada to the Chicago area.
The sale is expected to close within 60 days, subject to regulatory approvals and the rights of other Alliance owners to acquire their pro rata share of Williams' interest.
Williams is retaining its interest in the Aux Sable natural gas liquids plant, which processes all gas transported on the Alliance pipeline.
Williams' subsidiaries wholly own and operate 20,400 miles of natural gas pipeline, comprised of the Transco, Northwest and Texas Gas systems. These pipelines serve major markets like Seattle, Portland, Ore., Atlanta, New York City and Memphis.
Rescuers found the pilot of one of the two Su-34 fighters that had collided in midair in the Far East on January 18