Equity - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions									3 Months Ended		9 Months Ended
	Sep. 01, 2016	Jun. 03, 2016	Mar. 02, 2016	Sep. 03, 2015	Jun. 05, 2015	Mar. 06, 2015	Jan. 13, 2015	Dec. 18, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Class Of Stock [Line Items]
Cash dividends declared per share to shareholders									$ 0.250	$ 0.225	$ 0.750	$ 0.850
Cash Distribution Approved on September 1, 2016
Class Of Stock [Line Items]
Cash distribution declaration date											Sep. 01, 2016
Cash distributions to unit holders, date of record											Sep. 30, 2016
Dividends Payable, date declared											Sep. 01, 2016
Dividends payable date of record											Sep. 30, 2016
Cash dividends declared per share to shareholders	$ 0.25
Cash distribution and dividend paid date											Oct. 20, 2016
Cash Distribution Approved on June 3, 2016
Class Of Stock [Line Items]
Cash distribution declaration date											Jun. 03, 2016
Cash distributions to unit holders, date of record											Jun. 30, 2016
Dividends Payable, date declared											Jun. 03, 2016
Dividends payable date of record											Jun. 30, 2016
Cash dividends declared per share to shareholders		$ 0.25
Cash distribution and dividend paid date											Jul. 21, 2016
Cash Distribution Approved on March 2, 2016
Class Of Stock [Line Items]
Cash distribution declaration date											Mar. 02, 2016
Cash distributions to unit holders, date of record											Mar. 31, 2016
Dividends Payable, date declared											Mar. 02, 2016
Dividends payable date of record											Mar. 31, 2016
Cash dividends declared per share to shareholders			$ 0.25
Cash distribution and dividend paid date											Apr. 21, 2016
Cash Distribution Approved on September 3, 2015
Class Of Stock [Line Items]
Cash distribution declaration date											Sep. 03, 2015
Cash distributions to unit holders, date of record											Sep. 30, 2015
Dividends Payable, date declared											Sep. 03, 2015
Dividends payable date of record											Sep. 30, 2015
Cash dividends declared per share to shareholders				$ 0.225
Cash distribution and dividend paid date											Oct. 22, 2015
Cash Distribution Approved on June 5, 2015
Class Of Stock [Line Items]
Cash distribution declaration date											Jun. 05, 2015
Cash distributions to unit holders, date of record											Jun. 30, 2015
Dividends Payable, date declared											Jun. 05, 2015
Dividends payable date of record											Jun. 30, 2015
Cash dividends declared per share to shareholders					$ 0.225
Cash distribution and dividend paid date											Jul. 23, 2015
Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash distribution declaration date											Mar. 06, 2015
Cash distributions to unit holders, date of record											Mar. 31, 2015
Dividends Payable, date declared											Mar. 06, 2015
Dividends payable date of record											Mar. 31, 2015
Cash dividends declared per share to shareholders						$ 0.14
Cash distribution and dividend paid date											Apr. 23, 2015
Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash distribution declaration date											Jan. 13, 2015
Cash distributions to unit holders, date of record											Jan. 20, 2015
Dividends Payable, date declared											Jan. 13, 2015
Dividends payable date of record											Jan. 20, 2015
Cash dividends declared per share to shareholders							$ 0.26
Cash distribution and dividend paid date											Jan. 29, 2015
Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash distribution declaration date											Dec. 18, 2014
Cash distributions to unit holders, date of record											Dec. 18, 2014
Dividends Payable, date declared											Dec. 18, 2014
Dividends payable date of record											Dec. 18, 2014
Cash dividends declared per share to shareholders								$ 0.31
Cash distribution and dividend paid date											Jan. 16, 2015
Accumulated Deficit | Cash Distribution Approved on September 1, 2016
Class Of Stock [Line Items]
Cash dividends declared to shareholders	$ 10.9
Accumulated Deficit | Cash Distribution Approved on June 3, 2016
Class Of Stock [Line Items]
Cash dividends declared to shareholders		$ 10.9
Accumulated Deficit | Cash Distribution Approved on March 2, 2016
Class Of Stock [Line Items]
Cash dividends declared to shareholders			$ 10.9
Accumulated Deficit | Cash Distribution Approved on September 3, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders				$ 9.8
Accumulated Deficit | Cash Distribution Approved on June 5, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders					$ 9.8
Accumulated Deficit | Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders						$ 6.1
Accumulated Deficit | Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders							$ 9.0
Accumulated Deficit | Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash dividends declared to shareholders								$ 10.8
InfraREIT, L.L.C. | Cash Distribution Approved on September 1, 2016
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit	$ 0.25
Cash distribution to unit holders	$ 15.2
InfraREIT, L.L.C. | Cash Distribution Approved on June 3, 2016
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit		$ 0.25
Cash distribution to unit holders		$ 15.2
InfraREIT, L.L.C. | Cash Distribution Approved on March 2, 2016
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit			$ 0.25
Cash distribution to unit holders			$ 15.2
InfraREIT, L.L.C. | Cash Distribution Approved on September 3, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit				$ 0.225
Cash distribution to unit holders				$ 13.6
InfraREIT, L.L.C. | Cash Distribution Approved on June 5, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit					$ 0.225
Cash distribution to unit holders					$ 13.6
InfraREIT, L.L.C. | Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit						$ 0.14
Cash distribution to unit holders						$ 8.5
InfraREIT, L.L.C. | Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit							$ 0.26
Cash distribution to unit holders							$ 11.7
InfraREIT, L.L.C. | Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash distributions declared to unit holders, per unit								$ 0.31
Cash distribution to unit holders								$ 14.1
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on September 1, 2016
Class Of Stock [Line Items]
Cash dividends declared to shareholders	$ 10.9
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on June 3, 2016
Class Of Stock [Line Items]
Cash dividends declared to shareholders		$ 10.9
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on March 2, 2016
Class Of Stock [Line Items]
Cash dividends declared to shareholders			$ 10.9
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on September 3, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders				$ 9.8
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on June 5, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders					$ 9.8
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on March 6, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders						$ 6.1
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on January 13, 2015
Class Of Stock [Line Items]
Cash dividends declared to shareholders							$ 9.0
InfraREIT, L.L.C. | Accumulated Deficit | Cash Distribution Approved on December 18, 2014
Class Of Stock [Line Items]
Cash dividends declared to shareholders								$ 10.8